Pontiac Grand Prix Forums : Grandprix

Just ported and polished my front exhaust manifold, and noticed that the boost gauge at full throttle is showing 7psi. Anyone explain this? Car feels stronger in mid and upper RPM's.

What were you getting before the P&P? Someone correct me if I'm wrong but I understand that as you open things up, boost pressure drops due to more efficient processing of air. I saw a slight drop when I had my 3" DP installed and another slight one when I did the P-Log. I was at 12-13 before, and now get 11-12 max.

Oh and it will feel a bit stronger up top. More so with more flow mods

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'97 GTP: 9.5:1 Diamonds, XP'd, 3.4, Lucas 42.5#, Shiny Headers, Ported S/C and heads, N*, HPTuners
Coming Up: A 4T65E with a functioning TCC solenoid...

Stock pulley 6psi....

You are correct! When you lessen the restriction on the intake and exhaust sides, you make the engine more efficient. Meaning you're scavaging the exhaust gases much easier than you were before. You're probably about ready for some more goodies now with a tune tweak.

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GreenBastardPerformance2000 GTP Coupe (the green bastard)
XP, Pacesetters, LS1 TB & MAF,MSD System, P&P LIM, P&P GenV w/ 3.2, 3.0, 2.8, Devil'sOwn Injected 100% Methanol,PowerTuned, TripleEdge Trans w/3.29's
12.92 @ 105mph

6 psi?

That's about right with what he may have done to it.

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GreenBastardPerformance2000 GTP Coupe (the green bastard)
XP, Pacesetters, LS1 TB & MAF,MSD System, P&P LIM, P&P GenV w/ 3.2, 3.0, 2.8, Devil'sOwn Injected 100% Methanol,PowerTuned, TripleEdge Trans w/3.29's
12.92 @ 105mph

He said 7psi at first then he said the stock pulley gives him 6psi. You are wrong. Get back to work!

Don't argue with me!

ok, maybe you should argue with me....for some reason I was thinking he showed a drop in boost.....

More coffee Brian.....more coffee.

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GreenBastardPerformance2000 GTP Coupe (the green bastard)
XP, Pacesetters, LS1 TB & MAF,MSD System, P&P LIM, P&P GenV w/ 3.2, 3.0, 2.8, Devil'sOwn Injected 100% Methanol,PowerTuned, TripleEdge Trans w/3.29's
12.92 @ 105mph

YES SIR.

Could it be that sense his exhaust is flowing out better, his engine is hitting the rpm's quicker pulling in more air to create the extra boost??? Don't really know, just trying to throw some ideas out there and learn about the system more.

Well, he is actually loosing boost due to the fact that his exhaust is more free flowing wich means less back pressure.

Alright, I can see that.

Maybe I got a ghetto gauge..lmao The stock pulley is normally 6 psi and has peaked to 7psi before, so i dont know whats going on. The car does feel stronger tho.

im guessing the boost will drop more with a u-bend delete. With the decrease in boost, is off the line acceleration going to suffer since the powerband should shift into higher RPMs? Im just trying to keep my 60' times close or better than they are now @ 2.02

You shouldnt notice a change in psi with just a u-bend deleate.

damn your 60' times....im still jelious :/

and i aint got an answer to your question

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white 04 comg G gtp. wizair, pacesetters, slp 1.8 rr
its slow.

isent the stock stall around 3000 tho. so you should still be in mid range power off the line... i would think

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white 04 comg G gtp. wizair, pacesetters, slp 1.8 rr
its slow.

Yes but remember that you'll spin like crazy unless you have some sticky tires. Hince the reason i stall 1800 to 2200'ish Rpm's or so.

yea but the stall converter. if you hit it around 1500 or so it jumps up to 3000...

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white 04 comg G gtp. wizair, pacesetters, slp 1.8 rr
its slow.

Yeah... I see what your saying now.