_Remi

Hi,

I am not using X or H pipes on my 67 and was wondering if I am loosing something somewhere. I have dual exhaust with super comp long tubes and flowmasters 40 series and it sounds great.

Would it make sense to modify something?

Thanks!

groho

The H / X pipe promote low end torque and helps to evacuate exhaust and improved scavaging (valve overlap, pulling fuel in as it's pushing exhaust out). I've heard the X pipe is better than the H piper for it's directional flow, but no hard information. I've alway ran a cross-over pipe with a dual exhaust simply for the torque.

Norm Peterson

The X is generally a little stronger in the higher rev ranges, particularly when running through mufflers that are a little more restrictive than necessary.

They also sound a whole lot different than completely separate duals or duals with an H-pipe (crossover).

The S197 section goes through this very same discussion ad nauseum, if you want to read more of the same an almost endless number of times without having to ever leave the site.

Here's a picture that I've posted there (more than once) that might help a little here. Ignore any reference to "Odd" or "Even" banks, as the original purpose was to demonstrate sound pulsing in a SBC. Other than the cylinder numbering scheme and the Amplitude values, there is no difference between the SBC and the SBF (and most all production V8's, for that matter) as far as this is concerned.

The top chart is essentially what happens in true duals and to a lesser extent in most H-pipe crossover setups. Not enough volume flow sharing to quiet down the heavy pulses that occur when two cylinders in the same bank fire in sequence. The big peaks are your heavy bass component of exhaust sound, and also represent momentary backpressure spikes that tend to cost a little HP. Note too, that the heavy pulses alternate between the banks, which adds a 3-D effect to that part of the sound. Most folks prefer this arrangement for the sound alone.

The bottom chart is for an X-pipe with full flow sharing. No heavy pulsing or heavy bass tone, so the end result is more of a smooth, higher pitched snarl. If you appreciate NASCAR racers, high-winding smallbore sixes, fours, and bullet bikes, you'll like this. A lot if you like being different.

Power-wise between the two assuming otherwise adequate exhaust system dimensioning, there isn't enough difference for your butt-dyno to feel, but there is enough to theoretically show up in timed competition. If you really are consistent enough to pull a small (but real) difference out of the noise of your own personal range of data scatter, that is.






Take your time. There's quite a bit of new information for most folks in this post.



Norm

Starfury

Personally, I'd have a muffler shop weld in an H-pipe. It smooths out the exhaust note, making it less raspy and tinny, and it does help the engine rev a little more freely.

I don't really like X pipes on classics. Like Norm said, they have a weird higher pitched snarl at high rpm's. I prefer the lower, more uneven tone on an un-catted car.

kalli

i have true mdual setup as well and as soon as my buddy (talented pipe welder) has some free time we're installing H-pipes in mine. the true dual setup was great for the stock 289 with flowmasters (rumbly, bassy), but i have a feeling (and no other proof) that i'm restricting nthe engine now a bit with this. It's more of a fart can effect now. it's more blatty as if there was was just too much pressure. I'm not sure on this but I think I have to go either bigger pipes (from 2.25" to 2.5") so I'll just weld in a balancer and see what happens

Norm Peterson

I think every psi of backpressure costs you about 2.5% power. That's probably with respect to some sort of "mean backpressure" rather than to backpressure peaks or spikes. Marks' Handbook for Mechanical Engineers, IIRC.


Norm

urban_cowboy

Do what you want, but I think it is far more important to have the right size pipe and have as few restrictions as possible. Mandrel bends and proper pipe size will eliminate most all of your exhaust restriction and flow problems. If you still have issues after that is done, an X pipe MIGHT, and I emphasize MIGHT help, but there is little empirical data on this. I put crossover pipes in the chrome category of things that are nice but do not help you much. You can find articles that claim they work and articles that claim they do nothing. I have not experimented with them, so I cannot say first hand, but the number of differing opinions on them should tell you something .

Deviousfred

Norm Peterson

Exactly where you place an H or an X will affect the outcome as well. Either one causes some changes in the exhaust resonances, and from there, in the tuning that takes advantage of that phenomena. Consider having to make jetting or fuel map and possibly ignition curve changes.

You'd like these exhaust tuning changes to be beneficial and to be able to take advantage of them. But as cowboy suggests, it cannot be guaranteed that simply slapping one or the other of these refinements wherever it might fit, or fit with the least difficulty is going to give you that.


Neither the H nor the X will give you the potential for resonance tuning that is possible with headers that merge 3 cylinders from one bank and 1 from the other into each collector, with the merged cylinders all uniformly separated by 180° in the firing order. No, I'm not claiming that something like that would be at all easy to build. And yes, it would sound a lot like a V8 Formula 1 car from the late 60's.


Norm

Deviousfred

Hmmmm... Thanks a lot Norm. I like the idea.

Now that I think about it. Last week at the dirt track there was a limited late model there that sounded like that. I, for the life of me, could not figure out why. Now I know.