[notbluelightsagain]

I have a Magnacharger and also Mopar catbacks on my 2010 R/T. When I am cruising at a relatively stable speed/RPM range, it feels like, for lack of a better description, pressure slowly builds up and then there is a release through the exhaust almost like a mini-backfire, but much more quiet. I feel a faint lunging of the car when this happens. I have noticed that, particularly around 2000 RPM and 60 MPH, the tach will quickly drop from 2000 to 1800 when I feel the pressure releasing, then build back up.

I noticed the same thing today when cruising at about 80 MPH. Can anyone explain what this may be, and if it is a problem that should be addressed or a normal side effect of supercharging?

 

[CTPCam]

More than likely a odd spot with the bypass system. Check and make sure the vacuum lines to the bypass are in good shape and the bypass actuates properly. Also if you have the jet/orface in the line that it's clean. There is a fine line where the vacuum/boost signal allows the byass to open and close and that rpm may just be at a odd spot.

If you have a boost/vacuum gauge, you would be able to watch this.

Also it's not uncommon for the cats to collaspe, but you would down on power all the way thru the rpm band.

 

[CruzKing]

automatic?

maybe MDS.

 

[notbluelightsagain]

automatic, but I think they shut down the MDS with the Predator when they installed the supercharger

 

[notbluelightsagain]

More than likely a odd spot with the bypass system. Check and make sure the vacuum lines to the bypass are in good shape and the bypass actuates properly. Also if you have the jet/orface in the line that it's clean. There is a fine line where the vacuum/boost signal allows the byass to open and close and that rpm may just be at a odd spot.

If you have a boost/vacuum gauge, you would be able to watch this.

Also it's not uncommon for the cats to collaspe, but you would down on power all the way thru the rpm band.

CPT, I don't know that much about engines. Is the bypass something that re-routes the boost built by the supercharger when I am street driving at lower RPM/acceleration ranges? If so, are we talking about vacuum hoses that route the compressed air directly to the exhaust manifold? I did check all the hoses and everything seemed snug, no heat friction, no loose connections.

 

[CTPCam]

CPT, I don't know that much about engines. Is the bypass something that re-routes the boost built by the supercharger when I am street driving at lower RPM/acceleration ranges? If so, are we talking about vacuum hoses that route the compressed air directly to the exhaust manifold? I did check all the hoses and everything seemed snug, no heat friction, no loose connections.

CPT...LOL. Sorry I know you don't know but my name is Cam ya know. Normally I sign up as Cam, but that was already taken here. I'm simple like that.

During idle or low throttle position, the intake manifold pressure is under vacuum. In a naturally aspirated motor, at wide open throttle in a perfect world, you would be at 0 pressure in the manifold (remember, vacuum is pressure too). In a forced induction motor when it comes into boost, you have positive pressure in the manifold.

Sorry if covering the basics was uncalled for, but I did just in case.

Anyhow, the bypass is a internal valve that remains open during low to mid part throttle operation and allows the pressure build up downstream of the rotors to bleed off (and in this case) internally. What actuates it is that cheap black plastic unit on the driver’s side that has a line to it off the blower cavity.

What holds this unit open is vacuum. And once it goes into boost (or zero pressure) the unit closes the valve. Now some of these units have internal and external springs that help during the transition of the valve to slow done the rate of closure. As is the case with the Kenne Bell. Magnacharger has a orifice (just like a carb jet) inline to slow the pressure equalization down and help with the transition into boost. Otherwise it's like a light switch going into boost.

Take your hand and with the car turned off, actuate the linkage off the bypass diaphragm, make certain it move freely. Sometimes these are internally spring loaded, so you may feel some resistance to movement. On the Magncharger, I don't remember if it is.

Also check that office and make sure the rubber line to it is in good shape.

I would suggest a good boost vacuum gauge if you don't already have one. That really help in trouble shooting certain types of issues.

Also if you don't find anything, give Magnacharger a call. Maybe they'll have something for you that I've over looked. It could also be a tune issue.

 

[DCX Depot-Tim C]

Great answer Cam. I though I was going to have to type all of that out and was hoping someone else already did.--LOL
Tim C