What size h-pipe?
#948334
03/11/11 11:13 AM
03/11/11 11:13 AM
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Joined: Apr 2007
Posts: 2,327
Glendale, AZ
69L78Nova
OP
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Glendale, AZ
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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?
1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser
1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)
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Re: What size h-pipe?
[Re: JohnRR]
#948336
03/11/11 02:08 PM
03/11/11 02:08 PM
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Joined: Apr 2007
Posts: 2,327
Glendale, AZ
69L78Nova
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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.
1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser
1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)
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Re: What size h-pipe?
[Re: 69L78Nova]
#948340
03/11/11 04:28 PM
03/11/11 04:28 PM
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Joined: Jun 2005
Posts: 1,534
Florida
CHRGR69
pro stock
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pro stock
Joined: Jun 2005
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Florida
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2.5! Just did the same to my Cuda
Grandma always said I had "hands of gold"!
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Re: What size h-pipe?
[Re: CHRGR69]
#948341
03/11/11 07:38 PM
03/11/11 07:38 PM
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Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog
Striving for excellence
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Striving for excellence
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Posts: 18,493
Granite Bay CA
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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.
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Re: What size h-pipe?
[Re: Kern Dog]
#948344
03/11/11 11:39 PM
03/11/11 11:39 PM
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Joined: Apr 2007
Posts: 2,327
Glendale, AZ
69L78Nova
OP
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Excellent info! Thanks everybody. I'll go with the 2.25" pipe
1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser
1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)
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Re: What size h-pipe?
[Re: Kern Dog]
#948345
03/12/11 05:36 PM
03/12/11 05:36 PM
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Joined: Jan 2003
Posts: 75,005
U.S.S.A.
JohnRR
I Win
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I Win
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U.S.S.A.
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Quote:
He IS a guru. I would take his advice over "Spike" the tattoo'd tailpipe tweeker.
Ha, he also states that all big block mopar blocks cast after 73 are THIN WALL and should not be bored more than .030 ...  ...
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Re: What size h-pipe?
[Re: HYPER8oSoNic]
#948348
03/13/11 03:31 PM
03/13/11 03:31 PM
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Joined: Jan 2003
Posts: 75,005
U.S.S.A.
JohnRR
I Win
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Quote:
Quote:
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. 
Sorry , that is incorrect, AndyF. did an article a number of years ago that dispelled that MYTH , the later blocks are usually thicker.
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Re: What size h-pipe?
[Re: HYPER8oSoNic]
#948349
03/13/11 03:42 PM
03/13/11 03:42 PM
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Joined: Nov 2007
Posts: 21,822
Kirkland, Washington
Pacnorthcuda
Too Many Posts
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Too Many Posts
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Posts: 21,822
Kirkland, Washington
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Quote:
Quote:
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.
100% Truth!! 2.125" - 2.250" H pipe works WELL in a 2.500" system. For 3.000", try a H pipe with 2.500" - 2.750" INSIDE diameter. 
And the other factor to consider is the size of the hole cut into the pipes! Its easy to cut a tiny hole (or NONE---hey, its been done more than once) into the pipes before welding in the H, takes a little more work to cut holes closer to the ID of the H.
And I agree, 1 pipe size smaller, 2.25 on 2.5, or 2.5 on 3" works just fine.
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Re: What size h-pipe?
[Re: JohnRR]
#948350
03/13/11 08:48 PM
03/13/11 08:48 PM
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Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog
Striving for excellence
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Striving for excellence
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
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Quote:
Quote:
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.
Sorry , that is incorrect, AndyF. did an article a number of years ago that dispelled that MYTH , the later blocks are usually thicker. [/quote
Either Mopar Muscle or Mopar Action did a comparison as well. They tested 383s, 400s and 440s from the mid 60s to 1978. They found that the heaviest block was from a 77 440. It weighed 234 lbs. They sonic checked each block and also found variances that were surprising. Some later blocks were thin in some areas while others of the same vintage were really thick. One thing that was evident was that the later blocks were made of a slightly softer material. Larry Shephard may have been merely "echoing" the memos from the engineering department without any personal knowledge of the cylinder blocks he spoke of. The magazine that did the testing stated that the reasoning behind the "Thin wall" moniker may have had more to do with the actual material hardness rather than the thickness of it. They also went on to give this sage advice: always sonic test before going beyond .030 in any block.
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Re: What size h-pipe?
[Re: Kern Dog]
#948351
03/13/11 10:38 PM
03/13/11 10:38 PM
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Joined: Nov 2009
Posts: 2,275
Desert Tracker
HYPER8oSoNic
top fuel
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top fuel
Joined: Nov 2009
Posts: 2,275
Desert Tracker
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Quote:
Quote:
Quote:
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.
Sorry , that is incorrect, AndyF. did an article a number of years ago that dispelled that MYTH , the later blocks are usually thicker. [/quote
Either Mopar Muscle or Mopar Action did a comparison as well. They tested 383s, 400s and 440s from the mid 60s to 1978. They found that the heaviest block was from a 77 440. It weighed 234 lbs. They sonic checked each block and also found variances that were surprising. Some later blocks were thin in some areas while others of the same vintage were really thick. One thing that was evident was that the later blocks were made of a slightly softer material. Larry Shephard may have been merely "echoing" the memos from the engineering department without any personal knowledge of the cylinder blocks he spoke of. The magazine that did the testing stated that the reasoning behind the "Thin wall" moniker may have had more to do with the actual material hardness rather than the thickness of it. They also went on to give this sage advice: always sonic test before going beyond .030 in any block.
Sorry, don't mean to be 
The material that was in the earlier blocks, was it the nickel content in the iron? 
"Stupidity is Ignorance on Steroids"
"Yeah, it's hopped to over 160" (quote by Kowalski in the movie Vanishing Point 1970 - Cupid Productions)
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