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Olin18 05-18-2005 07:58 AM

Exhaust Opinions.
The time in my jeep build has come to put together the Exhaust system. I have been planning dual 2-1/2" exhaust right from the get go on my jeep, and I am now being faced with the realization that I do not have room for that.

The motor is a SBC 350, mildly built to deliver +/- 300 hp. My plan was to run 2.5" duels down each side, through a pair of Flowmaster 40 series mufflers, and exit out the back behind each tire.
Now that everything is together, there is no chace that I have room for that. I am going to have to run a single exhaust? I am thinking that I will run a Y connection from the headers, and run 3" exhaust back, into a Cat, then into a 3" Flowmaster 40 series (because I have a flowmaster guy) then out the back.
Does 3" sound right for about 300 hp. I seem to remember seeing a chart in a catalog.. (thought it was summit) that gave ball park exhaust size related to HP... But I can't for the life of me find it.
Any opinions on the subject would be great.... I am going to miss the beautiful sound of True duels out of a V8.

Thanks for any info.

**DONOTDELETE** 05-18-2005 08:26 AM

Re: Exhaust Opinions. would be ok with 2 1/2" as well.....but 3 is better, anything over that is a waste.

Note, even with 3", it's going to be tight. I'm doing an SBC as well...not at the exhaust yet, but I already talked to the muffler guy about it. He recently did a jeep just like yours....3"...and it was tight...the biggest problem is the y connection....there is no room behind the have to go under the pan..

Expect to pay about $800 or so....less if you don't have a Cat....and make sure your following any state smog laws....

LEVE 05-18-2005 08:36 AM

Re: Exhaust Opinions.
Will there be a crossover pipe?

Olin18 05-18-2005 09:49 AM

Re: Exhaust Opinions.
1 Attachment(s)
You are not kidding about it being tight. I don't have any body lift, and I will be very tight getting through my cross members.
There is no room anywhere behind the motor for a cross over. So my passangers side header outlet will run right under the motor.
Here is a pic of the design I am going to copy. Very slick. And about the only place it will fit, and stay high.

$800 sound very high. Did that include the cost of the headers?
I am planning on building my own exhaust, I will run a Cat, and I already have the headers.
I fuigure by the time I am done I will have about 3-4 hunderd in it... and I am thinking that might be a little high. Depending on the deal I can get for the muffler and Cat.

**DONOTDELETE** 05-18-2005 09:58 AM

Re: Exhaust Opinions.
The $800 included the muffler and Cat, but not the headers. The pic you have is the right way....and basically, the only way. As you have found, there is no way to get it down the right side.

One of the reasons for the high cost is the difficulty of working with 3" pipe...and the fact that the above jeep owner wanted the front pipe section to be easily unbolted...hence, you can unbolt it at the headers and muffler and pull the front pipe out (something you might want to consider).

I take it that you are using aluminized pipe?

Tim 05-18-2005 11:34 AM

Re: Exhaust Opinions.
Unless you plan on running in excess of 4000 rpms most of the time, 3" exhaust all the way would be overkill. I would try to go 2 1/2" to the Y, then 3" aft. It's a very good idea to make the exhaust in sections with flanges to unbolt so you have easy access for component removal without removing the entire exhaust. I would also definately wrap thoroughly the pipe that crosses under the oil pan to keep from cooking the oil. [img]/ubbthreads/images/graemlins/burnout.gif[/img]

Infernozx 05-18-2005 12:45 PM

Re: Exhaust Opinions.
This is what I was planning on doing when I re-do my exhaust this summer.

My current one was only meant to be temporary.. its just the 4.2L exhaust welded together in new and interesting ways.

This would probably be 2" back to the Y pipe, and then continue on at 2.5" I've only got a 305, so it doesnt need as much flow, and I'm looking for some more low end torque. Dont want to give it all away with a huge exhaust.

I should have the room, and will probably use sections of clamp together corners and bits of pipe that I can then weld up..
Should be atleast a flange before the Y, and one between the flowmaster and the Y, and another between the flowmaster and the tailpipe.

the muffler will sit right where the stock 4.2L one did.. under the same heat sheild on the same bushing.

Drawings are kinda rough.. but the frame i know is dead accurate (except for the sharp corners) and then the engine/tras/case should be very close to their actual size..

Olin18 05-18-2005 12:48 PM

Re: Exhaust Opinions.
Thanks for the info. I can really see the benifit in being able to take the exhaust apart. I will for sure work in some flanges that I can unbolt.
Yes I do think I will be using aluminized pipe. And on top of that I will probably paint it with some high temp paint.

I do plan on running smaller sizes up to the Y. My headers actually came with extensions, and lucky enough the passangers side extention is long enough to get under the oil pan, and the header extensions are coated.
And the extensions are 2.25". So the plan will be 2.25 from headers to the Y, and then from the Y back it will be 3".

I will plan on some flanges for easy demo. Thanks for the tip.

**DONOTDELETE** 05-18-2005 01:17 PM

Re: Exhaust Opinions.
Infer....looks like SolidWorks

pontiac58 05-18-2005 01:48 PM

Re: Exhaust Opinions.
Forget about the flanges. All they end up doing is leak. Use stainless steel band clamps. Summit has them. They are on just about every tractor trailer running down the road. So they will hold up just fine. I use them on everything thing. I hate welding the entire exhaust system. And for ubolt clamps you may as well weld it.

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