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mike you seem like you know what your talking about ...i have one for ya, ive got a set of pistons in my garage they're jun pistons i beieve (ctr cut down to make em lighter)they came out of mt friends car which ran like crap (cali 91 octane!)i forgt to add that they are domed and theyre on gsr rods. i believe my friend told me that they were 13 to 1 , i was wondering, if i put them in my car how could i make the set-up work? could i lower the compression by using thicker gaskets? i have the basics on my car right now
 

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Street/Occasional Weekend Track Motor

Most people agree that 12.6:1 is about the highest you can go on a street motor tuning-wise, although people like Larry Widmer of Endyn will tell you that CR has nothing to do with detonation...as long as there is adequate mixing and a proper combustion chamber shape.

Since we really don't have a full Endyn head that delivers air and fuel without mixture separation or an full Endyn chamber, I suggest we stick to some conventional guidelines. So you want to get that CR down to around 12.5:1. You Californians are really screwed over big time with the 91 octane max pump gas stuff.

Yes, adding more shim layers to a head gasket will lower the CR. The downside is that you are increasing the total internal area of the chamber. Remember that lean burn theory (which Honda engines are based upon) depends on a compact combustion chamber. The more chamber area, the less complete the combustion or burn will be. Why? temperature. You want to maintain just enough cylinder temperature in an optimal range to help the air fuel mix burn off completely. If you have too much area, it dissipates the heat out too quickly. The domestic V8's have this problem with the huge chambers they have, like the Chrysler Hemi for example.

So you are facing a double edged sword. You want to lower the CR but the one way you chose (i.e. head gasket) decreases burn efficiency and also enhabnces detonation risk.

The other option is to have a machine shop lower the dome height on the pistons so that you get 12.5:1. That will take some calculating though...something I don't have time to do for you but they can.

If you are going to run that much CR, you'll need a compatible cam, bigger injectors and fuel pump, and of course, a ton of wideband O2 sensor tuning of the ECU fuel map on the dyno to make it all work.

Race-only Motor

If this is a motor for a trailer queen then we have a different story since you can run race fuel. You can leave her at 13:1 and tune the fuel map on the dyno as stated before.
 
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