FI plenum gaskets

[E S.]

Hi- I've seen these over the years, but never really knew their purpose. These are fairly thick (.128), and made of a very stable material, that could maybe described as "composite", but are certainly not asbestos, or normal "gasket material".
Since these are between the "intake", or "adapter",and the fuel meter- could they possibly help the "hot start" or "fuel percolation" issue that a lot of us have with our FI engines?IMG_20200923_174412825.jpg

[Jim L.]

Re: FI plenum gaskets

Hi- I've seen these over the years, but never really knew their purpose. These are fairly thick (.128), and made of a very stable material, that could maybe described as "composite", but are certainly not asbestos, or normal "gasket material".
Since these are between the "intake", or "adapter",and the fuel meter- could they possibly help the "hot start" or "fuel percolation" issue that a lot of us have with our FI engines?

Although I work on FI units for folks who somehow find me, I've never seen those gaskets for a C2 before. Yes, their purpose would have been to reduce the severity of fuel perc. That said, they won't help.

If you have a C2 FI unit it already has the most significant anti-percolation change GM ever implemented: the re-circulation of fuel to the spider and back to the fuel bowl.

If fuel perc is your concern, there are a couple of other things you can do to the unit but they won't pass NCRS scrutiny.

[E S.]

Re: FI plenum gaskets

Jim- Thanks for the info.- As you said- I have had several C2 units in the past

[E S.]

Re: FI plenum gaskets

Jim-Have you seen these gaskets for the C1 units? I bought this 380 unit years ago,and these gaskets were included. I was just curios about their purpose. I have not had the fuel perc problem with the C2 units, but I have fought it with my 62.
Thank you for the info.

[Jim L.]

Re: FI plenum gaskets

Jim-Have you seen these gaskets for the C1 units? I bought this 380 unit years ago,and these gaskets were included. I was just curios about their purpose. I have not had the fuel perc problem with the C2 units, but I have fought it with my 62.
Thank you for the info.

Early on, C1 FI units had a thick, one piece gasket between the doghouse and the adapter plate. It didn't do much to reduce fuel perc and was replaced by four individual gaskets, one for each doghouse leg. There are reproductions of the one piece gasket if you want one.

[G B.]

Re: FI plenum gaskets

Early on, C1 FI units had a thick, one piece gasket between the doghouse and the adapter plate. It didn't do much to reduce fuel perc and was replaced by four individual gaskets, one for each doghouse leg. There are reproductions of the one piece gasket if you want one.

GM used the one-piece thick gaskets with '57 - '59 FI units that had sand-cast fuel bowls. I've found they must still be used with those bowls or you will have interference with the passenger aluminum valve cover.

[Gary C.]

Re: FI plenum gaskets

FWIW, I've used thin foil backed insulation under a '57 large gasket and it seemed to reduce gas percolation.

Gary
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[Jim L.]

Re: FI plenum gaskets

FWIW, I've used thin foil backed insulation under a '57 large gasket and it seemed to reduce gas percolation.

Gary
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I don't doubt that the thick gaskets and a reflective layer reduce the amount of radiated heat reaching an FI unit. They don't address the problem of conducted heat, however.

Conducted heat is that which reaches the plenum from the engine through the eight hold-down studs. That heat is further conducted to the fuel bowl via the metallic connections it has to the plenum. Also, the nozzles receive conducted heat by virtue(?) of the metal hold-downs and the metal bolts which tie back to the conductively heated plenum.

On a mongrel FI unit I use for testing my goofy ideas for reducing the tendency for fuel perc, I found the nozzles cool off significantly faster after a hot re-start if the steel hold-down bolts are replaced with nylon bolts.

I suspect, but have not yet verified, that thermally isolating the fuel bowl from the plenum with, say, nylon shoulder washers through slightly larger mounting holes would pay similar dividends.

A judge would, of course, notice such deviations from an as-manufactured configuration. However for folks who enjoy driving their fuelies without fear of having to deal with fuel perc, these and other minimally visible modifications can make a huge difference.

Jim

[Ray K.]

Re: FI plenum gaskets

The solid gasket when Chevrolet offered it for service was part #3741316, it is listed as application for 1957 - 59 F.I. , Corvette and pass car. Corvette started the individual gaskets in 1960 using #3768235. The 1963 - 65 FI units require gasket #3832280.

Ray