Home » Public Forums » GMCnet » exhaust crossover
| exhaust crossover [message #209885] |
Tue, 04 June 2013 23:01  |
homer
Messages: 73
Registered: April 2011
Location: arizona/ BC canada
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not being to mechanically minded would some one explain to me why the exhaust cross-over is blocked off? what is the advantage/ what is gained by it, why was it not a feature in the original engine, still in the leaning curve.all-ways great info on the net thanks guys keep in coming. Homer :
homer
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| Re: exhaust crossover [message #209892 is a reply to message #209885] |
Tue, 04 June 2013 23:32  |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
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The exhaust crossover on carbureted American V8 engines
was used to heat the air/fuel mixture and help
atomize the fuel. This is useful in cold climates
and helps the engine warm up faster (and lower emissions).
The Old 455 has a giant crossover that many believe to
be excessively large. It also may boil the fuel
in the carburetor on hot days and make vaporlock worse.
If there is a fuel leak the exhaust crossover makes
it more likely to catch fire. The temperature of
the manifold above the crossover is hot enough to
melt plastic and many other materials.
There is also a crack that develops in the cast iron manifold
from all the heat.
When you consider all the above, it seems that blocking
the exhaust crossover is an excellent idea.
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: exhaust crossover [message #209893 is a reply to message #209892] |
Tue, 04 June 2013 23:42 |
homer
Messages: 73
Registered: April 2011
Location: arizona/ BC canada
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thanks Bill gives me a little more insight into the 455 never doing the cold climates makes great sense for me. Homer
homer
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| Re: [GMCnet] exhaust crossover [message #209941 is a reply to message #209912] |
Wed, 05 June 2013 10:15 |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
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So $50 for the Applied kit, pull the carb and intake off, install plates and new gaskets, and that's it? Are there other advantagee of the aluminum intake upgrade beside weight and crossover blockage?
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: [GMCnet] exhaust crossover [message #209953 is a reply to message #209892] |
Wed, 05 June 2013 11:03 |
Ron77
Messages: 91
Registered: August 2012
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There has also been discussion about if there is a muffler on each exhaust
bank, one will surely be more restrictive than the other, resulting in flow
equalization taking place in the crossover. By running both bank exhausts
into one muffler the flow should be equal or near equal, reducing the flow
through the crossover. Miguel had my system changed from two mufflers to
one, when we had to redo the system anyway.
Ron Johnson
77 Eleganza II
Escondido, CA
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Bill Wevers
Sent: Tuesday, June 04, 2013 9:32 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] exhaust crossover
The exhaust crossover on carbureted American V8 engines was used to heat the
air/fuel mixture and help atomize the fuel. This is useful in cold climates
and helps the engine warm up faster (and lower emissions).
The Old 455 has a giant crossover that many believe to be excessively large.
It also may boil the fuel in the carburetor on hot days and make vaporlock
worse.
If there is a fuel leak the exhaust crossover makes it more likely to catch
fire. The temperature of the manifold above the crossover is hot enough to
melt plastic and many other materials.
There is also a crack that develops in the cast iron manifold from all the
heat.
When you consider all the above, it seems that blocking the exhaust
crossover is an excellent idea.
Regards,
Bill
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| Re: [GMCnet] exhaust crossover [message #209965 is a reply to message #209953] |
Wed, 05 June 2013 12:09 |
Kathy and Fred Estabr
Messages: 55
Registered: May 2013
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If you are going to do the exhaust blockoff with the kit from Applied I
would suggest you ask Rob to describe the jig that he wrote about a couple
of weeks ago. It makes the job so much easier to remove and install and you
may not run into the problem I had with a gasket that slipped. I had to
remove everything and start over.
Fred Estabrook
Florence AZ
76 Ell
On Wed, Jun 5, 2013 at 9:03 AM, Ron Johnson <Ron77@gltcinsurance.com> wrote:
> There has also been discussion about if there is a muffler on each exhaust
> bank, one will surely be more restrictive than the other, resulting in flow
> equalization taking place in the crossover. By running both bank exhausts
> into one muffler the flow should be equal or near equal, reducing the flow
> through the crossover. Miguel had my system changed from two mufflers to
> one, when we had to redo the system anyway.
>
> Ron Johnson
> 77 Eleganza II
> Escondido, CA
>
>
> -----Original Message-----
> From: gmclist-bounces@temp.gmcnet.org
> [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Bill Wevers
> Sent: Tuesday, June 04, 2013 9:32 PM
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] exhaust crossover
>
>
>
> The exhaust crossover on carbureted American V8 engines was used to heat
> the
> air/fuel mixture and help atomize the fuel. This is useful in cold climates
> and helps the engine warm up faster (and lower emissions).
>
> The Old 455 has a giant crossover that many believe to be excessively
> large.
> It also may boil the fuel in the carburetor on hot days and make vaporlock
> worse.
>
> If there is a fuel leak the exhaust crossover makes it more likely to catch
> fire. The temperature of the manifold above the crossover is hot enough to
> melt plastic and many other materials.
>
> There is also a crack that develops in the cast iron manifold from all the
> heat.
>
> When you consider all the above, it seems that blocking the exhaust
> crossover is an excellent idea.
>
> Regards,
> Bill
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
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| Re: [GMCnet] exhaust crossover [message #209967 is a reply to message #209953] |
Wed, 05 June 2013 12:14 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Ron,
I'm sorry but I'm going to disagree with that "discussion", in my opinion as long as both mufflers are the same part number and have
the same internal design and are close to the same age I don't believe there would be any appreciable difference in the flow each
one would pass.
HOWEVER, if one muffler is plugged or partially plugged that will cause exhaust to cross from the cylinder bank with the plugged
muffler to the side with the clear muffler.
Regards,
Rob M.
-----Original Message-----
From: Ron Johnson
There has also been discussion about if there is a muffler on each exhaust
bank, one will surely be more restrictive than the other, resulting in flow
equalization taking place in the crossover. By running both bank exhausts
into one muffler the flow should be equal or near equal, reducing the flow
through the crossover. Miguel had my system changed from two mufflers to
one, when we had to redo the system anyway.
Ron
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] exhaust crossover [message #209975 is a reply to message #209968] |
Wed, 05 June 2013 13:44 |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
Karma: 0
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Senior Member |
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Thanks everyone for the feedback, I know there are more than a few strings on this topic in the forum, and esp Rob's contributions on the jig and the notes on manifold crack behaviour B4 and after the block off recently.
Like many, I'd rather do the Rockwell AL manifold, but have a few $$ priorities in front of that kind of expenditure. But the blocks using some method has been on my list since I bought this coach last year and drove it cross-country to get it home. Severe vapor lock in Florida turned to mild/intermittent after Cliff Golby installed an effective vapor return, but it was scary pulling uphill when I got to Wyoming-Utah-Idaho.
So, either do the kit now, or wait and do the AL manifold upgrade later. Hmmmm.
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: exhaust crossover [message #209977 is a reply to message #209885] |
Wed, 05 June 2013 13:59 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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I blocked mine this spring. It was not too difficult, but I did have to learn a few things.
the hardest part of the job, was it was messy. lots of stuff to clean up. have to clean up the gasket surfaces. just have to be careful. lots of shop vacuuming, and just plain cleaning.
You have to be prepared, if for some reason your intake is bad. however chances are it is just fine. Mine was just fine.
it cost me $50 to have the intake tanked and cleaned at the machine shop. I tried to clean it myself, and did an OK job. but for the $50, I got back a really clean nice manifold. then I had to spend $20 on paint to keep it looking nice.
a jig to pull and install the manifold is handy. I can see that. I did the same. I had my front seats out, so had plenty of room to work.
correct gaskets are a must. there might be some other opinions, but I found that NOT using the rubber end gaskets and just using RTV was important. (first install, the rubber moved on me, and had to re-do). get a good inspection mirror, and make sure the RTV filled up the gaps.
don't leave the hatch open overnight. animals might come in and eat your dinette, causing more work.
I used grey permatex RTV. I bought it as a caulking tube. that made things pretty easy. first time I tried to set the intake(when the next day I noticed the rubber pushed aside., I had the tube. took alot of squeezing. The caulk tube RTV made it really easy to get the right amount of rtv in place.
the kit from JimK I am sure works the same.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: [GMCnet] exhaust crossover [message #209993 is a reply to message #209967] |
Wed, 05 June 2013 17:03 |
Jim Bounds
Messages: 842
Registered: January 2004
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Rob is correct, if the mufflers are the same there should be no off balance issues. When we can, we too are installing single muffler systems, we put the muffler in the back. This way, the Y pipe acts as a balancer to eliminate the off balance condition thus allowing a better balance to the motor. I think also it is a positive to have the heat and noise associated with the muffler in the back provided there is good shielding. The main reason for mufflers "blowing up" is equalizing the pressure from the backfire. Sounds pretty cool too. What I have found to be true,
Jim Bounds
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________________________________
From: Rob Mueller <robmueller@iinet.net.au>
To: gmclist@temp.gmcnet.org
Sent: Wednesday, June 5, 2013 1:14 PM
Subject: Re: [GMCnet] exhaust crossover
Ron,
I'm sorry but I'm going to disagree with that "discussion", in my opinion as long as both mufflers are the same part number and have
the same internal design and are close to the same age I don't believe there would be any appreciable difference in the flow each
one would pass.
HOWEVER, if one muffler is plugged or partially plugged that will cause exhaust to cross from the cylinder bank with the plugged
muffler to the side with the clear muffler.
Regards,
Rob M.
-----Original Message-----
From: Ron Johnson
There has also been discussion about if there is a muffler on each exhaust
bank, one will surely be more restrictive than the other, resulting in flow
equalization taking place in the crossover. By running both bank exhausts
into one muffler the flow should be equal or near equal, reducing the flow
through the crossover. Miguel had my system changed from two mufflers to
one, when we had to redo the system anyway.
Ron
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| Re: exhaust crossover [message #209997 is a reply to message #209885] |
Wed, 05 June 2013 17:21 |
Cadillackeeper
Messages: 464
Registered: October 2012
Location: Fort Lauderdale
Karma: 1
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Those heat passages are to get to operating temps instantly.Nothing to do with fuel.That of course is a fallacy.
I would block them if you must but I personally would never mix metals like using copper or steel or aluminum on something cast iron.Everything needs to heat and cool together not seperately.
If you are in a 1/4 0r 1/8th mile vehicle then maybe a ported aluminum intake manifold Might be beneficial.
77 455 Elaganza II and 67 Animal, Built 500 Powered Eldo
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| Re: exhaust crossover [message #210060 is a reply to message #209885] |
Thu, 06 June 2013 08:27 |
Cadillackeeper
Messages: 464
Registered: October 2012
Location: Fort Lauderdale
Karma: 1
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Senior Member |
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Holy Crap,I have mine in the Animal blocked as I do live in Florida.No heat used in that car ever.But the motorhome I just don't know. The PO was pretty sharp and also used money to put in a bunch of places.This guy has property all over the place.Even a building on 42nd st in NY.They could in fact be blocked.I also see the heat riser on the exhaust is also gone!
77 455 Elaganza II and 67 Animal, Built 500 Powered Eldo
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| Re: exhaust crossover [message #210170 is a reply to message #209885] |
Fri, 07 June 2013 07:18 |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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Senior Member |
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Has there ever been a confirmed Rockwell equipped Vaporlock? Unfortunately my engine didn't run long enough with crossover to get some images, but I intend to take some this weekend with my FLIR thermal imaging camera(my crossovers are blocked). I will post them, perhaps we could do the same for a Rockwell installation and an unblocked cast iron manifold...I used the camera to discover my 75 Fiat spider misfire, one of the header pipes was not the same temp as the others, grossly obvious with the ir camera.
Sean and Stephanie
73 Ex-CanyonLands 26' #317 "Oliver"
Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD Honda 6500 inverter gen.
Colonial Travelers
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