I recently had a magnaflow flow thru muffler put on with 3" exhaust from the cat back. It was done at a local muffler shop. What would i be experiancing if this install had created a lack of back pressure and is that possible. It just seems that the truck is not quite running right. I cant really put a finger on it but maybe even a loss of power. Any help would be appreciated.

 

I'm not sure it's back pressure that your missing. Do you have a loss of power? What has caused you to think that it's the mufflers fault?
I have 2 1/2 inch pipes ran straight out the factory location with no mufflers at all and I gained performance. I really think I'd check else where for your problem.

 

Magnaflow recommends disconnecting the battery during the installation to permit the PCM to adjust to the new conditions...did your muffler shop do that?

 

Did they change the y out? If they did, that probably is the culprit. Having done this to my truck, I can tell you the stock y needs to be left alone. I had noticeable power loss between 2500 and 3000 rpm. lost about 1.5 mpg also. When I went back to the stock y, and put a Stainless Magnaflow SIDO system on in place of the muffler shop system, power and gas mileage were restored to at least where it was with stock system...Kevin

 

No the wye was left in they just increased to 3" right after the wye. Its not the magnaflow kit , just the stainless steel muffler and 3" aluminized mandral bent pipe. single outlet

 

I would second this motion...

 

Well mines Magnaflow cat back system came with SS 2.5" tailpipes and 3" tips at exit and no signal of loss power but of course noticeable powerful and nice sounds/rumbles!!!

Maybe thats why your tailpipe a bit too big- 3" ??

YOMAN!

 

Thanks for the sugestion, As soon as it quits raining here in sunny san diego I'll give it a try.

 

With the incredible dependence that our trucks have on technology and computer based systems, I have a hunch this will solve your problem.... there are simply too many 'flow' sensors in the mix... I really think resetting them will be a golden bullet.

-RP-

 

bigger pipe = less back pressure?

3" seems a little big, don't the use 3" pipe for diesels?

 

SteveVFX4,

yeah it ll lose some back pressure.

YOMAN!

 

The problem is not flow, its exhaust gas velocity. When you go to a bigger pipe the exhaust gas looses velocity. This hurts exhaust gas scavenging, which in turn kills the low end torque. If you go to the Maganflow site, they post the instuctions on how to install there kits. They start from the second slipjoint and put in a 3" pipe which is about a foot long (roughly). This is way past the y connection.

The only reason I know this is that I talked to Mike Troyer last week about this exact issue. He explained to me why I didn't want to do anything at the Y, or for that matter anything other than what Maganflow designed in there cat back exhaust kit. They are one of the few companies that actually do flow testing. It was designed to increase torque not loose it. The fact that you get about a 12HP bump isn't bad either.

Hope this helps.

 

The Magnaflow SI/SO Catback 15609 uses 3" Mandrel bent SS pipes with a 4" Tip.

If you have SI/SO 3" is recommended

If you have Duals, it should be 2 1/2 or 2 1/4 I believe.

I have the SI/SO, and I gained performance, I didn't lose anything

Try resetting your computer.

 

rbraughn,

Thanks for catching that. I didn't mention I have the SIDO. And it is 3" in and 2.5" out.

 

Disconnecting the battery will force the PCM to relearn the adaptive strategy again but two or three drive cycles will do the trick too.