How much is too much? Depending on who you talk to, you get totally different answers!
First- I have Probe "10.25:1" pistons- but this compression ratio is based on a 62CC head. I have 64's. I am not sure what my final static compression ratio is because this depends on the head gasket thickness and where the piston sits in the bore. For the sake of discussion, let's assume it's 10.25:1
I'm running a TFS Stage II cam (Brian from AFM told me this is the old AFM B-4 cam)
Tuner #1, who built my engine a few years back, says DO NOT RUN BOOST UNDER ANY CIRCUMSTANCES. He's not a big "blower guy" and specializes in N/A combos. Says cam does not matter either, too much compression is too much compression and that is what I have.
Tuner#2 is a bigtime S-Trim dealer who says that many factors besides static compression ratio determine the final outcome, and says if I follow some suggestions I will be fine. He says he has much more power adder experience than tuner#1 and that they try things like this all the time to find the limits and the ragged edge.
Tuner#3 is well known for all sorts of combos, both N/A and Forced Induction/Nitrous.
He tends to be right in the middle between #1 and #2.
Couple other tangents:
On the subject of cylinder pressure- Tuner#2 said to do a cranking compression test and average out the results. He said if that average exceeds 165PSI, not to run boost. Tuner#1 says that cranking compression means NOTHING and not to listen to tuner #2
Tuner #3 says that they are BOTH right to a degree, that once your cranking compression is above 165, you really can't tell if the motor's static compression is 10.50 or 11.00 or whatever, however he said if my cranking compression, which averages 149 PSI (and is very consistant between all cylinders) that I can run boost if I follow tuner#2's suggestions.
Are we confused yet???
I already have the SQ installed, and right now I have base timing at 10 and have the BTM cranked up to 2.5 and have stuck a 5200 RPM pill in the MSD until I get a chance to sort this out.
Tuner#2 suggested to run an AFM Powerpipe (which I have) and to underdrive the blower with 3.70" pulley. Says this will result in the same boost level as the stock pulley with the crappy stock inlet tube (1994-95's have a very restrictive inlet tube from Vortech) but will result in much better efficienciency and lower the chance of detonation. He said to keep timing in check and use the BTM, run good gas, pay attention for detonation.
Tuner#1 is flat-out against running boost, does not care about tuner#2's experience or knowhow, says I am crazy and not to come crying to him if I melt down my motor (which has forged crank, pistons, and Eagle H-beam rods)
Tuner #3 says he tends to side with tuner#2 and says that since my cranking compression is only 149, it is likely that I do not have 10.25:1 compression and the only way to know is to take the motor apart.
Now in asking this question on other boards, I am told that NMRA and NSCA guys have to deal with pulley size restrictions and what they do is increase compression and tune accordingly. Have had some say that 10.25:1 is not that high compaired to what others have done. Then I read similar critique that tuner#1 gives- that this is a BAD idea under ANY circumstance. Then of course you get guys who then chime in and claim they run higher compression and a lot higher boost than I plan to run.
So by now of course I am totally paranoid to get on this thing and drive it hard for fear of a major meltdown. I have been driving it around and giving it part-throttle blasts and it runs right into the boost, 4-5 PSI but then I chicken out and let off the gas. So far no hint of a rattle or problem.
Looking for thoughtful, experienced replies and am willing to listen.
Heads are small-valve GT40X's with a AFM "stage three" port job (heavily favored exhaust side)
Running 190LPH in-tank and the T-rex. 30lb injectors and FMU, have FMS EFI Extender.
Thanks in advance, great website you guys have here!
Bookmarks