Ok I'm about to pull the trigger on my CP Pistons for my build. Either CP SC7061 or CP SC7065. What are the advantages/disadvantages of both. Power goals are 500-600 RWHP only because of the weak diff. I'm in El Paso where we can on get crappy 91 fuel but I'm 90% sure I'm gonna switch to E85.

 

Go with the 10.0

 

If E85 most of the time: 11 if not 10.

 

10:1 if running pump gas. 11:1 If running on E85.

If you think that that motor will see pump gas at all in its life, id air on the side of 10:1. 1 point of compression isn't going to make or break you on power, but it can your motor.

 

Not to thread jack, but say someone builds their car with 9:1? would it benefit more from E85 or pump?

 

Pump within a particular goal for the sake of overall efficiency. But E85 will always allow for more power headroom no matter the compression of the engine. By going to a low comp, you have increased your safe tuning and or boost window. E85 burns cooler and less complete then pump. On low compression this can make it feel sluggish around town and idle quality isn't as great as a more volatile fuel like standard low oct fuel.

Think of lower compression as a necessary evil to run safe on a low octane fuel. More compression means more power. So the goal ultimately is to balance safety with power, and that's as simple as matching the right fuel with the right compression and understanding the engine platform and tuning window your working with. In general there is a safe range in there, so it takes an experienced engine builder and tuner to know what's feasible. Boost is just a method of forcing air into the engine aka pump, which the amount is not a constant relative to any particular one of those facets I mentioned, its a collection of the whole as long as the engine components and Head Gasket are designed to hold the pressures. On our particular platform, we have narrowed down pretty well by now what the thresholds are and general figures for particular fuels and boost, power levels. Every engine is different.

 

Thanks for all the input and advise fellas. I'll be purchasing the 10.0:1s just for the safety factor.