True dual header question

Hello,

This is my first post!

Anyway, my factory exhaust on my otherwise stock xj has started to fall off... I've been waiting for this day for a long time, because now I have the chance to upgrade!

So I have been considering going all-out and putting in a completely new system, from the manifold back. I found a header manufactured by Clifford Performance that actually splits the exhaust so that it would be possible to run a true dual exhaust system. It runs about $350 for the header itself.

My question, then, is this: has anyone else done this successfully with either this brand or any other brand of header, and does it seem to make a difference? They claim a gain of 18-20% increase in horsepower. I don't know if that is right.

DOes anyone else think this is worth it? Does it make sense, or should I just go with a single exhaust and upgrade to something like a Flowmaster 40? Just curious, any thoughts or suggestions would be greatly appreciated!

I'm pretty new to the world of working on my Jeep myself, although I have owned it for a long time.

It's a 2000 stock XJ, by the way. WOuld this affect the O2 sensor and the engine computer's reading of the fuel/air ratio?

Thanks!

why do you need true duals? its a straight 6. just get decent catback (with whatever muffler you perfer soundwise) and call it a day

Spend the money on something better.

No, I know I don't *need* it, just curious if it was worth it. I get what you're saying, though; probably better ways to spend my money.

Just seemed like an easy way to get some extra horsepower/torque without doing anything major to the engine itself... which I don't have the knowledge or tools to do.

Why does the inline factor make a difference? I mean, you could run true dual exhaust on a V6, right? I mean, if the goal is to help open up the exhaust to help the gas flow more freely, I don't see why that matters...

Certainly not trying to argue with those who know more about it, but I'm just trying to get a better understanding of exactly why or why this doesn't make sense to think about doing this.

And although I hadn't seen them before, I have now found some other threads relating to this topic, so I hope I am not repeating something that has been over-discussed.

a header, 2.5" down pipe, freeflow cat, freeflow muffler, and 2.5" tail pie is perfect.

There is only so much you can get out of this motor without spending the money for a stroker or a small block. Plus if it can exhale better it will need to inhale better to really see a real change.

Here is a great thread to read - http://www.naxja.org/forum/showthread.php?t=39186

There are other less expensive modifications that you can do that will have better HP per $ spent gains. Custom exhaust work may cost as much as the header itself.

There is little to no room for dual exhaust, little actual benefit, and you would need to install an additional cat converter. And as mentioned you should have some intake modifications as well to get full benefit from a header.

.

5-90 said:

Clifford makes a "dual exhaust" header for the I6 - but I don't think there's much of an advantage unless you are going to balance the thing to spin up around 7Krpm anyhow.

The principal advantage to a header is that the tube length can be tuned to take advantage of exhaust pulse timing, and that exhaust pulses can therefore be used to carry other pulses out simply because each pulse has a "low-pressure" area behind it in the pipe. That's why you'll notice that headers tend to look odd - all the pipes are meant to be the same length - synchronicity is the key.

Problem is, headers tend to be tuned for a fairly narrow exhaust range. They're a great idea for high-speed/high-performance engines and as a complement for forced induction, but you probably won't see a lot of advantage on a low-rev driver like your XJ.

I'd also have an issue with pipe routing and component location - the underbody area of the XJ just isn't very flexible in that regard. Throw in that a true dual exhaust tends to work best with a crossover pipe between the two halves, and where the Hell is THAT going to go?



5-90

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I wouldn't bother, not that much gain. If you do feel like it though, on a 2000 your exhaust header is already split for the two precats, all you need to do is modify the downpipe where it leaves the precats and combines into a single pipe and replace everything behind it with a dual pipe setup. You are going to have trouble finding space to fit all that exhaust stuff under the jeep though, and I don't think it's likely to be worth the time and money spent.

imo for exhaust on the i6 just stick with 2.25 pipe from the header back and put on whatever cat/muffler combo you like the sound of. if you put too big of an exhaust pipe on it you'll loose power. every naturally aspirated motor needs back pressure to run properly.

goes with that quote from 5-90.

louder may sound cooler to alot of people but it doesn't really mean more power.

Duals are not worth it. Extra weight, extra cost, extra complexity, more weight, no HP gain. Go with a 2.25" or 2.5" single pipe.

aintright said:

imo for exhaust on the i6 just stick with 2.25 pipe from the header back and put on whatever cat/muffler combo you like the sound of. if you put too big of an exhaust pipe on it you'll loose power. every naturally aspirated motor needs back pressure to run properly.

goes with that quote from 5-90.

louder may sound cooler to alot of people but it doesn't really mean more power.

Click to expand...

Back pressure is an old myth, what you really need is scavenging.

In the case of an i6, you're just not going to find a dual header setup that has good scavenging. You're much better off just getting a decent single header and a decent exhaust and calling it a day. No horsepower awards will ever be won with the 4.0L!

Porch951 said:

Back pressure is an old myth, what you really need is scavenging.

Click to expand...

x2 :thumbup:

You should learn whatever 3'd modeling software allows you to develop a long-tube header system (to maximize scavenging) for the 4.0 then report back to us. Thanks.

Anyone mention lack of room for a 2nd pipe running back?
Just pickup a header with equal length tubes, custom downpipe, flex tube, cat, whatever muffler you want (or straight pipe) run 2.25-2.5" all the way back.
Even if you were to run a small block V8, you don't NEED duals. The optimal size single pipe (or what fits) for your application is what you need.
For a muscle car or race car, sure duals make sense in most cases.

Ok here is my opinion, go for it! I know it seems pointless on an XJ to do true dual but thats not the point, atleast not to me. I suggested this to my cousin since his 2000 already has the split manifold, it would be unique to have it dual all the way back. The pipes wouldn't have to be that big, 2" at most. Use a dual in, dual out catalytic converter and a dual in, dual out muffler and then run the pipes out along each side of the gas tank. Again probably not a whole lot of horsepower gains but you would have the only XJ out there with true dual. I have a dual exhaust set up but only from the muffler back. I am running a single in, dual out flowmaster 50 series and two chrome slant cut 2.5" tips and it looks great and I get compliments on it all the time. It sounds great too in my opinion it sounds as good as the 4.0L can get before just dropping in a V8 haha. If you go for it just make sure when having all the pipes made for it make sure you put all the 02 sensors back in the right spots so the computer doesn't freak out. Any muffler shop will have 02 bungs that they can weld onto the pipes anywhere they need to put the sensors. If you do end up doing it post up some pictures of the finished product!

Link to caculator: http://www.mk5cortinaestate.co.uk/calculator5.php as you will see, a 190hp engine only needs a 1.56" pipe.

You will get better performance out of a single. A 2.5" single is good to an easy 250+hp.

I ran a dual setup on my stroked/bored Triumph 6 cylinder back in 1970. It had (at sea level) a tad over 250hp (@6900rpm) and I ran 1.5" pipes from the header to the Stebro dual inlet muffler at the back of the beasty.

I love the idea of running duals but if youve ever heard true duals on a 6cyl it sounds like crap. But thats just my opinion.


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I have true duals. On my 73 Ford F-250 with a 390 BB...and love it

nfletche said:

No, I know I don't *need* it, just curious if it was worth it. I get what you're saying, though; probably better ways to spend my money.

Just seemed like an easy way to get some extra horsepower/torque without doing anything major to the engine itself... which I don't have the knowledge or tools to do.

Why does the inline factor make a difference? I mean, you could run true dual exhaust on a V6, right? I mean, if the goal is to help open up the exhaust to help the gas flow more freely, I don't see why that matters...

Certainly not trying to argue with those who know more about it, but I'm just trying to get a better understanding of exactly why or why this doesn't make sense to think about doing this.

And although I hadn't seen them before, I have now found some other threads relating to this topic, so I hope I am not repeating something that has been over-discussed.

Click to expand...

You dont have a v6, so why would you want dual exhaust?

Jaguar 6s run dual exhaust and I invite you to go look at the pipe diameter. I can not express just how detrimental it is to run oversized exhaust. You will lose hp in the bargain.

I have a Supercharged engine and am running 2.5" exhaust all the way. Any more would be too much and my torque/hp would simply disappear.

You, of course, can do whatever you like. Will it gain you anything? Nope... But you will fit right in with the tuners and their fart cans...

Thing is, the idea is to keep the velocity of the exhaust as high as possible. As you dump any given flow rate into progressively larger pipe the velocity drops off.
where

• V is, as above, the average velocity of the fluid flow, equal to the volumetric flow rate per unit cross-sectional wetted area;
• Q is the volumetric flow rate;
• Aw is the cross-sectional wetted area;

So, as you can see, the Velocity drops as a direct function of the Cross Sectional Area of the pipe in question.

Not Rocket Science, just Fluid Dynamics.