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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old May 27th, 2018, 09:36 PM
1972RedNeck 1972RedNeck is offline
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Default "H" or "X" Pipe On A V6?

Most any half decent engine builder out there can tell you about the benefits of an "X" or even and "H" pipe in the exhaust system as it is pretty well known that they "balance" exhaust pules and can even increase scavenging if designed properly. In my mind, they are a no brainer on pretty much any application utilizing dual exhaust manifolds and pipe.

But then there is the Big GMC V6 family with their unique firing order where it is perfectly staggered from one side to the other unlike most all (if not all) other "V" engines that have one cylinder firing right after another on the same side.

With this being the case, in my mind, there is no exhaust pulse "imbalance". If this is the case, there is no benefit to an "H" pipe as they really only balance the exhaust without increasing scavenging.

If I am still on the right track, then the question begs, "does an 'X' pipe provide any benefit?"

It doesn't provide any gains from balancing the exhaust, but could it still increase scavenging?
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  #2  
Old May 28th, 2018, 12:30 AM
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Default Re: "H" or "X" Pipe On A V6?

I just hope that's not on the top of your list of things to do.
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  #3  
Old May 28th, 2018, 01:13 AM
1972RedNeck 1972RedNeck is offline
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Default Re: "H" or "X" Pipe On A V6?

Not on the top, but it is on the list - along with head porting, cam grinding, building headers, offset grinding the crank, custom pistons, BB Mopar rods, balancing, etc.
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Old July 17th, 2018, 06:08 AM
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Default Re: "H" or "X" Pipe On A V6?

Quote:
Originally Posted by 1972RedNeck View Post
Not on the top, but it is on the list - along with head porting, cam grinding, building headers, offset grinding the crank, custom pistons, BB Mopar rods, balancing, etc.
Not sure about any increases or decreases but I've thought about that here and there....personally been happy with the true duals thus far.
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Old August 5th, 2018, 10:49 PM
POWERSTROKE POWERSTROKE is offline
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Default Re: "H" or "X" Pipe On A V6?

The 478 cid V-6 in the single axle tractor Dad drove to the Peoria Stock yards one night 50 years ago seemed to do real good with just dual exhausts, no X-pipe. Old girl rattled the windows at 2 AM really good loaded. It was Dad's second trip there that day, I was supposed to keep him awake.
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Old August 6th, 2018, 03:35 AM
1972RedNeck 1972RedNeck is offline
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Default Re: "H" or "X" Pipe On A V6?

Quote:
Originally Posted by POWERSTROKE View Post
The 478 cid V-6 in the single axle tractor Dad drove to the Peoria Stock yards one night 50 years ago seemed to do real good with just dual exhausts, no X-pipe. Old girl rattled the windows at 2 AM really good loaded. It was Dad's second trip there that day, I was supposed to keep him awake.
I'm well aware that true duals work "real good". But if there was 10 or even 5 HP to be had out of an "X" pipe, why wouldn't you for the extra $50 it would cost?
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Old August 6th, 2018, 02:37 PM
lizziemeister'sV6 lizziemeister'sV6 is offline
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Default Re: "H" or "X" Pipe On A V6?

Your question of installing an H or Y pipe is a great addition to the V6 no matter what other people say on the benefits or the cost. On my 1965 suburbun with a 351M which has the spec cam (Pete's) that is talked about on here, "H" pipe directly behind the PG followed by 2 1/4" pipes and Magaflows all dumped straight out the back of the bumper sounds great. By mixing both banks of cylinders the sound is unique - so much so that most people have no clue what is under the hood - most will not believe it's a V6 - somewhere my truck was even filmed and sound recorded on Face Book - what a surprise to me. I say "install the pipes! "
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Old August 6th, 2018, 05:35 PM
POWERSTROKE POWERSTROKE is offline
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Default Re: "H" or "X" Pipe On A V6?

Quote:
Originally Posted by 1972RedNeck View Post
I'm well aware that true duals work "real good". But if there was 10 or even 5 HP to be had out of an "X" pipe, why wouldn't you for the extra $50 it would cost?
Whether it was a lowly little LoadStar with a 345 cid V-8, or a FleetStar with 478 V8, or a C65 with 366 V-8, or C70 with 427, anywhere from early/mid 1960's to late 1970's, they all had true dual exhausts. I think that was to manage heat in the engine and exhaust system. The duty cycle on trucks is amazing, hours on end wide open, exhaust manifolds glowing orange hot except for 3-4 hot spots that are bright yellow hot. An H pipe would add several more hot spots, and X pipe probably one big one that could cause problems. Not sure what current production trucks have to run for emission equipment. Big Block V-6's definitely none,

5 or 10 hp added to the 205 or 235 net hp of the 478 or 125 hp of the 305 "Might" be noticeable. True story, Buddy and I driving identical tractors, 320 net hp, first loads one day I was 400# heavier than his 70,000#. He walked away from me every 10 miles or so for 175 miles. Coming home I was lighter by 250-300#, I walked away from him 5-6 times in the 175 miles, maybe could have done more but I wasn't trying too hard.

I think lightening the truck by a couple hundred pounds would make more difference than the hp. Added hp usually costs burning more gas, lighter weight saves hp and gas.

I really think it's more than just a coincidence that a Chevy, GMC, Ford, and IH with big gas V-8 power had almost identical exhaust design.
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Old August 7th, 2018, 02:49 AM
bigblockv6 bigblockv6 is offline
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Default Re: "H" or "X" Pipe On A V6?

Quote:
Originally Posted by lizziemeister'sV6 View Post
Your question of installing an H or Y pipe is a great addition to the V6 no matter what other people say on the benefits or the cost. On my 1965 suburbun with a 351M which has the spec cam (Pete's) that is talked about on here, "H" pipe directly behind the PG followed by 2 1/4" pipes and Magaflows all dumped straight out the back of the bumper sounds great. By mixing both banks of cylinders the sound is unique - so much so that most people have no clue what is under the hood - most will not believe it's a V6 - somewhere my truck was even filmed and sound recorded on Face Book - what a surprise to me. I say "install the pipes! "
Which Magnaflow mufflers are you running? I've heard yours on youtube and it sounds far better than my 478M with the same came grind but with 3 chamber 50 series Flowmasters and 2 1/2 inch pipes, I'm looking for a more aggressive sound on my truck
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Old August 7th, 2018, 03:06 AM
bigblockv6 bigblockv6 is offline
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Default Re: "H" or "X" Pipe On A V6?

[QUOTE=POWERSTROKE;69517]Whether it was a lowly little LoadStar with a 345 cid V-8, or a FleetStar with 478 V8, or a C65 with 366 V-8, or C70 with 427, anywhere from early/mid 1960's to late 1970's, they all had true dual exhausts.

Powerstroke, you failed to mention the bigger GMC truck Powered by the bigger displacement V6 engines that also came equipped with dual exhaust? late 60's up to 1974 on H & J Series 7500-8500 trucks equipped with 401M. 432,& 478M engines. Also the 73-74 C6500 series equipped with 379 and 432 engines, the same should apply for T series tilt cabs of that era.
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