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P1SC ran outta boost?? WTF?!?!?!

4K views 30 replies 18 participants last post by  Raiden 
#1 ·
I'm confused here; hopefully someone can set me straight.

After forging my 4.6 and getting a proper chip in we dyno'd my car today. I used to pull 12-psi, then added BBK LTs and the off-road pipe. The boost went down to 10-psi.

Now after the forged motor, ported heads, and ported Bullitt intake the boost dropped to only 6-psi.

I actually LOST power from my last dynos. BEFORE the LTs and pipe I dyno'd 392 RWHP. With the LTs and pipe I eeked up to 399 RWHP, but then realized that 3 cylinders lost compression.

Now that everything is forged and correct I'm only at 388 RWHP.

My mechanic tells me that the P1SC has "run out of boost" and can't ramp up with the motor.

Is this true? If so, what can be done about it?? I'm not thrilled to shell out another $1200 to ATI for an impeller upgrade.

Any ideas, comments, questions, etc??

I'm lost here....


P.S. I'm NOT using the Univer MAF that's listed in my sig. Apparently JMS can't get it tuned without actually having the car in their shop due to the voltage changes...
 
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#3 ·
tommy303 said:

Now after the forged motor, ported heads, and ported Bullitt intake the boost dropped to only 6-psi.
You are going to loose boost since you ported your heads and intake because it now moves more air and is more efficient.

tommy303 said:

I actually LOST power from my last dynos. BEFORE the LTs and pipe I dyno'd 392 RWHP. With the LTs and pipe I eeked up to 399 RWHP, but then realized that 3 cylinders lost compression.
You might want to check your math again. 399hp is more than the 392 you had before the LT's. If you lost compression in 3 cylinders that would mean that you have more problems than your boost problem.

As stated above me, you need a new mechanic. He is an idiot if he thinks you maxed out your blower when it can reach boost levels of up to 30 pounds.
 
#4 ·
My math is fine, maybe I wasn't clear.

Base P1SC+10 lb pulley, 392 RWHP.

P1SC+LTs+pipe+12 lb pulley, 399 RWHP.

Forged motor+P1SC+LTs+pipe+12 lb pulley, 388 RWHP.

When I dyno'd 399 I thought something was wrong. I've read that LT's and an off-road pipe were worth more than 7 RWHP. That's when we discovered the 3 bad cylinders. I decided to forge the motor instead of just re-ringing it. I figured that the stock block wasn't going to go much further than 450 RWHP anyway; and I wanted somewhere in the 500 RWHP range.

About the P1SC reaching 30 psi: If it's only spinning to 6 now, it's due to the engine being more efficient, right?

So, how do I get more boost out of it without overspinning the blower? I've already got the 12-psi pulley on it, won't I risk breaking the blower if I change to an even smaller pulley??
 
#6 ·
I can't find any info about larger pulleys on ATI's website. I thought I read somewhere that the smallest is a 12-psi pulley.
 
#7 ·
The largest amount of boost loss you will see is about 2#'s, unless you increase you displacement a large amount. That little 4.6 isnt going to put any strain on that P1SC.
 
#9 ·
Boost is just a way of measuring backpressure.
You should have more power now since your engine breathes easyier.
Even if boost pressure went down, you have more air volume entering the motor, and it should make more power.
But if you have a restriction before the blower, or if the belt isnt tight enough, then what i said before doesnt apply.
 
#10 ·
Theres no way in hell he lost 6#'s of boost from his bolt ons and porting. Maybe if he increase his displacement to 7.0 liters, he could lose a few pounds.
 
#11 ·
You can get a smaller blower pulley that will make that blower produce more boost!!

What size do you have on there now? Take note of it, and start making some calls (start with Procharger, then maybe Auto Specialties who make custom pullies, I read above about Richard Racing) and find a smaller pulley. A 14psi pulley is not the smallest they make for those blowers and even if it was, you would be able to get a smaller one made!
 
#12 ·
The only thing that I'm concerned with by using a smaller pulley is over-spinning the blower and damaging it. The thing that really hurts is that I spent about $10k rebuilding the motor and getting the heads and intake, all the porting, etc.

Over at Stangnet one of the guys gave me a formula for determining what rpms the blower is spinning at:

Crank/blower*engine RPM*blower gear ratio=impeller RPM

If I went with the 8" crank pulley from ASP and kept the 3.10" blower pulley I'd overspin the blower at 6000 rpms.

8/3.1*6000*4.10=63483.9 RPM <---That's what's making me so nervous.

A question about the slippage: The belt was new, and my mechanic said that the blower was slowly building boost all the way to redline. He said that it was a continual buildup and that there wasn't any spiking; or it didn't ramp up suddenly then taper off.

Would the altitude make a difference? Being in Colorado I'm at 5300'.

Thanx again for all of the replies. I'm still trying to learn about all of this and you guys are helping out tremendously. :)
 
#13 ·
tommy303 said:
my mechanic said that the blower was slowly building boost all the way to redline. He said that it was a continual buildup and that there wasn't any spiking; or it didn't ramp up suddenly then taper off.
WELL, it is a centrifugal supercharger. boost is basically directly related to crank speed since the blower is hooked to the crankshaft. it isn't going to have the boost curve of a turbo or positive displacement blower where it makes full boost and holds there for 3K+ more rpm. what'd you expect the curve to be like? you're boost is relevant to rpm, you may have 4#'s at 4,000rpm, 6#'s at 5,000rpm, 8#'s at 6,000rpm, etc (this is a bit of an oversimplified example).

tommy303 said:
Would the altitude make a difference? Being in Colorado I'm at 5300'.
the problem is that you made the old boost numbers at that altitude, correct? it's not like you made something at sea level, did the new mods, and then moved to somewhere w/ 5300' of elevation and THAT'S why you're numbers changed. as far as i know that isn't the case b/c you haven't said anything about just moving there so i would say that is irrelevant b/c we're trying to diagnose a problem related to your old boost numbers at that same altitude.
 
#14 ·
Okay, so how would I know if the belt is slipping?

I was wondering if the low boost numbers were due to the altitude. When I changed to a 12-psi pulley and the LT's/pipe I was still at only 10 psi.

It's kind of disturbing that I'm down to 6 psi now.

Could there be something wrong with the blower itself??
 
#15 ·
You are running a 8" crank and a 3.1" blower pulley and only seeing 6#s of boost ?

Only 3 things are kepping boost down.
1) major belt slippage

2) Some how your inlet side of the blower is restricted..

3) your blower tubing connections are loose somewhere and you bleeding it off !!!

Dont even concider the mod factor, they might make you loose like a pound if that.. Im not familiar with the 99 set up, can you adjust the belt tention ? Check for belt dust around parts near the blower !!

Im running a 6.5 crank and a 3.05 blower pulley seeing around 10-11 psi @ 6100...
 
#16 ·
SOunds like you need a rr pulley to prevent slip.With all my motor mods.Cams,P&P heads,built motor .Im still seeing 10 psi with a 3.33 pulley @ 6k. Most other cars see 12 psi with the same pulley.I only lost 2 psi with all the air flow mods.

But i have seen few ati guys having the same complaint as you .More motor mods and less power and boost.
 
#18 ·
I've talked to ATI about this. They told me if I was going w/ a procharger on a stock motor (2001 Cobra) to go w/ the P1SC, if I was going to do intake/head porting etc to go w/ the D1SC b/c I would lose boost w/ the P1SC. Give them a call. They were very helpful when I gave them a jingle. :evil:
 
#19 ·
To correct something, I'm using the stock crank pulley with a 3.1" pulley. After reading some of the posts above I was considering going to a larger crank pulley.

However it seems that I'll overspin the P1SC if I do---especially if I go with a smaller custom blower pulley.

I also spoke with ATI a bit. As soon as I can I'll be sending my P1SC back to them to be upgraded to a D1SC.

Hopefully THEN I'll see some decent power.
 
#20 ·
None of this makes sense.

Regardless of a little belt slippage and porting etc. You should make more than 6 psi, and you should definitely make more than 388rwhp.

I would check for belt dust from slippage. I also agree you should check for leaks and restrictions on the intake.

I know that most every Procharged/intercooled 99+ GT including my old 02 made over 400rwhp.

My P1SC on my Cobra makes 13 psi at redline with a 3.2 inch pulley. I know your heads, ported or not, couldnt exceed the flow of my cobra heads by that much.

Before you shell out the dough for the upgrade, check you intake and tubing.
 
#21 ·
swinerton said:
Theres no way in hell he lost 6#'s of boost from his bolt ons and porting. Maybe if he increase his displacement to 7.0 liters, he could lose a few pounds.
I agree! Throwing a smaller pulley on that blower is not going to fix the proble that is causing your boost problem. You need to track down the problem first. Make sure ALL of your tubes are tight and fit together properly, make sure your B.O.V. is not leaking or the diaphram is not torn. Make sure you don't have a serious vaacum leak. You can do that by spraying WD-40 around the intake gaskets and listen for idle fluctuations. Make sure the blower is not puking it's guts into the intake path (oil leaks). and lastly, check for major belt slipping. 6 psi is a rediculous bleed off and you should not be loosing that much with a 4.6. Not at all.
 
#22 ·
sounds like the BOV is where your losing your boost
 
#24 ·
problems

Read what these people are telling you. You do head porting etc.. you are going to loose some boost. Boost is just the measurement of restriction to flow. Number 2 get rid of your shade tree mechanic, he sucks! Oh and get rid of JMS, they are the worst, and absolutely SUCK at tuning! HORRIBE!!!! They could not get the tune on one of my customers Saleen right at all. WE ended up giving the chip back did I mention THEY SUCK?
 
#26 ·
Re: problems

GS400 said:
Read what these people are telling you. You do head porting etc.. you are going to loose some boost. Boost is just the measurement of restriction to flow. Number 2 get rid of your shade tree mechanic, he sucks! Oh and get rid of JMS, they are the worst, and absolutely SUCK at tuning! HORRIBE!!!! They could not get the tune on one of my customers Saleen right at all. WE ended up giving the chip back did I mention THEY SUCK?
Yea JMS sucks:rolleyes: .They are one of the top tuners out there.But chris johnson is now with sct.So im unsure who is doing there mail order stuff.
But every tuner has problems tuning via mailorder.
 
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