Heat Passage Block-Offs

[dsags]

The intake manifold gasket set for my 401 nailhead has four metal 'tabs' that I presume are to block off the heat passages to the intake manifold. Has anyone installed these on their engine ? If so, what are the consequences?

Thanks in advance.

Dan

[Rollaround]

Dan,
 I have not used them on a Nailhead but I have used them in other Big Blocks and Small Blocks. The big plus, the manifold stays a little cooler. The drawback, slower warm ups, but then we don't normally drive our cars in the winter.

[WkillGS]

One line of thought is you'll get better fuel atomization with a warm manifold.
The opposing view is you'll have a denser charge with a cool manifold and gain a few hp.

The warm manifold would likely be preferred for better driveability and mpg.

A good compromise is to plug the two heat passage holes in the manifold just under the carb base. You'll have a warm maniford and a cooler carb.

[GreatScat1965]

The intake manifold gasket set for my 401 nailhead has four metal 'tabs' that I presume are to block off the heat passages to the intake manifold. Has anyone installed these on their engine ? If so, what are the consequences?

Thanks in advance.

Dan

Yes, I have usesd them for 20 years. If your car is bone stock with a choke stove tube, or the car is driven in exceptionally cold weather, leave them out the choke will not operate correctly. If you have an electric choke I would suggest putting them in. Even with the crossover blocked you can cook eggs on the intake manifold after a fun romp with the car. The cooler the better for performance, efficiency and to keep the car from vapor-locking (Boiling the gas in the carb). Kenne Belll sells a "Coolrunner intake and Edelbrock has a Air-Gap manifold both designed to keep the intake charge cooler. Seems like a cooler intake charge is their goal.

Jerry

[dsags]

Thanks for all the input. Car is straight cold so will be leaving the block-offs out.

Dan