Detonation is caused by two things.

1) Increase cylinder pressures. Which can be caused by either forced induction or higher compression pistons or both.

2) Gasoline that burns too fast and lights to easily. Race fuel is harder to light off, and burns slower. Cheap gas burns easier.

As you increase cylinder pressure you have to introduce fuel that burns slower. You have to do this because the molecules are closer together and the reaction will travel faster, thus concentrating the explosion time wise. What happens is explosion happeneds before you get to TDC, and the piston is trying to come up, and the explosion is trying to stop it from coming up. The piston then cocks side ways, and that is what you hear, the piston slamming into the cylinder wall. If you put a slower burning fuel (i.e. race gas) in the engine then the bulk of the explosion will take longer time wise and occur after TDC and stop the detonation, and you make more power.

You can also stop deonation be retarding the timing. What happens here is you light the mix later, or closer to TDC. By the time the explosion ocurrs fully, you have crossed TDC, and the explosion happens late enough not to cause detonation.

Timing and fuel are everything. As long as you control detonation, you can run whatever compression you want, but the higher the cylinder pressures go the more timing and fuel become critical.

Boost; 14.7 psi is the pressure of the air we breath at sea level. So we an engine that will draw in 2.0 litres of air at atomosphereic pressure. So if you put 7 pounds of boost on your engine, the engine thinks it is a 3.0 liter, because that is the amount of air you are moving through it. At 14.9 pounds of boost it thinks it is a 4.0 liter and so on. Ever notice that at 7 pounds of boost engines make about a 50% increase in power, that is because they think they are 50% bigger.

Compression ratio; Every 1 point you increase in compression gives you a 4% increase in horsepower. 9.0 to 10.00 on a 100 horse engine will yeild you 104 horse engine if everything else remains the same. And the same holds true for every point you increase. That is why a 12.5 engine runs better than a 9.5 engine. Now that holds true no matter what atmospheric pressure is. So a 12.5 to 1 engine will make more power than a 9.5 to 1 engine at 7 pounds of boost, at 14 pounds of boost and at 30 pounds of boost. BUT... the increase cylinder pressures require you to control detonation. As long as you can control detonation, you can run these boost levels.

Lets make this simple. We have a 100 hp engine with 8.5 to 1 compression. We put 15 pounds of boost on it, now we have a 200 hp engine. Now lets build a second engine with 12.5 compression. The first jump we goto 9.5 and get 4% to 104 hp, now we got to 10.5 anf get 108.16 horse, now to 11.5 and 112.48, and finally 12.5 we get 117 hp, now we add our 15 psi of boost and we got 234 horse power engine. So at 15 psi a 12.5 to 1 engine will make ruffly 17% more horsepower. That wins races.

Now because of detonation you may need to pull more timing out, and may loose part of that horsepower at high boost levels, but you will get there quicker, and on the bottom end of the race track you should make enough of a difference that the low compression car can't run you down on the big end of the track. With the electronics in timing we have a 12.5 to 1 15 psi street motor is a reality. Now if you go all out on a race engine. the 12.5 motor may be limited to 28 psi, where a 8.5 to 1 may be able to go to 30 psi without detonation, but I would put my money on the 12.5 engine.

My buddy has a drag bike running 35 psi on 13.0 to 1, but he is running on methanol which burns much slower than any gasoline. High compression and turbos do work.

gary

Visit the Howell Automotive Open House August 20th, 2005. The largest gathering of Chrysler 2.0 engines on the planet.

US Small Business Administration Export Business of the Year for 2003

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Thanks for explaing, it really helpped me understand on what is going on thanks for the time to type that up

Boca Raton, Florida
95 Eclipse GS- sold
99 Eclipse GSX- 386awhp
98 Eclipse GS- sold
92 Prelude

I know it can be done, it just comes down to can the engine take that abuse of 12.5:1 plus boost on pump gas on the street. Most likely no, thats why 12.5:1 would be a streetable all motor but in order to boost it, it would have to be race only.



current status unknown

http://hometown.aol.com/ohshootuhh/

Perf:
KYB AGX Struts
Neuspeed Sport Springs
5 Strut Bars (2 F/U, F/L, R/U, R/L)
Sprint Front Camber Kit
$15 Rear Camber Kit
Corbin's A/F Gauge
MSD DIS-2 Ignition System
Some Regrind Cams that need High Compression (which I don't have)
Ported Intake Manifold
Ported Throttle Body
Nameless Cold Air Intake with a K&N Filter
Custom 2 1/2 inch exhaust with Dual DTM Muffler
Empty Catalytic Convertor
Energy Suspension Motor Mount inserts
Hurricane_GS Short Shifter
Symborsky Shift Kit
Clutchmasters Stage 3 Modular
225/50/16inch Wheels and Tires


Audio:
Alpine CD Head Unit
Alpine Flex4 25W X 4 for Fronts and Rears
Alpine V-12 450W X 1 for Subs
Infinity Reference Series 5 1/4 and 1 inch tweeter component systems for fronts and rears
Blaupunkt 3 way 6x9's in the rears
3 MTX 5000 10" 12 ohm subs running 4 ohms mono

Flame Red SRT-4 GT40,8.5:1 Built Shortblock, Brian Crower Stage 2 Cams, etc etc etc...

>I know it can be done, it just comes down to can the engine
>take that abuse of 12.5:1 plus boost on pump gas on the
>street. Most likely no, thats why 12.5:1 would be a
>streetable all motor but in order to boost it, it would have
>to be race only.
>
>

It would be boardline at best, but it does leave the 10.5 option open. Or you could run 12.5 and a boost controller set for 4 psi on the street, and when you put the race gas in at the track, crank that baby up and kick arse

Visit the Howell Automotive Open House August 20th, 2005. The largest gathering of Chrysler 2.0 engines on the planet.

US Small Business Administration Export Business of the Year for 2003

Visit Howell Automotive at www.howellautomotive.com

that's awesome info man. It's so much better then anything we could learn at school. THANKS!

16.1 @ 87.11
http://www.virtuallyinfamous.com

ARD 57mm tb and p&p manifold, Neuspeed STB, Pro-kits, Illuminas, Injen CAI with K&N, 2.5" pacesetter catback,
AF/X UDP, Rear STB, Powerslot rotors, RRE SS Brakelines.

There is a guy here in Tampa running 8psi on 11.5:1 compression stock internals on a Honda S2000 on 93 octane.

Here's some pics:








current status unknown

http://hometown.aol.com/ohshootuhh/

Perf:
KYB AGX Struts
Neuspeed Sport Springs
5 Strut Bars (2 F/U, F/L, R/U, R/L)
Sprint Front Camber Kit
$15 Rear Camber Kit
Corbin's A/F Gauge
MSD DIS-2 Ignition System
Some Regrind Cams that need High Compression (which I don't have)
Ported Intake Manifold
Ported Throttle Body
Nameless Cold Air Intake with a K&N Filter
Custom 2 1/2 inch exhaust with Dual DTM Muffler
Empty Catalytic Convertor
Energy Suspension Motor Mount inserts
Hurricane_GS Short Shifter
Symborsky Shift Kit
Clutchmasters Stage 3 Modular
225/50/16inch Wheels and Tires


Audio:
Alpine CD Head Unit
Alpine Flex4 25W X 4 for Fronts and Rears
Alpine V-12 450W X 1 for Subs
Infinity Reference Series 5 1/4 and 1 inch tweeter component systems for fronts and rears
Blaupunkt 3 way 6x9's in the rears
3 MTX 5000 10" 12 ohm subs running 4 ohms mono

Flame Red SRT-4 GT40,8.5:1 Built Shortblock, Brian Crower Stage 2 Cams, etc etc etc...

Yes, for two cars running the same boost but one at 9.5 to 1 and the other at 12.5 to 1, the 12.5 to 1 compression car is going to be faster.

Although, as you described, running higher compression gives you a "modest" HP increase. (1 point is 4%) Now modest is a reletave term. 4% would be a huge increase for some forms of racing (which is why, as you pointed out, that wins races) but it could be considered modest when you compare the HP difference between a turboed vs. non turboed car, especially a "street" car.

My point being, since there is a "total" cylinder pressure you can run (which comes from a combination of your compression ratio and your boost pressure), if you are maxing out your engine internals to this "total cylinder pressure," wouldn't it be more advantageous to run a lower compression ratio and more boost? That way the total power would be the same, since you would be running the same total cylinder pressure. You are just doing it in a different way, with lower compression and more boost, not more compression and less boost.

That seems to be the route some 4G63 owners continue to take. I would think it is "safer" and more economical to run a lower compression ratio. It would be safer because you do not risk getting knock as much when you are not at the track. You can be safe running lower octane gas and save money in the process (lower octance costs less). When it's time to race at the track, you just turn that boost up to the max level the internals can take and run that race gas. The power loss from the lower compression, and the lower fuel economy, isn't too significant on the street since that drop in power is, again, "modest" with a drop in compression ratio.

If you are running 12.5 to 1, even if you turn your boost controller to 0 you STILL need high octane. You are going to be spending more on higher octane gas and at 12.5 to 1 you are putting your engine more at risk for knock.

Just want your opinion on this. I always like a good technical discussion

"Tutto fa brodo."

Todd Scungio
98 RS
15.173 @ 90.70 MPH

And also a 2011 Ralliart

I agree Todd. And even as Gary has mentioned, it's all about fuel and timing. It seems to me that your timing can be more aggressive if your CR is lower.

I'd rather have more aggressive timing with lower compression rather than conservative timing with hihg compression.

_____________________________________
Jason ESi-T

04' BMW 325Ci
91' Nissan 240SX
98' Eagle Talon ESi (sold)

>I agree Todd. And even as Gary has mentioned, it's all
>about fuel and timing. It seems to me that your timing can
>be more aggressive if your CR is lower.
>
>I'd rather have more aggressive timing with lower
>compression rather than conservative timing with hihg
>compression.

It is my assertion, that if we put our two theories to the test, that my theory would win races. In practice is winning races. Your theory was the prevaling theory not that long ago and it wone races, and at that time running that way was the very edge of want an engine would stand, but now we have moved the edge farther out. Our knowledge of how a turbo system works is ever changing. In the 60's the Chevy Covair Monza Turbos didn;t have wastegates, they used a restrictive muffler to control spool, rust up a muffler an you blew the engine. Progress marches on, we must embrace new theories and practics.

Visit the Howell Automotive Open House August 20th, 2005. The largest gathering of Chrysler 2.0 engines on the planet.

US Small Business Administration Export Business of the Year for 2003

Visit Howell Automotive at www.howellautomotive.com

>Yes, for two cars running the same boost but one at 9.5 to 1
>and the other at 12.5 to 1, the 12.5 to 1 compression car is
>going to be faster.
>
>Although, as you described, running higher compression gives
>you a "modest" HP increase. (1 point is 4%) Now modest is
>a reletave term. 4% would be a huge increase for some forms
>of racing (which is why, as you pointed out, that wins
>races) but it could be considered modest when you compare
>the HP difference between a turboed vs. non turboed car,
>especially a "street" car.

But then you not comparing apples and apples. The 4% is exclusive of other mods. If you took our base 100 hp engine, and added headers, air intake, intake manifold, cams etc, and got it to 150 hp, then put the high compression pistons in, then you still get 4% or 6 hp.

>
>My point being, since there is a "total" cylinder pressure
>you can run (which comes from a combination of your
>compression ratio and your boost pressure), if you are
>maxing out your engine internals to this "total cylinder
>pressure," wouldn't it be more advantageous to run a lower
>compression ratio and more boost?

That was the thinking a few years ago. That idea is a hold over from a bygone era. With today's ignitions and fuel management systems you can run a lot closer to the edge. The lower is better idea came in an era of carbs and points, we have much better systems now. Volvo sells a factory 10.5 to 1 turbo engine now.

> That way the total power
>would be the same, since you would be running the same total
>cylinder pressure.

That is not what Boyles Law states. With the higher compression you are starting an explosion in a smaller space. So the intial hit is harder since it is not spread out over a a larger area. The flame travel propogates better.

> You are just doing it in a different
>way, with lower compression and more boost, not more
>compression and less boost.

It is different. But the higher compression works better in practice. In Pro Star Funny Bike classes, which are running turbos, they are running high compression some 15 to 1. Once the first guy went to high compression everybody was left scratching there heads, as they could not keep up. When they went to high compression they caught back up. So in reallity the high compression guys, are beating the lower compression guys.


>
>That seems to be the route some 4G63 owners continue to
>take. I would think it is "safer" and more economical to
>run a lower compression ratio.

It is safer, but it is not faster. If your racing high compression will win, on the street we can probably find a compromise. 10.5 with 8 psi, or 12.5 with 5 psi. The higher compression will yield better fuel economy as well.

> It would be safer because
>you do not risk getting knock as much when you are not at
>the track. You can be safe running lower octane gas and
>save money in the process (lower octance costs less). When
>it's time to race at the track, you just turn that boost up
>to the max level the internals can take and run that race
>gas. The power loss from the lower compression, and the
>lower fuel economy, isn't too significant on the street
>since that drop in power is, again, "modest" with a drop in
>compression ratio.

It all comes down to who is the most modest, the guy willing to let it hang out there for the world to see wins. We learn new stuff everyday, if you don't build on what you know you stay in the same place. If you keep running low compression, you may not learn the next secret.
>
>If you are running 12.5 to 1, even if you turn your boost
>controller to 0 you STILL need high octane. You are going
>to be spending more on higher octane gas and at 12.5 to 1
>you are putting your engine more at risk for knock.

Pull timing out, we have been runing 12.5 pistons on the street for 2 years in a 420A, with a timing retard close to 30K miles now on pump gas, and then we crank the timing and fuel to it at the track.

>
>Just want your opinion on this. I always like a good
>technical discussion

It comes down when you playing the game who get to the other end first, and that is the only rule, then you have to bring your biggest gun out first. Playing it safe is not an opition.

Gary

Visit the Howell Automotive Open House August 20th, 2005. The largest gathering of Chrysler 2.0 engines on the planet.

US Small Business Administration Export Business of the Year for 2003

Visit Howell Automotive at www.howellautomotive.com

<That is not what Boyles Law states. With the higher compression you are starting an explosion in a smaller space. So the intial hit is harder since it is not spread out over a a larger area. The flame travel propogates better.

Ugh, I forgot about Boyle's law. (and I'm one of the last people who should have forgotten it!) That alone makes sense that you would get more power. Expansion from that smaller space would make the combustion process more efficient, just as you stated.

Yes, I was thinking along the lines of the "total cylinder pressure" theory, and I guess with higher compression and better control of the fuel/ignition/all the other variables, you can push the envelope more.

<It is safer, but it is not faster. If your racing high compression will win, on the street we can probably find a compromise. 10.5 with 8 psi, or 12.5 with 5 psi. The higher compression will yield better fuel economy as well.

I was considering if someone is running lower compression and more boost they could be safer AND run the same power. It looks like you answered the question: it is safer, but you don't get as much power as a well tuned higer compression system.

<It comes down when you playing the game who get to the other end first, and that is the only rule, then you have to bring your biggest gun out first. Playing it safe is not an opition.

I know, I know, as Stirling Moss once said "First is first, second ain't shit." Which I agree with.

But they don't give trophies for the biggest engine explosion so make sure you keep your cars tuned well!

"Tutto fa brodo."

Todd Scungio
98 RS
15.173 @ 90.70 MPH

And also a 2011 Ralliart