H-Pipe costs HP

jesserose17 · Apr 30, 2004

According to Car Craft tech articile, H-pipe costs 10hp and loss of 8lbs torque compared to open headers. X-pipe fared better, gain of 2hp, but loss of 2lbs of torque compared to open headers, so it looks pretty much even.

http://www.carcraft.com/techarticles/69238/index.html

allcarfan · Apr 30, 2004

are you saying that an Hpipe robbed some horsies compared to just 'open headers' with no other exhaust on them?

DUH!!! If an hpipe helped with HP over open headers, then more dragsters wouldnt use just open headers.

ratio411 · Apr 30, 2004

The benefit of X and H pipes are for cars that run a full exhaust, mufflers and all.
To have a full exhaust with a crossover pipe, you gain power over a full exhaust with no crossover.

The arguement over which to use, X or H is pretty big...
I think that the X would be a little more efficient, but the price difference is usually not worth the trouble. The man that created the X pipe freely admits that it is only good for 4hp on a NASCAR and probably less on a mild engine, but every little bit counts in his sport.
The previous post reflects my feelings on comparing a crossover to open headers... it's a 'no brainer'.
Dave

jesserose17 · Apr 30, 2004

I am not saying anything - just that Car Craft did the testing and dyno results don't lie. I just wished they did the comparsion with the true dual setup with mufflers.

ratio411 · Apr 30, 2004

I wasn't picking on you, CC should know better than such a waste of time. I am disappointed in CC.
My subscription ran out last year, maybe that was a good thing.
I have been getting several mags for years and years... I just recently started cutting back.
Dave

allcarfan · Apr 30, 2004

also...

I think an engine actually produces more hp and torque with open headers and an 18" extension rather than just open headers.

67GTCOUPE · Apr 30, 2004

I just run straight pipe to mufflers after my headers.....old school, but it works like a charm for me!

K:^P · Apr 30, 2004

I thought the H pipe was to improve low-end torque

dumb comparison anyway...

ratio411 · Apr 30, 2004

A crossover definately gains torque. Flattens the curve.
HP gain is argueable. The margin of error on most dynos won't accurately show a difference.

Another interesting thing that a crossover does is quiet the exhaust. When you have 2 separate pipes, your exhaust wave frequency is twice what single exhaust is. This makes single exhaust quieter than dual. When you use a crossover, your exhaust reverts to single exhaust frequency. I picked this up in an automotive class along time ago, I wish I could remember the math/details...
Dave

skywalker · Apr 30, 2004

ratio411 said:
A crossover definately gains torque. Flattens the curve.
HP gain is argueable. The margin of error on most dynos won't accurately show a difference.

Another interesting thing that a crossover does is quiet the exhaust. When you have 2 separate pipes, your exhaust wave frequency is twice what single exhaust is. This makes single exhaust quieter than dual. When you use a crossover, your exhaust reverts to single exhaust frequency. I picked this up in an automotive class along time ago, I wish I could remember the math/details...
Dave

Being that a) that's my field and b) i just took af inal 2 hrs ago on digital signal processing I do know something about the math.

Mind you, this is just off the top of my head and is VERY simplistic.

A single exhaust is going to look something like this:
x(t) = A cos(w0t)

A true dual exhaust will look something like this:
x(t) = A1 cos(w1t +phi1) + A2 cos(w2t + phi2)

An H-pipe is going to look something like this:
x(t) = A0 + A1 cos( w1t + phi1 ) + A2 cos(w2t + phi2)

And an X-pipe is going to look something like:

x(t) = A0 + A1 cos( w1t + ph1 ) + A2 cos( w2t + phi1 + pi/2)

Now, in an ideal system, your w1 and w2 will be identical or close to it, as will A1 and A2 and phi1 and phi2. Which would instantaneously double your peak amplitude unless considering A0 the DC value. Now that's an ideal system which doesn't exist.

with an X pipe, the phase of the 2 pipes are thrown ~90 degrees (pi/2) apart thus in an ideal system, throwing the system into silence. Again, that doesn't exist and the phase won't be EXACTLY 90 degrees apart, but the effect is to quiet the system.

The H-pipe is louder than stock pipes because the cross-pipe adds in some DC value.

Now, in reality the amplitudes and frequencies will vary according to some other functions which come from acceleration and such but determining those is beyond me if not impossible.

10secgoal · Apr 30, 2004

Yeah, need to get me one of those things. All I have is straight pipes into mufflers also. Now I had read a while ago that each system of cross over works better with a certain type of muffler. A x-pipe better with straight thru mufflers like dynomax and h-pipe works better with the baffled like the tried and true flowmaster. This is also not to say flowmasters and a x-pipe will not make more horse power than nothing. But the article said that how the seems to match.

skywalker · Apr 30, 2004

I can see why an h-pipe would help flow. I'm at a loss on why the hell an x-pipe is better.

none67 · Apr 30, 2004

or you could be a man and just run true duals..

SadbutTrue · Apr 30, 2004

if you think about it an x doesn't change the direction as much. change in direction (ie when it makes a hard 90 degree turn with an h pipe as opposed to a smooth crossover with an x) means loss of energy and velocity, and lower flow rates. Thats the retard with no math version.

All in all we're talking about +/- 5 hp or less. It matters not.

85GTlover · Apr 30, 2004

85GTlover · Apr 30, 2004

none67 said:
or you could be a man and just run true duals..

My H pipe needs some welding along the seams I want to cut it right out and patch the holes so why not do this? I want to be a real man TOO! Why not?

skywalker · Apr 30, 2004

SadbutTrue said:
if you think about it an x doesn't change the direction as much. change in direction (ie when it makes a hard 90 degree turn with an h pipe as opposed to a smooth crossover with an x) means loss of energy and velocity, and lower flow rates. Thats the retard with no math version.

All in all we're talking about +/- 5 hp or less. It matters not.

Eh, that's also missing some of the physics of it.
See the gas that flows into the H helps flow upon initial hard acceleration by getting out of the way of the quick moving gases coming behind them so that the lack of momentum of those gases doesn't slow them down. In an x-pipe however, all I see are collisions of gases, though I'll admit my knowledge of such things is fairly limited and I'm sure there is a good explanation for it.

85GTlover · Apr 30, 2004

With an h pipe only some of the exhaust is going through and would not the flow from the other side kind of even it out? I really don't get the real advantage of the H part. But I cannot really type what I am thinking. or trying to say here.

skywalker · Apr 30, 2004

85GTlover said:
With an h pipe only some of the exhaust is going through and would not the flow from the other side kind of even it out? I really don't get the real advantage of the H part. But I cannot really type what I am thinking. or trying to say here.

It has to do with owhat happens in collisions. the ability for some of the gases to enter the H allows the gases leaving the engine under hard acceleration to kept their momentum. However once it reaches the higher RPMs it reacts like a normal dual exhaust. The advantage is only at lower RPMs at initial hard acceleration. That's why it helps low end torque. the X pipe I'm still trying to figure out.

Hack · Apr 30, 2004

The reason x or h helps is that there are pulses of exhaust gases, not steady flow. Obviously, the gas only exits the cylinder while the exhaust valve is open.

Something that should help is to consider the idea behind equal length headers, you gain when the pulses are kept spaced the farthest distance apart possible. With the header, you try to get the pulse from each cylinder to enter the main exhaust pipe at evenly spaced intervals. If two pulses try to enter the main exhaust pipe at the same time (worst case), the effective resistance to flow of the pipe is increased, and those two pulses are slowed down. The resulting extra gap between some of the other pulses doesn't help you.

With an x or h, some portion of the pulses from each tube can transfer to the other tube. That portion utilizes the space between pulses on the other exhaust pipe, since the cylinders on each bank fire at different times.

The 90 degree turn being bad applies. Even though the velocity of exhaust gases isn't high, a 90 degree turn will create more flow resistance than a smaller angle. That's why the x is better than the h. To some degree, the larger volume inherent in an x shape helps as well.

All that being said, I would just run straight duals. It's fun to think about the theory though.

H-Pipe costs HP

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