Need help: Boost falling off
 

2017 Z06 A8
F1R Procharger on 4.25

Experiencing issue where car won't build boost past 6,300 rpm originally, thought it was belt slip so purchased a 10 rib kit. Retaining the same pulley and boost setup the car noses over at 5,600-5,700 rpm.
Has anyone experienced this issue? We've checked kpa pre and post intercooler there is a 3# lost on post side (19 to 16).
Logs showing throttle command to actual to WOT, it's not closing down. Scratching our heads and need some assistance. Thanks!! I will attach log photos.

https://cimg4.ibsrv.net/gimg/www.cor...703ed4ce50.jpg

In reference to post above...

Check if there is a leak. Some small leaks would do that

Been checking for leaks, watching system (best as we can), it swells so its all charged. Has anyone had problems with the supplied procharged a2a intercooler? That's like our last suspected culprit.

Im sure its not the Intercooler, must be a leak or belt slip or something in the valvetrain

We're sure the belt is super tight and no slip there. No evidence of slip and we did 10 rib swap just to be sure. It looks like 17-18psi is where the system looses it's shit and dumps over. We're just hitting that psi at a sooner rpm now.
If it was drivetrain would their be other indicators? The car behaves and drives perfectly fine, car can rev through the roof in P / N.

Maybe its a valve float, did you do a leak test?

Going to pull covers and plugs again...

Was dead set on pulling the IC but after your posts im kind of pushing that to the rear. All BTR LT4 hardware, set up has under 2000 miles on it and only one trip to the track, no visible vavle train issues so was ruling that out. But going back that way with fingers crossed it isnt anything in there.

Did you make sure you have the right pushrod length? And make sure to do a boost leak test. That definitely where to look, if for any way you can make the outlet of the Intercooler 3.5” or even 4” that will help alot with the pressure drop I gained 4psi and 80whp midrange just from that!

BTR components rods are 7/850s.

That's great midrange power! I seen a few used intercoolers in the for sale section with 4" inlet/outlet i will see if they're still available. thanks for your help, going to keep working on this mofo!

keep the inlet the same size of the f1r outlet, just make the outlet of intercooler 3.5” or 4”

I had same problem after 6300rpm my car was just nose diving. I went ahead and changed the valve springs from .660 to .680 and push rods. That fixed the problem for me. Try doing that. It's an easy fix never hurts to put new springs.

Your whole system checked out im terms of boost leaks etc??? Just sucks to have to pull the springs and rods, set up has less than 2000 miles on it.

There is no way it from the spring at that boost level, if the boost was higher i would think so, pushrods maybe yes but you will have to measure the pushrod first i think a 7.825 would be better than a 7.850 (thwt what happened for my case).

Before checking any mechanical issues I would do the boost leak test first, you can do it your self if you have air compressor with airgun,
pm me if you have any questions.

good luck

Had no leaks or belt slip but again ever car is different. What kind of cam do you have? If it's an NA cam that could be the problem too

Do you happen to know the push rod lenght you went with? Were your rods bent at all?


It seems to be a progressive issue, the car would run out to redline. This was on the stock 4.5 pulley. Come seasons end it was failing off at 6300rpm and 16-17# of boost. Now with the 4.25 pulley its hitting that boost much sooner and falling on its face at 5300-5500 rpm.

Comp cam 32% Fuel Lobe 231/242 116LSA 653 .651 lift blower spec'd ... have to find my full card to check full detail...

Pressure test checked out...
Super small leak at the MAF, going to adjust the fitment and seal that up. Dont think it was enough to warrant the issue at hand. So now on to the leak down testing. Messaged BTR on proper push rod lengths, i just think the issue would have showed up before. However we're getting more boost much sooner and maybe stuff just cant keep up. Was really hoping it was a small leak to fix the problem. Dreading a piston issue or something now :leaving:


https://cimg9.ibsrv.net/gimg/www.cor...2d69240490.jpg

Sometimes you get leaks past the throttle body! I would put a tire tube on the inlet of the procharger with a clamp to hold it in place, and take a vacuum line (the one goes to the bov ) and put some air using airgun and see if the tire tube start to stretch then stop adding air and see if the tire tube keep at the stretch point or just goes back flat.

My setup had a boost leak on the map sensor and on the headunit volute

To the OP, are you sure the tensioner is doing it’s job properly? Also is the tuner experienced in tuning the LT? I’ve seen this before when the tuner couldn’t get the throttle to stay open.

What's the best way to test the tensioner? To mitigate slip we went to 10 rib setup, so brand new pulleys and belt. Belt isnt showing any sign of slip/extra wear.
The throttle commanded to actual via the logs are showing its staying open. Will the logs show something different than actuality? The line peaks and holds as everything climbs, kpa falls over as does torque but rpm and mph climb for brief stint, by then we're out of it...