David I suppose I was wrong about his intake mods. Sounds like what you did was not as hard to do or expensive as ARP. Wonder if you could do something like that for the heads or not? I'm shocked you can't get better than 10 psi out of that non gated turbo. I can hit 6 with mine if I really stand on it now that I have no muffler and 4" from the downpipe back. I guess you still have a stock injection pump? I keep hearing these things can boost till it runs out of fuel or the engine blows up, however you probably have to be driving really fast or really hauling heavy to even spool it much at all with 3.08s. What would you say your CR is with the 20 thou you took off your pistons and any other mods you did?
Guessing around 21:1 with stock being 22.5:1. Dave S would know, he's always good with numbers above 10 (unlike me
). I think Dave mentioned that he had 20.25:1 with 40 thou off the top, but don't quote me on that. ARP studs are still stronger than grade 8 bolts though, so while grade 8s may be good enough for the manifolds I would be leery of using them for the heads.
The way this turbo is set up it can't really spool that much unless you are already on your way past 2500 RPM. I've seen as high as 14 psi before I rebuilt the engine and that was with the fuel screw maxed out (minus about 1/6th turn to keep from killing the pump) and turning the sky black. Not sure where the fuel setting is now, but its pretty mild. I don't want to turn it up any higher because its already pushing a little smoke at full power at anything below 2500. if I turn the fuel up any higher I want to make sure I can burn it all.
I'm still not sure if a bigger compressor would spool much better at low RPM and thats the other reason I'm hesitant to try it. I don't really care about turbo lag as long as I could get it to spool more pressure below 2000 RPM. I tend to run the RPMs as consistent as possible and throttle up gradually even when I floor it. Dunno, still have some reading to do.
What you have to remember about the ATS turbos is that they were not really intended to boost more than 8 psi even though they can. The idea being that a stock 6.9 can't reliably take much more, at least not in ATS's opinion. The 088 that I have seems to loose efficiency after abour 5 psi. 5 psi comes almost instantly, and then its like pushing through a wall to get the boost any higher. And then the smoke starts to roll on.