i'm with you on that one Glen
you still get benefit from a pipe with tri-y's
my take on the gas distribution is slightly different.
its more that the gas creates a vacuum behind it. the gas follows the path of least resistance whether its x or h, but the combination allows the vaccuum to be released...same as those vents on the end of a military rifle barrel. i'm prolly barking up the wrong tree here too

anyways, the evidence suggests that you get benefit from either. I havent seen anything that would justify the extra expense of an x over an h in a stock to mild engine and any gain can easily be lost if the mufflers are restrictive

 

If you look at the tri-y's you will see that the tubes run from cylinders that are exhausting 180 degress apart then flowing into the collector again at 180. With an x or h pipe you get 90 degree pulsing in the entire system, same as with a stock late model Z/28 or with the 'pile of snakes' headers they used in NASCAR in the old days (except for Smokey Yunick who just ran both collectors into 1...like they all do today).
As far as tri-y's benifitting from an x or h pipe I have not seen a dyno camparision so I can't speak with authority.

 

I'm not following you Mike
you mean from opposite banks?

 

Back in the good old day, we ran Jardine, Ballanger or Headman headers with two bolts on the end flange of the collector to whatever was behind them that was supposedto keep the car sort of quiet and without any 'H' pipe. There were three holes for bolts on each but with two, we could move the exhaust out of the way quickly and we were ready do it. A muffler was not a concern, it was extra weight.
Rt US20 West Springfield, MA; Rt I291 over the Chicopee River; plus others. (Hey, I was a kid too.)
Jim

 

I hear ya Aussie. I don't know what Mike is talking about. Sure, if it is coming from the opposite bank, then there is no problem, but if the gases are coming from the same bank at approximately the same time, how does the Tri-Y headers compensate for the massive flow of exhaust gases that are not prevalent in the other bank?

 

the only thing i can think of is maybe.... lets say for example on one bank we have piston 1,2,3,4 with the tri-y design, if piston 2,4 fired or even 1,4 fired it would use that design of the tri-y header to give less resistance, however it all goes into the same tube later on so honestly i dont understand mikes logic either..

 

It's about what happens downstream of the collector. As long as your headers connect to only one bank, no matter how you pair or don't pair the individual exhaust tubes, you end up with 90°-180°-270°-180° pulsing after everything has finally come together in a single pipe. This happens on both sides.

The cylinders that fire 90° apart tend to give a heavier total pulse, since the first hasn't finished before the next one starts. And the 270°'s represent a brief "quiet" period. That's at least partly responsible for the V8 low frequency rumble.

In addition to the heavy 90° pulsing, the pressure isn't going to be constant anyway, since cylinder pressure and valve opening vary with time.

What I think is happening, X vs H, is that the X allows for better overall flow balancing, which ends up with the two mufflers having closer to equal flow all the time. When the flows are unequal, you have slightly greater backpressure, and slightly less overall volumetric efficiency. I've read where it's somewhere around 2% or 2.5% power cost per psi of backpressure, and we're probably talking about less than half of that as an overall average in this comparison. So the difference is there, in favor of the X, but it's not likely to be a whole lot. Resonance effects could easily be worth more at some rpm's (and ifresonance helps you in one portion of the rev range it will probably hurt you in a different part of it).

I think I might have a spreadsheet with a plot for some of this stuff at home.


Norm