What compression to use?

[4g63telantra]

Just wanted to know what compression to use with what turbo? Like how you guys know whats the best piston/compression to use? and what if u use a too low or too high compression?

 

[TargeT]

8.5:1 ~ standard stuff, don't re-invent the wheel..


of course like any FI engine, the compression rate changes with boost

 

[dsm10sec]

This is WAYY too generic of a question to ask and extremely basic; you need to go read up. :thumbdown

 

[MNGSX]

If you want to like set a pump gas record go with around 1g turbo comp specs....

Other than that yes around 8.5:1 with race gas.

With Alcohol around 10:1 to 11:1... They run like 15:1 naturally aspirated...

I ran perfect on 85% alcohol with 8:1. Acted like race gas (not 102 but real race gas) with less knock.. On 98% Ethanol.. Idle sucked (esp cold and cold start) but at the MAX pressure ratio for a 56 trim in the mid RPM (high rpm was too much CFM or LB/Hr for that PR) IT NEVER PULLED ANY TIMING...

Mid rpm where full boost is just reached is where knock is most likely but I had none... I could have added timing but I realized I'm better off dialing it in later with a higher CR motor.. Maybe a cold start injector with 87 octane too...

 

[suicidal2af]

8.5:1 ~ standard stuff, don't re-invent the wheel..


of course like any FI engine, the compression rate changes with boost

8.5:1 is only standard on 2G DSM's. And dynamic compression changes with boost, static compression will always be the same...and will be a variable in dynamic compression.

That being said, what CR to run is going to be entirely up to you. Higher CR will produce more power at a given level of boost. It will also spool a turbo faster. Every good thing has its price though...with a higher CR you're going to have to do a better job tuning to avoid knock and detonation. You're going to have to run lower boost than you otherwise would.

There's really no "ideal" CR and turbo. It all depends on what your goals are.