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Discussion Starter #1
Hey guys,
Planning the exhaust for my 5.0 EFI conversion, and have some long tube headers I got from a local Mustang enthusiast. These fit great, clearing the AOD and everything else, and have a 2.5" outlet with a 3 bolt flange.

I want to do an exhaust system myself (with my buddy's help that has done a bunch) so just shopping for the bits, and feel like i'm getting no where.

Hoping to stay with 2.5" pipes, I already have a pair of Dynomax Turbo mufflers with 2.5" in and out. I came across this kit that is a 2.5" header back system... requires long tubes, cool. In the details it says for 3" headers reduced to 2.5" pipe.


I know I am going to need to factor in a crossover pipe, but outside of that, does a 2.5" header outlet not transition to a 2.5" pipe? I would have thought a 2.5" system would be the right thing for these headers. Was wanting to do this myself to continue to upskill, see the satisfaction in working on my own car, and also trying to save a few bucks. Logistically it'd be difficult to get the car to a muffler shop as its not driving yet, and I don't have the right stuff to tow it.

Any ideas? Should my headers be a 3" outlet for a 2.5" system? Am I just looking at the wrong bits?

Thanks,
-Rob
 

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The crossover should be as close to the engine as possible.

The diameter of the exhaust depends on the use intended for the car. 2.5" on a 5.0 is pretty big. Will this car be driven on the street, track, or both? For street only, 2.5" is excessive. You could use 2.5 to 2.25 reducers on the header outlets and it would still be likely more than you need. Even the 428 Drag Pac SuperCobraJet engine had a 2.25" exhaust system.
 

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I think you're looking at the kit for 3 inch collectors into 2 and 1/2 inch reducer. Your kid does not include reducers, you would need a 3 bolt 2 and 1/2 in reducer Inlet with a two and a half inch Outlet. Basically a 2 and 1/2 inch reducer on both ends.
 

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Actually 2.25" is more then sufficient. I'm running a 2.50" only because I MAC headers and they sell a companion system which is 2.50".

For a while I was giving thought to making a single exhaust using 2.25" Y pipe to a 3" single. The 3" pipe has the same area as the two 2.25" pipes which are good to around 500 hp.
 

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Hey guys,
Planning the exhaust for my 5.0 EFI conversion, and have some long tube headers I got from a local Mustang enthusiast. These fit great, clearing the AOD and everything else, and have a 2.5" outlet with a 3 bolt flange.

I want to do an exhaust system myself (with my buddy's help that has done a bunch) so just shopping for the bits, and feel like i'm getting no where.

Hoping to stay with 2.5" pipes, I already have a pair of Dynomax Turbo mufflers with 2.5" in and out. I came across this kit that is a 2.5" header back system... requires long tubes, cool. In the details it says for 3" headers reduced to 2.5" pipe.


I know I am going to need to factor in a crossover pipe, but outside of that, does a 2.5" header outlet not transition to a 2.5" pipe? I would have thought a 2.5" system would be the right thing for these headers. Was wanting to do this myself to continue to upskill, see the satisfaction in working on my own car, and also trying to save a few bucks. Logistically it'd be difficult to get the car to a muffler shop as its not driving yet, and I don't have the right stuff to tow it.

Any ideas? Should my headers be a 3" outlet for a 2.5" system? Am I just looking at the wrong bits?

Thanks,
-Rob
A lot of performance headers use a 3" outlet and you can buy a reducer that goes down to 2 1/2" that bolts to the header and gets welded on to your exhaust pipe. If your header has an outlet of 2 1/2" just buy a 2 1/2" to 2 1/2" reducer like Myke B has suggested JEGS 30002: Steel Reducers without O2 Fittings 2-1/2" to 2-1/2" OD | JEGS
I would definitely use a 2.5" exhaust system as it will have zero negative effect on performance and you will have room to grow if you add more power in the future. Do it once and do it right
 

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Discussion Starter #7
This is great feedback... I think I have worked out what I need, and the link you mentioned above makes perfect sense... a 2.5" to 2.5" reducer (which doesn't reduce a thing lol)...

I'm pretty sure if I use this H pipe kit, I'd want the reducer mentioned above that is 2.5" OD, not the version that is 2.5" ID? As the flared end of the H pipe kit would slip over the 2.5" OD of the reducer?

Thanks everyone!
 

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If you're staying with 2 and 1/2" pipes, Flowmaster sells a nice pair of aluminized mandrel-bent (no flat spots or creases in curves) tail pipes for just over $100, and you can cut them to length. The fit is very nice. The straight intermediate pipes are easily cut to length from the same kind of tubing in any shop.
 
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