LX Forums Forum banner

Supercharger bypass valve flutter/surge

64K views 74 replies 16 participants last post by  Ev0lv3 
#1 ·
Looking for some input. I have a 2016 Scat with forged internals and a Gen 3 Whipple (2.9L). Put a smaller pulley on it (went from 3.25" to 2.875") and currently making about 12lbs of boost. I was running the stock Whipple tune with the smaller pulley and the car was running decent.

I took it back to my tuner so he could data log and make some fine tune adjustments for long term driveability. He said it was knocking under partial boost and made some timing adjustments.

Engine seems to be running well and is a rocket under WOT, however, the bypass valve is now surging/fluttering under partial boost, and it has a slight "light switch" throttle with the boost coming on hard at about 75% throttle. It seems right around the point where the pressure goes from vacuum to boost the valve can't decide whether to open or close. Checked the throttle body, and it is maintaining a consistent 25% open (no fluttering with it) under partial throttle.

How are these two things related? I'm not a tuner, but trying figure out how timing (a computer adjustment) can affect the bypass valve (a mechanical part). It was not fluttering at all before the tuner got a hold of it.

Any pointers on what we need to look at to tune the flutter out?
 
See less See more
#52 ·
I’ve never seen a car do that before, I had no idea you were experiencing fluttering like that. I assumed it was like the usual in/out of boost hesitation most deal with. It’s like the bypass itself is fluttering open/closed. Any chance the throttle body is actually doing the fluttering and causing the bypass to follow suite, possible tune possible bad TB?
 
#56 ·
We data logged the last couple times I was with the tuner, and when it began its fluttering fit, the throttle blade was rock solid steady. We are fairly certain it's not the TB.
Damn, that is what I thought of as the most likely issue. Have the vacuum lines been checked for leaks and made sure routed properly?
 
#61 ·
I’m glad to hear your making some headway even if not 100%, it’s better than nothing or going backwards. When you finally get an answer for the issue please share the findings, I for one am more than just a little curious about it.
 
#62 ·
Just wanted to update this and bring this to a close.

Went again to the tuner yesterday, and I can finally report he got this car dialed in. Many thanks to Black Market Racing and their patience and persistence working on my car.

I put the Hellcat throttle body back on because there is a noticeable difference between it and the stock one. After trying different things which were not working, he loaded a stock hellcat TB table into my tune, and made a few very small adjustments. It worked like magic....

Great shifts
Linear acceleration
Idles perfect

The flutter I once had is all but gone. There is a slight movement of the needle in my boost gauge at a very particular RPM and throttle input if I want to be really picky - but you can’t hear it and can’t feel it at all. I’m content with that! It’s running like it would from the factory.

So, problem solved. I’m using the original bypass valve and set-up as it came from Whipple. As has been said in other posts and forums - the flutter is a tuning issue.
 
#65 ·
Glad to hear that. My tuning begins again this Thursday, finally have the 392, KOOKS headers and 88mm throttle body in car. 65lb inj i bought from a whipple kit were too short, so I left the 52lb inj in, have to address that later when I see how they perform. Some say they will be fine, others say be safe and go larger.
 
#69 ·
Seems many end-users have been told by tuners that whipple superchargers are the root cause of jerky operation while applying throttle.

It has nothing to do with the (any) hardware...the problem - and therefore solution - is in the tune itself.

Go to =68.ARB-bfOtOTunzcCWWt7pSL7N4f1uvgeFXjHXQDTRT4X...book Page and look for the post showing before / after clips from customers' data logs..


Sent from my iPhone using Tapatalk
 
#70 ·
BlackCharger06 PM’ed me about this link to OST Dyno’s FB page. I took a look, and it seems they are saying the issues lies in the throttle. For some, that may be the case. For me, it wasn’t.

When we data logged my car, the throttle position was consistent. There was no throttle body modulation or flutter. For me, it’s in the bypass valve. For whatever reason, my supercharger/bypass valve/cam shaft/pulley/throttle body combo have a hard time all playing well together. We have it as good as it’s going to get, but there is still some flutter here and there depending on a few variables.

What I have found is that in my particular case, the acceleration is linear to a point - and then the bypass valve closes, giving you full boost near WOT. The only time my car bucks is if I’m not fully ready for the boost while I’m gently pushing the pedal - this pushes my foot away from the pedal ever so slightly as the car launches and causes me to let up on the pedal just enough for the car to go out of boost and then as my foot hits the pedal again, the car goes into boost again. This bucking is caused by my foot. Not sure that makes sense, but the throttle modulation is caused by me, not the tune. Probably need to adjust my seat... haha.
 
#71 ·
BlackCharger06 PM'ed me about this link to OST Dyno's FB page. I took a look, and it seems they are saying the issues lies in the throttle. For some, that may be the case. For me, it wasn't.

When we data logged my car, the throttle position was consistent. There was no throttle body modulation or flutter. For me, it's in the bypass valve. For whatever reason, my supercharger/bypass valve/cam shaft/pulley/throttle body combo have a hard time all playing well together. We have it as good as it's going to get, but there is still some flutter here and there depending on a few variables.

What I have found is that in my particular case, the acceleration is linear to a point - and then the bypass valve closes, giving you full boost near WOT. The only time my car bucks is if I'm not fully ready for the boost while I'm gently pushing the pedal - this pushes my foot away from the pedal ever so slightly as the car launches and causes me to let up on the pedal just enough for the car to go out of boost and then as my foot hits the pedal again, the car goes into boost again. This bucking is caused by my foot. Not sure that makes sense, but the throttle modulation is caused by me, not the tune. Probably need to adjust my seat... haha.
What you are saying makes sense, but it still doesn't seem correct. The bypass valve shouldn't snap closed giving you a large change in boost for a small change in pedal. It seems like the vacuum required to close the bypass valve is too high....or the bypass valve is getting stuck close to being closed. Did you check to ensure the vaccum is getting delivered to the bypass valve properly and the line is not collapsing?

Admittedly I don't know much about how a non-centrifugal supercharger/bypass valve is tuned. I know the supercharger makes instant boost irrespective of rpm, but I'm not sure how the bypass valve is tuned to deliver the boost vs throttle. Did whipple give you any examples of what it's supposed to look like?

2007 Charger R/T, Supercharged
 
#73 ·
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top