11-12PSI on a 3.1" Pulley?

**JoshMcMadMac** · 09-03-2009

So I finally took some time out and start scanning/tuning the GTP again. I have it tuned well enough to be brave and go WOT. I still got a few degrees of knock, but nothing critical and I am still working on the tune. What surprised me was to see the boost gauge pegged at 11-12psi...I would have thought it would be a little higher with everything I have done to the car. I seem to recall it making that much with the 3.4, downpipe, intake, and tune.

**blueguy** · 09-03-2009

Maybe it just flows that good? Intercoolers also substantially lower boost levels to make more power with colder intake temps...I mean...that could be why your still making the same boost with a pulley .3" smaller.

**JoshMcMadMac** · 09-03-2009

Originally Posted by bluegtp91

Maybe it just flows that good? Intercoolers also substantially lower boost levels to make more power with colder intake temps...I mean...that could be why your still making the same boost with a pulley .3" smaller.

That very well could be. The intercooler, rockers, and PLOG all should help flow, I just had it in my head that it should be a few PSI more. I guess I will know better when I get it to the track.

**gtpsleeper** · 09-03-2009

^^^ you are pushing more air in yes...but your not gonna create more boost technically... Think of it this way, the air your pushing in, while being alot more, its also less dense because its cooler than the hot air before your IC was on. Its the same reason a ported blower is gonna make less boost than a stock one with the same pulley size...the air just isn as hot. Therefore, not expanding as much, and producing less pressure...

this help?

**blueguy** · 09-03-2009

Originally Posted by gtpsleeper

^^^ you are pushing more air in yes...but your not gonna create more boost technically... Think of it this way, the air your pushing in, while being alot more, its also less dense because its cooler than the hot air before your IC was on. Its the same reason a ported blower is gonna make less boost than a stock one with the same pulley size...the air just isn as hot. Therefore, not expanding as much, and producing less pressure...

this help?

Since when do you use google? LOL

**gtpsleeper** · 09-03-2009

Originally Posted by bluegtp91

Since when do you use google? LOL

gimmie more credit than that

**Bio248** · 09-03-2009

i was seeing 12 on a 3.2 without the intercooler, so i say that is about right for you.

**01gtspecial** · 09-04-2009

cold air is more dense than hot air. the reason you're not making more boost because even though you increased how much air (mass) thats making it into the motor, you also increased the volume. boost is a measure of pressure. so basically you cancelled it out. your MAFs should be way higher...

**gtpsleeper** · 09-05-2009

Originally Posted by 01gtspecial

cold air is more dense than hot air. the reason you're not making more boost because even though you increased how much air (mass) thats making it into the motor, you also increased the volume. boost is a measure of pressure. so basically you cancelled it out. your MAFs should be way higher...

whoops meant more dense in my post...not less sorry! but you get my point...^^^^^ he pretty much just said the same thing i did

**gtpsleeper** · 09-05-2009

now that i think about it 11-12 psi is pretty high for a 3.1 on an IC...but if your not knocking then thats a pretty good number to have dude

**superv6** · 09-05-2009

and honestly who cares? i mean, if you have an intercooler, rockers and a decent amount of exhaust work, that means ur probably flowin pretty damn good and makin good power at the same time. engines are nothing more then glorified air pumps and we all know the more air an engine can get in and pump out as effeciently as possible the more power it makes. honestly even though it looks cool to have 13+ psi of boost i would rather have a very good flowing engine then have 20 psi and possibly pop my motor

**gtpsleeper** · 09-05-2009

Originally Posted by superv6

and honestly who cares? i mean, if you have an intercooler, rockers and a decent amount of exhaust work, that means ur probably flowin pretty damn good and makin good power at the same time. engines are nothing more then glorified air pumps and we all know the more air an engine can get in and pump out as effeciently as possible the more power it makes. honestly even though it looks cool to have 13+ psi of boost i would rather have a very good flowing engine then have 20 psi and possibly pop my motor

you cant get 20 psi through an M90...

**Bio248** · 09-05-2009

these cars actually run the best on low boost, but i was a high boost advocate. i liked seeing more boost and less timing because of how the car ran.

**JoshMcMadMac** · 09-05-2009

Wow, alright guys, enough. I figured this would just die, but everyone has to keep posting on here with their 2¢. I know how an engine works, I know what boost is, and I know more than enough about the entire workings of it all that I do not need folks to try and convince me why less boost is better in any given application. All I was looking for was experienced input from those that have been there, done that. Most of the time I wonder why some folks need the feel to qualify their posts with "I have done XX" or "I do XX for a living" but in this situation, I will publicize that I am an engineer, and I know more about the characteristics of flow than I would like to admit. We will see how well it runs and how well I can tune once I get it on the tarmac.

**gtpsleeper** · 09-05-2009

Originally Posted by JoshMcMadMac

Wow, alright guys, enough. I figured this would just die, but everyone has to keep posting on here with their 2¢. I know how an engine works, I know what boost is, and I know more than enough about the entire workings of it all that I do not need folks to try and convince me why less boost is better in any given application. All I was looking for was experienced input from those that have been there, done that. Most of the time I wonder why some folks need the feel to qualify their posts with "I have done XX" or "I do XX for a living" but in this situation, I will publicize that I am an engineer, and I know more about the characteristics of flow than I would like to admit. We will see how well it runs and how well I can tune once I get it on the tarmac.

you dont want our input...then dont post...we were trying to explain why you have that much boost with a smaller pulley. and since your an engineer you should have been able to figure that out on your own. forgive us...we wont try to help you anymore since your so "qualified"...our mistake

**silverstreak** · 09-05-2009

Originally Posted by JoshMcMadMac

Wow, alright guys, enough. I figured this would just die, but everyone has to keep posting on here with their 2¢. I know how an engine works, I know what boost is, and I know more than enough about the entire workings of it all that I do not need folks to try and convince me why less boost is better in any given application. All I was looking for was experienced input from those that have been there, done that. Most of the time I wonder why some folks need the feel to qualify their posts with "I have done XX" or "I do XX for a living" but in this situation, I will publicize that I am an engineer, and I know more about the characteristics of flow than I would like to admit. We will see how well it runs and how well I can tune once I get it on the tarmac.

LOL. That is all.