Blocking off intake heat crossover

[72wedge]

I’ve done some research here on FABO, but I’m hoping to gain some concrete knowledge for my setup from those who have experience in blocking off the intake heat crossover by using a steel shim between the intake gasket and cylinder head. I live in California where most days are warm and summer days are 90-100+ degrees, and I won’t be driving when/if it’s below 50 degrees in the winter.

Here’s my setup:
340 ci / 10:1 compression
Edelbrock Performer RPM intake (non-airgap)
474 lift cam
QFT 650cfm double pumper carb
X-heads
Dougs D453 headers

If I’m using a 26 gauge (0.019” / 0.5mm) stainless steel shim, will that be too thick between the intake gasket and the cylinder head if I just lay the gasket over the steel shim?
Or, should I cut a hole in the intake gasket, just big enough for the steel shim to recess into the gasket?

What intake gasket is best for the block-off steel shim?

- Fel-Pro 1213? Do I lay it over the shim or cut around it?

- Fel-Pro 1213S has a steel core, but reviews say it still burns through. Would this still be a good option to lay over the shim or cut around it?

- Mr.Gasket 307G (composite)? This one says it comes with block-off plates. Does anyone have experience with this intake gasket and using the included block-off plates?
https://www.summitracing.com/parts/mrg-307g


Thanks in advance for the advice. I know this topic has been beaten to a pulp, but FABO is my #1 source for gaining knowledge on these Mopars and I always like to feel sure about something before making modifications.

 

[Professor Fate]

Don't overthink it, back in the day we'd cut a piece from a tin can and slap it on there- never had an issue.
But if it makes you feel better, cut a slightly oversized piece of sheet metal and carefully bend the edges until you get a nice tight fit in the passage, and drive it in. Sort of like a freeze/core plug.

 

[72wedge]

Thank you. Yea I tend to have a habit of over thinking things lol

 

[RustyRatRod]

Block it off or run an intake with no cross over. It'll be fine.

 

[72wedge]

Block it off or run an intake with no cross over. It'll be fine.

Would it best to cut the gasket around the shim to recess it into the gasket? or just slap the intake gasket over the shim and call it a day?

I just want to make sure it'll seal

 

[RustyRatRod]

Would it best to cut the gasket around the shim to recess it into the gasket? or just slap the intake gasket over the shim and call it a day?

I just want to make sure it'll seal

I'd put a light coat of red high temp RTV on it and call it done.

 

[72wedge]

Cool. As far as which gasket to use... I have a set of the Fel-pro 1213s with the steel core, is that a good option?
or should I opt for the standard Fel-pro 1213 with no steel core?

 

[kick]

I plan to use the FelPro 1213 S-3 with my factory 71 iron on top of the 340. It has a stainless steel core so you shouldn’t need shimms. Just bolt it up.

 

[furrystump]

I just run the 1213 gasket and it has never burned through. Way back I took a small 3/8” air belt sander and recessed the manifold to fit a small sheet metal plate. Ran it that way then just stopped using the plate. Did drag week with it that way.

 

[72wedge]

I just run the 1213 gasket and it has never burned through. Way back I took a small 3/8” air belt sander and recessed the manifold to fit a small sheet metal plate. Ran it that way then just stopped using the plate. Did drag week with it that way.

Thank you kick and furrystump. My initial plan was to run the 1213 S-3 gasket with the steel core, but I seen a review on summit racing that the heat crossover still burns through the steel core gasket. That's what sent me down this rabbit hole lol. Of course there wasn't much context behind that review, but it seems some guys on here have it burned through the 1213 S-3 and some don't. But again, not much context on what their setup is. Being my car is just a weekend cruiser/warrior and I'm running headers, I would think I'm not going to get much exhaust heat heading too the crossover and the 1213 S-3 should be ok to not burn through. There's also the Mr.gasket 307G that comes with the block off plates, some good reviews on here about them, So thats another option.