Heat shield for Holley 3810

[Alexander D.]

Today I ordered a brand new Holley 3810 carb from Crane's Corvette for my '67 Coupe with 300hp engine w/ OEM cast iron manifold. I'm told the new carb comes with a gasket in the box.

I read here that I should also install a "heat shield" between the manifold and the carb gasket to reduce the chances of percolation on hot days. However, I'm having trouble determining what this "heat shield" is looks like so I can order the correct part.

I found an eBay listing for a "1964-67 HOLLEY CARB TO INTAKE GASKET CORVETTE 3124 2818 3247 3367 3810 ALUMINUM"

https://www.ebay.com/itm/1964-67-HOLLEY-CARB-TO-INTAKE-GASKET-CORVETTE-3124-2818-3247-3367-3810-ALUMINUM/251912499498?hash=item3aa727b12a:g:eNoAAOSwpDdVJqiU

This is not expensive at $6.95. This single piece has two round holes and one larger slotted hole. However, in the listing photo it is grayish-black, not reflective metal. I'm suspecting this is merely the gasket that's included with the new carb, so isn't what I need.

I searched the Holley website for "heat shield"and got this:

https://www.holley.com/products/fuel...s/parts/108-70

This is a 3-piece "kit" ($34.30) including two gasket-sized pieces with a single large square hole in the middle (i.e. no slot or holes), and one large aluminum plate that would cover a fair bit of the intake manifold. Although I imagine this would be quite effective at shielding the carb from manifold/engine heat, it sure wouldn't look stock, and might interfere with linkages, etc.

So, what is the proper "heat shield" I should get for my new Holley 3810?

Thanks,

[Timothy B.]

Re: Heat shield for Holley 3810

It's shown in the AIM for your car if you have one. The arrangement is intake manifold, then gasket with the hot slot passage then a stainless shield that goes directly beneith the carburetor.

If you do some research in the archives you will probably find a picture of the shield. Do not run the engine until you have the stainless shield in place because the hot slot exhaust gasses will damage the aluminum carburetor. Many people block the hot slot under the carburetor, there is information about that also.

I am sure there is a picture in the aftermarket Paragon catalogue.

[Larry M.]

Re: Heat shield for Holley 3810

Alexander:



For your 300 HP car with the cast iron manifold, I would instead install plugs (2) in the hot slot gas holes in the manifold that are under the carb.

You can carefully use Dorman welch plugs to seal the hot gas holes, or as some have done, pull the manifold and have these holes drilled and tapped for a threaded plug with a recessed hex drive connection (Allen wrench needed to thread in).

Either of these is far better than installing the heat barrier plate. JohnZ and others have said without the plugs, warpage of the carb base may result for high heat and regular use.....that this was a factory mistake to approve this design for regular production. Maybe OK for Montana in the winter, but not for Texas in the summer.

Probably not what you want to hear, but something you should hear and act on.

Larry

[Alexander D.]

Re: Heat shield for Holley 3810

Alexander:



For your 300 HP car with the cast iron manifold, I would instead install plugs (2) in the hot slot gas holes in the manifold that are under the carb.

You can carefully use Dorman welch plugs to seal the hot gas holes, or as some have done, pull the manifold and have these holes drilled and tapped for a threaded plug with a recessed hex drive connection (Allen wrench needed to thread in).

Either of these is far better than installing the heat barrier plate. JohnZ and others have said without the plugs, warpage of the carb base may result for high heat and regular use.....that this was a factory mistake to approve this design for regular production. Maybe OK for Montana in the winter, but not for Texas in the summer.

Probably not what you want to hear, but something you should hear and act on.

Larry

Hi Larry,

Most interesting info!

Where do I get Dorman welch plugs?

Can I install the plugs myself without risk of damage to the manifold?

When you say "plug the hot gas holes" do you mean the heat riser crossover passage in the manifold?

I should mention that I live in Vancouver, BC in the Pacific Northwest. In our maritime climate we rarely get the 90+ temperatures that are common in places like Texas, Florida, or S. California. We might get 5 days a year where the temps go above 85 degrees. I never got heat soak/vapor lock/percolation here, but have suffered it during road trips elsewhere.

So,I'd prefer to inoculate my car from the possibility of percolation/vapor lock during those times like last weekend when we traveled to Pasco, WA. The car vapor locked on me twice and I had to wait 15-25 minutes before it would re-start. I was very hot there, with 90-95 degrees each day! The first time I just waited it out until the car cooled down. The second time I put ice packs from my cooler on the gas line to the carb, which helped reduce the time before the car would restart.

Your advice is always appreciated, so I look forward to your thoughts on this.

[Joe L.]

Re: Heat shield for Holley 3810

Hi Larry,

Most interesting info!

Where do I get Dorman welch plugs?

Can I install the plugs myself without risk of damage to the manifold?

When you say "plug the hot gas holes" do you mean the heat riser crossover passage in the manifold?

I should mention that I live in Vancouver, BC in the Pacific Northwest. In our maritime climate we rarely get the 90+ temperatures that are common in places like Texas, Florida, or S. California. We might get 5 days a year where the temps go above 85 degrees. I never got heat soak/vapor lock/percolation here, but have suffered it during road trips elsewhere.

So,I'd prefer to inoculate my car from the possibility of percolation/vapor lock during those times like last weekend when we traveled to Pasco, WA. The car vapor locked on me twice and I had to wait 15-25 minutes before it would re-start. I was very hot there, with 90-95 degrees each day! The first time I just waited it out until the car cooled down. The second time I put ice packs from my cooler on the gas line to the carb, which helped reduce the time before the car would restart.

Your advice is always appreciated, so I look forward to your thoughts on this.

Alexander------


It's not the heat riser cross-over passages that are being referred to here. On the forward side of the carburetor flange you will see a groove. On the ends of the groove are holes which pass through to the heat cross-over passage. The purpose of the groove and holes is to provide extra heat to the carburetor to improve fuel atomization, especially during warm up. You do not need this regardless of where you live. GM completely abandoned it after 1969. Many carburetors have been ruined by this feature.

There are two ways to plug the holes. The simplest method is to use welch (drive) plugs to plug the holes. As I recall, the size is 3/8". You should be able to get these at any good auto parts store. They are cup-shaped plugs that you can simply drive into the holes. Dorman is one manufacturer but there are others. You can also drill and tap the holes and install internal hex drive plugs. However, it's best to do this with the manifold off the engine so you can remove the drilling/tapping filings.

I would still install the stainless steel baffle plate between the carburetor and base gasket. It's not absolutely necessary with the heat slot decommissioned but I would still use it.

[Garwood A.]

Re: Heat shield for Holley 3810

Here is a good article from Lars on the other forum.
https://www.corvetteforum.com/forums...tle-plate.html

[Larry M.]

Re: Heat shield for Holley 3810

Alexander:

Good advice from Joe and Garwood. There is not much more to add.........but let me know if questions.

Larry

[William F.]

Re: Heat shield for Holley 3810

I think the correct gasket for a 300 hp sb has four holes ( and the stainless heat shield plate). the higher performance sb's use the gasket with 2 holes and one elongated hole on one side. SB's with aluminum intakes do not use the additional stainless steel plate between gasket and carb.

[Joe L.]

Re: Heat shield for Holley 3810

I think the correct gasket for a 300 hp sb has four holes ( and the stainless heat shield plate). the higher performance sb's use the gasket with 2 holes and one elongated hole on one side. SB's with aluminum intakes do not use the additional stainless steel plate between gasket and carb.

William------


Yes, the correct gasket and stainless steel baffle for 66-67 with 300 HP had 4 holes. For L-79 there was an elongated opening on one side and 2 holes on the other and no stainless steel baffle was used.

[Alexander D.]

Re: Heat shield for Holley 3810

Here is a good article from Lars on the other forum.
https://www.corvetteforum.com/forums...tle-plate.html

Thanks Garwood for the link to Lars' article. Very informative! Amazing what I'm learning from this forum, and guys like you.

[Darryl D.]

Re: Heat shield for Holley 3810

Alexander:



For your 300 HP car with the cast iron manifold, I would instead install plugs (2) in the hot slot gas holes in the manifold that are under the carb.

You can carefully use Dorman welch plugs to seal the hot gas holes, or as some have done, pull the manifold and have these holes drilled and tapped for a threaded plug with a recessed hex drive connection (Allen wrench needed to thread in).

Either of these is far better than installing the heat barrier plate. JohnZ and others have said without the plugs, warpage of the carb base may result for high heat and regular use.....that this was a factory mistake to approve this design for regular production. Maybe OK for Montana in the winter, but not for Texas in the summer.

Probably not what you want to hear, but something you should hear and act on.

Larry

I have a 1965 with the original 300 h.p. engine with the original AFB. Is this a problem for these carbs and intakes of just the Holley equipped cars?

[Tom D.]

Re: Heat shield for Holley 3810

Darryl: IMO you should create a new thread and change the subject line to include 1965, 300 HP and AFB exhaust heating issues...
Or, something like that. Refer folks looking at the bottom here to also look at your new posting. Use your link in this thread, perhaps...

[Darryl D.]

Re: Heat shield for Holley 3810

Darryl: IMO you should create a new thread and change the subject line to include 1965, 300 HP and AFB exhaust heating issues...
Or, something like that. Refer folks looking at the bottom here to also look at your new posting. Use your link in this thread, perhaps...

It is a pretty simple question that should have either a yes or no answer. I don't see a need to start a whole new thread for that.

[Joe L.]

Re: Heat shield for Holley 3810

I have a 1965 with the original 300 h.p. engine with the original AFB. Is this a problem for these carbs and intakes of just the Holley equipped cars?

Darryl------


1965 L-75 (300 HP) did not use a manifold with heat slot.

[Darryl D.]

Re: Heat shield for Holley 3810

Darryl------1965 L-75 (300 HP) did not use a manifold with heat slot.

Thank you.