Hi,

right now I'm overhauling my BP4W. New pistons might go in. What would you prefer for a Rotrex build on 93 pump gas? The stock 9.5 or the VVT 10.0 CR pistons?

Thanks!

 

What is your power goal and what do you want out of the car?

 

8.4 or 8.6 CR.

 

So you mean the lowest available pistons CR?

No special purpose or power goal. I'm just wondering if I should trade the advantage of higher CR for a higher prone to knock?

 

Our engines are very limited by detonation with regard to timing. Unless using e85 or race fuel which prevent this problem you will find much more advantage to the lower CR. You may give up 2hp in the low end with the lower CR pistons off boost but being able to better optimize timing in the midrange and top end will net you around 30hp and 30tq or more when in boost. Timing enables the power because it optimizes the combustion pressure for applying force to the crankshaft. When the combustion force is necessarily later some of the potential is lost.