Just an idea i had.. passed it by gary howell.. not something i'm going to do myself.. perhaps someone here might be interested.

Take a 2.4L block.. put a 2.0L crankshaft in it and destroke the engine.

The rods would need to be approx 1" longer.. the long rod/short throw should be good for a 12,000 rpm + screamer if you were so inclined.

Of course you'd need aftermarket ECU.. but this would be an engine that could make close to 300hp NA when your done.

Again.. just an idea for the ones with the time/$

-- WheatKing

>Just an idea i had.. passed it by gary howell.. not something
>i'm going to do myself.. perhaps someone here might be
>interested.
>
>Take a 2.4L block.. put a 2.0L crankshaft in it and destroke
>the engine.
>
>The rods would need to be approx 1" longer.. the long
>rod/short throw should be good for a 12,000 rpm + screamer if
>you were so inclined.
>
>Of course you'd need aftermarket ECU.. but this would be an
>engine that could make close to 300hp NA when your done.
>
>Again.. just an idea for the ones with the time/$
>
>-- WheatKing

I've thought of this idea before... i like it... No reason to believe that this would be any more expensive than your normal hi performance rebuild. Do you think your average billet rods would hold up or would you maybe want to spring for titanium conrods to hold up better at high rpms,(at about 2-3k per set of 4)? Some Huge cams... or turbo powah...... I wish my wallet was as big as my to do list.

"Michael_97RS: Why bother, you'd have an easier time getting Mother Theresa to give you head than getting MrLocalPimp to behave."

>I've thought of this idea before... i like it... No reason to
>believe that this would be any more expensive than your normal
>hi performance rebuild. Do you think your average billet rods
>would hold up or would you maybe want to spring for titanium
>conrods to hold up better at high rpms,(at about 2-3k per set
>of 4)? Some Huge cams... or turbo powah...... I wish my wallet
>was as big as my to do list.

You'd want the smallest, lightest, ti rods you could get.. AL might work too.. the less mass the better when your whipping the pistons around at 12K rpm..

-- WheatKing

wheatking, you got aim? My name on there is theallpowerfulhe, hit me up.

>wheatking, you got aim? My name on there is theallpowerfulhe,
>hit me up.

Helps if your actually on aim.. hahaha

What you want?

-- WheatKing

First a question: Do longer rods help to reach higher rpm? Seems to me longer rods would have more mass and lead to lower revs. If this is so why don't you just do this to the 2.0 block?

ok, now my concerns.

1) Cams, we have no form of variable valve control and we already start to lose power over 5k rpm. In order to make any power at 12000 rpm you would need one mean nasty set of cams, problem with this is you will have shitty low rpm performance and bad idle.

2) Tranny, I dunno how much on an issue this is, but trannies have a limit too. The automatic tranny is redlined at 6500 rpm, now even if you have a manual, none of the synchronizers are designed to shift at 12k rpm.

>First a question: Do longer rods help to reach higher rpm?
>Seems to me longer rods would have more mass and lead to lower
>revs. If this is so why don't you just do this to the 2.0
>block?
>
>ok, now my concerns.
>
>1) Cams, we have no form of variable valve control and we
>already start to lose power over 5k rpm. In order to make any
>power at 12000 rpm you would need one mean nasty set of cams,
>problem with this is you will have shitty low rpm performance
>and bad idle.
>
>2) Tranny, I dunno how much on an issue this is, but trannies
>have a limit too. The automatic tranny is redlined at 6500
>rpm, now even if you have a manual, none of the synchronizers
>are designed to shift at 12k rpm.

HEEHEH..

#1) USE A BIG CAM.. this would be a race engine not something you'd want to street.. aka.. if someone took an eclipse/neon into an all-motor race.. chassis's are cheap now..

2) no one in their right mind would use an automatic with an engine like this.

As for the long rods.. it changes the rod ratio.. the longer the rod, the less extreme the force vector on the crank journal is.

On a piece of paper.. draw a line vertically that's 2" long.. and one 90 degrees to the base 1" long.. the bottom line is the crank journal.. the top of the vertical line is the piston pin.. now connect the two..

Now draw a line 1" longer.. notice that the angle has decreased in relation the the crank journal and piston pin.. the more vertical, the easier it is to apply force. the big end of the rod still moves the same distance.. but the force vector from the explosion is reduced.

Long Ti rods :)

-- WheatKing

>2) Tranny, I dunno how much on an issue this is, but trannies
>have a limit too. The automatic tranny is redlined at 6500
>rpm, now even if you have a manual, none of the synchronizers
>are designed to shift at 12k rpm.

http://www.quaifeamerica.com/transmissions/fwd/32g.htm

that is a race only transmission that has no reverse.

Uhm...and did you see how much it costs? The money involved in this idea is far more than what is worth to make your car fast....shit....by the time your done with buying custom titanium rods and that tranny and bla bla bla to get this done you could just buy a fuckin viper.

>Uhm...and did you see how much it costs? The money involved
>in this idea is far more than what is worth to make your car
>fast....shit....by the time your done with buying custom
>titanium rods and that tranny and bla bla bla to get this done
>you could just buy a fuckin viper.

Yeah... but just imagine the look on a viper owners face after he just got smoked by a "little 4 banger". There are somethings money can buy... for everything else, there's WHOOPASS.


"Michael_97RS: Why bother, you'd have an easier time getting Mother Theresa to give you head than getting MrLocalPimp to behave."

BTW... how would you determine proper rod length in this Hybrid motor? would you simply add the diference in stroke to the regular 2.0's rod length? or would it be way more difficult than that?


"Michael_97RS: Why bother, you'd have an easier time getting Mother Theresa to give you head than getting MrLocalPimp to behave."

Or.. you can just boost the hell outta it and save u'rself about 15 grand..!:thumbsup

>Or.. you can just boost the hell outta it and save u'rself
>about 15 grand..! :thumbsup

True... but honestly, IF you had the money, and the time, to do something that NO ONE else has done, Wouldn't you at least consider it? and i dont think it would be 15 grand... i think that it maybe 25% more than your average HI-performance forged internals rebuild... certainly no more than that. I mean... how much have these guys like brynden spent doing the 2.4 swap? I highly doubt that it would cost more than that.


"Michael_97RS: Why bother, you'd have an easier time getting Mother Theresa to give you head than getting MrLocalPimp to behave."

ill look into it for the next race motor although i still like teh idea of a filled 2.4 block with 30psi and water inlets tappedinto the head....

Bill

howell came out with long rods crate motors? what is long rods and whats the difference between that and the regular motor?

Some people seem to think this would be really expensive..

nope..

also.. you could boost it.. ;-)

Just need an AFX or other standalone ECU.

-- Dave

why be like everyone and boost it or juice it if you have the money? how many people can say "my 2gnt redlines at 12k rpm"?? i think it would be bad ass. i was watching indy racing and they are just cruzin around at 9000rpm i was like holy fuck. this would be an awesome idea. of course its gona be hard and costly and you may destroy a few engines in the process but the end results could be well worth it. when people first started boosting 420a's everyone said it was too hard and pointless and so on and so forth. now everyone who has the money does it. same for the 2.4, and hell, nobody even really talked about a boosted 2.6 like brynden's. be different, you dont have to be like everyone else. isnt this what we are all about? making our cars differnt from every other owner out there?

now take your 12,000 rpm redline and 300 NA HP....Do weight reductions like mad. You could be lookin at whoopin, or at least hangin with, exotics nwn. I am gonna be building a 2.4 soon and was contemplating something like this. I'ma have to look more into it now }(

5.47 inch Rod stock
3.27 inch Stroke stock

1.67 rod:stroke ratio stock
1.98 rod:stroke ratio w/long rods

3935 fps mean piston speed at 7250 rpm
102028 ft/s^2 peak acceleration at 7250rpm with stock rods
98348 ft/s^2 peak acceleration at 7250rpm with long rods

6514 fps mean piston speed at 12,000 rpm
279517 ft/s^2 peak acceleration at 12,000rpm with stock rods
269433 ft/s^2 peak acceleration at 12,000rpm with long rods


-=Whittey=-

>why be like everyone and boost it or juice it if you have the
>money? how many people can say "my 2gnt redlines at 12k rpm"??
>i think it would be bad ass. i was watching indy racing and
>they are just cruzin around at 9000rpm i was like holy fuck.
>this would be an awesome idea. of course its gona be hard and
>costly and you may destroy a few engines in the process but
>the end results could be well worth it. when people first
>started boosting 420a's everyone said it was too hard and
>pointless and so on and so forth. now everyone who has the
>money does it. same for the 2.4, and hell, nobody even really
>talked about a boosted 2.6 like brynden's. be different, you
>dont have to be like everyone else. isnt this what we are all
>about? making our cars differnt from every other owner out
>there?


true true.. Last week I saw a crack whore old lady, probably in her 50's in a red 2gnt with a wing and a carbon fiber hood. At that point I decided to go balls out on my eclipse, so ill be watching this thread very closely!

why do you think you would need an af/x ecu or standalone unit?

>why do you think you would need an af/x ecu or standalone
>unit?

standalone.. AFX only goes up to 8XXX rpms... theres no point in loing out on 4000 revs..

This topic is interesting, so I decided to look into it a little. I found an interesting site that explains how rod length affects piston acceleration. http://e30m3performance.com/tech_articles/engine-tech/rod-ratio/index.htm Threre's even a spreadsheet you can download to calculate the piston acceleration for different rod lengths and strokes.

The bad news is that destroking a 2.4L motor with a 2.0L crank simply does NOT change the acceleration by that much. First of all, the rod would be .7" longer. I suppose you could squeeze another .3" if you really tried, so I ran the simulations with a 1" longer rod. What I came up with is that the pistons accelerate just as fast in a 2.0 motor at 8000 RPM as they do in the 2.4L hybrid motor at 8140 RPM. Blackdog is running a built 2.0L block to 9500 RPM. That's pretty high. Even still - the pistons in a 2.4L hybrid motor would have the same piston acceleration at 9670 RPM.

Essentially - you can't run any hybrid destroked 2.4 block up to 12000 RPM...unless you can rev a similarly prepped(bottom end wise) 2.0L to 11800 RPM. Pistons/Rods can only accelerate so fast before they become terminal and fly off. It's a nice thought and all, but I think 12,000 RPM is just way off. Also, this "2.4L hybrid motor" has a 2.0L displacement - 2.0L stroke with a 2.4L bore...which is the same as the 2.0L bore. I'd trade off a couple hundred rpm for an additional .4L any day.


95 Eclipse RS : 5 speed
15.901 @ 88.34mph
Jeep TB writeup - http://www.dimensia.com:81/jimbo/JeepTBfor2gnt.html

there is an idea kicking around our shop about boring outa 2.4 and destroking it a bit to make it rev super fast like the 377chevy motors..

when we get a project car and try it we'll let peoples know unless somone wants to volenteer?

Bill

>I'd trade off a couple hundred rpm for an additional .4L any
>day.


Me too. :D
-=B-=

Dont forget that with the long rod motor you gain a significant amount of dwell time at tdc and bdc. A long rod 2.0 will not feel like a 2.0. It isn't just about the redline ;). It does seem though that running a 2.0 crank in the 2.4 wouldn't be worth it. Not only for the reasons mentioned above, but the size of the 2.0 mains are too small for the journals in the 2.4. You would need to use somewhat excessive oversized bearings to make it work.

That was actually my first source of confusion in this thread: the crank wouldn't fit without serious modifications. Hell, the 2.4L block is a bit longer (er, wider for all of you who think in the transverse state of mind), so the crank would be wider. I wouldn't want to try t omake it fit. I wouldn't worry too much about dwell time at TDC and BDC, especially when an extra half litre of displacement can be attained no revlimit penalty (we can't go over redline, anyways, so a motor that revs beyond that is wasted).
-=B-=

Another point of contention is that long rod engines don't really have much of an advantage in dwell time, and lose the advantage of peak angle when it counts.

The short rod engine puts the unit force vector closer to the perpendicular to the crank at an earlier point then a long rod engine. For example, in this simple drawing (MS Paint OWNS!):


The rod angles are the same at TDC, but the rod moves towards the tangent of the rod journal's path radius quicker then the long rod engine. In other words, the piston will push harder on the crank earler then the long rod motor will. At "just after TDC," the short rod engine will create a higher torque moment, based on the force vector. At "way after TDC," neither will have a real advantage, and at "90 degrees past TDC," the long rod motor is optimal, as the rod angle from the piston to the rod journal is a smaller number of degrees. Unfortunately, most of the force exerted on the crank occurs right after combustion. This gives the advantage to the short rod motor. Even at high RPMs, there will not be a high amount of force on the piston near 90 degrees. This means that not only do you lose the force vector advantage, but you lose the rotational mass and inertia advantage. Rotating mass is the enemy of rev speed.

There is one advantage, however, to a long rod engine, and it isn't a huge one, either. The shorter rod engine will suck harder on the intake valves earlier then a long rod engine will on the intake stroke. This means that the short rod engine will be sucking on the intake valves pretty hard before they even open all of the way up. The long rod engine, which creates more vacuum later, has the advantage of sucking more in while the intake valves are actually open. On a naturally aspirated motor, this will create a higher peak VE in the long rod motor, but it will come at the expense of intake gas velocity (since it isn't pulling air in as hard), and consequently, low end torque. This is why this motor would prefer to rev to the moon. The short rod engine, however, will suck the air in harder and faster, and create more low end torque.

How much of a difference will this all make to a 420a? Probably not a great deal. I think that the positives and negatives would weigh themselves out. The motor with less rotational mass loses effeciency earlier then the motor with more rotational mass. It's a cruel irony, but it allows another factor to play a part. In a high revving motor, short rods have the advantage of being more aerodynamic. This proves to be more of an advantage at 10K RPM plus on a 2.0, when the journal can reach speeds of 86.9 M/S (260.5MM/revolution * 10,000RPM / 60 sec/min). This is 97 MPH. On a 2.4, spinning it to 10,000 RPM would be almost certainly fatal for the motor, creating a speed of 119 MPH at the journals. Less mass moving slower is better for reliability and longevity at any given RPM. so, at high RPMs, this becomes a huge factor, since wind resistance goes up by the fourth power with speed.

So, which setup is best? I am not sure, and it would be difficult to build a motor in one thread to try things out. But, based on my experience, my educated guess would be that a short rod engine would be best, especially if more displacement can be gained. So, if I could do it again, I would do a 2.4 with a 101.5 MM stroke and and an 87.5 MM bore. Maybe a bit more bore, and a tad more stroke, but I will be using a 2.4 crank in a 2.4 block.
-=B-=

HT = (r + c) - (r cos (a)) - SQRT(c2 - (r sin (a))2)

r = s/2
dtor = PI/180
a = d x dtor

HT = The height of piston
r = The stroke divided by 2
c = The rod length
a = The crank angle in radians
d = The crank angle in degrees
dtor = Degrees to Radians

----------------------------------------------------------------

http://www.coolmath.com/graphit/
For a stock 2.0 with an 83mm stroke and a 139mm rod this is the calculation:
(41.5 + 139) - (41.5 cos(x*pi/180)) - sqrt(139^2 - (41.5 sin(x*pi/180))^2)

Xmin = 0
Xmax = 360
Ymin = 0
Ymax = stroke (in this case, 83)

----------------------------------------------------------------

When comparing the results, think of the difference a degree of cam duratation or degree of timing (cam or spark). Think of what 1mm difference piston height means.


-=Whittey=-

{edit} Do 420A pistons have a wrist pin offset? That will offset the entire graph above by a slight amount. I'd have to sit down and work it out (or break out what little google-fu I have left) but really this is just for comparison. If the crank center isn't centered to the bore, that will offset it as well.

>{edit} Do 420A pistons have a wrist pin offset? That will
>offset the entire graph above by a slight amount. I'd have to
>sit down and work it out (or break out what little google-fu I
>have left) but really this is just for comparison. If the
>crank center isn't centered to the bore, that will offset it
>as well.

the piston pin offset (if that's what you're talking about) on a stock 2.0 420A is 1mm, or .04".

>Another point of contention is that long rod engines don't
>really have much of an advantage in dwell time, and lose the
>advantage of peak angle when it counts.
>
>The short rod engine puts the unit force vector closer to the
>perpendicular to the crank at an earlier point then a long rod
>engine. For example, in this simple drawing (MS Paint OWNS!):
>
>
>The rod angles are the same at TDC, but the rod moves towards
>the tangent of the rod journal's path radius quicker then the
>long rod engine. In other words, the piston will push harder
>on the crank earler then the long rod motor will. At "just
>after TDC," the short rod engine will create a higher torque
>moment, based on the force vector. At "way after TDC," neither
>will have a real advantage, and at "90 degrees past TDC," the
>long rod motor is optimal, as the rod angle from the piston to
>the rod journal is a smaller number of degrees. Unfortunately,
>most of the force exerted on the crank occurs right after
>combustion. This gives the advantage to the short rod motor.
>Even at high RPMs, there will not be a high amount of force on
>the piston near 90 degrees. This means that not only do you
>lose the force vector advantage, but you lose the rotational
>mass and inertia advantage. Rotating mass is the enemy of rev
>speed.

What you are saying here doesn't completely make sense to me. You want peak cylinder pressure to occur 20 deg ATDC. If that happens, the long rod motor will create more torque because it's got a better rod angle to push the crank downward. Near TDC where cylinder pressures are the highest is where you gain the most torque. Because a long rod setup causes the piston to stay in that region for a longer period of time, it will exert that high amount of force longer than a short rod will and still turn the crank the same distance. The long rod will always have the rod angle advantage (except at TDC and BDC as you pointed out lol). As for the rotating mass, that is not as much the enemy of rev speed as steeper rod angles that are created by short rod motors. The rod:stroke ratio is much more critical than the rotating mass in this case. If you were trying to build a 10k+ rpm motor then obviously you would want some billet aluminum or ti rods.

Here is a post by somebody I have spoken to on many occasions about engine dynamics. This was posted on www.eng-tips.com, and basically echos what I had said. It might, however, do a better job of explaining then did my crack-infested drawings. At 1-20 degrees past TDC, the short rod engine will generate force in a direction more tangental to the rotation of the rod journal on the crank. This is a more direct way of exerting force on the crank. Well, go ahead and read the post. Hope it explains better then I do.
-=B-=



Most of my opinion is based upon looking at what happens when you change R/S ratio. For my examples, I assume a stock 350 Chevy, 4.000 bore and 3.480 stroke with zero wrist pin offset. Assume stock rod of 5.700 inches (1.638 R/S) and a 8.700 inch rod (2.5). The first thing Smokey said is that a piston dwells longer at TDC with a large R/S ratio. Let’s look at the numbers. I assume dwell at TDC occurs while the piston is within 0.200” of TDC displacement.

Down R/S Ratio
in 1.638 2.5
0.200 335 334
0.150 339 339
0.100 342 342
0.050 347 347
0.050 372 372
0.100 377 377
0.150 381 381
0.200 384 385

The super long R/S ratio only gets a 2 crank angle degree (CAD) advantage over a stock R/S ratio. In time, that’s a only a 0.045 msec advantage at 8000 rpm. Not much. When it comes to allowing more time for combustion to occur, the difference between these two drastically different R/S ratios is not much, hundredths of a millisecond.

Now, let’s look at what I think are the most important parameters R/S ratios change, combination unit force and “how hard the piston sucks on the intake port.” Combination unit force is the percentage of combustion pressure force that causes a torque on the crankshaft. More torque on the crankshaft is the goal of anything to increase power and torque of an engine.



Combination unit force is determined by the geometry of the slider/crank assembly. If you keep stroke constant, combination unit force is driven by R/S ratio. So, if our goal is to increase power and torque, the higher the combination unit force, the more power and torque we’ll make. However, you also have to remember most torque transferred to the crank occurs during the first 20 to 25* after TDC. I think it’s more important to have a good combination unit force during the 20 to 25* after TDC than to have a good number later in the power stroke, say 75 to 100* after TDC. Looking at the example below, a shorter R/S ratio is much better at extracting power from the combustion chamber force than a longer ratio WHEN IT COUNTS. The peak values increase with increasing R/S ratios, but the peak occurs when virtually zero cylinder pressure is available to push on the piston.

“How hard the piston sucks on the intake port” is also important, and I have to get a better way to describe it. The plot below shows the change in cylinder volume with respect to crank angle. This helps to determine the volumetric efficiency of the engine. But, you can’t just look at how hard it sucks, but when does it suck in relationship to valve lift. A shorter R/S sucks harder, but it’s peak is roughly 70 degrees after TDC, the longer R/S doesn’t suck as hard, but they suck when the intake valve is open more. Translated, it’s easier to get more mass flow and higher VE when the R/S ratio is higher.

So, we have two parameters that want two different R/S ratios. To take advantage of the cylinder pressure you have, you want a short R/S ratio. To get more mass flow and higher VE, you want larger R/S. It’s all a trade off.

Does this analysis solve much? No. I don’t think an ideal R/S ratio exists for all engines. It’s all dependent on the rest of the engine. If an engine is under valved for its displacement, it may benefit with a longer R/S to enable more air and fuel at higher rpm. If airflow is sufficient for the desired speed, a shorter R/S may give more power by utilizing the cylinder pressure you already have. It’s all a trade off and compromise.

On the short deck pro stock engines, I agree with your conclusions. Plus, I’ve spoken to some Comp guys who run old pro stock engines, and he concurs. The reason for short decks is to get better airflow mainly with a side benefit of stiffer pushrod.

On F1 R/S ratios, I looked at paper I have. On the 1989 Honda F1 engines running 2.5 bar of boost. It’s R/S ratio is roughly 2.28. But, I would imagine the engines of today are more concerned about a physically smaller engine to get better aerodynamics rather than a longer R/S ratio.

Chris

I adjusted the equation above in a downloadable graphing
calculator and took a somewhat large screenshot. Its only
43.3k to download though if you're interested (3169x1085 PNG):
http://www.bigblocksix.com/whittey/long_vs_short.png

Blue is stock (short) rod and red is the long rod. The
horizontal orange line is the 0.200" dwell time. In this
map, X=0 is TDC and X=180 is BDC.

Here are some thoughs:

A long rod will have a higher MEP during those beginning crank
degrees due to decreased cylinder volume.

The more 'suck' of a short stroke engine increases pumping
losses. The higher the vacuum, the higher the energy per unit
pressure drop is needed (wordy).

I somewhat disagree with the statement above involving
rotating mass and rpm. The higher the conrod mass the:
1) less power due to inertia
2) increaseed streeses on the crank due to increased inertia
3) increased tension stresses on the rod itself before and
after TDC on the exhaust stroke

Naturally that increases the rod bearing/cap/bolt loads as
well. 

Long rod motors will have higher main bearing stresses than
short rod motors.

A short rod has more dwell at BDC allowing you to keep the
intak open a couple degrees longer (allowing intake inertia to
do some more work instead of just compressing itself against a
closed valve).

How it all averages out? Your guess is as good as mine.


-=Whititey=-

 short rod has more dwell at BDC allowing you to keep the
intak open a couple degrees longer (allowing intake inertia
to do some more work instead of just compressing itself
against a closed valve).


I don't know if you misquoted, but the long rod will have more
dwell time at TDC and BDC. I think everyone is missing the
point with this engine. The RPM gains are a minimal advantage
to the long rod and the torque to the short, the reason you
build a long rod engine when you can is to relieve side load
on the cilinder wall, and transfer more of the energy down the
centerline of the rod as opposed to diagnally across it. I
have pulled many of the same race engines apart with the only
difference being the R/S ratio and rod length and you can see
the difference in the cilinder walls and piston skirts. To
visualize this draw a tall letter I and a short letter Z. The
two horizontal lines are the piston and the crank, the two
vertical lines are the rods. Even with the longer vertical
line in the I, which vertical line do you think will bend or
break first. my example is a little exagerated but I wanted
everyone to get the point. Everyone was getting a little to
far in the wrong direction. As far as the long rod turning
more rpm because of the decrease in piston speed, that benefit
is minimal. The reason the long rod can turn more RPM is
simply because it can phisically do it without breaking parts.

Just my 02
Nick

>I don't know if you misquoted, but the long rod will have more
>dwell time at TDC and BDC.

Nope. Look at the graph I linked above. The red line is the long rod and the blue is stock (short) rod. 180 degrees is BDC. If you were to make a line 5.08mm above BDC (similar to the orange line depicting dwell at TDC) you would see that the short rod has more dwell at the bottom of the stroke.

>I think everyone is missing the
>point with this engine. The RPM gains are a minimal advantage
>to the long rod and the torque to the short, the reason you
>build a long rod engine when you can is to relieve side load
>on the cilinder wall, and transfer more of the energy down the
>centerline of the rod as opposed to diagnally across it. I
>have pulled many of the same race engines apart with the only
>difference being the R/S ratio and rod length and you can see
>the difference in the cilinder walls and piston skirts. To
>visualize this draw a tall letter I and a short letter Z. The
>two horizontal lines are the piston and the crank, the two
>vertical lines are the rods. Even with the longer vertical
>line in the I, which vertical line do you think will bend or
>break first. my example is a little exagerated but I wanted
>everyone to get the point. Everyone was getting a little to
>far in the wrong direction. As far as the long rod turning
>more rpm because of the decrease in piston speed, that benefit
>is minimal. The reason the long rod can turn more RPM is
>simply because it can phisically do it without breaking
>parts.

One interesting thing I looked up... (Forgive me, i'm a Ford guy) Powerstroke diesel has 1.71 R/S which is better than the somewhat buzzy 4.6 liter (1.67 R/S). The 5.4 liter has a 1.6 R/S, which is only marginally better than my favorite motor, the 4.9L (1.56 R/S). When you compare typical life of the gas motors, the 4.9L wins hands down, yet has the worst R/S of the bunch. Yet the buzzy 4.6L has a worse R/S than even a 460 (1.72 R/S). Going through a database of many engines, the largest R/S i'm seeing is on the 4.9L's little brother, the 240cid six at 2.14. That motor peaked hp at less than 4000rpm. Yet you have the Honda H23A4 which put out 195hp at 7000rpm with a R/S of 1.49.

That all said, I think the general consensus is this... Any motor is a compromise. This is just one of them. Would I rather have a long rod over a short rod? Yes. Would I personally pay for that difference with custom rods and pistons? No. If I were already going for custom rods and pistons, of course I would go long rod. Would I consider a short rod to be holding me back? I'd be more worried about tuning.


-=Whittey=-

>Another point of contention is that long rod engines don't
>really have much of an advantage in dwell time, and lose the
>advantage of peak angle when it counts.
>
>The short rod engine puts the unit force vector closer to the
>perpendicular to the crank at an earlier point then a long rod
>engine. For example, in this simple drawing (MS Paint OWNS!):
>
>

This picture does a very good job depicting side load.
Look at the rod angle compared to the cilinder wall at 90 for both engines.

The graph you are using does not apply to this. Remember that the piston pin is the same distance away from the crank pin at TDC or BDC. Your graph would be correct if the piston were not moving with the stroke. Use the ms paint picture, not the graph.

The graph is piston movement. The pictures show a representation of what is happening, the graph shows what is happening at what time. Horizontal is crank degrees. Positive Y is above crank centerline and negative Y is below crank centerline. Do the math yourself if you don't believe it.


-=Whittey=-

http://forums.2gnt.com/dcboard.php?az=show_topic&forum=5&topic_id=48389&mesg_id=48389&listing_type=search

I thought of it first :P

~Tacoman

And I thought it was a bad idea then, too. :P
-=B-=

It really wasn't a bad idea, and it still isnt a BAD idea. It just may not yield the results that people had originally hoped for.

<Rant>

This thread just rubs me the wrong way though. Its ridden with misinformation, and contridicting technical jargon. Please people, if you don't absolutely know 100% for sure that what you are saying is accurate, then don't preach your possibly incorrect information like it's gospel. It's one thing to make a mistake. It's another to make a mistake and keep making it over and over again because you don't truely know what you are talking about. Please think and do some research before you push your theorys on the people who read these threads and would have no idea that what you just said is 100% wrong.

Even though this post is under your's Bill, this rant is not directed at you or anyone in particular. This thread is just a good example of something that's been driving me nuts for a long time now.

</Rant>

What exactly is incorrect?


-=Whittey=-

Since you asked, I will say that what you said about there being less dwell time at BDC with a long rod setup is wrong. Forget the graph that you posted and look at the drawing. It is physically impossible for the piston to have more dwell time at TDC, but less at BDC. TCD and BDC dwell time will always be 100% equal and a long rod setup will always have more dwell time than a short rod will.

It was also mentioned earlier that a short rod motor would create more power because it pushes harder in a tangential direction and it pushes harder earlier on in the stroke when cylinder pressures are higher. He suggests that a short rod motor would actually be advantagous to a long rod because of this.

In response to this, what was said here makes sense, but these factors do not give an advantage to a short rod motor. Because of the increased dwell time at TDC of a short rod motor, and the fact that it has smaller rod angles, it WILL create more power. The more dwell time you have, the more power is conserved in the crank. This is because the more dwell time you have, the less time you spend wasting power moving the piston vertically. Also, it allows the crank to spin relatively freely, instead of having your rings soak that energy up creating friction against the surface of the cylinder walls. Granted, the short rod may convert more vertical force to radial force for the first few degrees of rotation, but with a long rod, after combustion the piston remains where cylinder pressures are the highest for a greater amount of time. Ideally, cylinder pressures are highest near 20 deg ATDC, and the piston remains in that region for a longer period of time with a long rod. At every following point of the rotation, the long rod has the advantage because the rod angle is smaller. All of this adds up to a higher average amount of force on the crank for every 180 deg of rotation. And then you eat the pudding and its all good. The less you have to make the vertical motion move horizontally, the more power you'll make.

Anyway, the amount of actual gain in power of a long rod setup is not the main goal of a long rod setup anyway. It's just a small side effect because you wont be gaining much. Its main purpose is to decrease the side load on the cylinders.

I don't feel like picking this thread apart anymore though... You get the point :). If I came off negatively here, I'm sorry. It's not that it bothers me when somebody posts misinformation on accident. It more bothers me that people read it and accept it as the truth because of who said it... like God himself came down from the heavens and said that short rod motors are better than long rod motors or something lol. I don't like it when people argue with me based solely off of someone else's opinion which is what happened to me last night and got me all annoyed.

I've been on the net a while and have long since been bothered if it seems that people are pissed at me. Written word doesn't convey nearly enough emotion. Then again, even if people are pissed at me, I don't worry about it :)

As for the dwell at BDC vs TDC, it is true. There is less dwell at BDC than at TDC. At 90 degrees (horizontal crank), is the piston at the same spot with a long and a short rod? No. At only two specific points will the piston lift be the same no matter the rod length. TDC and BDC. At all other times they are at different places at any particular degree.

Lets think of it this way. You know that a long rod has a lower peak piston speed. Well, how would speed be on a graph with angle and lift. Steepness of the angle. You also know that a long rod motor will have more dwell at TDC. So the only variables right now are steepness of the line on a graph (speed of the piston) and where that line 'connects' with the BDC dwell curve. If the BDC dwell curve is wider (more dwell), how can it have a lesser angle than a short-rod setup?


-=Whittey=-

From my favourite M3 crowd... http://www.e30m3performance.com/tech_articles/engine-tech/rod-ratio/kin2.htm

From page 2: "As the rod gets shorter, on the other hand, the max. piston acceleration is increased, but only at TDC. At BDC, the piston acceleration is actually reduced by a shorter rod (at least intially). The piston acceleration curve also begins to form a characteristic "double-hump" shape. If one were to keep making the rod shorter until it was only as long as the crank arm radius (a shorter rod than this would prevent the crank from completing a rotation), then the piston essentially would come to a "sudden" stop at 90° ATDC and it would "suddenly" start moving upwards again at 90° BTDC. These sudden stops and starts lead to infinite acceleration at 90° after and before TDC, and this is what the double-hump is starting to show."

>>But wait, there's more!<<

This man has forgotten more about engines then I think that I will ever know. Great guy, and a guru, if anyone can be called that.

http://www.iskycams.com/techtips.html

"In fact, this may surprise you, but I know of a gentleman who runs a 5.5" Rod in a 350 Small Block Chevy who makes more horsepower (we're talking top end here) than he would with a longer rod. Why? Because with a longer dwell time at BDC the short rod will actually allow you a slightly later intake closing point (about 1 or 2 degrees) in terms of crank angle, with the same piston rise in the cylinder. So in terms of the engines sensitivity to "reversion" with the shorter rod lengths you can run about 2-4 degrees more duration (1-2 degrees on both the opening & closing sides) without suffering this adverse affect! So much for the belief that longer rod's always enhance top end power!"

So Whitey isn't wrong. In fact, the "gospel" that he is "preaching" happens to be based on real theorums and observations. The math is real, and real good, at that. Pot, meet kettle.

-=B-=

>From my favourite M3 crowd...
>http://www.e30m3performance.com/tech_articles/engine-tech/rod-ratio/kin2.htm
>
>From page 2: "As the rod gets shorter, on the other hand, the
>max. piston acceleration is increased, but only at TDC. At
>BDC, the piston acceleration is actually reduced by a shorter
>rod (at least intially). The piston acceleration curve also
>begins to form a characteristic "double-hump" shape. If one
>were to keep making the rod shorter until it was only as long
>as the crank arm radius (a shorter rod than this would prevent
>the crank from completing a rotation), then the piston
>essentially would come to a "sudden" stop at 90° ATDC and
>it would "suddenly" start moving upwards again at 90°
>BTDC. These sudden stops and starts lead to infinite
>acceleration at 90° after and before TDC, and this is what
>the double-hump is starting to show."
>
>>>But wait, there's more!<<
>
>This man has forgotten more about engines then I think that I
>will ever know. Great guy, and a guru, if anyone can be called
>that.
>
>http://www.iskycams.com/techtips.html
>
>"In fact, this may surprise you, but I know of a gentleman who
>runs a 5.5" Rod in a 350 Small Block Chevy who makes more
>horsepower (we're talking top end here) than he would with a
>longer rod. Why? Because with a longer dwell time at BDC the
>short rod will actually allow you a slightly later intake
>closing point (about 1 or 2 degrees) in terms of crank angle,
>with the same piston rise in the cylinder. So in terms of the
>engines sensitivity to "reversion" with the shorter rod
>lengths you can run about 2-4 degrees more duration (1-2
>degrees on both the opening & closing sides) without suffering
>this adverse affect! So much for the belief that longer rod's
>always enhance top end power!"

Nice quote by someone else. I can give you 100 quotes by other people with 350 engines that will tell you that long rod motors will give you slightly more power. There are more arguements that long rod motors will produce more power than short rod motors will. That is of course to a point. For example, a chevy 350 motor, as you quoted earlier, uses a 5.7" stock rod if I remember correctly. A 6" rod has been proven to consistantly add more power than a 5.7" does. Not much, but if there is no cost difference then why not go for it... With a 5.5" rod, even if that guy were able to gain a tad bit more power than you did with a 6" rod by gaining a few degrees in intake duration, what you lose in the durability of your engine would not be worth it. And by the way, he would not have the ability to increase the intake duration without aftermarket cams. Using stock cams only, which setup do you think would make more power? I highly doubt there are many if ANY 2gnt guys that are looking to trade a significant amount of engine life for just a touch of extra HP.

Also, where you are gaining a extra few degrees of duration at the opening and closing of the valve, you gain more airflow when it counts with a long rod WITHOUT using aftermarket cams. Peak piston velocity is usually somewhere around 75° ATDC and since most cams cannot fully open the cam until at least 106° ATDC, it leaves the valve as a major obstacle when airflow demand is at its greatest. By delaying peak piston velocity, even if it's only 1 or 2 crankshaft degrees, it can allow the valve to open another 0.010-0.015", before peak airflow demand is reached. Not a huge help, but a step in the right direction.

>Pot, meet kettle.

Whatever, maybe if you are talking about pant sizes. I'm done arguing here Mr. Knowitall.

"Whatever, maybe if you are talking about pant sizes. I'm done arguing here Mr. Knowitall."



You sir.....are a dick.....good day.

Wait a sec. "keep making the rod shorter until it was only as long as the crank arm radius." :nono I hope you realize in the name of all that is holy that you CANNOT do that. Why? Try to visualize exactly where the piston would be located at bdc and 90 degrees from bdc and tdc. If the rod is only as long as the crank arm radius...the piston would have no choice but to be positioned IN THE MIDDLE OF THE CRANK!!! :thumbsup I mean...for real

Ok I'm not going to get into some big argument here. The only thing I am going to say is I agree with Matt. The only thing I am going to back my arguement up with is the fact that we build 2500 horsepower 50psi alcohol engines, 12,000 rpm endurance engines, Trans Am engines, winston cup engines, street engines, You get the point... Whenever longevity is a concern, We will ALWAYS design in the longest rod possible, keeping the pin out of the oil ring. If anyone has more experence Doing what we do for a living, with avarage experence around 25 years (building race engines, not rebuilding your dads 350 chevy) We probably know them. Everyone we know in this field of high end engine building share our view.

i think its pretty fair to say that vt knows their shit

u all got owned.
_________
96 talon esi-t
san clemente, ca

Well, I guess that I am through with this, since I seem to have offended the guru.
Sorry about that.
-=B-= <=== Mr. Knowitall

By the way, you were the one to start with the ad hominim attack. If you think that I am wrong, I am perfectly willing to read why you think so, and if I am indeed wrong, admit so. I am not denying that the long rod motor could generate more output, but I am not sure that the 420a could would be compatable with a long enough rod to make this worthwhile. Don't take my dissent to mean that I disagree with absolutely everything that you say. There is just one point that I felt needed clarification, and that is dwell time at BDC. You explained why it isn't important, and that is good enough for me. What Whitey said, however, was true about the BDC dwell time. There is a longer period at BDC with a short rod engine. He isn't preaching anything false. What him and myself may have erred on was the importance of said dwell time.
And the waistline comment... well, I didn't appreciate it. I won't attack you personally, and I would appreciate the same courtesy.
-=B-=

>And the waistline comment... well, I didn't appreciate it. I
>won't attack you personally, and I would appreciate the same
>courtesy.

You did attack me personally. "Pot, meet kettle" to me is an arrogent attack at me suggesting that you are greater, or wiser than I am. It was a whitty remark that I followed with a quick, less mature response. I apologize for that remark, but understand that it wasn't coming out of nowhere. You can't just call someone inferior and then expect them to say nothing.

As for the TDC vs BDC dwell time, I think we are on different pages. You guys are correct that the piston velocity is greater nearing the bottom of the stroke, but the actual time that the piston sits at the bottom of the bore while the crank rotates is what I was talking about. I think that we have mixed definitions of what dwell is. If not, I dont want to keep going on this anyway, so I call a truce. No hard feelings.

Dwell is, in this case (as established above) time spent in the sub 0.200 inch margin. Dwell for a longer rod is shorter at BDC than for a short rod. It's math. That is where the graph came from. If you do not believe what I am saying, please prove it wrong. Mathematically.


-=Whittey=-

Well, I spent about an hour today messing with different numbers and creating different graphs on the same program you used. I double checked your formula and found it at: http://members.bellatlantic.net/~vze2p5sj/engine1.htm. I must say, you have me stumped... Mathematically, it does work out, but the physics of it seem impossible. I'm still not sure how sound that formula is though. That is the only place I was able to find it and it was posted by some guy as a reference for 2 stroke engine tuning. Coming up with a physical explanation of how TDC and BDC dwell could be different surpasses my skills. Hmm, that will give me something to think about for awhile :+. I don't suppose you have a good physical explanation for how this would be possible??? Either way, I retract my previous statement. I'm still not totally convinced, but you definately had good reasoning behind your statement.

http://www.engineersedge.com/engine_formula_automotive.htm is where I originally got the equasion from.

I'm at work now and can't quite think about this, i'll try to think of something tomorrow (circle track racing tonight, wewt).


-=Whittey=-

**That's** what I have been saying. My Pot, meet kettle comment was to explain how I was stumped about how you could find the flaw in other people's logic without working it out. No hard feelings intended, it just seemed kinda funny.
-=B-=

well now wasn't that an interesting thread to read =)

Bill

>**That's** what I have been saying. My Pot, meet kettle
>comment was to explain how I was stumped about how you could
>find the flaw in other people's logic without working it out.
>No hard feelings intended, it just seemed kinda funny.

Well, I obviously took that comment differently than it was intended. I truely apologize for that remark. It's difficult to find the true meaning behind what people say when you are reading it instead of hearing it. On a side note, it was a mind stimulating discussion, so I suppose some good came of it... even though the topic motor isn't even possible hahaha. Anyway, as I said before, no hard feelings. You're alright in my book and I hope the feeling is mutual.

by reading this thread i just owned myself....I bow down to you seemingly all knowing masters of the 420a

it seems like every controversial topic on this forum either winds up two ways, a "mutual agreed apology" or a thread lock :P

wow, thought i would read this thread cuz im gonna be rebuilding my engine soon and wanted to check out some poss. and now im just totalled confused, but i do see what matt is saying that tdc and bdc dwell times should be equivelent, just doesnt make physical sense, but anyway so ur saying if u had a choice between a 420a standard rod or a 420a long rod which would u pick, for the $100 diff. in rebuild kit prices from howell i wouldnt see y not go for the long rod if your increasing engine longevity and some power gains, So here is my question for u, putting the $100 diff. aside would u go long rod or standard on a boosted car, and does the long rod create any valve clearence issues on our car?


Mods:
CAI, OBX exhaust, Grillcraft grills, altezzas, ard ryver g6 17's wrapped w/ falken's, VIS racing c.f hood, 2 12" kicker comp's w/pioneer h.u, streetglow blue undercars, red dash kit, indiglo guages, n other shit

Well, the long rod engine uses the 2.4 block, which is not a direct bolt in.... you'd have to have custom engine mounts & custom oil pan fabricated...

"Michael_97RS: Why bother, you'd have an easier time getting Mother Theresa to give you head than getting MrLocalPimp to behave."

i didnt think the long rod used the 2.4 block, im pretty sure it uses our block w/ a longer rod and custom pistons so that it would clear the valves.

Mods:
CAI, OBX exhaust, Grillcraft grills, altezzas, ard ryver g6 17's wrapped w/ falken's, VIS racing c.f hood, 2 12" kicker comp's w/pioneer h.u, streetglow blue undercars, red dash kit, indiglo guages, n other shit

You're talking about two different things. This thread is about using the 2.4 block with custom long rods. The rods would be about 1 inch longer. The howell rebuild kit uses the 2.0l block and custom long rods and pistons. Howell's rods are 0.136 inches longer. They move the wrist pin on the piston higher to complement the long rod. There should be no inherent change in compression ratio or valve clearance with the Howell setup. These are very different animals.

Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire