I know this has been asked to death, but every combo is unique, so I'm asking for opinions.

Anyone think I'll gain a good amount of horsepower going from:

hedman shorties - custom 21/4" to 3" ypipe - 3" magnaflow cat - flowmaster 3" american thunder catback

to:

hooker super comps - mufflex y - mufflex 4" catback w/spintech race series muffler (dual outlet)

or:

keep shorties - mufflex y(get muffler shop to connect to shorties) - same mufflex catback

Basically the engine is a 355 - performer rpm heads - 9.8:1 compression - magnum 280H cam - 1:6 roller rockers - weiand stealth (egr blocked) - qjet - L69 air cleaner

Any thoughts?

 

Im thinking just minimal top end HP increase.

 

No sense in getting the 4" Mufflex system if you have a single 3" cat and pipes. That is where the restriction will be.

The better situation would be 2 1/2 inch pipes from the headers to a 2 1/2" x 3.5" y-pipe to a 3.50" cat. Then a 3 1/2" Mufflex system on back to to a Magnaflow 3 1/2" muffler with either a dual or single outlet.

Another route would be 2 1/2 inch pipes from the headers to two 2 1/2 inch cats and then the 2 1/2" x 3.5" Y-Pipe. From there a Mufflex 3 1/2 inch system back to the Magnaflow muffler. This is actually what I'm doing. Just waiting on the 3 1/2 inch Magnaflow muffler.

 

i think it would make a a noticable difference...the american thunder doesn't flow that well, and the exhaust seems a little restrictive for that motor...i just put a set of LT's and hooker catback on a LS1, and he saw a huge increase...

I would go with the LT's, mufflex y, and full mufflex catback, and I'd probably tell them you want the magnaflow muffler, and have a single outlet.

I think it would be worth the money, then if you ever want nitrous or something in the future, you wouldn't have to change the exhaust...

 

If you run shorties don't bother with the mufflex y pipe. I would get a flowmaster Y collector 2.5 into 3.5 for 40 bucks from jegs along with a couple 2.5 mandrel turns and have the muffler shop hook that up to your headers and then run the 3.5 mufflex with a magnaflow muffler.

 

yea thast a good point...if you run shorties, there is no point having a big high flowing exhaust on the back end, because you'll already be restricting it right outta the block...

 

If you gain HP, it will be because you got rid of the restrictive flowmaster muffler and you went to long tubes. Stuffing that kind of sewer tube under there will gain you nothing but some weight.

 

i don't mean to steal away from the question at hand, but has anyone run the 4" mufflex catback system with say a moser ford 9" bolt in rearend? clearance issues?

 

This is a Moser 9 inch, turbo 400, and a 4 inch Mufflex system. I have had no clearence issues. My car is lowered too.

Check this out

 

Thanks for the replies. I don't want to spend the $$$ (it's even more expensive in Canada) if it isn't going to get me minimum 20 horsies.

Any real world experience from anyone switching from a decent flowing 3" system to the 4" mufflex?