2.5" vs. 3" exhaust
Thread Starter
Staging Lane
Joined: Feb 2006
Posts: 96
Likes: 0
From: Denver, CO
2.5" vs. 3" exhaust Looking for oppinions on exhaust size. It's a jeep, so I realize that normally people would go with a 2.5" exhaust to give it a bit more torque and sacrifice some high end power. I will be towing about 1000-1500 lb trailer now and then, but I think the engine will be able to do that either way.
The guy doing my exhaust thinks I should put on a 2.5" to get more torque. I don't know enough about the engine as it is to know if it'll need more torque or not. I just have one shot at this, and I don't want to get it done and wish I'd gotten the 3" exhaust... or if I get the 3", am I going to wish it has more low end?
The vehicle has 35" tires and 4.56 gears, so it does need to turn some big rubber. It does have a 4:1 first gear though, so it's geared down enough that torque shouldn't be an issue. I have a low range for offroading anyway, so that's not really even a consideration. Heck, I thought my 4.0L I6 did okay at it... not good enough, or I wouldn't have put the LS1 in... but ya... just looking for oppinions.
The guy doing my exhaust thinks I should put on a 2.5" to get more torque. I don't know enough about the engine as it is to know if it'll need more torque or not. I just have one shot at this, and I don't want to get it done and wish I'd gotten the 3" exhaust... or if I get the 3", am I going to wish it has more low end?
The vehicle has 35" tires and 4.56 gears, so it does need to turn some big rubber. It does have a 4:1 first gear though, so it's geared down enough that torque shouldn't be an issue. I have a low range for offroading anyway, so that's not really even a consideration. Heck, I thought my 4.0L I6 did okay at it... not good enough, or I wouldn't have put the LS1 in... but ya... just looking for oppinions.
is noise a consideration?.. with the low gears, off road tread pattern, short mufflers and short wheel base bring the exhaust exit close to you. (my guess you might be running 1800 to 2000 rpm at 65mph at best? ) 3" many be putting out some noise along with the tire noise, if you got to travel any long duration of time you might need ear muff's from all of the noise. But if you can live with all of that.. 3" might not hurt too much.. but IMO...I'd go 2 1/2".
Just a thought...
Just a thought...
I typed this up in another thread so I'm just copying and pasting it over to here. That guy in that thread was running dual 2.5" into a Y and then 3" back after that.
Unless you are running more than 500 Crank HP, go 2.5" and you should be just fine:
"According to Corkey Bell in his book called "Supercharged! Design, Testing and Installation of Supercharger Systems" on page 184 he has a graph that shows what different size exhaust pipe will flow for power. The graph shows that a single 2.5" pipe is good for around 500 HP and the single 3" is good for around 700 HP. The dual 2.5" pipes he has before the Y will flow okay for up to 900 HP and they will flow almost as much as a single 3.5" pipe which looks to be close to 925 or so HP on the graph."
Unless you are running more than 500 Crank HP, go 2.5" and you should be just fine:
"According to Corkey Bell in his book called "Supercharged! Design, Testing and Installation of Supercharger Systems" on page 184 he has a graph that shows what different size exhaust pipe will flow for power. The graph shows that a single 2.5" pipe is good for around 500 HP and the single 3" is good for around 700 HP. The dual 2.5" pipes he has before the Y will flow okay for up to 900 HP and they will flow almost as much as a single 3.5" pipe which looks to be close to 925 or so HP on the graph."
Thread Starter
Staging Lane
Joined: Feb 2006
Posts: 96
Likes: 0
From: Denver, CO
yes, noise is a concern since it's my daily driver. I think I'll go with a 2.5 based on the replies. I just didn't want to be missing out on a bunch of power because of it, but it doesn't look like that's really a concern.
Thanks!
Thanks!
TECH Resident
Joined: May 2004
Posts: 792
Likes: 2
From: SoCal
2 1/2" and add a cross-over pipe as they generally reduce the noise from pulsing. A dual chambered muffler ought to help as well. I doubt you have room, but resonators would be helpful too. IMHO.
Andy1
Andy1
Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
On my 5.3L I am running stock 02 f-body exhaust manifolds and convertors to dual 2.25" pipes with an x pipe and 2 flowmaster 40 series mufflers. I checked the backpressure at the manifolds and it never got above 3psi. Last time I was at the track I tried dropping the exhaust behind the cats just before the x-pipe and it made no difference in ET or MPH at all. The 2.25" pipes seem to have enough flow for a 5.3L so I would say 2.5" duals are fine for a 5.7L
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I think he meant a single 2.5 or a single 3"...
I'd go 3". Your LS1 will have plenty of torque, and choking your exhaust isn't the way to make more.
Your gearing is fine, even for an engine with much less power.
I'd go 3". Your LS1 will have plenty of torque, and choking your exhaust isn't the way to make more.
Your gearing is fine, even for an engine with much less power.
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Verdad Gallardo Joined: Sep 2004
Posts: 3,148
Likes: 12
From: Downers Grove, IL
If you meant single exhaust I would probably go 3". When I first put my car together I had a single 2.25" and it was a choke point even with a flowmaster 40 series muffler. When I dropped the exhaust at the track it was worth almost half a second, and if you checked the backpressure it was above 7 pounds by 3500RPM if you put it to wide open throttle.
With a single exhaust I don`t think you have to worry about noise, when I had the single exhaust you couldn`t even hear the car, it sounded completely stock.
With a single exhaust I don`t think you have to worry about noise, when I had the single exhaust you couldn`t even hear the car, it sounded completely stock.
