Boost psi Question

Mwilbur516 · Feb 5, 2012

I just wanted someone to explain to me why most tunes run 20-25psi @ WOT? On my Looney Wild I can see 32-35psi if I slowly roll into the throttle while the converter is locked in 6th gear, but when it downshifts and revs up, the boost drops to around 22psi. If you hammer the throttle it'll run to about 25psi then drop back to around 22psi as it runs out.

I've been told that high boost doesn't necessarily mean more power. I would just think that more boost would eliminate any smoke/haze during WOT throttle runs. If someone who knows more about this would explain, I'd appreciate it.

sickslow · Feb 6, 2012

My sct canned tunes are the same. except i never see over 25 lbs. not saying this is normal....i have often wondered why this is the way it is...I can tune back to stock and hit 28psi all day....Idk why i boost lower tuned...my guess is that the tuning fools the electronic boost sensor to thinking that you have less boost than you really have so that it wont throw a code.....I need an analog gauge to verify this though...Only have the cts right now.

Goose · Feb 6, 2012

Do you have a real boost gauge?

patrickke · Feb 6, 2012

I'm guessing he has glowshift gauges

PowerStrokeEnginuities · Feb 6, 2012

patrickke said:
I'm guessing he has glowshift gauges

Haha

Twan · Feb 7, 2012

I have autometer, and I see 28-30 psi stock and 25-27 with tow tune and street tune.

faster6.0 · Feb 7, 2012

I see 30 psi on x race stock turbo

Sprman · Feb 7, 2012

Hell, I've seen almost between 35-40 with Gearhead tuning and stock turbo. I pegged out my 35 psi gauge so I bought a 60 psi one and i can come close to 40 at times. Normal is around 25-30 though.

jdc753 · Feb 7, 2012

I see the same thing with Xtreme Race, factory 05 boost gauge.

With the converter locked in low RPM you are lugging the motor putting more load on it, that is why you are seeing the higher boost numbers, if you hold it out and get the truck running 85+ you should start seeing the boost drop as your foot goes down, as long as you stay in the same gear.

What will clear up smoke/haze is simply how much oxygen is being moved, CFM, which is going to get complicated. I don't know what the compressor maps look like for the stock turbo but I would imagine boosting over 30psi is going to start dropping out of efficiency where you are going to be building more heat into the air than you will be oxygen. Hotter air will be less dense and thus less oxygen per volume of flow CFM

Mwilbur516 · Feb 7, 2012

I'm looking at my stock guage. I can push it to over 30psi rolling into it, but at WOT it holds 22-25psi as I said in my first post. I just got the TSD Super Panty Dropper and Chris answered my questions about boost. I also talked to him about some fuel and air upgrades. We're thinking about some 190/75's and a PowerMax. I've got to do some supporting mods first (Regulated Return, TSD sump, undecided about which fuel pump).

BTW, PowerStrokeEnginuities, whats so funny about my gauges?

windrunner408 · Feb 7, 2012

What did Chris say??

Mwilbur516 · Feb 7, 2012

BTW, I have a Glowshift fuel pressure gauge and monitor other parameters through my Livewire. I'm going to get a Glowshift 60psi boost gauge, I was just waiting until I decided if I was buying a new intake elbow (pre tapped) or if I was using my stock elbow and drilling and tapping it. I think I'm better off using my stock elbow and putting the money toward the RR and TSD sump.

Mwilbur516 · Feb 7, 2012

windrunner408 said:
What did Chris say??

Chris said that the stock turbo's have a sweet spot around 22-27 psi where they are moving more air and after that they start generating too much heat and the efficiency drops dramatically. Basically exactly what jdc753 said in his post.

The SPD tune is amazing. Thanks to Pizzapig for helping me decide to go with TSD's tunes. I'll be getting a tow tune from TSD soon as well. Great guys to work with.

Goose · Feb 7, 2012

Mwilbur516 said:
BTW, I have a Glowshift fuel pressure gauge and monitor other parameters through my Livewire. I'm going to get a Glowshift 60psi boost gauge, I was just waiting until I decided if I was buying a new intake elbow (pre tapped) or if I was using my stock elbow and drilling and tapping it. I think I'm better off using my stock elbow and putting the money toward the RR and TSD sump.

Reading boost thru the OBD port with a custom tune is inaccurate. You need a real boost gauge.