Whipple Supercharger bypass valve flutter/surge after timing adjustments

[Capt. Nemo]

First, I am not a tuner. I am working with my tuner to resolve an issue we ran into yesterday. Looking for some input and direction. I've spent quite a bit of time trying to research this issue, and posting this seems like the next logical step.

I have a 2016 Charger Scatpack - 6.4L, forged rods and pistons (Modern Muscle Extreme), 2.9L Gen 3 Whipple Supercharger kit. Everything else is basically stock. I'm running 91 octane pump gas as well.

I put a smaller pulley on the supercharger (went from 3.25" to 2.875"), and it's currently making about 12lbs of boost. I was running the Whipple tune on the car with the smaller pulley, and the car ran fine. I took it to the tuner to make sure the tune was supporting the extra boost and that the engine wasn't detonating.

Under partial throttle/partial boost, the engine was pulling a lot of timing, causing some knock. The tuner adjusted the timing and the engine seems very happy. He adjusted some of the fuel trims as well.

Problem we are having is the supercharger bypass valve is now fluttering/surging under partial throttle/partial boost. Just at the point where vacuum turns into boost, it's as if the valve can't decide whether to open or close. In addition to this, the throttle now has developed a slight "light switch" effect, where at about 75% throttle it goes into full boost and takes off like a rocket.

Without any adjustments to the stock Whipple tune, there was no bypass valve issues and the throttle was very linear all the way until full boost. I'm trying to understand how a computer adjustment (timing) can affect a mechanical part (bypass valve) so drastically? The throttle body was looked at during the surging at partial throttle, and it looks like the throttle body blade is holding steady during the bypass valve fluttering (the throttle body isn't fluctuating).

Any input and tips as to what we should look at and adjust would be very helpful and appreciated. I'm about to head back in about an hour to mess around with the tune again.

[Homer]

Welcome to the forum, folks around here usually request a tune and a log as it helps diagnose the problem. Are you certain the tuner did not adjust the airflow tables?

Just out of curiosity, did you put a smaller belt on when you dropped to a smaller pulley?

[Capt. Nemo]

Welcome to the forum, folks around here usually request a tune and a log as it helps diagnose the problem. Are you certain the tuner did not adjust the airflow tables?

Just out of curiosity, did you put a smaller belt on when you dropped to a smaller pulley?

I can?t answer the airflow tables question. I was pretty happy with the canned Whipple tune that came with the supercharger kit, so he just made some minor adjustments without modifying the tune too much.

As far as the belt - no, I?m using the original belt that came with the supercharger kit. Going .375? smaller on the pulley I was able to adjust the tension to match what it was on the larger pulley. There?s no slip.

[lafrad]

Depending on the build, the vacuum bypass controller that whipple uses needs some tweaking.
Turns out, they use a reasonably standard one. You can get different setups with different strength springs, allowing the bypass to activate at different pressures.
you can also find bypasses that have ports to work on the boost side AND vacuum side of the blower, allowing it to progress more smoothly from low to high load.

This is a common theme in the space for *all* makes and models on these aftermarket blower units... start messing with that and see how things operate.... it most likely won't be tune related.

[coanan]

Could you post up both tunes, Stock whipple and current tune?

[Hemituna]

Stock bypass actuator will be fine...it is usually in the tune

[[email protected]]

Stock bypass actuator will be fine...it is usually in the tune

This is correct ^^^^
This is not a bypass issue. It's in the tune and the issue occurs on all of the 15+ Gen III Hemi's we have installed/tuned a Whipple on that is making decent boost.

[Capt. Nemo]

I've been reading other threads, and it's been mentioned how important cam timing is when trying to get rid of the bypass flutter. I have replaced all of my lifters with hellcat lifters, and MDS has been disabled on my engine - it is my understanding that any cam timing adjustments would have been made through the MDS solenoids effectively making cam timing on my engine non-adjustable. Correct?

[Homer]

Your cam is still VVT despite using non-MDS lifters. You just don't get the cylinder deactivation at cruise/low power. I would think your ETC air tables are not dialed in and would hold off on any cam adjustments. Again, this is were tune and log files come in hand, or have your tuner read these links.


https://forum.hptuners.com/showthrea...l=1#post519829

https://forum.hptuners.com/showthrea...l=1#post466902

https://www.lxforums.com/board/power...ml#post5082012

[coanan]

Your cam is still VVT despite using non-MDS lifters. You just don't get the cylinder deactivation at cruise/low power. I would think your ETC air tables are not dialed in and would hold off on any cam adjustments. Again, this is were tune and log files come in hand, or have your tuner read these links.


https://forum.hptuners.com/showthrea...l=1#post519829

https://forum.hptuners.com/showthrea...l=1#post466902

https://www.lxforums.com/board/power...ml#post5082012

Read those a while back, really good info. tweaked my tune and got rid of the on-off boost surge problem. On slow throttle ups it transitions right into boost pretty smooth now.