Turbo....

TT5.9mag said

Rusty, it’s really application and fuel dependent. Pick the octane level you are comfortable running, decide how much power you want to make, and how much boost it will take to get there. Then build to suit. You can run 14:1 with 30psi on methonal but 10:1 and 10psi will not last on pump gas. I’d say for a street car run as low of a static compression number as possible to keep the engine docile and easily tunable out of boost, but enough compression to keep some off boost torque. Typically that will end up around 9.5:1, a good compromise for a street car. The slant has a limitation on cylinder head sealing so careful attention must be placed on machining the deck and head and IMO studs and MLS gaskets are a must.

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I can have as little as 9:1 and as much as 9.5:1 depending on my head gasket choices. I am using the stock cast 2.2 dished turbo pistons, so those will be the limiting factor for boost. They do have a nice wide band around their perimeter that will be at zero deck and that ring is almost the dead perfect width to match up just right with the quench pad on this closed chamber head, so I'll still have just as much quench as I would with a total flat top, just with less static compression. That's why I swapped to the dished pistons. Static compression was going to be about the same as the engine I currently run at 10.2 and I did not want a repeat of that. Not that it was hard to tune it to run on pump gas, but pump premium is my only choice now. Not to keep it from detonating. It doesn't detonate on 87 even with 175 PSI cranking pressure......it just runs SO much better on premium. I guess the safest thing to do is just go ahead and run the thin head gasket, have quench at about .018-.020 and just run the engine N/A and be did wif all dat. It will be the most cost effective, too.