How free flowing should the XJ exhaust be?

[PurpleCherokee]

The problem with just a normal regulator is that it has to osilate correctly or it will set a CEL. This is what ya need

 

[gradon]

Yeah one can probably make that for $10-15 as well, but the $40 price was what I expected(they had to market it a few dollars cheaper than a replacement o2 would cost). I'm fine with my new cat and existing o2 sensor--I was just curious about the simulator.

 

[PurpleCherokee]

You're right, it prolly wouldn't be hard to build and as far as 10-15 bucks, honestly, it'd be more like 2-3 bucks via mouser.com Freakin love that place!

 

[wolfpackjeeper]

oh comon, the thread cant die now, its been going for so long. bumpity bump bump bump

 

[PurpleCherokee]

How bout we try to simplify what we're arguing... it's been so long I think I've forgot

 

[wolfpackjeeper]

just disagree with the last guy, works better that way anyway.

 

[alex22]

I believe it was how much back pressure do you want. Then it turned into a cat vs no cat arguement. and now it just won't die.

~Alex

 

[ehall]

What does Borla say -- http://www.borla.com/faqs/#7

Q. Is a bigger pipe and muffler system better?

No, there has to be a balanced design to enhance the maximum engine output, exhaust gas velocity, and sound. If the diameter of the tubing is too large, the exhaust gas velocity will be reduced and rob the exhaust of thermal efficiency. Unfortunately we often disprove accepted racer mentalities like bigger is better. We must spend a great deal of energy explaining to someone how a 4" exhaust pipe will not work as efficiently as a 3" pipe. That is hard sometimes, but it is why we have magazine editors. Even with our excellent "track record" winning more professional car races than all the other muffler makers combined, we still often have to prove our theories to very well know top racers. One of these issues is volume versus velocity. The late John Lingenfelter helped us prove this over and over with his legendary Corvette exploits. People were often amazed how he would run 600 plus horsepower Vettes with 2 1/2" exhaust. If 4" would have made John go faster, he would have run it. We need to have a pipe large enough to overcome the boundary layer restriction in a dynamic flow situation while maintaining exhaust speed and evacuation. This isn't a simple axiom to understand, but the second best explanation is to say in race classes where let us say the budgets are seldom limited and the rules are not restrictive regarding exhaust, you will observe much smaller exhaust header tubing and exhaust pipes than some kids run on their 190-horsepower hand-me-down Honda sports compacts on the street.

I wonder if they know anything about exhaust systems

 

[PurpleCherokee]

Is anybody here arguing that bigger exhaust diameter is better??? I'm pretty sure that discussion is closed... and if anybody bothers arguing it they might as well be talkin to a rock because it's pretty well known that the right size pipe is essential in exhaust performance. Also, I THOUGHT that we also have figured out that restricitions in the exhaust, (like non-straight through mufflers and cats) or backpressure, is bad when it comes to performance. But I guess that's what we're arguing.

 

[alex22]

What size exhaust should we use on the stroker engines, 2.25 or 2.5? I thought I read somewhere that the Borla catback uses a 2.25 diameter pipe, is that correct?

~Alex

 

[wolfpackjeeper]

I plan on a 2.5 on my stroker, just because thats what the down pipe I have is made of

 

[BBeach]

Purplecherokee, what have you thought of as far as the crush in the downpipe? That's obviously a major restriction albeit it may keep exhaust velocity up?

 

[PurpleCherokee]

Sorry, but I really don't understand what you're asking...
If you're trying to argue that a bend in a pipe creates the same restriction as a cat that's not gunna fly lol cause it's not even close. You are right however that excess bends do create backpressure, but not NEARLY to the extent that obstructions inside the pipe create. And the main part of the pipe design that matters is the diameter, not how the pipes are arranged, assuming there are no restrictions inside the pipe. Also, the crush in the downpipe on some XJ's is not a performance feature designed to keep exhaust velocity up.

 

[copbait]

i fail to see how the "crush" could ever help, if anything it is hurting the flow of exhaust. anytime you pinch a tube you're restricting flow and creating turbulence. i'm no fluid dynamics expert though...

 

[wolfpackjeeper]

the crush is so you dont smack the pipe with your drive shaft during articulation, it effectively knocks you down to 1.5in tube...

 

[seanyb505]

Works wonders on 2wd models though

 

[BBeach]

Sorry, but I really don't understand what you're asking...
If you're trying to argue that a bend in a pipe creates the same restriction as a cat that's not gunna fly lol cause it's not even close. You are right however that excess bends do create backpressure, but not NEARLY to the extent that obstructions inside the pipe create. And the main part of the pipe design that matters is the diameter, not how the pipes are arranged, assuming there are no restrictions inside the pipe. Also, the crush in the downpipe on some XJ's is not a performance feature designed to keep exhaust velocity up.

I'll reword my apparently retarded question....What are you going to do in your jeeps exhaust system as far as the downpipe? The downpipe has a crush in it for clearances. From what I remember, even people with lifts and improper bumpstops still crush it back even if they get a new one bent. Im not trying to argue so get it outta your head. Its obviously a restriction, have you ever seen one? It necks down a lot on mine. Go wiki fluid dynamics or something and tell me what you find out about all exhaust, especially at high rpms, going through a 1-1/2" dia crush. Something else you can consider in diameters on the way down is the temperature of the exhaust decreases lowering the internal energy. Having an exhaust too small has the boundary layer controlling most of the flow, lots of heat transfer and forces to fight against. Im not gonna go into it anymore. As far as the restrictions in the pipe, picture a muffler with all of the bends, which is obviously true and why i have a straight through magnaflow. party1:

 

[jeepinwi]

As long as we're talking exhaust piping size, here's what my Stroker setup will eventually be: stock exhaust manifold with 3" collecter welded on, necked down to a 2.75" downpipe, necked down to a 2.5" catalytic converter, to a 2.5" muffler, then through a 2.5" tailpipe.

 

[gradon]

My current setup is the Borla header w/ 2.25" downpipe, magnaflow 94065 cat(2.25"), and the Borla cat-back, which has a muffler w/ a 2.25" inlet and a 2" outlet and 2" tailpipe. They reduced the size to keep the velocity uniform and probably helps with the kick-@$$ exhaust sound. I will be using this same setup on my 4.6 stroker. I highly recommend this system and would buy it again(even though it's 20% more now--too much $#!++y exhaust products on the market so they probably raised the prices to reflect the quality that their product is worth over the competition).

 

[PurpleCherokee]

I'll reword my apparently retarded question....What are you going to do in your jeeps exhaust system as far as the downpipe? The downpipe has a crush in it for clearances. From what I remember, even people with lifts and improper bumpstops still crush it back even if they get a new one bent. Im not trying to argue so get it outta your head. Its obviously a restriction, have you ever seen one? It necks down a lot on mine. Go wiki fluid dynamics or something and tell me what you find out about all exhaust, especially at high rpms, going through a 1-1/2" dia crush. Something else you can consider in diameters on the way down is the temperature of the exhaust decreases lowering the internal energy. Having an exhaust too small has the boundary layer controlling most of the flow, lots of heat transfer and forces to fight against. Im not gonna go into it anymore. As far as the restrictions in the pipe, picture a muffler with all of the bends, which is obviously true and why i have a straight through magnaflow. party1:

Ummm... see... the thing is... I've already done it. And there is no "crush" anywhere in my exhaust system. Why would there be? Did you really think that there was a dual-exhaust kit for an XJ??? So it looks like your whole, "well your exhaust is just as restricted because of the "crush" in your downpipe as would be cause be having a cat" argument is done. Also, two wrongs don't make a right. Just because you have to have a crush in your downpipe doesn't mean that ANOTHER restriction in your exhaust won't matter... sorry. So go wiki "not being a dumbass" and tell me what ya find
And can anyone decifer this sentence: "Something else you can consider in diameters on the way down is the temperature of the exhaust decreases lowering the internal energy"???