badass1g

Hey guys just trying to figure out whats going on with my boost levels. Usually I am right around 9-10 psi at the top of 3rd gear. But I feel like its been a bit slower lately (which I thought was just from the heat) but haven't really been watching the boost guage. I recently installed an axle back 3" system from hooker which is an awesome upgrade. I measured parts on the factory NPP system that choked down to 2.2" in a couple spots while the new exhaust is full 3", even the valves themselves. The car sounds so much better but it feels a little slower to me with this mod so I look at the boost guage and im now maxing out to 7 psi at the top of 3rd.

I know that headers would do this (make the boost drop) but this is also the case with just an axle back? I really do not think there are any leaks or problems with the car. I do have one pulley lower that I have never installed because I haven't wanted to go over 10 psi but now that I am down to 7 psi im thinking maybe I should install it and hope for ending up back around 9-10 psi? I have an AA kit with meth injection and exhaust. Otherwise the car is stock. It was sitting at about 650 whp but at the moment I would guess im down to about 600. Does it sound normal to lose boost and hp with an exhaust upgrade? Would I be ok to install that new lower pulley without retuning the whole car since I would likely be right back to around 9-10 psi which the car is tuned for? I think the car is running a little rich (I am guessing) since the install and the lower boost but maybe the maf is making the needed adjustments automatically?

I really hope I do not need a retune because in Boise where I moved to I do not know of anyone that is capable of retuning my car to my standard. Thoughts?

Suds

BrunoTheMellow

Definitely retune for a pulley change and maybe wait until the same temp as last tune.. Maybe your belt is slipping? That's a big drop. Maybe it's the heat. Texas?

I was down from 7 psi to 3-4 psi due to belt slip at top of 3rd

badass1g

moved from 4500 ft to 2700 ft and that didn't change much but now with the crazy hot days we have lately it must be causing some type of boost problem. So the air temp for summer temps high enough to dprop psi or is it from the upgraded exhaust axle back>? What is my next thing to check>\?

badass1g

I live in Boise its been over 100 degrees lately. How do you know if the belt is slipping? The setup only has 4k miles on it, is it possible to slip that soon?

IM4A2Z

You would have to Data Log in order to see it. If you don't have the ability to do that than take it to a shop with a dyno and have them do a few pulls along with data logging at the same time.
Your mod's along with the summer temps would definitely cause a drop in boost of several psi.

BrunoTheMellow

With a boost gauge you will see it rise linearly then plateau.

badass1g

Ok thanks for your input. I did some testing over the last few days. I don't really ever go full throttle very often so I just didn't notice how much of a difference the heat made.
So in 100 degree weather the car maxes out at 7.5 psi (in 3rd gear, I don't do this often but this was for testing), the next day I was able to get out in 90 degree weather and the boost was the same 7.5 psi max in 3rd.

Then this morning I was able to get out in 80 degree weather and holy crap what a difference that makes, I gained a full psi went to about 8.5 and it felt like an additional 40 hp then the previous days. I cant even imagine how it will feel when it drops to 40-50 degrees I am stoked. I feel like I def picked up some power from the axle back, how much would you guys guess of a gain? The car was right at about 650 whp with the stock exhaust.

helga203

I bet from the higher temps it was pulling timing for safety