[GMCnet] Doug Thorley Headers D755Y vs 355YC

[Beach Coach]

Can anyone clarify which header; the D755Y and/or 355YC; can be used as replacements for the exhaust manifolds? The only difference between the two
headers is that the D755Y is made with 16 gauge steel and the 355YC is made with 14 gauge steel. The sales specs for both headers are stating that
they are a fit for the GMC Motorhome 1973 - 1978.

Thanks

Hugh MacDougall, Antigonish Nova Scotia Canada, 1975 Eleganza II
--
hugh MacDougall
Antigonish, Nova Scotia
1975 Eleganza II, 1977 Trans Mode


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[John Wright]

Hugh,
The one that has been used over the years has been the 355YC version and it does have the thicker tubing which is what you need. Unsure that thorley headers are still in production, Jim K now markets the Doug's headers and both ceramic and SS headers are available and the price difference is small.

http://www.appliedgmc.com/prod.itml/icOid/1610

http://www.appliedgmc.com/prod.itml/icOid/672

Contact Jim with your questions.

JR Wright
GMC Great Laker MHC
GMC Eastern States Charter Member
GMCGL Tech Editor
GMCMI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan

[Jim Kanomata]

We sell both, however the 355 is not produced but once a year so the
availability is the problem.
The 355 is primarily designed for the 403 engine and few years ago the late
Joe Mondello and I had the header designed for the 455. This has the O2
bung on the collectors and the flange at the collector has a built in
conical end to allow a perfect seal when aligning the collector to the
header and does away with the donut gasket that crumbles as it gets older.
The 355Y does not always have the 14 gauge , just published.
There is also a trick to torquing the headers that we explain when you
acquire it.

--
Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[Larry]

Just Curious, does the newer design allow removal of the Transmission governor WITHOUT having to remove that drivers side header. IIRC that has/was a
problem?
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.

[Jim Kanomata]

We can provide you a SS header that will allow changing of Governor w/o
removing header.
I know the advantage and disadvantage of that unit, plus how often do you
need to replace the governor by itself

--
Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[Larry]

IMHO, you only need to have one Governor gear go out for that header to pay for itself. Lots of us carry an extra gear and there have been a number of
inquiry's on this net where the trans would not shift out of first and it ended up being that governor gear. Just say'n...

[James Hupy]

There is a direct relationship between governor gears, speedometer cables,
transmission shift cables and headers. It is kind of a "Yeahh-Boooo" one.
Let's say you have a cracked cast iron exhaust manifold, can't find a
replacement, so, you choose to install a set of headers. If you spend a bit
of time under the hatch, you will notice that a header tube runs parallel
and quite close to the speedometer cable, especially if you have a gearing
change in the final drive and install the correction gearbox with the exit
cable up instead of down. All that header heat melts the outer covering of
the speedometer cable, fries the cable lube and before long, the cable
freezes up. This shears the governor gear, and you need to remove the
governor to fix the gear. So, along comes the bright idea to move that
header tube to provide clearance to remove the governor. Ahhh Haaaa,
problem solved, right? But wait, when the header got re-designed, one of
the tube now comes close to the transmission selector cable. Guess what
happens, next. The shift cable does what the speedometer cable did, and you
can't put your transmission in gear. All that I am saying here is that when
your headers are installed, your job is only half done. You need to make
some effective heat shields to protect those cables, no matter which design
you choose. If not, don't say you didn't read it here before you are broken
down beside the road.
Jim Hupy
Salem, Or
78 GMC ROYALE 403 with reduction box, Doug Thorley headers, and new
speedometer gear and governor gear. Yes, I learned the hard way, but you
don't have to.

[Jim Kanomata]

--
Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[Larry]

James Hupy wrote on Thu, 09 November 2017 14:20

> On Nov 9, 2017 11:28 AM, "Larry" wrote:
>
> IMHO, you only need to have one Governor gear go out for that header to pay
> for itself. Lots of us carry an extra gear and there have been a number of
> inquiry's on this net where the trans would not shift out of first and it
> ended up being that governor gear. Just say'n...
> --
> Larry
> 78 Royale w/500 Caddy
> Menomonie, WI.
>
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Good points Jim. It really has everything to do with paying attention to details, and for other things on our GMC...preventive maintenance. JMHO

[D C _Mac_ Macdonald]

Here's an eBay item that very well might help.

http://www.ebay.com/itm/302333843484

The seller here has other sizes.


D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com



[http://i.ebayimg.com/images/i/302333843484-0-1/s-l1000.jpg]<http://www.ebay.com/itm/302333843484>

DEI Heat Protection Sheath Aluminized Sleeving 1" x 36" Wire & Hose Shielding | eBay<http://www.ebay.com/itm/302333843484>
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Heat Sheath is constructed from a Hi-Temp fiberglass fabric bonded to an aluminized material with sides sewn together forming a sleeve. Heat Sheath will reflect up to 90% of the radiant heat and insulates up to 500°F direct continuous heat. | eBay!





________________________________
From: Gmclist <gmclist...@list.gmcnet.org> on behalf of James Hupy <james...@gmail.com>
Sent: Thursday, November 9, 2017 14:20
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] Doug Thorley Headers D755Y vs 355YC

[John Heslinga]

Here is the strategy I used to protect the Speedometer cable from the heat of the headers. It can be used with both types of headers, and seems to
have protected my cable well. It works by both being a heat shield and using convection airflow through the tubing. Check the entire album as it
describes the strategy.
http://www.gmcmhphotos.com/photos/g7112-speedometer-cable-heat-protection.html

Sample photo
[url=http://www.gmcmhphotos.com/photos/speedometer-cable-heat-protection/p63940-governor-end-of-speedometer-cable.html[/url]

--
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta