1G Low or high Compression

[4G63Tlove]

Hello guys I'm going to be rebuilding my 6 bolt I will be running a 20g turbo should o stick with the stock or go lower or higher CR ?

 

[thakingcb7]

Stock would be fine. Slightly higher wouldn't really hurt either. It really just depends on your end goal.

 

[Dan90tsi]

I just did mine and upped it to 8:5.1...wanted to go 9 but the pistons were already bought. I'm running a new 68HTA

 

[4G63Tlove]

Okay my goal is just to build a hi hp dd i want to run at leat 20 psi right now the car is Really low compression about 120 across all four I already have an Intercooler intake, exhaust, Boost Controller the car just doesn't seem so responsibe right now

 

[RipperXX]

Will the car run on 93oct pump or E85?
What size turbo is on the car now, and will it be staying for a long time?

93oct smallish turbo engines don't need real high compression I would stay at or below 8.8:1
If you have E85 all over your area, you can move that up some, turbo setup makes a difference too and how hard you are going to push it. If you're going to be pushing a lot of hot air high CR is a bad idea short of race gas. To get the best idea of IF you will be pushing a lot of hot air or not, look at a compressor map for your turbo and where you are going to want to operate it, as well as how much you can expect whatever intercooler you are going to use to drop that and you should be able to determine if you are going to be pushing an air charge of say 112*F into the engine at full tilt or 180*F. If your setup can keep things cool, you can bump CR a little more. With a good setup on E85 9.5:1 is fine, how far beyond that, I duno I lack experience in that area, I do believe I have seen several people build 10:1+ engines for E85, but I'm not sure how successful they were.

P.S. Standard 20g or some variation? It has become a pretty generic term over the years. And why a 20g?

 

[1990TSIAWDTALON]

Very successful here on 10:1's and E85. But pump gas is super low timing and I have to use water/meth. Pump gas, stay lower on CR so you can have more timing and not knock.

 

[donniekak]

The biggest problem with small turbos, high compression, and knock isn't the heat of the compressed air. Any decent intercooler will take care of that. The issue is high drive pressure in the exhaust manifold causing exhaust gas reversion into the cylinder. Even with poor intercooling, 150* air coming in through the intake valves is less likely to cause knock than 1500* gasses coming back through the exhaust valves.