| [GMCnet] 2" or 3" exhaust? [message #90198] |
Sun, 27 June 2010 20:15  |
pete lyons
Messages: 81
Registered: June 2010
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This may be one of those things that opinions are split down the middle.
Hopefully i will finally have the Thorley headers i purchased 6 years ago
installed.
The question is, should I do a 3" system or 2"?
One single muffler at the rear, or two just past the engine in an original
configuration?
Anything need to move when installing the headers?
Thanks!
Pete Lyons
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| Re: [GMCnet] 2" or 3" exhaust? [message #90201 is a reply to message #90198] |
Sun, 27 June 2010 20:30  |
Charles
Messages: 455
Registered: January 2004
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Your correct. You probably will get multiple answers.
I went with the two mufflers where they were. I mounted
the headers on the engine and drove it to my local muffler
shop and had him make a "Y" and connect everything
up. I was given a 3 inch stainless pipe to go down the side
like the original 2 inch system was. The 3 inch went in
quite easily with a sledge hammer wood blocks and a
giant that was twice my size. I don't know if the
headers , the 3 inch exhaust system or what but I
definitely felt I had more power after the installation.
Good luck, what ever you do.
Charles
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Charles Wersal
Duncanville, Texas
26 foot 1975 Glenbrook
Pandora's Box
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| Re: [GMCnet] 2" or 3" exhaust? [message #90202 is a reply to message #90198] |
Sun, 27 June 2010 20:36 |
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FWIW I believe in the school that less exhaust backflow is better so I went with the mandrel bent 3" exhaust. I also used the single Flowmaster muffler in the rear. I really like the rear muffler. The cockpit is both quieter and cooler.
Bill Brown - '77 Buckeye Cruiser
Coshocton OH
carguybill@sbcglobal.net
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| Re: [GMCnet] 2" or 3" exhaust? [message #90203 is a reply to message #90198] |
Sun, 27 June 2010 20:37 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Pete,
The factory stock system on the coach is a 2 1/2" system and works
pretty well. What year is your coach. It would be good if you added
that to your signature line.
I have run with both the 2 1/2" and now the 3" on the 77 403 coach.
Our 75 coach has a 3" system.
Will you see a vast difference between the 2 1/2" & 3", probably not
really. The biggest thing that I notice with the 2 1/2" was when I
put high flow mufflers. Coach was peppier and seem to run better.
When the 2 1/2" piping failed I just upsized to 3".
As for muffler location I have only run with the mufflers up front. I
have no experience with the single rear. Both seem to run well.
J.R. Wright
GMC GreatLaker
TZE Zone Restorations
77 Eleganza Custom (For Sale)
1975 Avion (Under Reconstruction)
Michigan
On Jun 27, 2010, at 9:15 PM, pete lyons wrote:
> This may be one of those things that opinions are split down the
> middle.
>
> Hopefully i will finally have the Thorley headers i purchased 6
> years ago
> installed.
>
> The question is, should I do a 3" system or 2"?
>
> One single muffler at the rear, or two just past the engine in an
> original
> configuration?
>
> Anything need to move when installing the headers?
>
> Thanks!
> Pete Lyons
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] 2" or 3" exhaust? [message #90206 is a reply to message #90202] |
Sun, 27 June 2010 20:49 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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If you are redoing the exhaust there is no reason NOT to go 3".
The rear muffler is nice too (unless you have a Royale or a rear tank of some sort)
The 3" fits right in, well the rear frame rail needs a little adjustment to get the pipe to go in. But the rest of the hangers are made for 3".
I assembled mine from parts from Car Quest. They sell pipe and 90 degree elbows. The hardest part was the Y pipe.
http://www.gmcmhphotos.com/photos/showgallery.php?cat=5477
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] 2" or 3" exhaust? [message #90213 is a reply to message #90198] |
Sun, 27 June 2010 21:49 |
Douglas Norton
Messages: 191
Registered: April 2008
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Senior Member |
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Just another penny worth of info. When my mom was older she had an unusual number of under vehicle events (bent suspension, squashed fuel tank etc.). One of those was a squashed tail pipe. Car drove fine for her; when I drove it, it lost power at high revs and at highway speed. A crow bar opened the pipe and the highway power was instantly improved.
I think the GMC, with the original 3.07 differential, will not IMHO, be impacted noticeably by a 3" pipe at normal RPM (under 2700 rpm). However, with higher rpm as happens with 3.50 or 3.70 gearing (20% more rpm and 20% more exhaust volume), the 3" exhaust (44% more area than 2.5") would be expected to make a real difference. Someone may correct the math or explain the real physics of pipe area vs. pipe volume in dynamic situation. Feel free to comment on the quality of what you may think I have been smoking.
--- On Sun, 6/27/10, pete lyons <meandmygmcmh@gmail.com> wrote:
From: pete lyons <meandmygmcmh@gmail.com>
Subject: [GMCnet] 2" or 3" exhaust?
To: gmclist@temp.gmcnet.org
Date: Sunday, June 27, 2010, 6:15 PM
This may be one of those things that opinions are split down the middle.
Hopefully i will finally have the Thorley headers i purchased 6 years ago
installed.
The question is, should I do a 3" system or 2"?
One single muffler at the rear, or two just past the engine in an original
configuration?
Anything need to move when installing the headers?
Thanks!
Pete Lyons
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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| Re: [GMCnet] 2" or 3" exhaust? [message #90232 is a reply to message #90212] |
Mon, 28 June 2010 02:26 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| WD0AFQ wrote on Sun, 27 June 2010 21:28 |
Pete, I really like my 3 inch with rear muffler. Much quieter in passenger area. Teri was in the car last week, behind me. She radioed to tell me the coach is really loud outside. We were climbing a small hill. I just laughed, was quiet inside.
Dan
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You want loud, try replacing that rear muffler with a straight pipe. I did. You will need to be in the next county to get away from the noise.
I've got the 3" with the rear Flowmaster. Thank Emery for the design. It is much better than the two up front.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] 2" or 3" exhaust? [message #90237 is a reply to message #90232] |
Mon, 28 June 2010 06:26 |
pete lyons
Messages: 81
Registered: June 2010
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Member |
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Thanks for the clarity. I found an archived file that was saying that the 3"
would actually be bad at low RPM's and needed some updated opinions. I'm
heading out to have the 3" system put on with a single flowmaster at the
rear. But hey, who drives these things slow anyway? :o)
It will be nice to actually have the exhaust come out in a single location,
instead of the entire length of the straight pipe!!!
pete
On Mon, Jun 28, 2010 at 3:26 AM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> WD0AFQ wrote on Sun, 27 June 2010 21:28
> > Pete, I really like my 3 inch with rear muffler. Much quieter in
> passenger area. Teri was in the car last week, behind me. She radioed to
> tell me the coach is really loud outside. We were climbing a small hill. I
> just laughed, was quiet inside.
> > Dan
>
>
> You want loud, try replacing that rear muffler with a straight pipe. I
> did. You will need to be in the next county to get away from the noise.
>
> I've got the 3" with the rear Flowmaster. Thank Emery for the design. It
> is much better than the two up front.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Pete Lyons
New Albany, IN
76 Eleganza II "Optimus Prime"
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| Re: [GMCnet] 2" or 3" exhaust? [message #90241 is a reply to message #90237] |
Mon, 28 June 2010 06:54 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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you could read this
http://www.gmcmotorhome.info/engine.html#manifold
gene
>
> It will be nice to actually have the exhaust come out in a single location,
> instead of the entire length of the straight pipe!!!
>
> pete
>
>
> On Mon, Jun 28, 2010 at 3:26 AM, Ken Burton <n9cv@comcast.net> wrote:
>
> >
> >
> > WD0AFQ wrote on Sun, 27 June 2010 21:28
> > > Pete, I really like my 3 inch with rear muffler. Much quieter in
> > passenger area. Teri was in the car last week, behind me. She radioed to
> > tell me the coach is really loud outside. We were climbing a small hill.
> I
> > just laughed, was quiet inside.
> > > Dan
> >
> >
> > You want loud, try replacing that rear muffler with a straight pipe. I
> > did. You will need to be in the next county to get away from the noise.
> >
> > I've got the 3" with the rear Flowmaster. Thank Emery for the design.
> It
> > is much better than the two up front.
> > --
> > Ken Burton - N9KB
> > 76 Palm Beach
> > Hebron, Indiana
> > _______________________________________________
> > GMCnet mailing list
> > List Information and Subscription Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
>
>
>
> --
> Pete Lyons
> New Albany, IN
> 76 Eleganza II "Optimus Prime"
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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