I'm looking to replace the exhaust system from the manifold to the tail pipe on my 1998 classic cherokee. Is it worthwhile (any power gains)to step up from the factory 2.25" size to a larger 2.5" size, or is the smaller size o.k. since the new system will be mandrel bent?

My particular engine set up includes:

Stock bottom end, 4.0 liter with 140k miles - great shape

Decked, intake gasket matched, bowl blended/re worked factory '98 head

'99 up intake manifold

60mm ported factory throttle body

Air intake setup w/K&N air filter, modified factory air box

Would it be best to replace the factory crimped (more like crushed!) factory down pipe/header pipe with either a pipe matched in diameter to the rest of the exhaust (I assume this would be the way to go if using 2.25" pipe) or keep it 2.25" to the cat then step it up to 2.5" for a scavenging effect?

Any and all input/help will be appreciated.
Pete

 

i woulkd go with 2.5" and a good quality mufler such as a flowmaster you might not notice it but it will allow the engine to breath better

 

JD4x426 thanks for the input, anyone else have an opinion on exhaust diameter?

As far as a muffler goes, any one have any idea/experience with a muffler that gives a deep, low burble at idle/cruise RPM? I am NOT looking to have a "p.o.'d bee" sound as I roll down the freeway or through neighborhoods - I'm not afraid of the banshee wail if I step on it just not wanting extreme resonance driving around.

Any personal sound clips of your rig(s) and experience with different mufflers would be great.

 

Well if you can wait a couple days i'm installing a similar setup Tuesday. the PO install 2.5 up to the cat and from there it was stock. Now i'm going to install a 2.5 tail pipe thats mandrel bent,, new HF cat and Flowmaster 40. Also a KN 9/6 filter. So the sound produced should be somewhat similar. I can post a vid tuesday night if no one else has a similar setup.

 

kitsapfreerider, that will definitely work as I won't be starting on mine for the next 3-4 weeks (I need to finish the '97 country I purchased for my sister and get it shipped to her in Michigan!) The down pipe that you mentioned, is it a one off custom made piece or an aftermarket replacement? If it's aftermarket, any idea of who made it?

 

I'm not 100% sure but the PO dad owned a repair shop that mandrel bent pipes and I think they did it. I'm pretty sure the stock down pipe is 2.25. and i know the current pipe is 2.5.

 

Go with the 2.5" to the cat and three inch behind if you want, but not less than 2.5". I have three inch behind my cat and it works really well.

 

On a stock 4.0 .... my vote goes for a 2.25 exhaust from the converter back. The key is to make sure you purchase something with mandrel bends in the exhaust.



2.25 may seem small ... but let's look at the logic for one minute. First, the factory downpipe is 2.5 inches and necks to 2.25 at the converter. Why? Speed. As hot air cools, it slows down. How to increase the velocity? Decrease the diameter slightly. The exhaust gases are nice and hot for the first few feet of the exhaust. As such, it can flow very well with the 2.5 pipe (never mind the major neck/crunch down area by the front driveshaft). By the time it reaches the converter (almost 3 feet away) it has dropped several hundred degrees and needs to continue moving well in order to scavenge the cylinders of constantly produced "spent exhaust gas"


The slightly smaller exhaust will maintain the velocity well if you have mandrel bent pipes. You did do some breathing enhancement ...but IMO ... not enough to justify needing a 2.5


You may choose to do it if you wish ... but I think you'll find the powerband shifting slightly higher than factory.


FWIW .. my 4.7 stroker is only going to run a 2.5 exhaust



Joe

 

well this upgrade is taking a lot longer than i thought. To make a long story short i had to do a lot of cutting and pulling and welding. I should be able to get the sound clip tomorrow. It sounded really good on the drive home tonight.

 

Looking forward to hearing the results. If possible, include your list of modifications with the sound clip.

 

Are you putting a tip? Where's the exhaust coming out from? I've kinda thought about shooting mine out in front of rear passenger tire...Anyone ever done this?

 

Heres the link i need to use a better camera. It's not very good. I'll try again tomorrow with some better equipment.

KN 6/9 intake
Rustys air tube
complete 2.5in mandrel bent pipe
high flow cat
Flowmaster 40

 

the problem there becomes, i dont know if you wheel or not, but the chance of trail carnage becomes high with that location

 

I did mine exiting in front of the rear tire for a little bit while I waited for my new muffler to come in. I just did a 90 degree bend off of the cat to a tip and it put the tip in about the right place. I don't know how onw would deal with the extras length of a muffler and still have it exit before the wheel in a decent spot. Mine was SUPER loud set up like this though, it sounded pretty cool and was fun but I was really glad to get my new muffler and full tailpipe back, haha. By the way I run 2.5" diameter exhaust all the way from the cat back.

 

Thanks for the tip! I'm not usually in rocks, but the salty mud around here can get me sunk down pretty deep...I'll just exit the rear like normal!