Intake manifold gasket restrictor inserts 1

[marcgyver77]

I am doing a valve job on a ’85 GM 350 small block in a GMC 3500 ‘lift-gate’ truck. The heads have the passage ways for the EGR. The stock manifold has the passage ways but not drilled out for the EGR as it was not a requirement for that vehicle.
Included in the FEL-PRO intake manifold gasket set is a package labeled "Manifold Restrictor Insert". Also on the package, it states, "Important - Before assembly read fit (Fel-pro Installation tips) included with this set". There was no “installation tips” included. I searched the Fel-Pro website and online but did not find any information on it. I posted on other forums and got various “questionable” replies.

These ‘Inserts’ are two pieces of stamped metal, that fit into the intake gasket and attached together. They restrict the flow through the EGR passage way down to the size of a half inch opening.(See attachments)

(Question) When should these inserts be used?

One of the replies I got was: “those were included when GM used a piece of stainless steel tubing inside the intake manifold to supply heat to the choke. If your engine does not have that kind of choke you don't need the block offs”.

Another reply I got was: “Only the stock replacement gaskets have them. The next step up that most people use don't even have the holes in the gaskets. Not sure if you actually need them. Do it the same as the ones you took off is my opinion”.

Another reply I got was: “It's not just an EGR thing. If your manifold has a heat riser/choke passageway that goes between the heads and you're not using a thermal choke driven off of it then I'd block that passageway. It helps keep the exhaust heat off the bottom of the intake.
If you block it you have to remove the heat riser valve piece from between the passenger exhaust manifold and the down pipe, or modify it so the valve is never closed”.

Edelbrock has changed their Performer Series intake manifolds with the addition of Edelbrock's patented Air-Gap. The Air-Gap design features an open air space that separates the runners from the hot engine oil for a cooler, denser charge for more power.

(Question) With that in mind, would it then be a good idea to block off completely the EGR passageway to keep the exhaust heat off the bottom of the intake? What would be the best way to block off the passageway?

 

[TheBlacksmith]

I don't know where you are, but if you have cold weather, the exhaust flow through the manifold would aid warmup and driveability during warmup. If you only have warm weather (or like my boat which was laid up in cold weather), blocking the passage should have no detrimental effects and may improve power and mileage by keeping the intake cooler much as you note with the Edelbrock air-gap manifolds. EGR block off plates are readily available for all popular engines (certainly a small block Chevy) at any speed shop.

 

[tbuelna]

Since your '85 SBC engine was for a commercial vehicle, it may have not required the internal EGR feed from the center exhaust ports in the heads to the intake manifold. The stainless inserts regulated the EGR flow and prevented the gasket hole edges from eroding.

As TheBlacksmith suggested, get some EGR block-off plates for your 28-year-old engine.

 

[MikeHalloran]

It used to be traditional for hot rodders to insert shim steel blockoff plates in the crossover passages as soon as the weather got warm. The idea was that the plates would rust out and restore carburetor heat before the weather got cold again.



Mike Halloran
Pembroke Pines, FL, USA