Blocking off manifold's exhaust crossover

[Q1SVT]

think part of the problem is to only focus on the melting point of the metal. We need to look at the strength of the material over temperature. While aluminum (beer can or turkey pan) will melt near 1200F,

LOL, piston are in the combustion chamber and would see some of the hottest temperature and they do not get anywhere near five hundred degrees... Exhaust valves get hottest because the have no place to shed heat and are in the middle of the exhaust flow.

How often do you change your pistons? Aluminum heads...
Oils @ 300* begin to breakdown

The crossover never sees the exhaust temperature ... shoot it with a heat gun.
A blocked crossover stops the flow of exhaust into that area of the head from the exhaust pocket hole 1/8"-3/16". Gasses like water find the easiest path out.

SCE gaskets and Mr. Gasket both sell intake gaskets with blocked heat crossover. I confirmed several years ago that the gasket will not burn through at the heat crossover. Chuck

+1

 

[basstrix]

Good idea, but how do you access the bottom of the intake to measure the gap? Should I use some type of clay?

Just a feeler gauge...torque the intake down also.

 

[tony-muscle]

LOL, piston are in the combustion chamber and would see some of the hottest temperature and they do not get anywhere near five hundred degrees... Exhaust valves get hottest because the have no place to shed heat and are in the middle of the exhaust flow.

How often do you change your pistons? Aluminum heads...
Oils @ 300* begin to breakdown

The crossover never sees the exhaust temperature ... shoot it with a heat gun.
A blocked crossover stops the flow of exhaust into that area of the head from the exhaust pocket hole 1/8"-3/16". Gasses like water find the easiest path out.


+1

I am not the argumentative type but you are bringing the materials engineer on me so i will expand. First, keep in mind that i am backing up what i wrote with scientific data (btw, if you read the article it is very interesting since it talks about exhaust applications). And yes, the type of aluminum alloy used in pistons and cylinder heads is very different than that used in beer cans. The aluminum used for aerospace is also very different. Those alloys are designed to withstand very high temperatures compared to a beer can. Otherwise beer will be very expensive.... Just throwing this out there since you brought it up.
Again not picking an argument here and by no means saying that a beer can wont work. I have heard of many people like you that have used it successfully. All i am implying is that you can use SS to increase the safety factor because i have also heard others indicating that the beer can trick has failed.

 

[Big Red Mach 1]

Did you have any issues with leakage?

Not to my knowledge. Have had no need to take the intake off. I installed mine into the intake, not the heads. Put the gaskets on as normal, with no turkey pan. Only additional thing I wish I had done was get the bottom of the intake ceramic coated. This photo is before I added Hi-Temp JB Weld to fill the gaps.

 

[Stanglover]

Are we done yet??

 

[tony-muscle]

Just a feeler gauge...torque the intake down also.

View attachment 62046

Thanks for the picture. I didn't think of it in that way. I just checked yesterday and it fits very flat.

 

[giantpune]

SCE gaskets and Mr. Gasket both sell intake gaskets with blocked heat crossover. I confirmed several years ago that the gasket will not burn through at the heat crossover. Chuck

I reckon I'm going to find out.

I bought the edelbrock 2750 intake. The intake has holes that look like the crossover ones. The instructions recommend using their gasket #7265, which do not have crossover holes. There is nothing in the instructions about adding anything else to block off the crossover. I installed it exactly like they said to, so nothing blocking the hole except the gasket itself.

 

[basstrix]

I reckon I'm going to find out.

I bought the edelbrock 2750 intake. The intake has holes that look like the crossover ones. The instructions recommend using their gasket #7265, which do not have crossover holes. There is nothing in the instructions about adding anything else to block off the crossover. I installed it exactly like they said to, so nothing blocking the hole except the gasket itself.

This past weekend, I pulled an offenhauser intake off a 351 that was installed with Fel Pro gasket that did not have crossover holes. The gasket, at the crossover port, was in good condition. It had a layer of soot, but I wiped that off and gasket was fine. I will add, however, that the total mileage on that intake was low....certainly less than 5000 and more likely half that.

 

[c9zx]

Go in 1/4 inch with an aluminum plug and use an inverter TIG welder to weld it shut, for sure no worries. Chuck

 

[jctodd66]

Check out this video for carburetor heat soak solution by blocking of crossover.

 

[Stanglover]

Check out this video for carburetor heat soak solution by blocking of crossover.

What I see as a possible problem is the fact that the metal insert sits on top (or underneath) the gasket which in effect, thickens it at the cross-over points. If the intake, when bolted down, does not crush the paper gasket, I see that as a potential leak point.
When I did mine, I cut the .020" SS larger and the same shape as the gasket hole, trimmed out the gasket so the insert fitted INSIDE the paper. I then used Permatex #2 to hold it in place while the intake, original steel 4V, was installed. The gasket and inserts are therefore the same thickness within .002". Paper gasket was .018" uncompressed.
An aluminum intake may be a bit more forgiving than a steel one.

 

[basstrix]

What I see as a possible problem is the fact that the metal insert sits on top (or underneath) the gasket which in effect, thickens it at the cross-over points. If the intake, when bolted down, does not crush the paper gasket, I see that as a potential leak point.
When I did mine, I cut the .020" SS larger and the same shape as the gasket hole, trimmed out the gasket so the insert fitted INSIDE the paper. I then used Permatex #2 to hold it in place while the intake, original steel 4V, was installed. The gasket and inserts are therefore the same thickness within .002". Paper gasket was .018" uncompressed.
An aluminum intake may be a bit more forgiving than a steel one.

When I turned wrenches, I accumulated a few sets of the blockoff plates. Some of the performance intakes came with them. I had an apprehension about using them per the instructions for the same reason you stated, but I never had a problem. They were only used with fiber gaskets....not with the "turkey pan" style. This picture is the closest I could find. I have one in the garage...I may take a picture of that, along with the gasket I just removed. FWIW, the plate I have measured right at 0.015 .020.

Edit: .020 was from memory...measured one yesterday @ .015.

 

[Stanglover]

When I turned wrenches, I accumulated a few sets of the blockoff plates. Some of the performance intakes came with them. I had an apprehension about using them per the instructions for the same reason you stated, but I never had a problem. They were only used with fiber gaskets....not with the "turkey pan" style. This picture is the closest I could find. I have one in the garage...I may take a picture of that, along with the gasket I just removed. FWIW, the plate I have measured right at .020.

View attachment 79514

That's interesting.
Back to my case, I was using the turkey pan (Fel-Pro) with the gaskets. Maybe I was being too over cautious, but then that's my training and nature.

 

[3pedals]

This past weekend, I pulled an offenhauser intake off a 351 that was installed with Fel Pro gasket that did not have crossover holes. The gasket, at the crossover port, was in good condition. It had a layer of soot, but I wiped that off and gasket was fine. I will add, however, that the total mileage on that intake was low....certainly less than 5000 and more likely half that.

That's encouraging to hear as I just installed my new edelbrock intake with the felpro 1228 gasket and nothing else to block the crossover. Like @giantpune I just followed the instructions which said nothing about adding anything to block. If it was needed I imagine felpro would have thrown in the pieces of metal in the package. They were kind enough to include a distributor o-ring already.