Going to make an X-pipe exhaust

Well there isn't a whole lot of room from the end of my headers to the back of the car (about 18 inches or so to play with) so I was planning to go with an H pipe connecting around the end of my collectors. The thing is I know that an H-pipe just isn't as efficient as an X-pipe and that was really bugging me. All of the X-pipe mufflers I saw were WAY too long to work for me, so I thought, why not. I'll make one (with the help of a good welder I know).

So, I just placed an order for a stainless steel X-pipe that's about 12" long total (see image). I'll cut some stainless sheet to go around it, drill about a bazillion holes into the X-pipe, fabricate oval ends about 9" wide and 5" deep to weld the sheet metal to and put some sound deadening material in.

I'll share what it ends up looking like later. Just thought I'd put this here so folks might think about it for them as well.
 

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Renato

Lifetime Supporter
Hi Darrin,

Will be following this thread closely, this is my next task.

Is there a big performance difference between H and X? Or none?

What are you doing with exhaust headers?

I'm still not sure if I need cats, how is it in Texas?

Regards,
Renato
 
Hi Darrin,

Will be following this thread closely, this is my next task.

Is there a big performance difference between H and X? Or none?

What are you doing with exhaust headers?

I'm still not sure if I need cats, how is it in Texas?

Regards,
Renato

Hi Renato,

Assuming the design is right, the X-pipe will make more peak horsepower up high over an H-pipe. Given our engines rev high, to me, it was the right choice, but for the street, it's not a whole lot of difference and if the design isn't right, an X-pipe could end up not adding anything at all.

Here is a good video explaining why X-pipes make more horsepower:
Video: Exhaust X-Pipes vs. H-Pipes - OnAllCylinders

Here is another interesting video:
https://www.youtube.com/watch?v=Xi3TEO_nfqU

In short, the X-pipe causes a better scavenging effect than the H-pipe does.

One caveat though, if you put on an X-pipe your engine is going to pick up a more, how should I put this, European sound instead of a rumbling American V8. It is going to make more of that high rev pitch instead of the low grumble.
https://www.youtube.com/watch?v=lnI53sWqbcs

In TX, a 1966 car doesn't need the cats. If I had to run them, they would have to go where the X-pipe/muffler goes as there is no additional room on my setup unless I do some sort of 180 bend to go back into cats then out.
 

Keith

Moderator
Hey Darrin, you need to speak to Jac Mac about the X pipes. He's got a lot of experience with them...

I have read something about them on here but unsure of where it is but I suspect it's on Kaspa's F5000 project thread, as John was going X pipe until Jac intervened! Something to do with the angle of the X and how it allows firing across to the other pipe, oh and the firing order I think.
 
Hey Darrin, you need to speak to Jac Mac about the X pipes. He's got a lot of experience with them...

I have read something about them on here but unsure of where it is but I suspect it's on Kaspa's F5000 project thread, as John was going X pipe until Jac intervened! Something to do with the angle of the X and how it allows firing across to the other pipe, oh and the firing order I think.

Yes. If it's too steep (looks like a Y going in for example), it can interfere. I think the magic number is 15 degrees but it's been so long since I looked at it I might be wrong.

The X-pipe is best for a V8 engine running fairly high RPM but not one that has an awesome volumetric efficiency. Mine is up there, but it's not to worry from all I have read.

In any case, the X-pipe would really have to be screwy to hose it up. It can of course but the design I'm using doesn't have the high angle of attack (the Y look).
 
Why not use the crossover system if you're that short on space?

In theory, for a high RPM car (this one will spin past 8,000RPM) the X-pipe works a bit better.

I also think it might benefit engines with the sort of firing order I have better than the old 302/351 as well but that's just conjecture on my part.

I'm considering doing both...having it easily disconnect where I can try both out on a dyno after the build is done. I'm interested in seeing which one really works best myself as well.
 
Darrin, I have not yet started my build but I will investigate after-market Audi R8 exhaust systems. Some have x-pipes, some are very elaborate, but all emphasize weight saving over Audi OEM system. Google identifies several sources.
 
Planning to also add some form of kind of X cross inorder to reduce the sound. Last year I did some investigation on sound and drone effect on my 911 sport exhaust. My conclusion is that to reduce sound, all has to do with wavelengths and pressure waves.
Corrugated metal reduces the high pitch frequencies only.
To reduce low frequencies, you need to use the Helmholtz effect.
the helmholtz effect can be calculated. Parameters are number of cylinders, firing order, diameter exhaust, material exhaust etc.
If you google on it, you will find some calculations.
In theory, theory should be correct but in reality....
It is quite complex and in reality experiencing with different setups is needed to see what works best. For our gt40, space and looks are quite dominant and leave us not many choices. But perhaps we come up with some bright ideas. I was thinking of a H connection before 2 mufflers and the mufflers must need to have a resonance camber with the right volume and not an open exhaust. My setup is for the road so looking for quiet idling but on revving an agressive sound. Aston Martin style sound. The cam specs are also a big variable...damn its complex but interesting designing a sound machine using explosions in the cylinders
 
Step 1 complete. Drilled a few hundred holes into the X pipe. Monday or Tuesday I will pick up the pre cut stainless steel sheet. I already have the high temp ceramic mat for the sound dampening.
 

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One issue though... I have the intake to contend with. Think I can fIt the exhaust under but may want a heat shield.
 
I wonder if you could have taken a torch and heated spots and beat them down with smooth dimples down arranged 90deg from each other like the '69 z/28 factory chambered exhaust? Maybe not enough room or long enough to get enough dimples in?
 
Any update? Just curious if an X pipe will give a deeper tone.

The pipe, stainless sheet, and matting are at A&E Automotive now waiting to be bent (the piece covering the entire thing) and welded. I won't know how they sound until I get the engine fired up and that will be at least two more months.
 
On a related note: I'm picking up my headers from the ceramic coaters tomorrow and have the wrap ready to go on over that (I'm worried about both heat and rust...and also believe I will pick up a couple HP by having both the interior/exterior ceramic coated and the external wrap). The collectors on these are around 6" or so and the way the thing is situated, I either have to take off some of that to route to the center through the X-pipe muffler or make an S out of the 3" mandrel bent stainless I have.

So, I was doing a bit more research about collector length. As a kid, I always heard about the "cut where the metal turns color" with respect to collector length. Well, it turns out that is probably not all of that accurate. What also turns out though is that just about every GT40 I have ever seen has the exhaust set up wrong based on the research I've done. What we all could use is a much longer collector! In my setup, and probably everyone else's, that would necessitate two 180 degree bends...one to go back toward the engine after the collector and then one to turn the other way into the exhaust then into the muffler.

What is all boils down to is that we are losing a lot of torque running little, if any, collector. What is needed is an extension the same diameter as the collector added in at least 9" or so and preferably closer to 18". If you don't believe me, here is a little chart showing how much you pick up. Run 1 is without a collector and run 2 is with one. Note that simply having an exhaust system on the end is not the same as running a collector extension. Due to the resonance of the waves (who's intricacies into the mathematics I did not get into), the collector needs to be of the same diameter. Most exhaust systems will neck down...and that just isn't the same thing!

Anyway, here is the chart of one test. There are many others out there that show similar results. Long story short, I'll be running a long collector at 3.5" (OD), necking down to 3" (OD), doing a 180, routing back a bit, then do another 180 and into the X-pipe with 3" (OD) inlets/outlets.
 

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