Blocking the heat crossover in iron heads.

As in the title im looking for opinions on if still blocking the heat crossover is a plus or if anyone figured out it might keep more heat then wanted in the inner cylinders.

Even with an al. intake wont it heat sync nearly as hot sooner or later?

THANKS!

I like to keep the horse shoe openings in the middle of the head open to air & block the passages in the intake itself.

If your car is primarily driven on the street and used during colder weather, I personally would leave the cross-over open. I blocked the cross-over in a 383 powered car I had. The change made it very "cold blooded." If the car is equipped with a factory type thermostatically controlled choke, the choke will take way too long to pull off. If you have an electric choke, it will pull off too soon. Plus, blocking the cross-over didn't make any noticeable improvement after the engine was "warmed up". I think this is one of those questions to which the answer is, it depends.

This is what I have always done to any of my cars as well. They don't get driven in winter anyway.I just use a couple of small thin piece of sheet metal & sandwich them in with the gaskets. Never had any intakes leaks either.

There is no benefit to blocking the intake manifold heating system on a street-driven engine. The hot-spot under the carb is necessary to vaporize any fuel that falls out of the air stream and to replace the heat from the vaporizing fuel's cooling effect on the intake manifold. See the Carter, Holley, and Rochester references in Intake Manifold Heat.


Nope. Without a working cross-over passage you won't have a hot-spot under the carb either.

Limited street race/bracket iron heads oem al. intake. Ive never had a choke on this intake carb setup.

Sorry I should of included this info.

Not to high jack, but kind of the same subject...
Would it be beneficial to remove the heat riser valve in the exhaust manifold?
The reason I ask is mine are rusted in place.
Usually partially open.
Street cars, summer use.

That's a reasonable suggestion. Back in the day we used to take a piece of wire and wire the heat riser open.

O.K.
Open it will be.
I will remove 'em and drill and tap for plugs.
As well as the intake block-of R.R. recommended.
Thanx.

fel pro 1214 for b,1215 for rb.heat riser port is blocked.

I had to fill the cross overs with epoxy because one of the darn things sprang a leak...LOL, yeah, all iron heads, heavily ported, so it is conceivable that maybe this had something to do with it, although the machine shop did a pressure test first and there was NO air coming out of the ported exhaust valve area.

Anyways, to answer your question, on top of this I used FelPro 1213S-3 intake gasket, which has the passages blocked off.

This is on a street car, but not a daily driver. Car heats up just fine (I only drive it in late spring, summer and early fall months), no issues to report.

The aftermarket heads seem to work just fine without a heat crossover passage.

So block off the exhaust heat riser, but not the Intake cross-over?

Good to know.
Now I can use the pan gasket I already have.

The smog heads I just did, they go up on both center exhausts unlike the older j or x for instance that just go up on one, thats why I asked about heat buildup.

Back in the 70'S I used tin foil which worked OK. Then some gasket manufacture had little squares of thin metal gasket material to place over the hole. Later race type gaskets were introduced that didn't have the crossover opening.

I always found/thought those little metal plates that came with the intake gaskets were way too thick and was afraid it might crack the manifold in the center when torqued down.

Ever since I use an old intake valley pan and cut out a few plates myself with tin snips.

Non of my cars have a (working) heatriser in the exhaust anymore, but then again they're not daily driven either.
The only old car that gets driven daily is my '73 Dodge Dart and since it runs on propane I preferrably don't want any heat in the intake as it simply because it robs power, makes the engine heatsoak more and feel lazy.

I’ve also found exactly the same thing 2many62s describes especially on cold mornings.

“……If the car is equipped with a factory type thermostatically controlled choke, the choke will take way too long to pull off. If you have an electric choke, it will pull off too soon. Plus, blocking the cross-over didn't make any noticeable improvement after the engine was "warmed up". I think this is one of those questions to which the answer is, it depends…….”

While not as bad as eliminating the heat crossover, eliminating the heat riser will also slow the warm up period considerably. None of my cars have a heat riser valve and a few in the past have run manifolds and/or heads without the heat crossover. As I often drive my cars year around and during the winter and we get some pretty chilly early mornings I can say first hand it can be a real PIA.

The one band-aid I’ve found that really helps during the warm up period is to add an MSD box. The multiple spark during low RPM really makes a big difference in firing off the cylinders until the car warms up.

I've always wanted to try the trick I read in one of David Vizard's books-
welding up the (aluminum) intakes' heat riser entrances, drilling, tapping, and fitting the topside of the passages with heater hose fittings and ball valves (remove the handles for clearance; use only for opening/ shutting, or use a pair of pliers).
Best of both worlds;some heat when needed, but not so intense. And the ability to shut it off without much fuss.
An iron intake would require molten aluminum or some sort of epoxy, but could be done, too, I imagine.
Wish I had access to the pic that accompanied the idea. I think it's in his "How to Build Horsepower" volume 1 book. Mine's in storage.