Home » Public Forums » GMCnet » [GMCnet] mandrel bent
| [GMCnet] mandrel bent [message #92470] |
Sun, 18 July 2010 19:08  |
pete lyons
Messages: 81
Registered: June 2010
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For the sake of time and money, what am I losing between purchasing mandrel
bent exhaust fitting vs. going to my local shop and having them bent for me?
thanks!
pete
--
Pete Lyons
New Albany, IN
76 Eleganza II "Optimus Prime"
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| Re: [GMCnet] mandrel bent [message #92473 is a reply to message #92471] |
Sun, 18 July 2010 19:33  |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
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If you use 3", probably nothing performance wise
2 1/2" maybe a little top end
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] mandrel bent [message #92475 is a reply to message #92470] |
Sun, 18 July 2010 19:38 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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The configuration of the GMC exhaust system is such that it's almost as
easy, and not much more expensive, to use stock mandrel bent elbows. Any
muffler shop should either have them in stock or be able to get them the
next day; Jegs & Summit are almost as fast. Be sure you use band clamps,
NOT U-bolt clamps, for security and future ease of disassembly.
Ken H.
On Sun, Jul 18, 2010 at 8:08 PM, pete lyons <meandmygmcmh@gmail.com> wrote:
> For the sake of time and money, what am I losing between purchasing mandrel
> bent exhaust fitting vs. going to my local shop and having them bent for
> me?
> thanks!
> pete
>
>
> --
> 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
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] mandrel bent [message #92487 is a reply to message #92475] |
Sun, 18 July 2010 20:45 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Yes, mine was a totally welded system. It made it a real pain when I moved from 2 front mufflers to one on the rear. During the change I welded some of it back and used band clamps in other locations.
The band clamps are the way to go.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] mandrel bent [message #92506 is a reply to message #92487] |
Sun, 18 July 2010 23:16 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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One thing that headers do exceedingly well is to remove heat from the
engine. I call this scavenging. They do very little horsepower wise until
the rate of flow exceeds that of the stock system. At the RPM our engines
turn, with the restrictive air cleaners and intake manifolds, you almost
can't tell any difference between cast iron manifolds or headers except for
the sound. Kinda like what sells Harley Davidson Motorcycles. Design
unchanged since 1907 or so and crude beyond belief, but the company is
successful because of appearance and the sound of the engine. ANY
restriction in an exhaust system will delay heat removal from the engine.
That is what is most important in this application. Mandrel bends have been
dyno tested to prove that they work more efficiently at heat removal over
other types of bends. Too bad that they are more expensive, but in this case
I think you get your money's worth. My personal experience has been that
they also last longer because they don't have hot spots caused by
restrictions.
Jim Hupy
Salem, Or
78 Royale 403
On Sun, Jul 18, 2010 at 6:45 PM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> Yes, mine was a totally welded system. It made it a real pain when I moved
> from 2 front mufflers to one on the rear. During the change I welded some
> of it back and used band clamps in other locations.
>
> The band clamps are the way to go.
> --
> 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
>
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| Re: [GMCnet] mandrel bent [message #92533 is a reply to message #92470] |
Mon, 19 July 2010 06:59 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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here are some hints on when to change exhaust components
http://www.gmcmotorhome.info/engine.html#manifold
I find, what to use, is usually determined by your situation
time- cost- ability- patience
just do what you can do, you will still get 8 to 10 miles per gallon no
matter what you do ;>)
gene
On Sun, Jul 18, 2010 at 5:08 PM, pete lyons <meandmygmcmh@gmail.com> wrote:
> For the sake of time and money, what am I losing between purchasing mandrel
> bent exhaust fitting vs. going to my local shop and having them bent for
> me?
> thanks!
> pete
>
>
> --
> 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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| Re: [GMCnet] mandrel bent [message #92582 is a reply to message #92506] |
Mon, 19 July 2010 14:06 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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The Tri Y headers are designed to operate best at low RPM.
The 2 small tubes join together in a proper firing sequence the t the
collector.
All the ones we have installed (over50) the customers tell us positive
stories.
Exhaust system on a coach is more important as your running under load from
weight and wind drag all the time.
We had a customer run it on a dyno after install and picked up 40hp.
On Sun, Jul 18, 2010 at 9:16 PM, James Hupy <jamesh1296@gmail.com> wrote:
> One thing that headers do exceedingly well is to remove heat from the
> engine. I call this scavenging. They do very little horsepower wise until
> the rate of flow exceeds that of the stock system. At the RPM our engines
> turn, with the restrictive air cleaners and intake manifolds, you almost
> can't tell any difference between cast iron manifolds or headers except for
> the sound. Kinda like what sells Harley Davidson Motorcycles. Design
> unchanged since 1907 or so and crude beyond belief, but the company is
> successful because of appearance and the sound of the engine. ANY
> restriction in an exhaust system will delay heat removal from the engine.
> That is what is most important in this application. Mandrel bends have been
> dyno tested to prove that they work more efficiently at heat removal over
> other types of bends. Too bad that they are more expensive, but in this
> case
> I think you get your money's worth. My personal experience has been that
> they also last longer because they don't have hot spots caused by
> restrictions.
> Jim Hupy
> Salem, Or
> 78 Royale 403
>
>
>
> On Sun, Jul 18, 2010 at 6:45 PM, Ken Burton <n9cv@comcast.net> wrote:
>
> >
> >
> > Yes, mine was a totally welded system. It made it a real pain when I
> moved
> > from 2 front mufflers to one on the rear. During the change I welded
> some
> > of it back and used band clamps in other locations.
> >
> > The band clamps are the way to go.
> > --
> > 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
> >
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] mandrel bent [message #92618 is a reply to message #92470] |
Mon, 19 July 2010 21:22 |
jknezek
Messages: 1057
Registered: December 2007
Karma: 5
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Senior Member |
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Some PO had put 2.25" pipe on my GMC at some point in the past. I could never figure out why the thing had no power and worked on about a dozen different possibilities. 12,000lb hot rod with plumbing? Mine was more like a house boat with an underpowered outboard. I had all kinds of vacuum problems, carb problems, spark problems. You can imagine what it was doing. Never thought to pull out a pair of calipers and check the exhaust. Felt like the world's biggest idiot when a mechanic finally figured it out.
Anyway, changed out the pipes, put on flow through mufflers, and put headers in place of the manifolds. The manifolds didn't look cracked, but I didn't have them scoped either. All I can say is a 40hp pickup would have been small change to the difference in my coach. I didn't go with mandrel bent, but I went 3" all the way around, stuck with the duel mufflers up front.
I will say the headers are noisy and there is no way I can sort out the performance difference attributable to each of the three components: proper size pipes, the new mufflers, and the headers. However, I will say to me it was definitely worth doing. Every time I have to get on an interstate or go up a small hill it brings a smile to my face.
Properly functioning exhaust system? Incredibly important...
Thanks,
Jeremy Knezek
1976 Glenbrook
Birmingham, AL
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| Re: [GMCnet] mandrel bent [message #92632 is a reply to message #92618] |
Mon, 19 July 2010 22:19 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Jeremy,
I have heard some complaint of header noise. I for one have never experience
noise that was loud enough to mention.
What I have heard is the exhaust pulse sound as it leaks through the gasket
when they neglect to re torque the headers correctly.
You torque only the 4 in line bolts and leave the top center sung only.
We have noticed most of the noise complaint is the lack of proper gasket
around the engine hatch. Fix it and you'll shut up about engine noise, or
wait many years till your hearing fads away.
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] mandrel bent [message #92648 is a reply to message #92470] |
Tue, 20 July 2010 06:57 |
jknezek
Messages: 1057
Registered: December 2007
Karma: 5
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Senior Member |
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Interesting JimK. I'll check the bolts but I did them to spec last time and I remember leaving the top once just snugged. That being said, a few of them are a real pain to get at. I hear my headers most under low RPM acceleration, or if not the headers, certainly what seems to me to be a louder frequency at low rpm acceleration. I don't even notice them being louder at speed and neither does my wife. Rather than "header noise," I wonder if it could just be the difference between my old and new mufflers. Like I originally said, all the changes were done at once so I might be wrong about the cause of the noise.
Either way, I'm very pleased with my setup. And if it's a little louder leaving a stoplight well... I do feel bad for the guy next to me. However, the guy behind me is very, very thankful I made the change.
Thanks,
Jeremy Knezek
1976 Glenbrook
Birmingham, AL
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| Re: [GMCnet] mandrel bent [message #92748 is a reply to message #92648] |
Tue, 20 July 2010 20:38 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Jeremy,
After the carbon starts building up in the pipe, they will quiet down some
and you'll as get accustom to the noise and think it quieted down.
On Tue, Jul 20, 2010 at 4:57 AM, Jeremy <jtknezek@hotmail.com> wrote:
>
>
> Interesting JimK. I'll check the bolts but I did them to spec last time and
> I remember leaving the top once just snugged. That being said, a few of them
> are a real pain to get at. I hear my headers most under low RPM
> acceleration, or if not the headers, certainly what seems to me to be a
> louder frequency at low rpm acceleration. I don't even notice them being
> louder at speed and neither does my wife. Rather than "header noise," I
> wonder if it could just be the difference between my old and new mufflers.
> Like I originally said, all the changes were done at once so I might be
> wrong about the cause of the noise.
>
> Either way, I'm very pleased with my setup. And if it's a little louder
> leaving a stoplight well... I do feel bad for the guy next to me. However,
> the guy behind me is very, very thankful I made the change.
> --
> Thanks,
> Jeremy Knezek
> 1976 Glenbrook
> Birmingham, AL
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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