I am looking to put a 3" stainless exhaust on my 55 Bel Air. Adding an X pipe in is going to mean it will have to be routed below the frame to clear the driveshaft and differential stabilizer, which i am willing to work with, if the benefits in HP are there. What I don't understand is how restricting the airflow at a certain point will increase the HP. Most people take two 90 degree elbows and just cut and weld the backs together, effectively reducing that point to the equivalent of 1 diameter of the tube rather that the 2 coming out of the engine. Since that is now the most restrictive point of airflow why even continue with 2 pipes beyond the x pipe and how exactly does this help. Thanks in advance for the help
the pic you posted has more than one diameter of area at the junction.- it's actually not a bad one for being homebuilt. The idea is not restriction- it's about blowing across the straw in your Dr. Pepper. One pipe has a "slug" of exhaust pressure traveling down it, with a low pressure area behind it. As the "slug" of exhaust crosses over the opposing tube, the negative pressure helps to siphon the slug thats coming down that tube. So it's like watching the Dr. Pepper climb your straw as you blow across the top.... plus it mellows the tone as the sound waves get tumbled around in there rick.
Don't do the "X" pipe.....I hate the sound.....Ya have a good running engine ,They are OK on Smog Stuff and Farm Trucks Its Only My 2 Cents so don't get alarmed over my thoughts on the "X" pipe I just hate them! Ol Deuce
The crossover point is not usually reduced as much as "1 diameter?" of the tube. It would either involve a small section removed from each side and welded (as shown) or a pipe added between. The cylinders fire alternately side to side and connecting them effectively increases flow. Also, when done as shown, the alternating pulses help to scavenge the opposite side. Though, with the challenge of getting around your support arm, I don't think it's worth the trouble.
if your sold on the idea, just put a connector pipe in and make it an H pipe, it does the same thing....
Is this for sound or performance, not sure I'm keeping up. If it's for performance, then I'm interested, and want to understand why.
really turns your exhaust into as close as you can a 180 header design without the packaging problems with 180 headers, and also gove that distinct sounds, not like an H pipe either, evens out the exhaust pulses and helps with scavenging, have a car with one and no super performance gain, but noticeable, but the sound is unbelievable.........but not any kinda traditional sound.......depends on the car and style....
There are performance gains based on what others have said regarding scavenging and balancing pulses. That being said, I am not a fan of the sound of x pipes or h pipes. The gains are minimal IMHO and you lose the sound of a true dual exhaust. For me, it's not worth the small gains for the loss of sound.
What on Earth engine are you running that would see some additional benefit from an x-pipe in an exhaust that is already dual 3" tubes?
Might as well run Methanol, change your blower pulleys, etc. The gains are anecdotal. I would liken this to telling a fat kid to not eat donuts with sprinkles, because there are extra calories in the sprinkles.
While carefull tuning can generate some power benefit of either an X pipe or an H pipe, the biggest benefit is that any one cylinder can exhale through both mufflers. Mufflers today can flow enough it's unlikely to be necessary to use an X or H, if they are properly sized. They tend to actually muffle nowadays too.
Leave the X-pipe out. The dual 3" system is already overkill for that application. A pipe will flow 115 cubic feet-per-minute, per square inch of cross-sectional area. 2.2 cubic-feet-per-minute of flow capacity is required per one horsepower. Based on this calculation, your system will support 738.99 horsepower. An engine with 450hp need a system that is about 2-3/8", as duals. Round up to dual 2-1/2's and you can support over 500hp. The dual 3" system might even be large enough that it is beyond peak volumetric efficiency for your application, causing a decrease, or total loss of the scavenging effect. Adding an X-pipe or an H-pipe to a system that is already too large will just make it worse. Each high pressure exhaust pulse has a low pressure area behind it as it travels out the exhaust system. This low pressure pulse pulls the next high pressure pulse along. It sucks the exhaust charge out of the cylinder and on down the pipe. This is scavenging. Having an exhaust system that is too large allows that high pressure pulse to expand and decrease in pressure. When this happens, there is little or no low pressure pulse to pull the next exhaust charge along. This can leave some of the exhaust charge behind in the cylinder, where it will be combined with the next air/fuel charge. Goodbye scavenging, goodbye performance.
To answer your question, run the x pipe. Tri five chevys usually end up with ridicuolously long tailpipes that tend to rap....some people like the rap but I think its only cool on straight sixes. In your case with an IRS tailpipe length may not be an issue as you will likely go right under the center section Like gimpy said, you really don't need the 3" exhaust, 2 1/2" will be more than fine and will actually sound better IMHO. As far as horsepower that could be debated either way for a long time but the fact of the matter is the optimal location for the x-pipe is likely NOT where it will end up anyways due to packaging so in most hot rod applications you won't see a significant power increase.....but the sound....the sound is awesome. Smooth, balanced, throaty, I love it. Now a question for Gimpy. Is there a formula for determining the opening in an x-pipe where the two pipes converge? For example is 75% of the surface area of one pipe or is it way more complicated than that. I usually try to get same amount of opening as the diameter of pipe I am running but maybe that is too big. Donny
In order for an x-pipe to be effective, it needs to be as close to the headers as possible. In the case of the OP, it would end up under the drive shaft and differential stabilizer. That far back in the system would likely limit any benefits that it would have (especially at that pipe diameter), v.s. how hard it is going to be to fit there. As per Donny's question. There is no strict discreet formula for determining the x-pipe opening, per se, as it depends on many factors, including the construction method. In the case of the one shown by the OP, it is the square area of the ellipse where the two bends are welded together. The area of an ellipse can be determined by: Area = Pi * A * B, with A being the semi-major axis of length, or half the long diameter (similar to the radius of a circle) and B being the semi-minor axis of length, or half the short diameter. As for a formula for determining the proper size of the port between the two pipes, that is a whole other animal. It would be dependent on a ton of variables, including everything from firing order, the exhaust valve size, exhaust port efficiency, header primary tube diameter and length, relational lengths between header primary tubes, collector diameter and length, pipe size, X-pipe location, muffler flow rate, etc. It should not need to be any bigger that the full size of one pipe in the system. I speculate that it could be quite a bit smaller that that, but determining that for sure would test the limits of my math skills and computing power. It also could be tuned to affect overall performance, but that would make my head a-splode.
It could be argued that even thought the x pipe is far, far away from the optimum position for a positive effect on scavenging it would still have a positive impact on the sound coming from the tailpipes. It has in my experience anyways. As far as sizing the hole in the crossover, it sounds like it would be safe to assume (we have to assume, I don't want your head to asplode) that if the crossover port were sized between 75% and 100% of the area of ONE of the tubes that you are running that would be acceptable for what we are doing with these cars......works for me. Donny
I kind of like the gravely "raspy" sound of un-siameesed duals. In the Model A in my avatar I curently have a 331 CI SBF built like a short deck 327 Chev. It has Sanderson SBF block hugger headers, 2 1/2 inch pipe to Dynomax Super Turbo 3 inch mufflers (Dynomax P/N 17769) just ahead of the rear axle with 2 1/2 inch stub pipes out the back (under the axle). The adapters (from 2 1/2" to 3") are the stepped kind, as opposed to the tapered kind with the pipes coming from the engine stuck roughly halfway into the muffler inlet through the adapter as sort of an anti reversion trap. It has a nice low mellow tone at idle and cruise, with no exhaust harmonics (the gearbox is getting noisy though ) fairly quiet too both inside and out, till you're "on it" then it's only quiet inside. I had been thinking of using a crossover, for tone control, but decided against it after I heard it. I had thought of using a restrictor in the crossover to regulate the sound, the larger the orifice, the less rasp to the exhaust note. Gimpy, I always figured on being able to tune the exhaust with an X or Y collector like a 3rd volume of a header, but you're right, the combination of both the design to get far enough to have that make a difference and the tuning (or "development" if you prefer) would likely make anyone's head asplode, while their wallet implodes.
X pipes I love them.If you have any kinda of hot engine,I would put 3''on it it will make a world of difference.
thanks for all the info! No x pipe, but kept the 3" exhaust. the engine was built to handle NOS and a blower, but I have no intentions of doing this...yet
I run an h pipe just because I thought it would mellow the exhaust some. FWIW my exhaust guy said adding an x-pipe would make it smoother/quiter/more betterer or something along those lines. It makes sense to me to get some bends in the pipe instead of having it all straight, it has to do *something* to the sound. I'm going to go check it out on youtube right now. EDIT: WOW the X pipe sounds a lot different than an H! Totally quieter and mellower. Definitely worth considering for me.
I`m not a big fan of that crackly exhaust note you get with out a balance pipe and I have allways ran a H pipe since about 1986 when the first car I owned picked up a 10th at the drags with a full exhaust after I fitted the H pipe.
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