my o6 ss i just put my magnflow exhaust on a week ago. but man going down the hi-way drives me nuts.its in and out of 8 to 4 all the time. do you think some thing is wrong ? if i drive in 3 its fine.

 

I do know that reduced backpressure in an exhaust system while increasing horsepower typically only increases the torque slightly, and moves the torque curve higher in the RPM range.

so, if you're wonder why that makes any difference....

Torque is the amount of power an engine has to speed up, or to maintain a speed. If you move the torque range up in the RPM curve, that means you have MORE torque when at WOT and at 3500 or more RPM. But, it also means you have less torque at a lower RPM, say like 1800-2200 RPM, where most vehicles cruise. When your engine goes into 4 cyl mode, it is because the engine THINKS that it has enough torque in the 4 cyl mode to defeat air resistance, or to go up a slight incline. When, it actually doesn't because your torque range has changed from stock. When the vehicle is slowed, it tries to accelerate, and if it doesn't have enough torque to accelerate sufficiently, it switches to 8cyl mode to give itself more power. The cycle continues from there.

Have you noticed if using the cruise control helps at all?

 

i always wondered about that...but from what everyone else was saying they didn't really notice a difference....but you'd think if it went down to 4cyl it would sound wierd...

 

With the factory exhaust it does change pitch slightly.It kind of sounds throatier,almost like a helicopter.You notice it mostly around 35 MPH or so.At speeds of 55-70 you can't really tell.

 

I notice that my 07 SS is starting to stay in the 4 cylinder mode longer than it did when I first got it. Initially, it would bounce around from 4 to 8 at the slightest difference in road condition, but now, on the same road, it seems to hold inthe 4 cylinder mode longer, where it takes a greater demand before it switches to 8 cyls. With the stock exhaust, you can't hear anything in the car, but I'm sure you would with a performance set up.

I remember reading somewhere, I think on this board, that another member with the 5.3 V8 noticed the exhaust sound changing, and if I remember correctly, he said that he drove the car in 3rd around town, to keep the engine in the 8 cyl mode, and not have the constantly changing exhaust note. With an aftermarket performance set-up, the sound would certainly be amplified, and I would think very annoying when changing back and forth.

I have a Magnaflow set-up on my 05 silverado which doesn't have the cylinder deactivation system, and you can definetely hear the exhaust note change when the tranny switches back and forth from overdriveto 3rd.

 

I'm confused, I thought only the '07 had DOD. The '06 does too??

 

The 06 called it "Displacement on Demand".It is printed on the engine cover.In late 06,GM began calling it "Active Fuel Managemant" and changed the engine cover as such.Check photos on e-bay for 06 vs 07 Monte Carlos or Impalas engines and you will see it.It is the same system though.That is probably one of the few ways to tell an 06 from 07.

 

Thanks for the clarificaton.

 

I have flowmaster on mine and when I first did it when it went to 4 cyl mode it sounded funny. Went back in and had the resonator taken off and it really dont sound to bad when in 4 cyl mode anymore. Made a huge difference in sound also. Much louder.