lliwxj98

What's a good high flow cat I have a stock one but want a better one

dukie564

Magnaflow

XJeepWerks

Cherrybomb anything sounds like garbage in my opinion. Cherrybomb products are generally pretty free flowing aswell which hurts the 4.0l performance wise. Your best combination for a legal exhaust with the best power would be a magnaflow cat and catback exhaust. I believe performance-curve sells both products.

Fyi: www.Performance-Curve.com is a vendor here on the forum. Find his thread in the vendor section and you'll be able to save 10% with their coupon code.

lliwxj98

Thanks man ill look it up

outlawtr450

yea i have a header,hollow cat and glass pack style muffler just to keep it up out of the way and i hate how it sounds and i lost so much bottom end with the setup im ordering a new cat tommrow, the 4.0 def likes its back pressure

dukie564

why would an engine like backpressure? You just need to keep enough pressure in the system to keep the exhaust pulses moving.

You mentioned exhaust upgrades for a more free flowing system, but what about your intake? An engine is like a pump. IN = OUT. If your IN is restrictive, you won't see much benefit from exhaust upgrades, or it'll hurt you (like you're experiencing).


Get a working cat on there (yes..it's a FEDERAL law) and a real muffler, and look into a bigger throttle body.

XJeepWerks

That glasspack is 100% what's killing your bottom end. When I ran a glass pack I honestly liked the sound it had from idle to about 1000rpms but after that it sounded raspy and cheap.

Things glasspacks are well known for: raspy exhaust tone, excessive exhaust noise inside the cabin, highway exhaust drone, and damn near zero backpressure.

If you look inside of a glasspack you will see that the inside looks like a cheese grater. Some glasspacks are directional and some are not. A glasspack should be installed with the openings of the "cheese grater" cutouts facing the engine. Doing this provides the maximum back pressure which is still close to nothing.



Just to make things clear: these inline engines do indeed perform better with backpressure, but there is a point where you can hurt performance with too much. Too much backpressure will start to choke the engine and greatly hurt performance. What you want is a good balance of free flowing exhaust and adequate backpressure.

outlawtr450

yea the glass pack was the main issue, but im ordering a highflow thunderbolt cat also, i dont need hp i want the torque and alittle more back pressure will help with that, plus it will be nice to be legal, i have a cat housing welded around a straight pipe right now, i wasant really asking questions about how to set my exhaust up anyhow, i have a bored throttle body/ gasket matched intake manifold and a pretty free flowing intake, if anything is needed to be upgraded at this point it would be my cam, i was just comenting on how bad jeeps sound loud

dukie564

mine's loud and it sounds amazing...

it's a truck, put a truck muffler on it

outlawtr450

i had a truck style muffler on it but they keep getting torn up offroad, thats the plus of a glass pack there pretty stout and compact

XJeepWerks

I'm not the best at explaining things, but I'll try to explain it as best as I can by trying to remember how my instructor explained it to me.

4 stroke engines need backpressure to create a vacuum in the exhaust system and promote exhaust scavenging.

To help explain it:

When cylinder 1 reaches bdc and the exhaust valve opens, the piston begins to travel up which pushes the exhaust out of the valve opening. This exhaust travels out of the combustion chamber, through the cylinder head, and into the exhaust manifold. With adequate back pressure these exhaust gases leave negative pressure behind (creates a vacuum in the exhaust system). Many 4 stroke engines (ours included) utilize valve overlap. Valve overlap is when both the exhaust and intake valves are open at the same time at tdc of the exhaust stroke. Remember that vacuum created in the exhaust system? Now at the end of the exhaust stroke, the intake valve opens and the vacuum in the exhaust system assists in pulling fresh air in through the intake port. (Remember valve overlap... both exhaust and intake valves are open at the same time for a short period of time) This is called exhaust scavenging.

Our engines were designed to utilize exhaust backpressure to promote exhaust scavenging. Don't believe me? Look at the exhaust downpipe on your Xj. Depending on the year, you will likely have a dent or kink in it. This is not a defect... it was accurately placed there by Chrysler engineers to work together with the rest of the exhaust system to fine tune the exhaust backpressure.

Why do we get performance gains from an aftermarket exhaust system if Chrysler engineers designed the exhaust system to provide the backpressure the engine needed? Simply put, an aftermarket exhaust system improves power output but sacrifices engine effieciency. When the Xj and 4.0l HO L6 we're being designed they focused on a couple key aspects. The engine needed to provide adequate power, comply with emissions standards for each model year, and provide the best fuel mileage. The stock exhaust system is tuned more towards emissions and fuel mileage rather than power output. A good aftermarket exhaust system for an Xj will utilize a muffler that provides adequate backpressure and a tail pipe that is free flowing and will allow the exhaust to travel easily.

An exhaust system that flows too freely will not create a vacuum in the exhaust system which will in turn provide no exhaust scavenging benefits.


Wow, that took me a while write up on my phone haha. Hope this explains it for you

Edit: I should have mentioned that my experience with performance gains/losses with aftermarket exhaust setups is backed by several other upgrades. The best exhaust setup for my rig may not be the best for others. My old setup before I started building this engine utilized an aftermarket intake, bored throttle body, gasket matched early style intake manifold, aftermarket fuel injectors, upgraded ignition system, and probably several other mods I completely forgot I even did.

outlawtr450

got 4 31/10.50/15 for sale tread wright guard dogs for 450 if any one is intrested less than 1000 miles

bighouts5591

Uh oh......how big are the new ones gonna be?

Zombie99XJ

New PA owner checking in. Any trips to rausch creek coming up?

xj81

Finally got her sittin right