2.5 to 3 in Pipe

[spaz1879]

hey me and my friend are doing a new exahust for his truck. it is a 4.0 high output straight 6 he has 2.25 in pipe now with a flowmaster super44. we are upgrading it to a 3in pipe and taking out the cat and putting in a flowmaster standard 40 series. what will happen with HP, toruqe and other specs also how loud do you think it will be. im not looking for exact science just wondering what you guys think any input will be cool i will post pics when we get it together this weekend.

 

[Wicked_Sludge]

im not overly famillier with the power curve of the jeep I6, but i know the ford I6 is a torque monster, with not much top end power. if the 4.0 is anything like the 300, youre overpiping for such a low-revving engine. your getting into the range where your going to start loosing torque...and unless you can make it up in the revs, id stick with 2.5 or down.

 

[doorgunner]

Yep, big pipes look good, but you might as well hook the engine exhaust up to the garage door. Small engines need 2.5" or less--gots somthin to do with reverb,bla-bla. Just put some big chrome tip(s) on it. Oh, kinda loud

 

[MikeInIdaho]

It's all about velocity. The larger 3" diameter of pipe being used will cause the exhaust gases to get "lazy" and not scavenge the cylinders completely, leading to an increase in exhaust gas temperatures and putting a nice, big dip in your torque curve.

 

[doorgunner]

yea, das wut I wuz tryin to say, thanks Mike---

 

[7.5L_STX]

on my old jeep cherokke with a 4.0 i had 2.5 inch and a ji flow cat with a thrush glasspack and it didnt really affect performance but that thing sure did have a nice raspy tone to it

 

[MikeInIdaho]

No problem. I love TRS because it gives me a chance to try and sound smarter than I really am lol.

Like Wicked and doorgunner have suggested, 2.5" and down would make the most sense for this application. I would personally go with 2.5" piping or just stay with the 2.25" that's already on there. I'm in the process of building up a high-output Buick v-6 and am sticking with 2.5" exhaust piping. I can make all the tire-frying and honda-eating torque and horsepower I need without using a larger diameter pipe.

 

[spaz1879]

well my buddy doesnt mind loosing torque its his DD and he isnt gonna be entering in any kind of competition is it really gonna kill the torque where its gonna matter for driving on the road?

 

[MikeInIdaho]

I think there will be a noticeable drop in lower RPM grunt and little to no gain in overall performance, if that's the only modification done to the engine. A 3" diameter exhaust can be used to make some decent high rpm horsepower gains if it's combined with a lumpier, "hotter" camshaft/rocker combo, modifications to the intake/throttle body, fuel system, extensive cylinder head porting/polishing/matching, ECU tuning etc. All of these modifications combined would radically alter the engine's powerband, to the point where it would be throwing down some serious top-end horsepower but be dead in the water up to 3,000 rpm or so.

On a daily driver, you want all the low-end power you can get, especially if you have to battle traffic and drive aggressively to get where you need to go. An engine tuned and built like I described above is a royal pain in the ass to drive in traffic and can even be somewhat dangerous, especially in stop/go traffic. Of course, using just the 3" exhaust without diving into an insanely over-the-top NA build won't cause your buddies' Jeep to behave badly in traffic. But, that is the only type of setup where I could see that large of a pipe being of any benefit performance-wise.

I actually went over to the summit racing website and checked out exhaust systems for your buddies' Jeep. The vast majority of them are in 2.5" and 2.25" diameter, but I did run into a couple that were 3". Good luck with the project

 

[spaz1879]

well sorry to keep everyone waiting for pics but here they are
this is the jeep that we put the new 3in pipe on

Out with the old In with the new
woot some cut stainless steel

pic of eric helping attach the flange for the manifold.

joe(jeep owner) holding pipe for test fitting

this mod was time consuming it took us about 4 hours to complete but well worth it.
p.s. it is extremely loud

 

[gettle03FX4LevelII]

how about some video so we can see what it sounds like!!

 

[spaz1879]

thats a good idea, ill see what i can do i used my sister camera so ill try and get some footage

 

[MikeInIdaho]

Looking good man, nice, shiny pipe you got there