I bought a 73. Because it was too nice to see it become a chicken coop in Iowa. Engine seems good. With compression readings from 135 to 145 psi. So one of the things that will make it more desirable is EFI. I DO NOT like lifting 455 intakes. So. As to EFI. Pro's/cons of blocking off of the heat passage? Rebuilding everything but the engine. Hoping that maybe I can make a dollar an hour. Bob Dunahugh
Blocking the heat passage in the intake manifold for EFI.
- Thread starter Bob Dunahugh
- Start date
Bob,
So often the muffler will give out and the baffels will create a restrition
on one side causing a big heat passage under the carberator.
Blocking off the passage is the most desirable way to control this.
You'll need to get an electric choke and a special electricl conector.
So far the easiest way to block off the exaust is at the intake using a
SS304 plat and a matchig intake gasket from Springfield, which we provide.
>
> I bought a 73. Because it was too nice to see it become a chicken coop in
> Iowa. Engine seems good. With compression readings from 135 to 145 psi. So
> one of the things that will make it more desirable is EFI. I DO NOT like
> lifting 455 intakes. So. As to EFI. Pro's/cons of blocking off of the heat
> passage? Rebuilding everything but the engine. Hoping that maybe I can
> make a dollar an hour. Bob Dunahugh
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
So often the muffler will give out and the baffels will create a restrition
on one side causing a big heat passage under the carberator.
Blocking off the passage is the most desirable way to control this.
You'll need to get an electric choke and a special electricl conector.
So far the easiest way to block off the exaust is at the intake using a
SS304 plat and a matchig intake gasket from Springfield, which we provide.
>
> I bought a 73. Because it was too nice to see it become a chicken coop in
> Iowa. Engine seems good. With compression readings from 135 to 145 psi. So
> one of the things that will make it more desirable is EFI. I DO NOT like
> lifting 455 intakes. So. As to EFI. Pro's/cons of blocking off of the heat
> passage? Rebuilding everything but the engine. Hoping that maybe I can
> make a dollar an hour. Bob Dunahugh
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
Bob,
The only issue I have with my blocked crossover is warm-up from stone-cold startup. Engine starts fine, then after about 30 seconds seems like its
running too lean, so I have added a bit more fuel to make it run smooth. But when I go to drive off, it chugs and blows some black smoke for a second
or two, then its fine for the rest of the day.
So what I think is happening is that fuel is condensing on the cold manifold walls leaving the mixture a bit lean. Then when I goto pull away, the
increased airflow in the intake picks up the condensed fuel making it way too rich until the condensed fuel is gone, then it runs fine. So what I do
is from a cold startup, I rev the engine to about 1500-2000 rpm for a few seconds to clear the manifold. It blows some black smoke for a couple
seconds, then its fine.
If the manifold wasn't blocked, I'm guessing the exhaust would heat the intake manifold quickly and this would not happen.
I've tried setting a high idle to keep the airspeed in the manifold higher, but that did not seem to help. Any ideas or suggestions are welcome... I
hate the black smoke to clear the extra fuel.
I would think a carb engine would have the same issues with a blocked manifold.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
The only issue I have with my blocked crossover is warm-up from stone-cold startup. Engine starts fine, then after about 30 seconds seems like its
running too lean, so I have added a bit more fuel to make it run smooth. But when I go to drive off, it chugs and blows some black smoke for a second
or two, then its fine for the rest of the day.
So what I think is happening is that fuel is condensing on the cold manifold walls leaving the mixture a bit lean. Then when I goto pull away, the
increased airflow in the intake picks up the condensed fuel making it way too rich until the condensed fuel is gone, then it runs fine. So what I do
is from a cold startup, I rev the engine to about 1500-2000 rpm for a few seconds to clear the manifold. It blows some black smoke for a couple
seconds, then its fine.
If the manifold wasn't blocked, I'm guessing the exhaust would heat the intake manifold quickly and this would not happen.
I've tried setting a high idle to keep the airspeed in the manifold higher, but that did not seem to help. Any ideas or suggestions are welcome... I
hate the black smoke to clear the extra fuel.
I would think a carb engine would have the same issues with a blocked manifold.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
I'm very aware of carb icing. Is an EFI system less prone to this issue? I really don't think so. And I'm sure there are more GMC's that have never had the block plates installed. Carb, or EFI. I installed the block offs in our 78 with EFI. As it sets in a climate controlled shop. And we don't take it out when it's cold out. The 73 is getting sold when completed. Bob Dunahugh
________________________________
From: Bob Dunahugh
Sent: Friday, May 4, 2018 11:06 PM
To: gmclist
Subject: Blocking the heat passage in the intake manifold for EFI.
I bought a 73. Because it was too nice to see it become a chicken coop in Iowa. Engine seems good. With compression readings from 135 to 145 psi. So one of the things that will make it more desirable is EFI. I DO NOT like lifting 455 intakes. So. As to EFI. Pro's/cons of blocking off of the heat passage? Rebuilding everything but the engine. Hoping that maybe I can make a dollar an hour. Bob Dunahugh
________________________________
From: Bob Dunahugh
Sent: Friday, May 4, 2018 11:06 PM
To: gmclist
Subject: Blocking the heat passage in the intake manifold for EFI.
I bought a 73. Because it was too nice to see it become a chicken coop in Iowa. Engine seems good. With compression readings from 135 to 145 psi. So one of the things that will make it more desirable is EFI. I DO NOT like lifting 455 intakes. So. As to EFI. Pro's/cons of blocking off of the heat passage? Rebuilding everything but the engine. Hoping that maybe I can make a dollar an hour. Bob Dunahugh
I know in a cold weather , the problem is going to happen.
Trade off as to if this is worth the problem or not.
Since the engine will be running in hot mode majorityb of the time, one
might favor the problem at cold .
> I'm very aware of carb icing. Is an EFI system less prone to this issue?
> I really don't think so. And I'm sure there are more GMC's that have never
> had the block plates installed. Carb, or EFI. I installed the block offs in
> our 78 with EFI. As it sets in a climate controlled shop. And we don't take
> it out when it's cold out. The 73 is getting sold when completed. Bob
> Dunahugh
>
>
> ________________________________
> From: Bob Dunahugh
> Sent: Friday, May 4, 2018 11:06 PM
> To: gmclist
> Subject: Blocking the heat passage in the intake manifold for EFI.
>
>
>
> I bought a 73. Because it was too nice to see it become a chicken coop in
> Iowa. Engine seems good. With compression readings from 135 to 145 psi. So
> one of the things that will make it more desirable is EFI. I DO NOT like
> lifting 455 intakes. So. As to EFI. Pro's/cons of blocking off of the heat
> passage? Rebuilding everything but the engine. Hoping that maybe I can
> make a dollar an hour. Bob Dunahugh
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
Trade off as to if this is worth the problem or not.
Since the engine will be running in hot mode majorityb of the time, one
might favor the problem at cold .
> I'm very aware of carb icing. Is an EFI system less prone to this issue?
> I really don't think so. And I'm sure there are more GMC's that have never
> had the block plates installed. Carb, or EFI. I installed the block offs in
> our 78 with EFI. As it sets in a climate controlled shop. And we don't take
> it out when it's cold out. The 73 is getting sold when completed. Bob
> Dunahugh
>
>
> ________________________________
> From: Bob Dunahugh
> Sent: Friday, May 4, 2018 11:06 PM
> To: gmclist
> Subject: Blocking the heat passage in the intake manifold for EFI.
>
>
>
> I bought a 73. Because it was too nice to see it become a chicken coop in
> Iowa. Engine seems good. With compression readings from 135 to 145 psi. So
> one of the things that will make it more desirable is EFI. I DO NOT like
> lifting 455 intakes. So. As to EFI. Pro's/cons of blocking off of the heat
> passage? Rebuilding everything but the engine. Hoping that maybe I can
> make a dollar an hour. Bob Dunahugh
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
