Zore

I am very new to this and just trying to do some research and was hoping maybe someone could give me a bit more insight on the ECR that evo 2 litre can handle without pre-ignition Running on 93 octane. I was reading another webpage in reference to this and if this is correct then is the stock engine with boost pushing pretty much all it can, but if this were true then these forums would not be full of people pushing 400 hp on 93.

9.0:1 plus 22 PSI=22.5:1 is that right?

I am just trying to figure out how hard I can push a 2.0 litre 4b11t engine before detonation comes into play on 93 octane.

Sea Level Houston


http://jimroal.com/perftheory.htm

it will detonate when ignited by the spark plug. Common gasoline can only handle a certain amount of compression or it will pre-ignite, usually about 10.5:1. Higher octane rated fuel can handle more compression, up to around 13:1. Alcohol can handle even more, up to about 15:1. Diesels use compression ratios from about 16.5:1 to 23:1.

Combustion chamber design makes a big difference in the octane requirement. In theory, 87 octane fuel can only support compression ratios up to about 7:1. In reality, it can be much higher. There are a few factors that affect this. It is very important that the air fuel mixture burn quickly and orderly.

If the flame path is too far, the mixture can actually hit the point of detonation prior to the flame front causing detonation. A good combustion chamber design will have a short flame path and have very high mixture turbulence at the time of ignition. This is where the terms "high-swirl" come into play in modern engines. The turbulence can come from intake swirl, combustion chamber "squish", or both.

Some modern engines can support very high compression ratios, or effective comression ratios, with much lower octane fuel. In some cases, like the Porsche 911 turbo, 93 octane (R+M/2) fuel can support up to 17:1 effective compression (9.4:1 with 12psi boost). Effective compression for boosted engine can be calculated by the following equation: [(absolute intake pressure)/(absolute barametric pressure)]x(compression ratio).

Jaguar experimented with compression ratios as high as 14.5:1 on 93 octane fuel but the NOx was too high to pass emissions. Higher engine speed will also reduce the octane requirement. Lower air and engine coolant temperatures will reduce the octane requirement as well. For more information about octane requirements, see http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html.

A high overlap camshaft will generally let you run a higher compression ratio without pre-ignition or detonation due to the EGR affect and poor filling at low speeds when the detonation tendency is the greatest. Detonation can also be reduced or eliminated by retarding the ignition timing.
Compression is affected by the piston design, head gasket thickness, and the combustion chamber volume. The crankshaft and the connecting rod length can also affect the compression ratio by moving the piston travel up in the cylinder.



Static
Compress.
Ratio Blower Boost Pressure (psi)
2 4 6 8 10 12 14 16 18 20 22 24 6.0:1 6.8:1 7.6:1 8.4:1 9.3:1 10.1:1 10.9:1 11.7:1 12.5:1 13.3:1 14.2:1 15.0:1 15.8:1 6.5:1 7.4:1 8.3:1 9.2:1 10.0:1 10.9:1 11.8:1 12.7:1 13.6:1 14.5:1 15.3:1 16.2:1 17.1:1 7.0:1 8.0:1 8.9:1 9.9:1 10.8:1 11.8:1 12.7:1 13.7:1 14.6:1 15.6:1 16.5:1 17.5:1 18.4:1 7.5:1 8.5:1 9.5:1 10.6:1 11.6:1 12.8:1 13.6:1 14.6:1 15.7:1 16.7:1 17.7:1 18.7:1 19.7:1 8.0:1 9.1:1 10.2:1 11.3:1 12.4:1 13.4:1 14.5:1 15.6:1 16.7:1 17.8:1 18.9:1 20.0:1 21.1:1 8.5:1 9.7:1 10.8:1 12.0:1 13.1:1 14.3:1 15.4:1 16.6:1 17.8:1 18.9:1 20.1:1 21.2:1 22.4:1 9.0:1 10.2:1 11.4:1 12.7:1 13.9:1 15.1:1 16.3:1 17.6:1 18.8:1 20.0:1 21.2:1 22.5:1 23.7:1 9.5:1 10.8:1 12.1:1 13.4:1 14.7:1 16.0:1 17.31 18.5:1 19.8:1 21.1:1 22.4:1 23.7:1 25.0:1 10.0:1 11.4:1 12.7:1 14.1:1 15.4:1 16.8:1 18.2:1 19.5:1 20.9:1 22.21 23.6:1 25.0:1 26.3:1 10.5:1 11.9:1 13.4:1 14.8:1 16.2:1 17.6:1 19.1:1 20.5:1 21.9:1 23.41 24.8:1 26.21 27.6:1 11.0:1 12.5:1 14.0:1 15.5:1 17.0:1 18.5:1 20.0:1 21.5:1 23.0:1 24.51 26.0:1 27.51 29.0:1

SOUL STEALER

Static compression is only a small factor. Dynamic compression is what matters. I use to build small block chevrolets in the 400" area with 13:1 to 15:1 static compression. These motors would run 93 octane shell and have sorda big size cams. The later you close the intake valve the more you can get away with. I have no experience with tuning mivec but I imagine you could run just about any compression you want with full timing as long as the mivec is set to bleed off cylinder pressure with late closing intake valve. In theory mivec should be capable but I haven't experimented with how well th valve events can be controlled. I'm sure someone here knows the limits of the mivec system and can comment on its control limits. For motors without the luxury of mivec, adjustable cam gears are the next best thing.

Julio@Bisimoto

iTrader: (1)

I agree with SOUL STEALER, not to mention proper engine management and tuning is going to become even more important as you start to bump your static compression ratio with pump gas. Another option if you plan to stick to pump gas would be to use a water/meth kit to help with increasing octane as well drastically lowering intake air temps. At Bisimoto we have tuned our high compression Civic wagon 1.6L SOHC with 91oct and a AEM water/meth kit to over 700whp with out an issue. Of course we are running a very radical camshaft with a well ported head, yet it still very streetable.

apagan01

iTrader: (299)

Wondering if someone has tried this on the 4G63 or the 4B11.
Although wondering how much will it matter even though the theory worked in the hot rod scene