How free flowing should the XJ exhaust be?

[BBeach]

Ok, for one thing, horsepower is a RATE, not a VOLUME. But what IS a volume is engine size. Which is why engine size matters when it comes to pipe size, but not horsepower.

Horsepower is rate and volume is not...very good. But you're forgetting whats important in the design of an exhaust system is the volumetric flow RATE. What defines a rate....density of that fluid * velocity * area.....oh wait, arent the two most important things about exhaust the velocity and the area (pipe diameter)???? Oh, I guess rates are important. :read:

This is the reason I put down the stock head CFMs for my jeep and yours. BTW mine flows better. :laugh:

 

[BBeach]

Dont forget that a lot of these actual high performance engines, its not just the displacement, but also rpm of the engine as well as the actual amount of fluid in the engine at once (displacement). You fail to remember than a mid 80s designed 4.0 cant be compared to a new vette or m3, etc.

 

[wolfpackjeeper]

single turbo supras tend to make more than twin turbo supras, just fyi. Most people remove the twin turbo setup and run 1 big turbo; it is done a lot with rx-7's too. And if we want to skip the turbo setup, the NA supra motor is a much better comparison. M3, right, the 4.0 doesnt even have the right to dream about being compared to that motor.

I will guarantee that my setup flows a larger volume of fluid than yours. I did my homework before I built the motor and port/polished the head. The next head that is going on after finals and research papers are due will have LS1 valves and a port matched intake exhaust on it. Even after all of that engine and head work, I still consider it not worth my time and money to dual out a cherokee. I am even looking at the pacesetter manifold(cant decide if I want to, they have a shitty reputation for welds breaking) or the clifford, and all those kits look to me like they come with a y-pipe to connect the collectors together and run a single exhaust...like it was designed to do that or something...

Once again I have not said a dual exhaust is not a performance gain, for some cars it is. But not a 4.0, it has way too many restrictions elsewhere for it to matter enough to pay for one

 

[whatevah]

just want to post something that'd been bugging me after reading the past few pages and I want to make clear...

1: The 1999+ manifolds (XJ and TJ!) are a two-piece design. That doesn't mean they are designed as a dual-exhaust, just in two pieces. The stock setup has them connected into a two-piece downpipe with dual precats that merge into a single pipe before connecting to the crossover pipe to run back to the cat. So, that's a single exhaust! That said, a custom exhaust shop could use that to create a dual exhaust kit, by completely replacing all of the pipes up to the manifold. Although I'd go with a header if I was having that much work done. (Banks and Borla headers for 99+ keep the same dual outlets to mate with the factory, but weld everything to a solid piece to bolt to the block)

2: Crown does not make a performance header for the I6. Their manifolds are copies of the factory. Just because they are aftermarket, doesn't mean they are performance!

 

[BBeach]

just want to post something that'd been bugging me after reading the past few pages and I want to make clear...

1: The 1999+ manifolds (XJ and TJ!) are a two-piece design. That doesn't mean they are designed as a dual-exhaust, just in two pieces. The stock setup has them connected into a two-piece downpipe with dual precats that merge into a single pipe before connecting to the crossover pipe to run back to the cat. So, that's a single exhaust! That said, a custom exhaust shop could use that to create a dual exhaust kit, by completely replacing all of the pipes up to the manifold. Although I'd go with a header if I was having that much work done. (Banks and Borla headers for 99+ keep the same dual outlets to mate with the factory, but weld everything to a solid piece to bolt to the block)

2: Crown does not make a performance header for the I6. Their manifolds are copies of the factory. Just because they are aftermarket, doesn't mean they are performance!

Thank you! Finally someone backing me up on the two piece exhaust manifold design. 2000-2001 (at least for xj's, 2000+ for other 4.0's). I remember seeing it before and thinking it was really cool (it was on a 2000, maybe 01 I believe). As far as the crown stuff, dont think Im saying its performance or anything but only that I was saying it was a factory lookalike (so purple can put 1 and 1 together, pun intended) . Either way if you read a little more into it I was using those links to show that it was an OEM replacement (several times had i said OEM replacement and the like, nowhere about performance). Id personally never buy one from crown because its not performance and damn expensive too. If you could get a pic up of a stock exhaust with the dual outlets thatd be nice to finally finish this, or at least this part of this endless thread.

 

[BBeach]

And on a side note, purple didnt realize it was for all 4.0's, not just xj's but also tj's and wj's (noting to the "Those are for a GRAND Cherokee you dumbass! You seriously don't know the difference between an XJ and a WJ!?" comment).

 

[wolfpackjeeper]

1) the endless thread cannot die

2) I was pickin up what you were putting down on the newer 2 piece manifold deal. I have seen it a lot at work, most people hate it. Didnt realize that was the point of contention or I wold have chimed in on that note, thought people were just being stupid.

 

[PurpleCherokee]

M3, right, the 4.0 doesnt even have the right to dream about being compared to that motor.

You're right, and it's things like true dual exhaust that make the M3 motor so much more advanced than the 4.0. There's a big reason BMW choose dual exhaust over single exhaust.

I will guarantee that my setup flows a larger volume of fluid than yours. I did my homework before I built the motor and port/polished the head.

Ok, since we're talking dual exhaust vs. single exhaust, let's see who's flows a larger fluid volume... hmmmmm... let's see... I'm gunna give you the benefit of the argument and give you 3" single exhaust. 3" exhaust has an area of 7.06". Dual 2.125" exhaust has an area of 7.09". WOW. Looks like my exhaust flows more volume than yours! But don't get me wrong, it's not about how much VOLUME a system can flow, but how effeciently it flows. I said it before but apparently you have a reading/comprehending problem so I'll say it again. Air flows more effeciently through many narrow tubes rather than one big one. Therefore, two pipes that are half the size of a single pipe is going to flow much better than the single pipe. Just like two 2.125" pipes rather than one 3" pipe in case you're having trouble connecting the dots. Simple as that. Now you can argue with that point and aerodynamic principles if you want to but you'll just make yourself look like a big idiot.

 

[BBeach]

You're right, and it's things like true dual exhaust that make the M3 motor so much more advanced than the 4.0. There's a big reason BMW choose dual exhaust over single exhaust.



Ok, since we're talking dual exhaust vs. single exhaust, let's see who's flows a larger fluid volume... hmmmmm... let's see... I'm gunna give you the benefit of the argument and give you 3" single exhaust. 3" exhaust has an area of 7.06". Dual 2.125" exhaust has an area of 7.09". WOW. Looks like my exhaust flows more volume than yours! But don't get me wrong, it's not about how much VOLUME a system can flow, but how effeciently it flows. I said it before but apparently you have a reading/comprehending problem so I'll say it again. Air flows more effeciently through many narrow tubes rather than one big one. Therefore, two pipes that are half the size of a single pipe is going to flow much better than the single pipe. Just like two 2.125" pipes rather than one 3" pipe in case you're having trouble connecting the dots. Simple as that. Now you can argue with that point and aerodynamic principles if you want to but you'll just make yourself look like a big idiot.

Im pretty sure the DOHC and 8000rpm redline make the M3 much more advanced. :looney:

I think what he meant by his will be flowing more fluids through it would be that he's going to have a stroker with a port and polished head. If I get the time I'll have to model a really basic exhaust and show how curves and diameters can change flow using CFD. Now that'd be interesting.

 

[wolfpackjeeper]

Im pretty sure the DOHC and 8000rpm redline make the M3 much more advanced. :looney:

I think what he meant by his will be flowing more fluids through it would be that he's going to have a stroker with a port and polished head. If I get the time I'll have to model a really basic exhaust and show how curves and diameters can change flow using CFD. Now that'd be interesting.

bingo, if your stock motor can outflow my stroker I will be impressed. I have already mentioned that I did switch pipes around earlier when this debate was centered around cats. Ran with and without, and played with a MAP adjustor both times, I was using the newer down pipe setup that is a larger diameter. Hell, I ran it wide open, no cat, no muffler, you cant get any better flow than that. No noticable change so I stuck the catted pipe back on and called it a day.

On an M3, the dual exhaust will help, but a DOHC motor is almost guaranteed to have a better flowing head. ANYTHING has a better flowing head than a cherokee. I am willing to bet that the dual exhaust on that M3 probably only runs about 10 hp better than a well setup single exhaust, if that. Out of all the things on an M3 that give it a sweet motor, you pick the dual exhaust as the one that make it advanced?

 

[makkman]

i don't know if i should say "Holy Retarded"
or "Wholly Retarded".
you dudes are quite bright. i'm sure if you sat down across a table with a brew for the two, you'd get along swimmingly.
lets put the units back behind the zippy thingy, stop the comparisons and settle down.
p.s. i don't care about the performance of the dual setup... that thing is sexy. nicely done.

 

[wolfpackjeeper]

There's a big reason BMW choose dual exhaust over single exhaust.

symmetrical looks better from the back. And you are right if I am paying for one of those it had better have every possible performance feature form the factory. But a cherokee is not an M3, and the money I will save by not having a super high flowing performance exhaust will get me a nice set of 1.6 roller rockers that will give me a higher performance gain anyway



Side note:
my exhaust is a 2.5in at its largest point.

 

[wolfpackjeeper]

i don't know if i should say "Holy Retarded"
or "Wholly Retarded".
you dudes are quite bright. i'm sure if you sat down across a table with a brew for the two, you'd get along swimmingly.
lets put the units back behind the zippy thingy, stop the comparisons and settle down.
p.s. i don't care about the performance of the dual setup... that thing is sexy. nicely done.

Never said it was not a well setup system, I think this started when I said I did not think it was worth the money compared to other mods.

 

[PurpleCherokee]

I got what I wanted. I just wanted it to be acknowledged that dual exhaust outperforms single exhaust... even on an XJ. Personally, I don't care who believes it and who doesn't. But let me say this, wolfpackjeeper, if you've got a stroker with ported and polished heads, let me encourage you as a friend, not to make a point at all, to seriously adopt my exhaust set up. For no other reason than that it would be very sad to see such a potent motor fall short of several ponies it could have. I'm just tellin ya from experience let me just compare it to other performance mods I've done. I first replaced my stock muffler with a FM40... very little. I eventually replaced the FM with a glasspack but it didn't seem to make much difference at all. Little enough that I wondered if it was in my head or if I was actually feeling some power. K&N drop-in, pretty much nothin. TBS, same as the FM40 but with maybe a little better throttle response. CAI, not much either. And I've always been told that it takes about 5 ponies before you'll feel it in the seat of your pants. According to that, it feels like I've gained between 5-10 ponies after ALL of the above mods but couldn't feel any of them individually. However, after this exhaust job I REALLY felt it, ESPECIALLY from peak torque on up. I'm not even gunna try to put a number on it cause I'll prolly be wrong but I'll let you draw your own conclusions. And I dunno who said it was expensive either, because it only cost me just under $200 for parts via 4wheelparts.com and $150 to have it installed. For a completely new performance system of this nature I'd say that's pretty darn cheap.

 

[alex22]

Alright, Velocity through a pipe as a function of flow and area: V = [(flow (cfm) x 2.4) / Area (square inches)]. I don't have the SuperFlow book with me right know, it might have the formula with a temperature coeficient. I know there are programs out there that will give a net CFM at a given rpm from a cam profile, but I don't know if there are any free ones. I'm not sure what the optimum velocity through the ststem is. With a IR temperature gun we can chart how the temperature changes as you go down the exhaust system. We will then have all the variables except for cross sectional area of the pipe. Then you can decide if yo would like to use one or two pipes to acheave the optimal velocity.
But then again remember that we have Jeep Cherokees. I think we are doing way too much thought into this. I will look into this a little further when I select/build an exhaust for my stroker.

~Alex

 

[gradon]

I have to chime in once more--most of us wouldn't put a single 3" exhaust on our 4.0 jeeps(even strokerheads, but maybe a nice turbo-stroked one could make use of it) because we would have better power with a true 2.25-2.5" setup. Yours has the potential to flow more, but until you let it breath more in, it's not gonna exhale more out.

 

[wolfpackjeeper]

turbo stroker is in the works, but with graduation and commissioning coming up I dont think it will happen till I after PCS to Florida. I was gonna buy a used turbo and start hacking up a manifold to bastardize it but decided to just wait and go new turbo and stainless. That one will have a 3in mandrel bent pipe.

And, I cant run an exhaust like that, need all of my wheel wells and undercarriage clear for articulation and obstacles

 

[alex22]

How much boost are you looking to run? and what are you going to use to retard the timing at high RPM's. I was going to do a turbo 4.0 instead of a stroker but I did not want to buy a new engine managment computer.
Glad to see you are not looking at twin turbos, no good for street use in a low rpm vehicle. I think 3 inch exhaust might be a little excesesive.

~Alex

 

[wolfpackjeeper]

I would like to run around 8-10 psi, and control it with a megasquirt setup. not sure on the exhaust yet, 2.5in at the least I think would be needed on the turbo setup.

I am also waiting on the programmers for megatunix to finish up the final program to control a megasquirt 2 setup from a linux based platform. I am one of those guys running a ubuntu/kubuntu setup and dont want to load windows just to run one tuning program.

 

[wolfpackjeeper]

i guess MSD is always an option too, but the megasquirt looks like a fun project