Ok guys I have a 4.8 with 317 heads should be 8.5to 1. Im running what we think is a hx52. Think of it as a gt45. How much boost are you guys running on 93 with air to air. Im at 12psi now. Just wondering what everyone is doing.

 

Would love a response to this. My dumb butt put 317's on my 4.8 with an LS6 cam. Haven't fired it yet, but I'm trying to spool an S475 with the 96mm turbine and was thinking closer to 15psi should be achievable with that low of compression on pump.

 

Do you have any tuning or datalog information? Where are your IAT's currently?

With that low CR I would imagine 15#'s on pump gas would be okay. Add meth injection, and I would be very confident in it holding up just fine.

 

I run 14-15psi on my 4.8L with stock cam. Stock compression 9:1??? It's not even fully intercooled (one turbo isn't intercooled) on 94 octane. 13-12 degrees timing. I have run multiple high boost laps around a road course with this and have not had an issue yet. I'm actually more afraid of drag strip and heat soak (have not taken it to the strip yet).

I'm putting in a Camaro camshaft this spring, hopefully it will still be safe enough.

In no way do I sugest anyone use me as an example of what is safe or efficient.

 

No I dont have any data log on it. I want to say iat hasnt been over 125.

 

4.8L + 317 heads = major dog and poor spooling.

Put the stock heads on there...no need to ever have compression below 9:1 with these LSX engines.

I had a 4.8L with 317's when this LSX craze started and now know that was mistake.

Learn from us all on this site (I'm sure others will chime in) and put some 853 heads on there..

 

ive done it, compression is in the ****, not really worth it

 

I'm on a stock lq4 with stock 317's (not sure what exact compression but probably more than 8.5:1) and I am about 15psi with pump 93 and no meth. Car has been 10.1 @ 139

 

I say keep your timing really low(10-12*) and turn it up a pound at a time watching the plugs. I'd guess 16-17lbs + would be fine at 8.5:1.

If you have good fuel, I would agree for most street cars. If your running pump gas only... Lower compression is fine.

You only loose 4-5% NA hp with a full point of compression loss. Anyone who says there is some massive difference between one point of compression is mistaken. (or more likely changed more than just the compression) At 270 FWHP there would roughly be a 10 HP difference with a full point drop from stock.

With pump gas only build, an 8.1 turbo motor will run circles around a 9:1 motor.

 

Allot of the turbo Buick guys run 8's:1 compression and some of them go as low as high 7's in compression ratio. They just run tons of boost. Less chance of detonation. On the street you might see a little bit of a difference but at the track i bet you'll be able to run quicker.