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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?
 
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#3 ·
I’m interested to see what others say, but the only thing that comes to mind is that he changed something that altered the vacuum vs RPM.

In the older gen cars they had a switch that told the computer it was at WOT (80 or 90%throttle) and that’s the only time you could affect anything with the table in the tune. Other than that the computer had control and it was adjusting for best fuel economy which is dangerous for part throttle boost situations. A tuner couldn’t really do anything for part throttle boost the driver just had to keep the car out of that mode. I guess the new gen cars do it differently. You might ask the tuner exactly what he changed....was it timing only or did he change some other thresholds.


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#4 · (Edited)
How can you tell the bypass is fluttering? Does the car feel like it's boosting then not, then boosting then not in partial throttle up? Then when the throttle gets to a point it goes into full boost, like a switch turned on.
 
#5 ·
The throttle blade is holding steady, so there's no surging, but 1) you can hear it distinctly, and 2) my boost gauge tells me. Boost needle starts doing the bob and weave. When accelerating, the car will accelerate normal, and then hit a little wall where it feels like it has to be pushed over an edge where all of a sudden it takes off like a rocket.

I shot an email to Mike at OST, and he mentioned it was pretty common in the model year 15 and up Gen III hemis. I just have to save my money to have him look at it. This current tuner has cost me $800, and the car still isn't right.
 
#8 ·
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#11 ·
I learned a long time ago when I was moding my vette that it was a must to have your own tuning software, so I bought HPT Pro and started. You have more control to compare tunes, make adjustments, and data log so others can see what's going on and help you.
I learned how to do everything else, may as well learn how to tune as well... Haha. Thanks for posting that thread - lots of good info. I forwarded it to the tuner since Hemituna posted his tune file.
 
#9 ·
I learned a long time ago when I was moding my vette that it was a must to have your own tuning software, so I bought HPT Pro and started. You have more control to compare tunes, make adjustments, and data log so others can see what's going on and help you.
 
#18 ·
Back in the saddle at VMP I see. I have a plaque for you.:rock:

It took my tuner 2 years and countless dyno time to get my eforce right. Had to revert back to a 08 cal and now I think it's as good as it's gonna get. Last test is vmp later this year to see how it runs in the 1/4

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#12 ·
So here's what I learned over the years tuning and working on my old 300 2.9L whipple setup. One thing everyone fails to understand is that even with the bypass fully open and your foot to the floor, you will still make 3-4psi of boost. The bypass isn't large enough to completely bypass ALL the boost to bring you to zero when it is open. So what this means is as you get nearer to the throttle body being saying 40-50% throttle and the bypass still wide open, you WILL MAKE BOOST. When that happens, you now have a circular pattern of behavior. The bypass needs vacuum to stay open, once you get near zero vacuum or some boost, the bypass will start to close. This is the start of the "lightning" switch problem. The bypass closing means less boost is being vented, so boost in the intake climbs, which means now more boost is being applied to the bypass acting to close it, which closes it even more, then boost goes up even more, and BOOM, bypass gets closed and you have full boost and the car takes off. All this happens in a matter of a second or two.The fluttering you are feeling is the bypass getting waves of near no vacuum then to some boost, forcing it opened and partially closed. You can tease it mechanically into this zone by slowly creeping up to the near zero vacuum point. Recall that there is always enough airflow to make boost, so you get the force of boost under the bypass blade pushing to open the blade back up versus the light spring inside the bypass acting to close it. They go back and forth for which is a greater pressure. What tuners have done to resolve a lot of this issue is simply slow down the ratio of your foot input to the opening of your throttle body, so that you can avoid this zone entirely. Playing with your power percent request table and your sonic airflow factors will delay what your foot wants versus what the throttle body and motor gives you. Let's say for example the maximum throttle you can give the motor before the ratio of boost versus vacuum forces the bypass closed is 35% throttle, a good tune will give you a 1:1 ratio of foot pedal versus throttle opening up to about 20% throttle, then about 75% of throttle opening versus foot pedal from 20-30%, then about 50% of throttle opening versus foot pedal for that last distance up to the closing point at 35% throttle. What does all that mean? Well the first inch of travel of your foot will react as you normally expect, the next half inch will feel a little slower reacting, but you can move the pedal easily without much reaction from the car, that last 5% will almost feel like a dead zone, a full 1/2" of pedal travel that virtually does nothing as far as increase power output of the pedal. This will give you a sense of much better control and will nearly never get into the lightning switch zone or flutter zone. But, when you want full boost, mash the pedal all the way and she will take off as expected.
 
#13 ·
It's been about a month since I posted this. I've taken the car back to the tuners a few more times, and we seem to have the car dialed in about as good as it's going to get. We adjusted the air tables and the cam timing at partial throttle. It's interesting to see how things affect the car. The last tune really woke the car up. Crisp throttle, hard acceleration, and my intake temps dropped over 20 degrees. It seems to be moving air much better. The bypass valve flutter is still there though. The tuner thinks the smaller pulley may require a different spring rate to compensate. Based on the results of the tune so far, I'm thinking he's probably right. Can anyone explain to me how a dual port bypass valve works? Whipple sells a dual port one, as well as others with different spring rates. I would think the dual port would have vacuum lines going pre and post supercharger to have an almost push/pull on the valve rather than relying solely on a spring to close it. That's me guessing. If someone could explain it, that would be great. I really want to get the flutter out. It's gotten better, but still present.
 
#14 ·
Just out of curiosity have you talked to the guys at Whipple? They were really helpfully in getting me the correct parts for my build. I think Mike is the guy I talked to there
 
#16 ·
I've called Whipple three different times and spoke to Jeff. He told me twice he would call me back after checking on some things, and I never received a call back. There is no pill in my vacuum line. That was one of the things Jeff from Whipple and I did discuss during one of my calls and he was supposed to get back to me about. I just went out and checked the vacuum line myself and there is no pill with an orifice in it. I made a new line myself and created my own pill with a small hole drilled in it. It didn't work and made things worse. I also tried routing the vacuum pre-supercharger, but that didn't work either. Right now the bypass valve is routed the way it was instructed by Whipple, which is post supercharger from the intake manifold plate.
 
#22 ·
Try swapping over to the F150 lightening dual port bypass. It has a much heavier spring and therefore shuts much earlier. I have vac lines going from TB and manifold vac sources. This was key to my combo. Boost transition is early, much lower rpm, and perfectly smooth even with my 18psi pulley.

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#23 ·
Try swapping over to the F150 lightening dual port bypass. It has a much heavier spring and therefore shuts much earlier. I have vac lines going from TB and manifold vac sources. This was key to my combo. Boost transition is early, much lower rpm, and perfectly smooth even with my 18psi pulley.Sent from my Pixel XL using Scat Pack Forums mobile app
This sounds promising. Whipple sells a dual port, which looks identical to the pics of the F-150 ones I searched except Whipple charges quite a bit more. Whipple Superchargers Bypass Actuators Can you go into greater detail how the vac lines are routed to the dual port - or have any pics?
 
#27 · (Edited)
Not sure. The Whipple uses a fairly standard Eaton bypass valve which bolts right under the intake snout. The little info I read on the 2650 is that it has an "integrated" bypass valve. Not sure what that means, or if it can be replaced/modified.

*EDIT*

Found a pic of one of these superchargers. The bypass valve is right up front. Not sure what brand it is, but looks like it could be swapped out for other bypass valves if you could find a part number. It's not a standard Eaton bypass valve, as it looks like it is mounted differently and the push rod is longer.

 
#30 ·
So, dual port didn't work. The valve only needs the rear port to work, and the front port seems to be for another sensor or something in the Ford application. The front port I had plumbed pre-supercharger, which just cancelled out the rear port and the valve didn't move. Live and learn. The dual port does have a noticeably stiffer spring, which didn't make any difference.





So right now I'm running the dual port with the front port left open.
 
#34 ·
Whipple emailed back and told me to use a restrictor pill in the vacuum line to the bypass valve. Was told to use one with a .022" or .024" orifice.

Put the restrictor in the line and used the original bypass valve... no change.

Kept the restrictor in the line and used the dual port WITH another restrictor on the second port... no change.

I'm pretty frustrated, and trying to brainstorm for other ideas. The car is running very well, other than this surging issue. I'd like to think it's not a tuning issue, but I'm leaning that way after trying a stiffer spring and restrictor pill.

I'm wondering if there's something about this particular boost level that the engine doesn't like? I need to get an aftermarket crank pulley dampener, and I'm considering an 18% overdrive pulley. Thinking maybe by changing the boost, it might help get out of the surging range... plus I'll get an extra pound or two.

The restrictor pill:



The dual port with another restrictor. It actually worked decent, really slowing down the movement of the valve.

 
#42 ·
Do you have access to both tune files, the before and after? I got rid of mine by tuning, may have gotten lucky, because I barely know what I'm doing. I tend to change more than one thing at a time, so I'm not sure what part really fixed it. I raise numbers in Throttle body airflow 00 to .90. 00 to .70 were small and progressively got larger .75 and .90 increased by 19 and 26, the rest stayed the same. Feed forward Control, max demand throttle 700 stayed the same and 1200 to 4800 change to the same 3.7998. then some timing increases. It transitions into boost nice and smooth now, no more on/off boost light switch crap that drove me nuts.. The mechanical **** I tried before that didn't work.
 
#43 ·
I recorded a short video on my phone and sent it to Whipple. They said it was for sure in the tune. I'm heading back to the tuner next Monday, and we are going to play with the throttle control and loads. I'll have him look at how you did things and see if it helps point us in the right direction.
 
#48 ·
Your video is nuts. Definitely have a problem with part throttle boost. What the problem is ? I wish I had an answer. But you did say it didn’t do it with the stock pulley. That leads me to beleave it’s either in the tune or there’s a problem mechanically with the gate that can’t handle the air being sucked in at higher rpm the blower is spinning. If that makes any sense to you.


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#49 ·
Your video is nuts. Definitely have a problem with part throttle boost. What the problem is ? I wish I had an answer. But you did say it didn't do it with the stock pulley. That leads me to beleave it's either in the tune or there's a problem mechanically with the gate that can't handle the air being sucked in at higher rpm the blower is spinning. If that makes any sense to you.

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That video was the worst it has ever been with the dual port valve and hellcat throttle body. I put the original valve back on with the Hellcat TB, and it still does it, just not quite as fast.

It didn't do it with the smaller pulley with the stock Whipple tune, but that tune was also causing detonation issues. It started after adjusting the timing to remove the detonation.

It could be the amount of air going through the supercharger and the placement/size of the valve. I don't really know - I'm not an engineer. I was thinking of it much like resonance similar to what you see with bridges and wind.

I'm thinking about the ATI 18% overdrive like I mentioned earlier to see if that helps. I go back to the tuner on Monday, so we'll see what he can do.
 
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