how high is your compression and how did you get it up there

[Guest Tim78zt]

Hi guys!

I'm wondering how high your compression ratio is on your turbo motor and what you did (flat-tops, head shaving, afternmarket EFI, ceramic coatings, etc. ) to get it over the 7.5:1 or whatever stock is on the factory turbo. There are a lot of new members so I thought a new survey in this area might help me. Also, do you consider it a grenade, or have you been racing it for more than a year? IOW, how reliable do you think it is at elevated ratios?

 

Tim78zt

[Arif]

Tim,

 

How's it going (Met you at the Z convention in S.A.)? I went with 88mm JE forged pistons which brought the cr upto 8.0. If memory serves me correct they read 160 or 170 across the board. Haven't had any problem with them and have had the motor in the car for over a year. What are you plans for that new motor?

[Guest Tim78zt]

Hi Arif!

Great to hear from you again! I guess I'll have to go with forged pistons to make the 8.5:1 comp work for my motor. It really doesn't sound that high when you factor in the DFI and IC on my car. I'm looking forward to hearing some positive feedback from others. I read an article in Turbo about a year or two ago where the opinion was stated that you could run very high compression as long as you had the Air/Fuel handled. So like Clint has told me, I need to find out what went wrong with my fuel delivery to cause the detonation. I wasn't really sure that the DFI was managing the Rev Limit function. How does yours limit revs?

 

Tim78zt

[Arif]

Tim,

I think a 8.5:1 cr is the max you would want to run on a street motor. I haven't tried a cr that high however from what I learned from other folks when I was building my motor that is close to the max. Just my .02 I am running a SDS and for the fuel map I just program in 1s at any rpm over 6250. Definitely find out why you are having fuel delivery problems. I traced mine to a bad bosch fuel pump and fuel regulator. After those were replaced the motor really came alive.

[jeffp]

I am running 8.5:1 compression in my car, and I can boost to 10-11 psi on pump gas with the car. You will need to be intercooled but it works out very well for the off boost power of the engine.