Recently dropped a 4.6 stroker into my 2000 XJ. The head is from a '93, so the stock 2000 exhaust collector is smaller than the exhaust ports on the head.

I picked up an aftermarket exhaust collector for a '93 and will take my Jeep into a shop to get the rest built up and replace the 12 year old cat and downstream O2 sensor (new O2 sensor upstream).

I need some advice on what size exhaust I should go for.

I know from various readings and forum posts that a 2.75" exhaust is appropriate, but since that's a bit rare, I figure on a 3" exhaust. But what I don't quite understand is where that comes into play.

Does the 3" start after the catalytic converter? After the muffler, or should the pipe be up sized after the collector? Or am I going to need to get the collector fitted to be 3" and have 3" pipe all the way through?

I figure the collector size isn't as important as preventing too much back pressure caused by the cat and muffler... I mean, the exhaust doesn't come out of all the cylinders at once... it's staggered. So 2" on the collector should be enough... I think but don't know for certain.

Also, I'm not into Cherry Bombs and obnoxiously loud exhausts. I like a smooth and subtle exhaust note. I don't have 12" bass speakers and 1000 watt amps in my rig... being loud just isn't my style. So which manufacturers or models make exhausts like that? I tend to think of Borla, but they can be pricey.

Thanks!

 

Appreciate any pointers!

 

if you're keeping the cat, a flowmaster 40 will sound good and not be obnoxiously loud, my '94 i had no cat and a flow40 on it and i didnt think it was too loud

 

I have a Flow50/Walker hi-flo cat and it's actually a little too loud for me; has a GREAT purr normal cruising but when I get on it it really opens up and roars.

When putting together exhaust, remember it cools as it passes out. You may want a smaller diameter towards the end to help keep velocity and scavenge effects active.

 

I spoke with an exhaust shop owner today - his recommendation is to keep the 2" exhaust output on my new header and just put a 2.5" adapter on it, then keep the exhaust 2.5" all the way through. Anything more, he says, and I need to have forced induction.

He was reluctant to remove the 2.25" pipe to the cat because it's stainless steel and his shop only has aluminized. Also reluctant to swap out the downstream O2 sensor... though its 12 years old. Wanted to know how I knew it was broke and I said I don't but it's 12 years old and should get replaced.

He advised that I avoid a hi-flow cat because he's worried that the temperature differences from the front to back won't be consistent for what the computer understands to look for, and will probably end up with it dumping fuel.

For the muffler, because I want something rather quiet, he says to go Mopar.

Whatcha guys think?

 

idk much about the exhaust size and o2 sensors but for the muffler i have a magnaflow and it sounds really good. nice sound when idling and sounds good when you get on it but when your just cruising its really quiet

 

The downstream o2 sensor just tells the ECU that the cat is working, if you don't have a CEL code for it don't waste your money. I'd go 2.5 all the way.

 

your shop guy seems really reluctant to do any real work...he seems like he wants to get paid but not do proper work

imo he is a guy who knows nothing and is just reading the shop manual and is probably also the type that thinks stock is always better...

i would look for another shop and get a second opinion

 

yeah i was thinking the same thing. i wouldnt go back to that shop. look for a good trusted shop that actually knows there stuff

 

Unless you've moved the redline up a couple thousand RPM and plan to live there, you should be fine with 2.5" tubing over 2.75"

You can go too large with exhaust, and actually end up hurting performance as a result! Overlarge exhaust plumbing leads to uneven exhaust pulse cooling, which cases internal turbulence and hampers exhaust scavenging.

If you're not having an exhaust setup made, the OEM 2.25" plumbing will be sufficient up through about 4000-4250rpm. 2.5" tubing will give you a slightly better flow, but I wouldn't bother unless you were going to go through with making the whole system up anyhow.

Bumping up the primaries a notch (if 1.5" OEM, go 1.75". If 1.75", go 2.00") would be helpful, since you've increased the displacement per cylinder. But, you don't want to go too large with the primaries, either.

I'd have to find the maths to prove all of this, I had it worked out. I just don't recall what notebook it's in at the moment...

A high-flow cat should not cause you any trouble, just make sure it's OBD-II compliant/ready (I don't know if the Air Police are particuarly difficult in Champaign-Urbana, but if they aren't too bad, you can go with a cat set up for, say, a single-unit Chevvy V8 application and have a bung welded into the pipe after it for the downstream HEGO. Last couple of times I needed cats, I got the unit for single exhaust under a late 70's G30 w/BBC, but I put them under RENIX. However, I had no trouble passing smog. Cost? Something like $70-80.)

Exhaust tone is a function of muffler - and it's all about what you want. I tend to use Walker Turbo II units - get them OTS locally for $20-30, they have just enough sound to remind you that the engine is running when it's idling, and they're not obnoxious on the highway.

(I've got a single 10" tubed driver with a 450W amp - it's just enough to fill in the low end on ZZTop bass riffs I'm not big into "loud" either - but the single driver gives a good fill-in when I get some halfwit listening to jungle-jump next to me, and I fire up GWAR in response...)

 

I have the 4.7L Stroker in my 2000 xj. I built it out of a 94 block and head. I used a rugged ridge stainless header, stock down pipe. Magna flow stainless hi-flow cat. And borla stainless 2.5" all the way back. It was a little pricey, but I will be the last exhaust system I ever put on this xj. It sounds nice while idling, not loud and obnoxious. When you jump on it, it has a bit of a roar but at cruising rpm the muffler does a great job at silencing the drone. Out of all the performance exhaust I have heard the borla seems to be the least obnoxious.

 

Followed up with the advice and hit up two more exhaust shops today for recommendations and bids.

The second shop says he can put 2.5" or 3" all the way through, no problem. Wants to sell me the Flow Master 50 series muffler and keep the cat out.

I asked him what the effect on the OBD-II would be with the downstream O2 sensor not picking up anything different from the upstream O2 sensor since the cat would be gone, and he wasn't sure what would happen.

I'm a tiny bit worried about the FlowMaster 50 series since ThatAintStock00 wrote: There is so much noise as it is in my rig on the highway that I don't want to add to it at all. Did a 7 hour drive a few days ago, between the noise, vibrations, stiff suspension and seats... I'm still sore.

Okay, so off to the next shop.

The third shop guy says he can't bend 3", so all he could give me would be 2.5". Plus, he says he wouldn't be sure if the 3" would fit around the axle given the tight bends.

I have a 5.5" lift, I don't think he'd have trouble, but anyhow.

He wanted to sell me a knock-off Flow Master 40 series, which he says is quiet and is every bit as good as a FlowMaster. He says FlowMaster lost their patent so everyone is copying them now and it doesn't make sense to spend more money for the same thing.

Anyhow, since rompnXJ says 40 series are nice and quiet.

Also, same as the last, this third exhaust guy says to go ahead and remove the cat to save money, but he couldn't answer how that would affect my OBD-II.

Whew! My head is spinning. I never had any intention of leaving off the cat, but these guys are recommending it and saying that I won't have anything to worry about with inspections or the police.

Personally, I don't care one way or the other. I'd like to spend less money, and I'd like for the OBD-II to work correctly and not just dump a bunch of unburned fuel into my exhaust.

In the mean time, I dropped my new header off at the machine shop to get the 2" connection removed and have a 3" put into place.

I'm not sure what the diameter primaries are. The way the header is setup is that there are 2 sets of 3 pipes each. Each set is 2", and then they connect again to a single 2" pipe.

I figure go ahead and get the 2" cut off and made to 3" because I can always neck down, but can't neck up... and this way the header will be ready for when I finally get the exhaust work done.

That's really good to know. I'm thinking it might be a good idea to get all the pieces I need, minus the pipe, and then have the exhaust guys weld everything into place for me.

I'll read up on those Walkers. Definitely don't want obnoxious on the highway.

Love it!

Yeah, I've looked at putting a couple of 10" in my rig... cut them into the rear hatch with an amp in the middle. I like a good balance of sound with my music, but I'm not trying to announce to the neighbors when I'm coming and going throughout the day. In my younger years, maybe... these days, not so much.

I've always had really good impressions of Borla systems, but they are so expensive. I admit to watching videos on YouTube of exhaust recordings - yeah, I'm THAT guy - and the Borla's always have a sexy tone to them, but not in your face loud.

That's what I'm looking for, minus the price.

So here's what I'm gathering:
1) 2.5" is fine
2) 3" is probably too big

What I'm curious about now are these things:
1) Can I start with a 2.5" or 3" to the muffler into a single exhaust, and go dual 2" pipes from there? (just to be a bit different, but not stupid)
2) Can I start with 3" to the muffler, and go 2.5" from there on back?
3) How would not having a catalytic converter affect my OBD-II?


Here's where I got the 3" into 2.5" idea:
http://www.angelfire.com/my/fan/Exhaust.html

Here's where I got the 2 to 1 dual pipes idea:
http://www.angelfire.com/my/fan/Exhaust_Pipe_Size.htm

Guys, this is all really great advice.

I'm definitely trying to make a good decision here and listen to everything ya'll have learned doing this. It really does help a bunch.

 

Hm. From what you're saying, the downstream is just giving a "Works" or "Doesn't Work" signal to the ECU, not variations of "Works Great", "Kinda Works" or "Works for Crap" signal?

So I could just trick the ECU into thinking that the downstream "Works"?

 

Ironically, the third guy I went to recommended I go and see this guy cause he apparently does the best custom work in town.

Of all three guys I saw these past couple of days, the second one is the guy that seemed the most willing to do whatever I wanted, and he was the cheapest. Its a family run business and the garage looks like scratch, but it's got some pretty good reviews on Google.

 

family rn buisness you can count on a few things, great personalized service, competitive prices, and employee arguments, cuz hell they are family right? lol

seriously though, im always gonna support the small town family busness over larger ones, as long as the quality is there