[67Fbird]

a similar method we used to "plug" holes in a die shoe Tap hole...NOT COMPLETELY thru....using a threaded rod or bolt screw it into the threaded area by hand until you get to the unfinished thread (where the taper of the tap does not finish size the threads.) mark bolt at surface level, then band saw bolt 1/2 way thru at 1/2 of a thread HIGHER than the mark. Run it in and twist it off!..file it flat!!! will never EVER move again.
Coincidently i was just evaluating this exact thing on my IRON heads and the HUGE opening between the middle ports. wondering if there is something I could do there other than blocking it off at the intake. As a Tool & Die & Mold maker i have the resources to make whatever is needed and typically do. Just wondering if it's WORTH the effort.

[74Grandville]

Originally Posted by 67Fbird

Just wondering if it's WORTH the effort.

i was thinking the same. is there back to back testing? what is this mod worth?

[Tom Vaught]

In a place like Florida, removing the heat from the carb area on a already hot upper engine would be a plus.

In a place like Michigan if the car is not driven in cold weather still maybe some benefit on a long trip up to the bridge.

In a winter environment, not worth the modification twice a year.

I think it has more to do with drive-ability vs any real HP gain.

Tom V.

[Schurkey]

There's two separate issues at play:

1. Smoothing exhaust flow out the exhaust port by eliminating the hole in the port for the exhaust crossover

2. Cooling the intake side of the head, and the intake manifold by eliminating the exhaust flow across the crossover.

Either one has benefits for a performance application; although a small-ish drilled hole in the Edelbrock head is likely less of a problem than the OEM crossover hole in the iron heads. And in cold-to-cool weather, losing the exhaust crossover will screw-up driveability.

[TransAm400]

I'm running 87CC d ports with a northwind and EFI. No use for a hot air choke. Am I possibly getting an exhaust leak here if I didn't plug the passage?

[steve25]

The Northwind has no Exh crossover section cast into it so the only leak you can get would be from a bad / burned out gasket.

[Tom Vaught]

And with no heat to the intake, the performance would be like a 72 cc head as far as heat goes but with one more potential exhaust leak point.
Only was to remove that potential leak is with Mike's exhaust passage plug.

Tom V.

[mgarblik]

My purpose for the plugs was 2 part. 1. Remove the disruptive hole from the valve bowl to even the exhaust flow in the center ports. They are pretty bad to begin with. 2. I am going to run one of the replica bathtub intakes with these heads. The manifold is going to be very expensive and I don't want any exhaust heat near the intake flange. Most other applications for these heads probably don't need to do anything. Possibly just stick a pipe plug in the intake flange as Paul K suggested.

[Cliff R]

"Even in Southern California filling in the crossover passage is a two edged sword. Great in the middle of summer when temps are warm, but it takes the carb a long time to stabilize on cold winter mornings when leaving for a show"

Be glad that you don't live up here in Ohio. Running a cold intake with a wet-flow system is fine for the way most folks use these vehicles. If they doubled as a snow plow in the Winter they'd be in BIG trouble as nothing works well until the intake fully heat soaks. That is why the factory used an exhaust passage in the intake manifold for carbureted engines and even with TBI. They didn't start running a dry intake until the MPI systems showed up......FWIW.......

[mgarblik]

Originally Posted by Cliff R

"Even in Southern California filling in the crossover passage is a two edged sword. Great in the middle of summer when temps are warm, but it takes the carb a long time to stabilize on cold winter mornings when leaving for a show"

Be glad that you don't live up here in Ohio. Running a cold intake with a wet-flow system is fine for the way most folks use these vehicles. If they doubled as a snow plow in the Winter they'd be in BIG trouble as nothing works well until the intake fully heat soaks. That is why the factory used an exhaust passage in the intake manifold for carbureted engines and even with TBI. They didn't start running a dry intake until the MPI systems showed up......FWIW.......

Absolutely true. The heat crossover combined with the warm air stove and vacuum controlled flap in the air cleaner beginning in 1967 made a huge difference in cold engine driveability. I rigged up a warm air stove and used a later model air cleaner on my 66 Ventura I used as a daily driver. It ran much better in cold/cool weather and got better gas mileage too. No down side in that situation. It was a great system for daily driver use in most climates.

[Cliff R]

Heat is actually your friend with these things. At least if you want optimum engine efficiency and to effectively burn lean mixtures, etc.

There are a lot of "myths" associated with blocking off exhaust heat to the intake, like more power and such. Outside of a dedicated drag race application where you are trying to cool things down for every run any benefits are purely superficial and about all that really happens is that you delay engine efficiency for about 15-20 minutes instead of 2-3 minutes........