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theres a guy running around here in a 400+hp ITR (daily driven), i believe he is using the drag kit....

 

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Most people don't understand the dynamics of compression and boost. For a street car, compressionc an be very beneficial.

maybe for low boost applications, lower compression takes away some power, but it gives less chance of detonation, which IMO is more important, i know i said this before, lower compression only gives you a little more room to work with when tuning...

 

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We have a engine. It's a 2.0L, 4 valve per cylinder, 4 cylinder type with a 9.0 to 1 compression ratio and it's turbocharged. On the dyno, the motor puts out 200hp at 4psi boost with the timing at the stock setting of 35 degrees on 92 octane pump gas with an air/fuel ratio of 14 to 1. We retard the timing to 30 degrees and can now run 7psi and make 225hp before detonation occurs. Now we richen the mixture to 12 to 1 AFR and find we can get 8psi and 235 hp before detonation occurs. The last thing we can consider is to lower the compression ratio to 7 to1. Back on the dyno, we can now run 10psi with 33 degrees of timing with an AFR of 12 to 1 and we get 270 hp on the best pull.


From all of the changes made, we can deduce the effect certain changes on hp;

Retarding the ignition timing allows slightly more boost to be run and gain of 12.5%.

Richening the mixture allows slightly more boost to be run for a small hp gain however, past about 11.5 to 1 AFR most engines will start to lose power and even encounter rich misfire.

Lowering the compression ratio allows more boost to be run with less retard for a substantial hp gain.

Increasing the octane rating of the fuel has a massive effect on maximum obtainable hp.

We have seen that there are limits on what can be done running pump gas on an engine with a relatively high compression ratio. High compression engines are therefore poor candidates for high boost pressures on pump fuel. On high octane fuels, the compression ratio becomes relatively unimportant. Ultimate hp levels on high octane fuel are mainly determined by the physical strength of the engine. This was clearly demonstrated in the turbo Formula 1 era of a decade ago where 1.5L engines were producing up to 1100 hp at 60psi on a witches brew of aromatics. Most fully prepared street engines of this displacement would have trouble producing half of this power for a short time, even with many racing parts fitted.

Most factory turbocharged engines rely on a mix of relatively low compression ratios, mild boost and a dose of ignition retard under boost to avoid detonation. Power outputs on these engines are not stellar but these motors can usually be seriously thrashed without damage. Trying to exceed the factory outputs by any appreciable margins without higher octane fuel usually results in some type of engine failure. Remember, the factory spent many millions engineering a reasonable compromise in power, emissions, fuel economy and reliability for the readily available pump fuel. Despite what many people think, they probably don't know as much about this topic as the engineers do.

basically, when your going to be running on pump gas 91or92, theres more of a chance of detonation occuring, you can either
1:buy high octane fuel
2:lower compression
the first choice would get expensive, the second choice makes more sense, it doesn't rule detonation out completely, just gives you a better chance that its not going to happen, and detonation my friend is what kills engines.

 

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it went on to talk about other methods of getting rid of detonation, but the topic here was compression, so i stuck with that. Sure if your going to be running low boost, just get your timing and fuel right, your set.
You have to consider though:
lower compression = small loss of power, but safer
normal compression = a little more power, but more of a risk of detonation