[135iDCT]

what r the benefits of lowering the CR, let's say the stock CR is 10.2 on 20psi
if i lower the CR to 9.6 at the same boost 20psi?

any gains?

[E90Company]

Simply put, it will allow more boost to be run on the same amount of octane. Reduces your knock limit.

[tcw]

So you would make less power with stock turbos as the limiting factor is the turbos up top, not the octane in most cases. But with a big turbo you could make more boost on the same fuel as E90Company said.

[Dave W.]

Using the same boost and lowering the CR would give you less power.
Two reasons to lower the CR is so you can run really high boost or so you can have a better safety margin with low octane pump gas.

[JETmn]

And the biggest benefit to running lower CR is that you get the same static compression ratio by running higher boost, but you get to cool off the compressed air with the intercooler. By using higher compression pistons the air is heated from the compression and not cooled.

[cookiesowns]

Wouldn't spool up times be slightly affected by the lower CR?

[JETmn]

Originally Posted by cookiesowns

Wouldn't spool up times be slightly affected by the lower CR?

It is an extremely small difference, as is very slightly decreased torque, but more power up top. Everything is a tradeoff. With stock turbos it is pointless though because they are tapped out anyway.

[USAF Rick]

What's a CR?

[ZTZ1010]

Originally Posted by USAF Rick

What's a CR?

compression rate.

[SharkBait]

Originally Posted by ZTZ1010

compression rate.

Ratio

[ZTZ1010]

Originally Posted by SharkBait

Ratio

+1.


I type faster than I think....