Im still planning the split manifold on my 251 Desoto L head. I am going to run duals all the way out the back with either Smittys or Porters located at different locations on the pipes, Ive heard this gives it a unique sound. Ive researched the hell out of this topic, but keep seeing H-pipes brought up. I know what it does, but when do you know if you need one? Also, If I split my manifold by slipping in a plate and leaving a small gap between the block off plate and the inner wall of the manifold would that help to equalize? Am I just over thinking this whole thing???
I think it's more to do with sound cancelation, than back pressure. Louder without the H pipe. I recall a "factory" dual set up with the cross over pipe, versus a home grown version without the pipe. Both had 327's and both had the same Cherry bombs. Even new, the home grown non crossover setup was louder, and the pulses were more individual sounding, especially when decellerating. On a six this would probably be more notacable with less pulses per revolution. I'm kind of torn on doing this myself on a 250 Chevy. I've got the manafold, I'm just not ready to hack it at this point. I've got a 292 manafold on it now, and will keep it that way until later down the road. Good Luck!
The answer to "when is an H pipe needed?"is never, if you want the distinct sound that a six with true dual exhausts is famous for. An H pipe would cancel that out. To hell with an equalization passage! The factory dual exhaust manifold that came on '53-'54 Corvettes was cast solid between the two outlets.
if you want the performance but without the buzz, then you run one. Otherwise you don't Do you run one?
never is the correct answer instead of a H pipe why not run a single and put a splitter on the tailpipe it will have the effect of looking pretty when running a split you are not really doing it for the scavenging of firing pulses way too much thinking going on here go out and shatter some windows
A H pipe or cross over or equalizer or X pipe is good for about 1 or 2% more power. Leave it out. If you don't like how it sounds, THEN put one in. Either way you'll never feel the diffence in power.
It has always been explained that an H or X pipe adds performance. How it does this is by keeping constant suction on the exhaust. It is the same principle as the collector at the end of header tubes, and the length of the collector. I have seen dyno results that support small gains on pushrod V8s. I am not sure on the L engines, I run a 230 in mine...
Im splitting the manifold for better flow, the sound is just a perk. I spoke with George Asche a few weeks ago about shaving my head, he says its pointless unless you're running a split manifold with duals. The gases can't leave fast enough.
Saw an interview with an exhaust maker recently discussing the reason they used an H instead of an X for a new car system (current Mustang). He explained that the H was good for 27 hp over the X. He didn't say how much over no cross-over. Everything I've ever seen about an H pipe said it had to be in just the right location to provide the power gain. Same for an X pipe. There are lots of wives' tales about how you find that spot, but I'll go with the dyno being the only sure way. Anyways, it will change the sound. It MIGHT make more power. It MIGHT make less. Just food for thought.... Consider your own reasons for choosing one.
I was at the Drag Expo in Chicago this year and in a seminar it was said that an H pipe outperformed a X pipe crossover every time. They tested several cars back to back and thought it may be engine or car specific but it turned out higher HP every time.
That's very interesting, do you have a link? FWIW, I've done both and the X-pipe setups can sound pretty nice at WOT...
A friend of mine had an H pipe on his '52 Chevy, I am not using one on my '53 truck. His setup was a little more mellow, mine is a bit more harsh. When I said "performance", I was refering to dual exhaust vs. single exhaust. Adding an H pipe to a six cylinder engine (especially a relatively stock 235) isn't going to net much HP over not running an H pipe. The decision to run one is more of an issue of how you want it to sound. Adding a larger diameter exhaust tip can also affect the sound. Usually gives it a deeper sound.
It is more important on a V8 because of the firing order. Most straight 6 cylinders use the 153624 order. If you split the exhaust manifold so cylinders123 are in front, and 456 are in the back, it fires front, rear, front, rear, front, rear. A V8 with a firing order of 18436572 and the exhaust split right and left will fire left, right, right, left, right, left, left, right which will cause pulsing that can be mitigated by an H pipe or X pipe.
OK, so I'm not going to run an H-pipe. I was underneath my car today eye balling the exhaust, and it looks like i have plenty of room to run duals straight out the rear. I have my new dump tube ready to install, and i was thinking about putting it directly underneath the heat riser. (the manifold on my car dumps out the rear, with the "pot" located in the center of the manifold) I figure it works on a chevy, should work for me.
The usually front dump is in the middle of the front 6. But watch for fuel pump interference. You can weld the heat flap in the vertical position. Here is an intake and exhaust set by G Asche. This is a 251 Desoto in a friend 48 Plymouth. I'm looking for his video with his dual Smitty's. No crossover.
Plym, Thats also how OldDaddy at RustyHope splits his. http://www.rustyhope.com/intakesexhausts.html My manifold doesn't look exactly like that one. Mine comes off at an angle towards the rear, your friends looks like it just dumps straight down. I was thinking of running the second dump from under the heat riser at an angle because in that location it would clear everything with ease. If i went straight down under the riser the oil pump is there. In front of the riser(like pictured) it runs a bit close to the fuel pump, and i would have to modify the fuel like(like pictured) I have no problem bending up a new line, I'm just worried about vapor lock. My car came with a heat shield on my fuel pump, so I am assuming this has been an issue. I was hoping to keep the heat riser operable, because this engine is a cold blooded *&^%$! (that being said, right now its now working, the spring popped off) I talked to George Asche a few weeks ago. Originally i called him to ask a few questions about shaving the head down and what i can safely get away with(he said .090 is fine, and you can still run pump gas) Anyway, he said shaving a head is pretty much pointless if you don't split your exhaust first. The gases need to be able to escape. George's order of hopping up a L-head six is: 1- split the exhaust 2- run multi carbs 3- shave the head. I'm skipping step 2 for a bit. On a side note, George claims that you instantly gain 5+mpg just by splitting your exhaust and re-jetting your carbs. From what i can see in those two pics your friends car looks pretty clean, and done right. I plan on running both of my pipes on the same side straight out the back. My current goal is not a rappin' sound, but that low flying airplane rumble. PS: Plym46, you should come up to the shop and check out the car sometime. We could discuss the rally a bit.
A visit was on my agenda, waiting a bit longer to so all the salt residue is off the road. Wondering about the reliablity run, I did a couple posts regarding interest and it only attracted three responses. Its a lotta work for negligable participation. My engine is a 230 with dual carbs and .040 milling of the head and deck. Not to argue with George as he does know his stuff, but I did ot split my exhaust, and do have a noticable difference in power. I put the car on a Mustang chassis dyno a couple years back. the set up wants a number for areo drag at 50mph, obviously the books don't cover 40's cars, so we put in 0, though figured a pick might be close at 50 HP, So I restricted the rpm to 3400, and got a yield of 77 HP (speedo at 64) at the wheels. Add in the 50 aero hp and you get 137 . The factory rating for the 56 engine was 125 at the flywheel. So it is apparent that my mods made some difference. Rustyhope is looking for manifolds for pieces and parts so I don't know how his is fixed for doing mods right now. I would think shaving the head can and will help as stock CR was only about 7 to 1. so it is probably the biggest bang for the buck you can do. I did increase the Ehaust to 2 in ID throughout, and run a low rstriction muffler. Also in 56 the factory had a 2bbl option the put anothe 8 HP on the out put. if you don't want to go the dual route, you might thing about getting an adapter and runing a 318 2 bbl on the stock intake. Have you taken a look at the headers that member moose fabs up??? He is in Mass, so not to far away. http://www.manifoldsbymoose.com/manifoldsbymoose/D-P_Combos.html
It's my opinion that most of the nit picking things that we do are actually a waste of time and money on the street. When I was doing exhaust most people wanted the largest pipe that they could get (usually 3"), when they rarely got over 3000 RPMS with 350 CIs. It's one thing if you are building a true race car. It's something else completely if you are cruising at 75 in O.D.. People love to talk race theory and try to apply that theory to a street driven car. It then just becomes empty talk but you will get lots of replies based on something that they have read in a magazine or on the internet. I don't drive my car like a dynamometer. Theory...smearory.
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