Posted By: 69L78Nova
What size h-pipe? - 03/11/11 03:13 PM
Going to go ahead and put an h-pipe on my Fury. It's an LA 360, Magnum heads and 1.6 rockers, XE256 cam, dual plane M1, Hooker comp headers, 2.5" duals out to the bumper with stock style turndowns, and 2 chamber 40 series Flowmasters. My problem is how loud and poppy the exhaust is under part throttle and wide open acceleration since I did the head swap. I need to know what size h-pipe to put in. I always thought the crossover pipe should be a little smaller than the exhaust system. If that's the case, would 2.25" be ok? I'm just trying to quiet it down and clean it up a little bit. I hope the 2.5" exhaust isn't too big for this setup. Any opinions?
Posted By: JohnRR
Re: What size h-pipe? - 03/11/11 05:13 PM
It's your mufflers , I don't think an H is going to do much for you ., X might be a better way to go .
Posted By: 69L78Nova
Re: What size h-pipe? - 03/11/11 06:08 PM
I just don't know about that. I had Dynomax hemi turbos on it after the head swap, and they were raspy too....whereas they weren't with the stock heads. I have been told to try an h-pipe to even out the exhaust pulses in the pipes. All I need to know is what size pipe to use with a 2.5" exhaust system.
Posted By: Dodgem
Re: What size h-pipe? - 03/11/11 06:21 PM
2" is enough but 2 I like 2 1/2 or 3" depending on the system.
Will make more power and quiet it down at the same time!
Have had friends add it later and were amazed at the results!
Posted By: CHRGR69
Re: What size h-pipe? - 03/11/11 08:28 PM
2.5! Just did the same to my Cuda
Posted By: Kern Dog
Re: What size h-pipe? - 03/11/11 11:38 PM
The exhaust pipe guys are not scientists. Sometimes they are just hourly dudes doing what they are told. The theory of the advantages of a crossover pipe is solid, but the sizing isnt. The principle is that a shared balance between two isolated pipes helps tone down the high frequencies and fill in the low ones. Its a sort of 'noise calcellation" effect. The dispute comes from your question, and this is where it gets muddy. MANY muffler monkeys know nothing about WHY something works, but some do. I knew of an old timer I met at the Reno Swap Meet at the Hot August Nights show in 2006. He was at a booth selling mufflers and X pipes, all that stuff. It was his contention that the X pipe is superior for power if the sizing matches the rest of the system.He said that in the case of a simple lateral crossover tube, size isnt as critical as you think because the gain in this instance isnt to increase FLOW, but to share SOUND waves. The theory sounded reasonable to me. He wasnt some wild haired, crazy eyed freak after all. Also, ONE 90 degree bend has the equivalent of 25 feet of additional pipe.
Posted By: can.al
Re: What size h-pipe? - 03/12/11 01:42 AM
Larry Sheppard(Mopar performance Engineer) says h should be slightly smaller diameter than exhaust,place 12" after collectors.
will quieten exhaust and make no additional power.
Posted By: Kern Dog
Re: What size h-pipe? - 03/12/11 01:46 AM
He IS a guru. I would take his advice over "Spike" the tattoo'd tailpipe tweeker.
Posted By: 69L78Nova
Re: What size h-pipe? - 03/12/11 03:39 AM
Excellent info! Thanks everybody. I'll go with the 2.25" pipe
Posted By: HYPER8oSoNic
Re: What size h-pipe? - 03/13/11 06:34 PM
Ha, he also states that all big block mopar blocks cast after 73 are THIN WALL and should not be bored more than .030 ...
...
He's pretty much on the mark about those 74-up
motors. Walls are not as thick as the earlier models, particularly the 70' and earlier. 
