is 2" exhaust really enough for a 4.0?

[kunar]

back when my truck was still a 2.9, dynomax had a $50 rebate on all their exhaust kits. i bought one of these (link) and all was fine. now, ive got a 4.0 in it and im trying to decide if that exhaust is really big enough for that engine. im suspecting the catalytic converter of being fouled or clogged, and i plan on replacing it with a universal cat but i cant make up my mind. what is the ideal setup for a 4.0? i thought about running 3" for everything after the y-pipe, or maybe even duals, all 2" including 2 cats. at this point i wanna get some idea of whats gonna perform best so i know what to start buying.

oh and btw, ive even thought about buying a 2nd kit just like the one listed and running them both side by side. thoughts on this?

 

[kunar]

nobody has any idea? i think im gonna run duals off of the y-pipe with 2 universal cats and dual 2" exhaust. i can get another one of those kits for about $100 and lay them side by side, should fit just fine.

that is, unless a single 2" exhaust is really enough for a stock 4.0??

 

[Hahnsb2]

Stock exhaust is 2". It's fine. I prefer 2 1/2" just because of sound. Duals are a waste of time, money, space and weight IMO.

 

[kunar]

Stock exhaust is 2". It's fine. I prefer 2 1/2" just because of sound. Duals are a waste of time, money, space and weight IMO.

stock exhaust is 2", even on a 4.0? man, that just seems really small. maybe ill leave it how it is then....

 

[treysdad]

My 2000 3.0L has a 2.5in exhaust shaped like oem pipe with a Magnaflow muffler. This was a cat-back installation. When coupled with a K&N air
filter made performance improve. No gain in mileage, but the truck seems
to perform better. It inhales/exhales better...

Forums on performance muffler/exhaust sites that argued against duals for a V6. The recommendation from the majority of the exhaust forums was -- increase the diameter of a single tube and forget duals. We did.

Doing the numbers: a 0.5in increase in diameter creates a 25% increase
in the area from the 2.0in oem exhaust. A local muffler shop did the work.

 

[85_Ranger4x4]

Stock exhaust is 2". It's fine. I prefer 2 1/2" just because of sound. Duals are a waste of time, money, space and weight IMO.

But they sound so sweet...

It was a extra $100 for true duals on my F-150 and I like it so much the Ranger is getting the same treatment... after I get the V8 in it though.

 

[rusty70f100]

When I did my modified 4.0L a few years ago, I put an about 18" section of 3" pipe right after the y-pipe, then reduced it to 2.5" and ran a turbo muffler. I was running headers also. It sounded real nice. Not loud, but it had a deep tone to it. I can't tell you if it made it perform any better, since the motor was modified at the same time.

 

[Andres629]

Run a single 2.5" pipe. That's as big as you need. Any bigger and you'll actually start to lose performance out of it.

*edit* On a mostly stock engine, anyway.

 

[kunar]

well ive already got a 2" exhaust in it now, so my options are either leave it as is and just replace the problem (cats) or spend $100 for another 2" kit and make it duals. would take just a little work but it should tuck in there nicely and look good. nobody really makes any other exhaust for the truck, and if they do, they are way more money than i would have in duals. if i run duals im taking advantage of what ive already got under there instead of throwing it away.

 

[parson2008]

on my 93 i have headers and down pipes to the stock cats, then off the cats its 2'' till the 3'' y-pipe 3'' pipes all the way back to the 3.5'' stainless tips. people love the way it sounds get complimented all the time.

 

[Will]

You won't lose performance with a larger exhaust, as long as you haven't mucked with the placement of the O2 sensors.

Thing is, how much horsepower do you really use? A pushrod 4.0 is a 150-160hp motor, but that's only possible at a full-load 4,200rpm. Most of the time you use a small percentage of what is theoretically possible. A 2" exhaust is adequate for a 150+hp motor.

Take whatever mpg you get, divide it into 60 and multiply by .08 (for gasoline) and that's your horsepower at that speed. My B2 gets about 19mpg highway so I'm using about 39hp on the interstate. The muffler off my 45hp Toro Groundsmaster would suffice. A 1.5" exhaust would run a 4.0 without serious drivability issues. A 2.5" is a good choice to make sure the exhaust is never a restriction.

 

[SchmigShady]

i just re did the exhaust on my truck was running headman headers no cat and a dynomax exhaust and it sounded like crap like a riced out 4 banger. so i bought a flowmaster super 10 its there new race muffler very small. then i had a new pipe made from where the cat was back to the muffler. and that was 2.5 inch then i just put a turn down from the back of the muffler no tailpipe. its an offroad truck and it would get ripped of anyway. but it sounds alot better now real throaty but it is kinda of loud but not too bad and there is a little popping when reving. so i'm probably gonna get a high flow cat or a resanotor to quite it down a bit. but at idel sounds like a v-8 and i love it.