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| [GMCnet] Headers question [message #101050] |
Sun, 26 September 2010 13:29  |
KB
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Registered: September 2009
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Our "new" beast has a pretty rusty exhaust system. In the not too distant future,
we'll need to replace it. My question: what's the difference in the way headers vs
the original cast iron manifold hook up?
More specifically, is it feasible to replace the exhaust pipes and mufflers now,
and then in the future go to headers if necessary? Or, would we end up having
to replace the exhaust system again to add headers later?
confused (as usual),
Karen
1973 23' Patience Tester
1975 26' Junkyard Karma
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] Headers question [message #101055 is a reply to message #101050] |
Sun, 26 September 2010 13:47  |
Steven Ferguson
Messages: 3447
Registered: May 2006
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You can do it either way. Not switching to headers now just means you
will have to buy new pipes to go between the header collectors and the
mufflers when you install the headers at a later date. Very doable.
I used the cast iron headers and three inch pipes, elilminated the
two mufflers beneath the pass area, and rear mounted a Flowmaster
muffler with a heat shield in the rear. Here's pix:
http://www.gmcmhphotos.com/photos/showgallery.php?cat=3170
The only thing you gain with headers is better sealing. A lot of
folks have problems with the cast iron manifolds leaking, especially
if they have been leaking for a long time and the leaks have eroded
the head or manifold mating surfaces.
On Sun, Sep 26, 2010 at 11:29 AM, KB <kab7@sonic.net> wrote:
> Our "new" beast has a pretty rusty exhaust system. In the not too distant future,
> we'll need to replace it. My question: what's the difference in the way headers vs
> the original cast iron manifold hook up?
>
> More specifically, is it feasible to replace the exhaust pipes and mufflers now,
> and then in the future go to headers if necessary? Or, would we end up having
> to replace the exhaust system again to add headers later?
>
> confused (as usual),
>
> Karen
> 1973 23' Patience Tester
> 1975 26' Junkyard Karma
>
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
Sierra Vista, AZ
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| Re: [GMCnet] Headers question [message #101061 is a reply to message #101050] |
Sun, 26 September 2010 15:14 |
KB
Messages: 1262
Registered: September 2009
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Thanks Steve. Turns out this is a much less academic question than I thought.
The other day, I had a backfire event (long dumb story). Scared the heck out of me.
Thought it hadn't done any obvious damage at the time, but looking today, we find one
of the mufflers was blown out. Oops. Unfortunately, if we can't get this
fixed asap, we won't be able to take it to Treasure Island. :-( Bad timing.
Rats.
Karen
1973 23' Patience Tester
1975 26' Junkyard Karma
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] Headers question [message #101062 is a reply to message #101050] |
Sun, 26 September 2010 15:18 |
Gary Casey
Messages: 448
Registered: September 2009
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Hopefully someone will correct me if I'm wrong: If the cast iron manifolds have
run this long without cracking, I'll bet they'll never crack. And therefore, I
don't think it is worth the time and money to change over to headers. As I
understand it, the big advantage of headers in our application is that they
seldom crack. Headers, because of the thin wall, will usually make more noise
and I think the flange is more apt to not be flat. If the iron manifolds don't
leak at the flange or have a crack I would leave well enough alone - at least if
it were my coach. Mine already had headers and I'm struggling with leaks at the
gasket surface.
Gary Casey
from Karen:
Our "new" beast has a pretty rusty exhaust system. In the not too distant
future,
we'll need to replace it. My question: what's the difference in the way headers
vs
the original cast iron manifold hook up?
More specifically, is it feasible to replace the exhaust pipes and mufflers now,
and then in the future go to headers if necessary? Or, would we end up having
to replace the exhaust system again to add headers later?
confused (as usual),
Karen
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GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] Headers question [message #101067 is a reply to message #101062] |
Sun, 26 September 2010 16:29 |
Steven Ferguson
Messages: 3447
Registered: May 2006
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Gary,
I agree about the cracks, if they're in good shape, keep 'em.
Headers make no measurable difference that I could tell over the 3"
pipes I installed. However, I was referring to erosion caused by a
previous leak. Like water does to earth, exhaust leaks will erode the
header or head surface, or both.
Take a good look at the offending side and check for straightness, or
perhaps a surface that isn't quite flat. A deep hacksaw cut in the
flange, but not through, will allow a header flange to seal better to
the head. Sort of allows it to flatten out easier. The cut should be
between the pipes on the flange.Another method of flattening out the
mounting flange is with a large belt sander.
You may also have erosion on the cyl head. Removal is necessary to
machine it down until the surface is completely flat. I think that
with the gaskets you are using, you should get a good seal unless
something else is wrong.
Whichever exhaust manifolds you use, you need to retorque several
times after heating and cooling cycles.
On Sun, Sep 26, 2010 at 1:18 PM, Gary Casey <casey.gary@yahoo.com> wrote:
> Hopefully someone will correct me if I'm wrong: If the cast iron manifolds have
> run this long without cracking, I'll bet they'll never crack. And therefore, I
> don't think it is worth the time and money to change over to headers. As I
> understand it, the big advantage of headers in our application is that they
> seldom crack. Headers, because of the thin wall, will usually make more noise
> and I think the flange is more apt to not be flat. If the iron manifolds don't
> leak at the flange or have a crack I would leave well enough alone - at least if
> it were my coach. Mine already had headers and I'm struggling with leaks at the
> gasket surface.
> Gary Casey
>
> from Karen:
> Our "new" beast has a pretty rusty exhaust system. In the not too distant
> future,
> we'll need to replace it. My question: what's the difference in the way headers
> vs
> the original cast iron manifold hook up?
>
> More specifically, is it feasible to replace the exhaust pipes and mufflers now,
> and then in the future go to headers if necessary? Or, would we end up having
> to replace the exhaust system again to add headers later?
>
> confused (as usual),
>
> Karen
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
Sierra Vista, AZ
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| Re: [GMCnet] Headers question [message #101069 is a reply to message #101050] |
Sun, 26 September 2010 16:42 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| KB wrote on Sun, 26 September 2010 11:29 |
... More specifically, is it feasible to replace the exhaust pipes and mufflers now,
and then in the future go to headers if necessary? Or, would we end up having
to replace the exhaust system again to add headers later? ...
|
<http://www.gmcmotorhome.info/engine.html#manifold>
Basically if they work, keep the manifolds.
-- It is cheaper. (BUT replacement manifolds might NOT be cheaper...)
-- Performance isn't really any difference. I seem to remember someone (Arch?) posting Dyno results on headers/manifolds. While they DO that show a HP gain for headers, the manifolds have better low end torque.... Pretty much a wash, but I like the torque!
-- When going from manifolds to headers you'll need to cut off a little of the pipe... easier than going the other way!
-- Some have been thinking (data is not in) that headers may add to the heat problems that contribute to vapor lock.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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