Im getting my new set up tuned, and the tuner thinks my crossflow flowmaster is costing me 20 rwhp or better. The car made 426 rwhp and 408 torque. Has anyone had experience on the dyno with the flowmaster, and changed it out? Besides a cutout, what should a guy put on instead. The flowmaster is plenty loud for me. I don't want to **** off the neighbors too bad. If it a 10 horse difference, I wouldn't care. If its 20-25, it would get me close to my original goal of 450. Any help or advice would be appreciated.

 

if you go to a thread a couple weeks ago listed low dyno numbers on the second or third page is a link to a thread on a 16 or so hp gain with cutout on a 350ish rwhp build so it is conceivable you would be hurting more. Not sure if same muffler but it was a flowmaster. Its possible you could be losing a few if your exhaust pipe is less than 4".(there is a sticky in the exhaust section when pipe becomes a restriction. If it were me and I could drop the exhaust somewere near headers I might try a run on the dyno like that and build my exhaust from that info. I went dual 3" with xpipe and 2 flowmaster 44 and it sounds very good and I will never have a resrtriction but down to 3.5" clearance and its a full exhaust with similar tips as my stock ones but bigger. Turned out nice especially since ive never done any exhaust work before and was working from a box of stainless pipe of various bends. I tilted the muffler and the are behind the rear end.


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Previous posts have seen 5-10 hp loss with a flowmaster.But the sound is great.Magnaflow members seem to like the raspy sound though with no hp loss.My02.

 

Hmmm slow-master... yup JUNK!

 

Is it single 3" to the back through the Flowmaster? If so I can see a easy 20+ at the tire with your setup running a cutout in the I pipe.

I picked up 2 tenths and 2 MPH from a cutout in the I pipe on my Magnaflow catback in the car below. Now going up to FM Y merge 3" - 4", a 4" cutout, and then a reducer to run through the Magnaflow when I need it quiet.

Vizard states a good exhaust will flow 2.2 CFM per FWHP, and that 1" squared of area will flow 115 CFM in a straight pipe. A 3" pipe has 7.06" of area, which equals about 812 CFM. 812/2.2 = 369 FWHP .. so more power and it becomes a restriction. A 4" pipe has 12.56" of area and flows 1444 CFM. It can support up to 650 FWHP.

This is more info than you asked for, but I figured I'd share because I am seeing nice gains from uncorking the bottle necks..

 

My current car with slightly ported heads and mild cam, picked up 16 RWHP and 16 RWTQ just buy dropping the exhaust at the Y. And yes its a flowmaster.

 

Thanks for the replies guys, I guess maybe a cut out is the best option. I have the 3 inch mufflex with the 4 inch merge y pipe. I wonder what would sound better, dual cut outs in the y pipe or a single after the merge?