90 degree crank V-8 exhaust system

I am sure that this is going to generate some snickers, but here it goes!
What I think I know:
90 degree crank V-8's do not generate equally spaced exhaust pulses in each bank. In order to improve scavenging, some systems incorporate an H pipe or X pipe to interconnect the exhaust systems of the two banks. Considering only the X pipe for the moment, this is my question.
Once the flows are combined at the X, why are they separated? In other words, why not a Y instead of the X? Rationale: If the flows have been "combined", continuing in a single pipe should be lighter since the circumference of the single pipe with cross sectional area equivalent to the two independent pipes will be smaller than the combined circumference of the two independent pipes. Additionally, since the circumference is smaller, there is less surface area to create drag on the exhaust flow.
I am not interested in becoming an exhaust system expert. Just trying to understand.
Thanks again, I will retreat to my bomb shelter.
Mike
 
No need to retreat, your correct on just about all points. The X-box needs clarification in that it should direct the flow from the RH bank toward the LH tailpipe and vice versa to function correctly. There are some versions on the market that do not do that and cause a lot of turbulence in the X box in the process. as for the Y pipe to go to a single large tailpipe that is my preference, both from a noise level and power factor.
attached dwg shows how the 'pulses' of exh gas merge within the X box in theory.
 

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Jac
Does that have the same sort of action regarding the traditional bundle of snakes GT40 exhausts that cross over? is there any advantage of those versus standard left bank and right bank into seperate mufflers with a balance pipe?
Cheers
 
Jac
Does that have the same sort of action regarding the traditional bundle of snakes GT40 exhausts that cross over? is there any advantage of those versus standard left bank and right bank into separate mufflers with a balance pipe?
Cheers
In theory yes, but it relies on a lot of variables to do that, eg it assumes that all cylinders will produce the same power/ex pulse, that all primary pipes will have the same flow characteristics.
With the balance pipe there should be no need on the 180° system, its more of a 'fix' or crutch for the normal side for side system where you get uneven pulses in each pipe as in the diagram in the post #2. With a muffler the collector tailpipe should enter an expansion chamber at the correct tuned length to give a clear signal of pipe end, after that it does not really matter other than the final exhaust exit should be in a low pressure area if possible. That expansion point can be in the muffler if its designed with an expansion chamber at entry. The TVR muffler was fabricated like that with two in one out.Had all the overseas cobra guys stumped at Hampton Downs opening meet a few years ago.
 

Howard Jones

Supporter
Does a X pipe or a H pipe for that matter really do anything at all in a GT40 kind of application where the length of pipe after the X or Y is so short. My SLC for example has less that 30 inches total including the mufflers after the collector. I can see where the "balance" works in a full length system like on a Mustang for example. Plenty of turns and length to build pressure.

I guess what I am asking is. Is there really anything to balance? There can't be much pressure in the exhaust system after the collectors. All there is, is a 4 inches of 3" pipe into a 22" straight thru 3" muffler with another 4 inch length of 4 of 3" diameter pipe on the end.

By the way I have been toying with a 2-4s into 1 system just to see what it sounds like.
 
Does a X pipe or a H pipe for that matter really do anything at all in a GT40 kind of application where the length of pipe after the X or Y is so short. My SLC for example has less that 30 inches total including the mufflers after the collector. I can see where the "balance" works in a full length system like on a Mustang for example. Plenty of turns and length to build pressure.As before, a balance pipe on a 180° GT40 system should not be reqd. your SLC is another can of worms since its virtually impossible to achieve a workable 180° system in the space provided and the variation of engine & transaxle sizes.

I guess what I am asking is. Is there really anything to balance? There can't be much pressure in the exhaust system after the collectors. All there is, is a 4 inches of 3" pipe into a 22" straight thru 3" muffler with another 4 inch length of 4 of 3" diameter pipe on the end.Your total length of 4+22+4 is 30 inches, not far away from what is likely to be an ideal length of 32"/36", Now if you were to remove the mufflers and get a decent X or Y box the extra difference of pipe length from the convergence might be enough.

By the way I have been toying with a 2-4s into 1 system just to see what it sounds like.
I think you might like it unless your an absolute original V*8 rumble fanatic. To Quote Howard Jones.." Its a hobby, its yours... do whatever makes you happy... there are no rules other than decibel numbers to stop you!:)

As an afterthought... a few years back I had a client with a Ford Falcon XD, 351c, Tunnel Ram, 4 spd , I built a single tailpipe system for that car. he was a long haul driver based about 15 miles from me, on quiet nights I could hear him driving home from the truck base for most of that 15 miles, yet I dont think he ever got a noisy vehicle ticket... sounded more exotic for want of a better term when on the open road.
 
Ok, so I have a flat plane crank in my V8, and was going to just run two straight pipes out the back. Any benefit of joining them with an X pipe like the one in this pic?
 

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I would think only from a noise aspect, but there might be some advantage in the extra length of that layout. That design of Xpipe would lead to quite a lot of turbulence at that point. I assume your headers from each bank are tri-y design going by the double port flange on each side in the pic.
 
Here is a slightly different system, but with the same arrangement, in full (this set has a bypass valve after the X pipe to alter the sound).
4 into 1 header, cats, X pipe, muffler, twin pipes to outlets

Forget the twin port outlet, it's more about the effect of that X pipe vs. not having it, and running them as completely separate banks from headers to tips.
 

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I see no need for the X pipe in that 180° crank race application.For street use it might be reqd for noise purposes. I guess not many Ferrari owners would want to get their hands dirty to remove the mufflers for a track day so the idea of pushing a button on the dash for straight thru exhaust would appeal.
Attached pic with notes from different angle might help. I had quick look at the site & still not sure if those are expansion chambers or Cats with a chamber.Again the Xpipe on a 180° system should not be reqd.
 

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Cheers mate, I could see no reason for it either. Great explanation on the pic too, regarding the effective tuned length. And those air injection rails on the headers are a US-only requirement.
 
I made 180° headers for my 40 and they ended up too close to the clam shell, even with heat protector the physical size of the engine made everything very tight. So I started again this time keeping the primary length shorter closer to where it should be and the secondary longer.
I made the X pipe in the secondary's only because it sounds better and defiantly quieter.
This new system picked up nearly 20 Hp. I believe the longer secondary is where the power is, being consistent with dyno runs in the past the primary length doesn't make as much difference as the secondary.
It doesn't look original but not a lot of this car does, however it is good fun
Woody
 
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