I just changed from a 3" Borla chambered to a 3" Magnaflow and single 3" out the back. Made a huge difference in sound. The Magnaflow is quiter but it is a straight thru muffler. Hopefully my back pressure is less.

 

Mission accomplished!

All the following were done with the same wastegate setting: full pressure applied to the "open" side (bottom) of the wastegate and none to the "close" side (top).

3.5" Hooker Aerochamber: 12 psi boost
3.5" no muffler: 19 psi boost
3.5" Magnaflow: 18 psi boost

AND, the Magnaflow is VERY quiet. The car sounds like a stocker with a Dynomax.

Mike

 

Did you happen to measure the backpressure difference between the hooker and magnaflow?

 

No. It seems to me that the wastegate is more dependent on backpressure than boost. So, based on that, it would be about the same.

Mike

 

Did you change your timing curve? Wouldnt you be able to add more timing with less backpressure. Not withstanding the extra boost.

 

Theoretically I guess you could since there is less exhaust gas in the chamber heating up the intake charge. However, I was running Methanol, so it didn't much matter.

Mike

 

what does your timing curve look like? At 12 lbs of boost, on pump gas, i would be in the neighborhood of 20 degrees, depending on air charge temps. I wouldnt run pump gas at 18 lbs, I'd prolly change to 109 unleaded, and still run 20 degrees at max boost, but i'd prolly add some timing back in in the lower boost tables.

 

To be honest, I don't have a good handle on my timing number. I adjusted the boost timing retard for max power but don't know how many degrees that is. Somewhere below 36.

I can tell you, though, that we gained 50 hp on a T-76 carb'd 377 SBC with FastBurn heads just by bumping the timing up from 28 to 30 deg. That was at 9 psi boost.

Mike

 

I seem to get eatin alive by timing, I wish there were a timing bible to go with that turbo bible

 

So the magnaflow only dropped boost 1psi from 19 down to 18 when compared to an open downpipe....
Thats pretty good. I need to get going on a 3.5" DP. I cant speak for everyone else, but i love the sound of a turbo v8 with a very free flowing exhaust. Its music to my ears.

 

so would you say the magnaflow muffler is one of the better/best flowing exaust/muffler yet quiet down the car?

 

What is the length of the Magnaflow ?



Chris

 

Absolutely!

Yes.

I think the case is 22" long.

 

Which magnaflow muffler are these? Is it the race series?


Jess

 

Regular series.

 

great testing!

what's the rule of thumb in back pressure? 2:1 is acceptable but closer to 1:1 is more ideal?

correct me if i'm wrong.. but ways to free backpressure (closer to 1:1):

bigger/more free exhaust/downpipe

bigger exhaust housing

bigger intercooler piping?

bigger inner diameter exhaust runners?

 

That's a pretty good rule of thumb.

Other ways to reduce backpressure:
larger exhaust trim (S versus Q, for instance)
clipped exhaust wheel
larger intercooler
larger TB
larger MAF

 

Nice info.

 

Good info!! Thanks!!!

 

The most over looked part of a turbo build, checking backpressure.
If you don't check don't build.....

Thanks Mike good info!