intake manifold vs intake gasket coverage

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Belgian1979
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intake manifold vs intake gasket coverage

Post by Belgian1979 »

Hi guys, how much of the gasket surface needs to be covered by an intake manifold?

Thanks
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Re: intake manifold vs intake gasket coverage

Post by Walter R. Malik »

Belgian1979 wrote: Sun Aug 09, 2020 10:54 am Hi guys, how much of the gasket surface needs to be covered by an intake manifold?

Thanks
The gasket NEEDS to provide a good seal, not exactly match the intake manifold outline.
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Re: intake manifold vs intake gasket coverage

Post by Belgian1979 »

I know, but the manifold I tend to go using has smaller ports than the head. The gaskets are matched to the heads. On the top of the port the cover is only minimal with that.
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Re: intake manifold vs intake gasket coverage

Post by ProPower engines »

Belgian1979 wrote: Sun Aug 09, 2020 12:46 pm I know, but the manifold I tend to go using has smaller ports than the head. The gaskets are matched to the heads. On the top of the port the cover is only minimal with that.
Get a manifold with a larger port.
The flow is ruined by going from a small port into a much larger port.
Think of a river running through the hills what does the water do when it gets to the mouth of the river??
It slows down right?? You follow where I am going here. Air does the same thing. It goes from a small space to tring to fill
a larger space which makes it slow down enough to lose large amount of HP depending on how bad the size difference is [-X
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Re: intake manifold vs intake gasket coverage

Post by BOOT »

How much vac does your setup run you could make a plate to bolt on the carb pad and test to see it it holds and then recheck later if you think it lost seal. Otherwise you may have to weld material onto the manifold or use a spacer of some type. Some make their own spacers out of alum or a phelolic/plastic type material, then use a sealer or two gaskets. I got some 1/4" I wanted to try it with if I ever get around to it LOL
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Re: intake manifold vs intake gasket coverage

Post by BOOT »

ProPower engines wrote: Sun Aug 09, 2020 9:00 pmGet a manifold with a larger port.
The flow is ruined by going from a small port into a much larger port.
Think of a river running through the hills what does the water do when it gets to the mouth of the river??
It slows down right?? You follow where I am going here. Air does the same thing. It goes from a small space to tring to fill
a larger space which makes it slow down enough to lose large amount of HP depending on how bad the size difference is [-X
I've herd this is a good way to band-aid a too large head port and may be doing so myself. Ideally everything would be perfectly matched but things aren't always ideal.
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Re: intake manifold vs intake gasket coverage

Post by ProPower engines »

BOOT wrote: Sun Aug 09, 2020 10:05 pm
ProPower engines wrote: Sun Aug 09, 2020 9:00 pmGet a manifold with a larger port.
The flow is ruined by going from a small port into a much larger port.
Think of a river running through the hills what does the water do when it gets to the mouth of the river??
It slows down right?? You follow where I am going here. Air does the same thing. It goes from a small space to tring to fill
a larger space which makes it slow down enough to lose large amount of HP depending on how bad the size difference is [-X
I've herd this is a good way to band-aid a too large head port and may be doing so myself. Ideally everything would be perfectly matched but things aren't always ideal.
Not really a band aid it really slows the flow
Its more like just to make it run. Too big of port or too big a cam needs to be changed to get it right.
Ideal is if it runs to most guys but top performance requires more effort as you are aware
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Re: intake manifold vs intake gasket coverage

Post by Belgian1979 »

It's possibly a temporary solution, not something that needs to stay on the motor.
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Re: intake manifold vs intake gasket coverage

Post by MadBill »

Since nobody else has answered your question, I'll take a shot: I'd be OK with 0.25"/6 mm wide contact band, maybe even 0.040"/1 mm less.

However, your engine is an SBC, correct? If so, there are many different port size gaskets available. (Or is the problem that the outside dimensions of the manifold flanges are almost the same as the port openings, offering only a very narrow contact strip for any gasket?)
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Re: intake manifold vs intake gasket coverage

Post by Belgian1979 »

The heads normally use a gasket type 1206 from Felpro. The intake manifold I temporarily might need to use is a standard 70's alu manifold for a Rochester 4bbl. The manifold is a little thin on the top and coverage is minimal. I didn't measure the coverage but think it will be less than 6 mm, maybe 4 or so.
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Re: intake manifold vs intake gasket coverage

Post by MadBill »

"Theoretically" the gasket width is not a leak factor, unless the whole span was so narrow that normal bolt torque translated to excessive clamping psi that might squeeze it out like toothpaste. Since it's temporary and no other easy options have been presented, I'd give it a try. Th worst you should expect would be possible vacuum leaks along the top of the ports.
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Re: intake manifold vs intake gasket coverage

Post by Mikej26 »

You can raise the manifold up by using a 1266 gasket which is thicker instead of a 1206. Will give you a better seal width up top. Be mindful that you check to see if you’re still sealing at the bottom of the port.
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Re: intake manifold vs intake gasket coverage

Post by Belgian1979 »

I might just give it a try and see what it does like it is. Coverage on the bottom, although better isn't great either.
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