>Armond, thank you for your thoughts. It makes much more
>sense now. Its what I intended out of this thread, really.
>This brings me to another question, though. From what you
>are saying, we cant have the best of both worlds, right? I
>plan on rebuilding with 8.5:1 pistons. I plan on at first,
>running 10 psi, then going up to 15 psi. What do you think
>will be the best setup for this? You are saying to run
>around 11.0 - 11.3 or so A/F ratio, at WOT boost? With NO
>spark retard, just running the stock ecu WOT timing curve?
>Is that right? How high of boost can I go with the 8.5
>compression, without using any spark retard, or before
>detonation sets in? I'm very curious.. I as are many others
>are going this setup, or may already have their motors set
>up with this or close compression ratio. At what point do
>you think we *need* to retard timing? From what I thihk you
>are saying, we need to add more fuel, increasing the actual
>A/F ratio, as boost pressure increases, INSTEAD of retarding
>timing? If thats the case, then all of the literature i have
>read up on, ect..is wrong? All of what i have read says with
>increased cylinder pressure, you need to retard timing, AND
>add the fuel of course..



hmm. that is a pretty full question. (me like ). you can not have the best of all worlds (when you are looking for power, there is more than just timing and boost). fuel grade, exhaust temperature, and intake temperature all are equally important on a turbocharged car. the type of turbocharger is really essential in figuring out maximum boost capable of achieving safely. if all you intend on running is 15 psi, a super 16g turbo with a short manifold (like the hrc setup) will do the job nicely and smoothly. the 16g has a lot of the same characteristics as my 20G, including the same turbine housing. wiht this turbo, you will start to notice "stuff happen" at around 15 psi. that is when the egt's jump up for no apperant reason at the same air/fuel ratio. if you run a missing link orvc-2 or whatever, keep a close eye on yoru ignition timing. at 10 psi, you can get away with 12.3 or so air/fuel ratio on the dyno (12.7 or so on the street max), and the car will be more efficient, but around the 15 psi range, the air/fuel ratio needs to decrease with the increase in egt's (which usu. puts it around 11.5 on the dyno, and 12.0 on the street. going slightly higher to around 20 to 21 brings you past the hump in the effiency curve and that's where your air/fuel ratio needs to stabalize around 11.1 on the dyno. everything beyond that is usu. ok at that air/fuel ratio, depending on yoru fuel grade. that becomes the main variable in extreme cylinder pressure conditions (meaning no matter what air/fuel ratio you go to, the fuel is going to burn too violently irregardless........unless you go with a thicker fuel . that happens when you get out of the linear range where fuel burns (between 10.5 to 17.0 air/fuel ratio). in a nutshell, what I am trying to say is when your turbo gets to work, and starts increasing engine load by a "good deal" (when you start getting exhaust backpressure, and heat starts seeping out of stuff). you richen up the car until you get to that point where fuel won't burn, then you have to go to another level of fuel, in which case, you start out adjustments at a higher point again because the extra control gtiven by the octane count can be counteracted by the intensity of the burn via the air/fuel ratio. (this is confusing even sayin it, so I will giv ea different comparison.....I wish I could use a graph). say you get into your engine/turbocharger's peak effiency range (where your car starts makign stupid power and starts makign wierd noises usually). for my car, that is between 15 and 21 psi with the wastegate open. below this point, on 93 octane gas, air/fuel ratio can be around 12.3 to 1 (minimum)on the dyno with no problems due to lack of load (less force). above this range, 93 octane gas can't be controlled well enough to give a safe consistent burn. in between this range there is a slope of safety, which extends higher in the lower range (that's why some all motor cars can run 14.5:1 on a daily basis and now blow up. this is all assuming constant ignition timing (in this case 18 degrees advance. at around 21 psi, you would have to run at about 11.5 to 11.3:1 in my car at that ignigion timing to keep the burn strength down in a controllable range (below 1550 degrees) on the street. on the dyno, the car must be tuned for even lower air/fuel ratio due to lack of load from drag (that is why I always blew my engine going around 130 mph). sure, you could run higher boost on the street if you tuned for even lower air/fuel ratio, but that is "very close to being either "hit or miss" as far as attomization goes at those cylinder pressures (which causes pre-ignition, and/or incompressibility of the fuel). when you go to a higher octane fuel, it burns slower, so less thermal energy is released (i.e. lower egt's.....which is usu. deemed becasue the engine isn't working as hard......that's wrong). with this more controlled fuel, you can run even higher air/fuel ratios to bring the combustion "violence" up to par, without havign to worry about overloading the cylinders with liquid. that is why you have to run high octane gas to run higher boost safely. this is also why I tune for 11.3:1 at 30 psi with 116 octane fuel. it has been proven that my ca rca rrun "drastically leaner" than that on high octane fuel, but dammage happens a LOT faster and a LOT les forgiveing at higher boost levels than at lower boost levels. (that is a mouthfull, but I hope that explains the entire air/fuel ratio curve deal). with 18 degrees of timing advance (stock with a missing link on a boosted 420A) you should be safe runnning 11.5:1 on the dyno at 15 psi. the street will increase load according to speed. if you run 130 mph plus on a regular basis, I would reccomend tuning a little richer than this. mayb 11.3 maximum on teh dyno). having a wideband o2 sensor in the car is even better, that way you can see exactly what is happening, and when your air/fuel ratio is increasing due to increased load on the motor. if you tune for 11.3 to 11.1:1 air fuel ratio on the dyno, at 18 psi, you should be able to run 93 octane gas safely without timing retard (granted your ignition timing stays at a max of 18 degrees). this will put you at about 11.7 to 11.5 on the street. that is pushing it for pump gas on a decently efficient 4 cyl car. I reccomend running a slight mix of high test gas if you can for 18 psi (I don't kno why I dont' take my own advice.......probably becasue I don't mind fixing my own car as much as I mind fixing others). over that, I would "really consider running "pure" 100 octane fuel for stock ignition timing. you can run a mixture of half and half after 18 psi........IF you retard the timing 3 or so degrees (keeping the car at around 11.1:1 air/fuel ratio on the dyno, and 11.5 on the street). the extra thick fuel will keep temperatures moderately down, and the retarded timing will reduce the extra force put on the entire system. retarding timing below 15 degrees advance is "iffy" and should never be necessary if the correct grade and correct ammount of fuel is used on any application. once you start doign that , you start transfering combustion energy from makign the piston go up and down, to making the turbocharger spin (which is good in some cases....i.e. if you need spool IMMEDIATELY like during a rally race), but it also transfers the dammage. 1600+degree heat will break "something" saying you have to retard timing under boost is a generic tip, like saying you have to have a blow off valve if you run over 6 psi. there is more to it that is really in-depth that most people skip over. I hope I explained it well enough.



this next one is kinda long. I will try to break it apart in steps.


>>
>"Understand that, in our quest to delay cylinder pressure’s
>peak time, more is not necessarily better. Instead, consider
>that the ideal cylinder pressure would be just short of
>detonation pressure


not true. detonation pressure is usu. EXTREMELY higher than the engine bearings and cylinder components can handle. this is why detonation hamers out rod bearings, whereas normal compression......even high hp compression doesn't.

and this pressure would be maintained
>from top dead center, and as long as possible after TDC. If
>timing is really late, you won’t build enough cylinder
>pressure to start the car, let alone drive it. The 1000 PSI
>pressure in the example is not the maximum allowable
>combustion pressure but, rather, a comfortable pressure for
>illustration of the work principle.
>
>Some nitrous manufacturers recommend, "retard the timing two
>degrees for each fifty horse power of nitrous". Other
>nitrous kits have the flame speed artificially slowed by the
>intentional use of a rich fuel to nitrous ratio. The maximum
>performance engine with a heavy nitrous load must achieve
>peak cylinder pressure progressively further after TDC. The
>heavy load engine will have the fuel and oxygen mix to make
>high cylinder pressures, with the combustion chamber size
>being drastically increased due to the piston being on its
>way toward bottom dead center. The strongest engines have
>less compression ratio, less spark advance, and more
>nitrous.

also not true.........the most reliable engines have less compression, lower spark advance, and more nitrous. the more timing advance you add, the more power you will gain, on anything (not saying that it will hold together, but it will make more power without question). same thing with compression. gary howell hit on compression and boost before amd made several good points about that.


>
>I have tried to explain the reason for a spark retard system
>in a Nitrous engine. However, many people just don’t like
>the idea of any retard. They say, "retard timing and exhaust
>heat goes up". It usually does in a stock nonnitrous engine
>because lower peak cylinder pressure slows the burning. If
>the timing is retarded in a non-nitrous engine, the exhaust
>opens before the fuel mix is finished burning and exhaust
>temperatures go up. Piston temperatures usually go down and
>exhaust valve temperature goes up.

exactly correct

In the nitrous engine,
>exhaust temperature goes up for several reasons. The first
>is that the power output has gone up considerably. More
>power usually produces more waste heat. Second, the need to
>keep maximum cylinder pressures within reason has dictated
>that the biggest part of the fire happens closer to the
>exhaust valve opening time. There just isn’t enough piston
>travel to extract all the energy out of the charge before
>the exhaust valve opens.


this happens anytime power generated is increased drastically (i.e. turbocharger entering it's peak efficiency range). Now, we could and sometimes do,
>open the exhaust valve later so more combustion pressure
>energy can be used to turn the crank. The trade off is
>negative torque on the exhaust stroke. If we still have
>significant cylinder pressure in the cylinder as the piston
>moves from BDC to TDC on the exhaust stroke, your net Hp
>falls drastically. A real problem at higher RPM."

I want to hear more




>
>This is the link to all of it:
>http://www.kb-silvolite.com/page14.htm

A.D.P.
"...If you do too much, people become dependant. If you do to little, people loose hope. If you do it right, people won't be sure you've done anything at all."
bring it on............

A.D.P.
"...If you do too much, people become dependant. If you do to little, people loose hope. If you do it right, people won't be sure you've done anything at all."
bring it on...........