Boost rising like a turbo, weird

[cray z1]

Wondering if anyone had an idea why my boost tends to keep rising thru the upper RPM range instead of peaking and remaining static like a typical supercharger should. Pretty much modified the car with most all bolt on to make more power
With my pulley combination 2.55 upper and 9.55 lower it should peak at 17-18lbs but it continues to rise with RPM to 21+lbs YIKES (at 6500rpm plus). You would expect the supercharger to peak quickly and remain static through the RPM. I'm having to adjust the actuator to open the butterfly to bleed off boost to protect the engine....weird
Any idea where my restriction might be? only seems to really do it in 3-4 gear on the top end of the RPM range. (the car is a M6). Would the 2 1/2" stock exhaust from headers back be the problem?

2.55 upper, 9.55 lower, ported blower, snout and heads, dual 100% meth nozzles, 5" intake, 1 7/8" headers, 102mm TB, no cats, GT14 cam, stock exhaust from headers back, lots of cooling mods, monster triple, I.D. injectors, BAP............blaa blaa

Will try to post a log

[tartagliazl1]

Your 17-18lb of boost is even high for your pulley combo. I’m running 2.5 upper and 9.55 lower and peak at 15.5lb-16lb. Did you say you have the factory manifolds with cats? If so that can be why your running 2lbs higher.

[cray z1]

I have 1 7/8" headers, no cats and after that the stock exhaust

[cray z1]

Here is a snap shop of a typical log. I ran the car hard for a while doing a bunch of pulls so the IAT2 were climbing fast and timing was been pulled. The odd thing I found with my similar logs is when the IAT2 temp went up and timing was being pulled, the boost also rises for some odd reason to 20-21lbs. you can see it clearly in the snap shop. Once the car cools down and do another pull (low IAT2 and no timing pulled) the boost stays around 16-17-18 lbs at around 100-122 degree F

So in conclusion why is boost starting to climb higher when IAT2 rises also?........Makes no sense?

Example......180 degree F IAT2 = 21lbs boost

[RobZL1]

Hotter air occupying the same space in the blower case has more energy = higher pressure.

[ZMEnow]

Originally Posted by RobZL1

Hotter air occupying the same space in the blower case has more energy = higher pressure.

YEssir..


When Roots blowers are turned at very high speeds, they actually can heat up the inlet air to such an extent that the air expands substantially. This overheated expanded air loses so much density that even though your boost gauge says the blower is making boost, in reality you aren't putting any more air into the engine than an unblown engine would get.

[silversleeper]

So at this point it might be wise to check for a collapsed brick, and ensure the intercoolant fluid is full and pump is working.
For example if your temp was 80degrees F and 17psi you heated it up to 120F you'd be at 18.26psi without any other things going on to make it even higher due to "backpressure" or lack of exhaust.

[cray z1]

Excellent, so it just physics as work, perfect makes sense.
I modified the brick so it's good as long as my tig welding holds up. This sample log was done before I made a trunk tank and bought a Prospeed pump. I wanted to use this as an example because it seem extreme to me

[cray z1]

yup, it works........my neighbours love me

[Annatar]

Originally Posted by cray z1

Excellent, so it just physics as work, perfect makes sense.
I modified the brick so it's good as long as my tig welding holds up. This sample log was done before I made a trunk tank and bought a Prospeed pump. I wanted to use this as an example because it seem extreme to me

But normal boost is 9 psi at maximum, dynamically dosaged; in this case, the boost pressure is doubled. How long do you expect the engine to last?