Making your own heat shield
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Making your own heat shield
Well after installing the BG carb and experiencing flooding after shutdown and constantly changing idle speed I chased down the gosts to no heat shield.
As per LARS
BG and Holley carbs need a reflective heat shield installed under the carb: The accelerator pump wells are close enough to the hot manifold that the fuel in the pump wells will boil after hot engine shutdown. As the fuel boils and vaporizes, it pushes fuel out the accel discharge nozzles, flooding the engine after shutdown.
Well I tried to follow his example.
Holley builds a shield, but it does not fit correctly. Seen here is a modified Holley shield: I have trimmed about an inch off the forward edge so it will clear the thermostat housing. The rear edge has been trimmed forward. The right side of the shield has been cut inwards to prevent the throttle shafts from binding on the shield. The right corners have been trimmed at a 45-degree angle to clear the carb inlet line. Finally, the shield has been bent downwards and “jogged” so that the accel pump levers will not hit the shield: If you install a flat shield, the accel pump levers will hit the shield, and will be partially depressed. This will cause an off-idle flat spot and stumble.
And I ended with this.
Holley Heat Shield (with gaskets): HLY-108-70 $35.95 and 2 days wasted away.
As per LARS
BG and Holley carbs need a reflective heat shield installed under the carb: The accelerator pump wells are close enough to the hot manifold that the fuel in the pump wells will boil after hot engine shutdown. As the fuel boils and vaporizes, it pushes fuel out the accel discharge nozzles, flooding the engine after shutdown.
Well I tried to follow his example.
Holley builds a shield, but it does not fit correctly. Seen here is a modified Holley shield: I have trimmed about an inch off the forward edge so it will clear the thermostat housing. The rear edge has been trimmed forward. The right side of the shield has been cut inwards to prevent the throttle shafts from binding on the shield. The right corners have been trimmed at a 45-degree angle to clear the carb inlet line. Finally, the shield has been bent downwards and “jogged” so that the accel pump levers will not hit the shield: If you install a flat shield, the accel pump levers will hit the shield, and will be partially depressed. This will cause an off-idle flat spot and stumble.
And I ended with this.
Holley Heat Shield (with gaskets): HLY-108-70 $35.95 and 2 days wasted away.
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
The expensive Holley shield bottomed out on the manifold runners and was impossible for me to create so I went to Home Depot and for $4.71 I bought
In order for the “jogged” shield to clear the base gasket, the gasket “ears” must be trimmed. Shown here is a trimmed base gasket that will allow the bent shield to fit properly.
Engine used to run cold idle 850RPM and warm idle 1200RPM. Now it's always 850RPM. Thanks LARS!
In order for the “jogged” shield to clear the base gasket, the gasket “ears” must be trimmed. Shown here is a trimmed base gasket that will allow the bent shield to fit properly.
Engine used to run cold idle 850RPM and warm idle 1200RPM. Now it's always 850RPM. Thanks LARS!
Last edited by Cali,68,L-79; Oct 24, 2004 at 09:47 PM.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
your bends came out great!!!!!!! mine are about 5/8" in height i was shooting for 3/8" but that didn't happen... i am thinking about a 1/2 phenolic spacer to go along with this, what are you going to do?? paper gasket or something else?
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
I ran the 1/2" Holley gasket and then took the heat shield sandwiched between to 1x4 wood blocks then put the whole thing in a vise and made a small bend. Took the contraption apart and checked it under the carb to make sure it cleared the acel pump rods on both ends. the "jogging" LARS refers to above is impossible without the proper tooling and as expensive as that would be I'd go for a simple bend. If you look at the last shot the heat shield is just about invisible. There is the 1/2" on the manifold then the heat shield then another thin holley gasket.
David
David
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Flooding after shutdown gone. Idle is stable at 850RPM. Ran car thru the streets 30 minuts and idles 20 minutes after that and it never creeped over 180 degrees and 850RPM. Also for the first time was able to get a nice screech at 60mph when shifting into 2nd gear, so yeah runs alot better than with that torquerII/ Eldebrock 600cfm carb.
Race Director
Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
i hope mine comes out as good looking as your stuff, i pick up my engine and 700r4 at the end of this week i'm psyched...does that "jog" in the front go up? (it may be an optical illusion) thks bob
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
No Bob both go down about 10 degrees, just enough to clear the acl. pump rods. The difference in space between the runner and the pump rod is tight so go with a little bend, mock it up and if not enough do another bend. P.S. what kind of shield are you goin with?
David
David
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Race Director
Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
16 ga stainless steel, all the cutting, holes and bends are done and it looks great on the carb, manifold is with engine builder so i just have to wait a couple or more days to see if my handi work was upto the challenge and do some finish trimming.
Race Director
Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by Cali,68,L-79
BOB what's the story with the engine? i.e. you building a stroker?
Race Director
Joined: Mar 2001
Posts: 11,322
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From: Living in the Hartland
Is pretty amazing that little heat sheild makes a diff, might do one up for my vette. What would be best is a return line like an EFI system has, just got done with a new manfold install on my formula, the fuel rails get hot as heck after shut down but are cool to the touch when the car is one with 50 lbs of pressure.
Le Mans Master
Joined: Oct 2002
Posts: 5,714
Likes: 6
From: Silver City NM
St. Jude Donor '05-'07
Nice fabrication Dave! Just curious...did you try the factory heat shield Chevy makes for Holley carbs? Part #3969835. And yes, it is made for a double pumper. Thry also make one for the Quadrajunk #3982944.
Dep
Dep
Drifting
Joined: Oct 2001
Posts: 1,699
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From: Westampton NJ
Originally Posted by DJ Dep
Nice fabrication Dave! Just curious...did you try the factory heat shield Chevy makes for Holley carbs? Part #3969835. And yes, it is made for a double pumper. Thry also make one for the Quadrajunk #3982944.
Dep
Dep
Le Mans Master
Joined: Oct 2002
Posts: 5,714
Likes: 6
From: Silver City NM
St. Jude Donor '05-'07
Originally Posted by rainman69
Where would one find one of these Part #3969835's? I tried a Google search and only found one for $325...
Check with Scoggin Dickey...
http://www.sdpc2000.com/
Dep
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
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From: San Diego CA
Dep yes I did you can see it up there about the 2nd or 3rd photo and I destroyed it plus wasted $36 and 2 days. This plate cost under $5 and 4 hours to make.
David
David
Originally Posted by DJ Dep
Nice fabrication Dave! Just curious...did you try the factory heat shield Chevy makes for Holley carbs? Part #3969835. And yes, it is made for a double pumper. Thry also make one for the Quadrajunk #3982944.
Dep
Dep
