Flat tops???

[danman6677]

hey people im going to order a motor soon and was looking at different options, first is the cam i know there are quite a few to choose from but what about flat top pistons is raising the CR going to affect the sensors?

 

[MOBS]

Raising your CR raises your chance to "ping", and therefore requires more stable(higher octane) fuel....the computer will retard the timing, but you lose more power retarding the timing than you do using higher octane fuel. You'll also probably need a tune to fine-tune the change in efficiency/performance of engine.....depending on how radical you go.

 

[DieselPower]

There are plenty of compression calculators that will allow you to pick the heads you want to use along with the piston shape and get the approximate compression ratio. You can tailor your desired compression with various pistons on "paper" before you commit to the purchase. If you want to run low test fuel in the engine, it's a good idea to check out some of the low compression performance builds that are documented on various magazine sites. The cam selection will make a bit of a difference too. Flat tops and 64cc chambers gives you ~ 10:1, which means high test fuel is what you'll want. 12+cc D-shape dish pistons will drop that compression closer to 9.3:1 (all numbers are approximate and will vary slightly with head gasket thickness, etc...). Aim closer to 9:1 if you want to be able to use the cheaper fuel.

 

[danman6677]

that is what im going for 9:1 and a torque cam and headers, stock heads.
i ve run a 9.9:1 motor on regular 87 octane with no ping at all, i sold it to a neighbor who has it in his woodhauler 3/4ton, still running.