Does an X need to be an even distance from each header?

[robroy]

Good evening,

Based on advice I've received here I've been planning on using an X pipe in my exhaust.

I've forgotten where, but I recently read something about it being important to install the X (or H) pipe so that the pipes coming from each header are an equal length. So if there's two feet of pipe between one header and the X, there should be two feet between the other header and the other port on the X.

Is this true?

On trucks like mine with an auxiliary gas tank, it's most practical, as you know, for the exhaust pipes to wrap over to one side after the headers and go down the truck on that side (on the passenger's side). With this setup, I can foresee difficulty installing an X or H pipe with equal pipe lengths from the headers. Hence my question.

Thanks very much for all the great advice,
-Robroy

[Jake11]

Where ever it fit's best. The engine does'nt care.

[FORDification]

Well, typically they do need to be as close to the engine as possible, typically 1'-2' behind the collectors.

On my '67 project I'm also going to be running duals with an auxiliary tank, so both of the pipes will run down the passenger side as well, probably stacked. With this setup, a X-pipe is probably out of the question, since there won't be room, but a short H-pipe connector between the two pipes will be easy, since they're right next to each other. The connector will probably only be a couple inches wide...but that's just fine. It's enough to connect the two banks to equalize the exhaust impulses.

But you're right....with this setup, by the time the left-side pipe snakes over to the right, close enough to install the H-pipe, it's going to be a foot or two longer than the passenger side. That's not a problem...you'll still see the benefits.

[robroy]

Hi Keith and Jake,

So an X pipe will have difficulty fitting because of the curves in the pipes needed to enter and exit it? I haven't seen these installed before so I can't quite imagine what they look like.

And would you say an H pipe will deliver the majority of the benefit of an X pipe (sorry, I know this question has been asked a thousand times)?

Thanks very much!
-Robroy

[Ranchero50]

It matters, but the math is so involved that you can't realistically calculate it. I tried reading up on fluid dynamics a couple years ago and it's fascinating stuff to be sure. Basically you are trying to tune the exhaust pulses so one cylinders pressure pulse creates a vacuum in the other bank to help pull the next pulse through. Of course the size and force of the pulse is determined by the size of the motor, the diameter of the pipe, and any restrictions in the pipe (bends, misalignment in the tubes). So at a certain RPM's the pulses are helping pull the next pulse through and at others they are fighting each other a bit.

As a best guess I'd come out of the drivers header and make a 45` mandrel bend into and through the passenger pipe to form the X and then another 45` right after the X to get them to run parallel. Note that the X usually works best at 3500rpm and an H works around 2300rpm. Longtubes make the mpost difference arounf 2700-3300rpm depending on primary length and diameter.

Jamie

[Thunderfoot]

Like Jamie said, there are a lot to what's going on; but for an X pipe to work properly (fullest effect) you would need to have equal length headers and the X would need to be installed at the same length from the collectors (and there are some theory's on how far from the collectors it should be as well).
The X helps scavenge the exhaust by using the pulses from the other cylinders like Jamie talked about above.
The H pipe helps by equalizing the pressure in the 2 pipes, this has a scavenging effect but not as efficient as the X setup. Also it can help no matter where it is but there are also theory's on how far it should be from the collectors as well…
The H pipe seems to help more with low end torque and the X pipe helps more mid to top end pull from all my experience with drag strip stuff.
Anyway, for what you are doing with the exhaust I would just do the H pipe as your not going to be able to utilize the X effetivly any, without it being the same distance on each pipe from the collectors.

[robroy]

Jamie and Shayne, thanks for responding!

It sounds like like an H is in order. That should be straightforward for the shop to install.

I see your point as to the technical nature of getting deterministic about the performance of different installation choices! But it does sound like an H installed somewhere nearby the headers is better than no H at all. And an X may not be practical for my exhaust pipe routing scheme.

Thanks again for your valuable advice; it's much appreciated.
-Robroy

[BobbyFord]

What you do is take a rattle can of paint and paint the exhaust pipes horizontally from the end of the headers back, fire up the engine, run the rpm's up and where the paint starts to burn off is where you want to put the X pipe.

[robroy]

Hey BobbyFord and Robert!

Bobby, that's an interesting method for determining where the X should go, but I'm probably not determined enough to use it. Partly because I'd have to have the exhaust shop assemble it first, then rip it apart to install the X. But that's definitely an interesting idea!

Robert, thanks for the suggestion on the low profile Magnaflow X. That might be just the ticket I've been looking for!

Is it true that the X pipes are more sensitive to being installed with an equal distance to each header than the H pipes? Or will either provide a partial benefit, equal to one another, regardless of this distance?

Thanks very much!
-Robroy

[Ranchero50]

Once again it's more a matter of pulses and flow. The X pipe may be more sensitive because the two pipes cross through each other. BTW, not all X's are created equally. The magnaflow part is very nice, it is a true X. The original X pipe was the old Dr' Gas X pipe that debued in NASCAR in the early 90's. It used two 90` mandrel bends, cut a calculated amount out of the outside bend on each and welded them together with the idea being a certain amount of the exhaust pulse would cross into the other pipe to pull the cross pulse out of the other header, but most of it would stay in the original side.

I'd be more concerned with where your engine is making power at. What cam rpm range are you using, what are you doing with the truck etc before you start theorizing exhaust strategy.

Jamie

[ROBT257]

I've decided to go with Hedman headers and all new from there back. Was planning to just run dual exhaust. Do I need the H or the X? This is just a recreational project vehicle for me. Not a racer, extreme fourwheelin, or pulling rig. Its a 72 F250 4x4 360. I'm a novice and learning as I go.

[fitzwell]

What you do is take a rattle can of paint and paint the exhaust pipes horizontally from the end of the headers back, fire up the engine, run the rpm's up and where the paint starts to burn off is where you want to put the X pipe.

yeppers...

we used to bolt a collector & a section of straight pipe on the headers. Take a tire crayon & mark the pipe. Run it thru the gears, where the crayon burned off, that's where the pipes got cut or the crossover got put.

I'm sure there are volumes about what size/style/etc the crossover should be. H pipe will quiet things down a bit, and boost the low end response/torque. Ford did "H" style crossovers starting in the '60s, Be a little hard to turn down their engineering theory

[Dragon]

What you do is take a rattle can of paint and paint the exhaust pipes horizontally from the end of the headers back, fire up the engine, run the rpm's up and where the paint starts to burn off is where you want to put the X pipe.

Thanks for reminding me that is the way we used to do it. On my hot rods the pipes are usually so short there is no room for an X before the turn outs in front of the wheels.