Dodge Challenger Forum banner

Supercharger part throttle flutter/surge

21K views 37 replies 18 participants last post by  y2krtaf 
#1 · (Edited)
So I've read a lot about part throttle boost and I have a question. Under part throttle, my car will shudder, as if the bypass valve is rapidly opening and closing. It's very rapid, as if it were a machine gun. There's no real way to avoid it unless you back off the throttle or increase throttle and go 100% into boost.

This was an annoyance when I was at 6 psi but now that I am at 13 psi it can be a rather violent experience.

I've had my tuner make adjustments, thinking it may be a tuning issue but got nowhere. I'm left to believe that it's the bypass valve trying to decide wether to be open or closed, but I don't know for certain.

I talked to Magnuson and they were no help. I asked if they had a stronger bypass that kicked in later and the answer was no.

Has anyone else had this issue and solved it? I have a hard time believing that every other Magnuson owner has the same issues and is just living with it.

Edit: Just to clarify, the shuddering happens when I am in semi aggressive part throttle. When I am at a lighter part throttle (accelerating up a grade on the highway) it is much milder. The surging feels like I am pressing the gas once per second and then letting off. The more throttle I give it, the quicker and harder the surging gets, until it eventually has the machine gun feel.

Thanks.
 
See less See more
#2 ·
No answers for you but I believe I have the same thing with mine. Whipple at 9psi. I thought it was something to do with the variable timing switching.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
#16 ·
there is very little you can do with mechanical bypasses, nearly all superchargers use a mechanically actuated by pass that relies on manifold vacuum to open and close, at 6/7 psi, not much issue but at higher boost, a serious issue, until someone designs and builds electronically control by pass that can programmed not a lot you can

what we have done to improve driveability, we have added small spring to the bypass arm making it more difficult to close, requiring more vacuum to close in order to delay the reaction, and to a point have been successful in improving the linear driveability, you do have to get unto the throttle much harder to go into boost

anybody that has been reading my posts from way back will remember that i have stated over and over that there is a fine line between street and race car, once you pass 600+ whps, driveability becomes affected and the pure joy of just driving is affected

Bigred is a monster, but also a monster to drive, parking lot maneuvers are a major pain in the butt

Luke
 
#18 · (Edited)
Luke,
It was great talking to you today.

You are correct, when I was at 6psi the surging was hardly noticeable and I could live with it. Now that I'm pushing 700whp, that surging is a beast. I'm fabricating a bracket for a spring setup as we speak, to hold that bypass open for a little longer.

Again, thanks for the phone call today.

As far as tuning goes, I had a revision that I installed this morning and it made no difference. I'm thinking this is mostly a mechanical (bypass) issue.
 
#25 ·
#26 ·
Is this a Maggie issue? I have a similar problem on my Vortech, when in either 5th or 6th, and I'm aggressive with throttle as it passes thru 2400 to 2600 RPM range I get a engine jerk, we have determined it is a lean condition with no knock, then it's gone.
 
#29 ·
Just as an added bit of info from my own experimentation, the part throttle boost somewhat depends on where the vacuum line to the bypass actuator is connected. I have much more surging and PTB if it's connected to the intake snout than if I have it connected to a port on the supercharger base plate.
 
#30 ·
what I found was that my car was attempting to go into boost way too easily in part throttle. I initially attempted to resolve it by lowering the voltage in which the car went into PE, thinking it was just going lean and commanding stoich under boost. That didn't resolve the issue. However, I also noticed that it happened that I could stab the throttle into boost and the car was fine. I did back to back scenarios where I went into boost gradually and one where I stabbed it and what I found was that when I went in gradually, the car commanded PE fueling as set up in the tune but the cam position was not following the WOT table. In the attachment you can see that the exhaust cam position is still retarded at 93* where the boost came in gradual. If you look at the white spark line you can see that it's choppy as the car shuddered. In the bottom pick you can see I stabbed the throttle and the exhaust cam position advanced to 120* and all is well.

The fix was to set my throttle % and it's inverse table back to stock as opposed to having it advanced. I think you Diablo guys call it throttle boost. I've since been able to advance some of the early columns so the car is still responsive around town but as it gets up into the 50% + ranges, I let things alone. The reason, I theorize, that this affected things is because the inverse table goes off NVRATIO, which is the Vehicle Speed / RPM. If your car thinks it's moving faster at a given RPM, than it really is, it won't shift (see the trans part throttle shift tables). If your car isn't downshifting early enough, it goes into load / boost too early and at too low of a voltage for your car to flip the cam VVT setting to use the WOT table.

Hope that helps someone. Between that and torque management I figured out the tune on a '14 Charger RT that also has heads, cam and headers with a Procharger. My car has heads, cam and headers with a Whipple. I had to start with no base tune so I figured it all out on my own.
 

Attachments

  • Like
Reactions: boostedscatpack
#35 ·
I'll grab a couple screenshots later but the short answer, that I found worked, was to set my exhaust cam position to mimic wot at each RPM range. Now there are not drastic variances in cam position when transitioning from part throttle to full throttle. I did this on my Whipple and my buddy's ProCharger and all stumble went away. We have tried to reproduce it and cannot.
 
#38 ·
In for the knowledge as well,was curious if this was due to the intake manifold swtching runner length and something the Eddy intake or a 6.1 intake may help.

May boost in the future so always curious since my choice would be positive displacement boost.
 
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