Blocking the heat crossover, IN the head.

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Bad Sport

Bad Sport

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Has anyone blocked the heat crossover in the head itself where it comes from the exhaust port?

If so, how'd ya do it?

I know it can be done between the head and intake, but I'm speaking of the whole tunnel that runs through there.
 
I would think it would be much easier "in" the intake, and less dangerous.

Intakes are generally cheaper so if you screw it up.............

You are not looking at something falling down into the valves.

Just some random thoughts, I've never done this.........completely clean the intake, grind the crossover into virgin material, and either braze a plug into an iron intake, or tig an aluminum plug into an aluminum intake.

I've actually considered doing so.

I've also simply considered completely filling the crossover with hi temp silicone LOL
 
Yeah, good point about droppings in the valve. I am cleaning up the heads, po mans porting job, lol.

That big hole that runs the opposite way just bugs me. Looks like a cave, lol.
 
high temp silicone would have to be very high temp, like 700-1300F. Forget it. Just block it as it fills up pretty fast and acts like a spring dampening the pulses, no harm done.
 
I would have to ask why?
 
I meant why block it at all? It is there for a reason. Especially where you live, you will regret it I believe.
 
RustyRatRod said:
I meant why block it at all? It is there for a reason. Especially where you live, you will regret it I believe.
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Well since I only drive it during warm weather, I'm trying to keep the heat away from the carbatraitor. I still suffer with hard starts when warm, not as bad as it used to was, but it's still there, lol.
 
I bought a big block several years ago that someone had blocked the heat passages in the heads with some form of hard white ceramic material. As I recall, it had formed cracks in the filler that we saw when we tore it down.
 
If you plan on street driving it at ALL I would leave that passage open.
 
I've seen it where aluminum was melted and poured into the passage. Naturally you need to do it from the inside of the port and block the intake manifold side. I don't recall the details, but I believe that high quality aluminum needs to be used (Pistons were mentioned, but there are a couple of different forging materials) and I don't know what type of cleaning needs to be done for best adhesion. Propery filled and contoured, it's suppose to be good for a few cfm of airflow in that exhaust port. But it doesn't sound like an easy job.

I've always blocked the passage between the intake and head on my race engines with a thin piece of aluminum sheetmetal at the intake gasket and coated any exposed surface with hi-temp silicone. Never had a blow-thru on them. Don't know how long it would hold up on the street.
 
I read about this years ago and remember that zinc was also used to fill that passage. As mentioned, it was melted and poured in.
 
Fel pro makes intake gaskets that have the cross over blocked off ive got them on my 273. It works just fine & keeps carb cooler cor sure. By all means DONT MAKE YOUR OWN BLOCK OFF PLATES!!!! I did & had the dr. side one get into the #5 cyl.!! I got soooooooo lucky it didn't do any damage other than dent the top of the piston a little. There is a thread on here I started about 1 1/2 ago on this very subject. I swore it was my mms head gasket failing but it was my home brew block off plate instead!
 
You could always get an intake that doesn't have the passageways cast into it. Edelbrock Performer, Weiand Stealth, & Edel. Air-Gap all come to mind.
 
69_340_GTS said:
You could always get an intake that doesn't have the passageways cast into it. Edelbrock Performer, Weiand Stealth, & Edel. Air-Gap all come to mind.
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True, but that's mo money. I already have a nice set of heads.

I have never done this, but it is an old hot rodders trick and is still common practice today with old school engine builders. The claim is that it increases the port flow for those two exhaust ports, essentially making them more equal to the other 6 ports.
 
Exhaust crossovers are helpful for the first 2 minutes after a cold start, then it's just robbing power and boiling the gas in your carb. Modern gas vaporizes a lot easier than back when these cars were new. Also the factory iron intakes take wayyy longer to heat up than modern aftermarket aluminum ones. If you really want to get creative and do something that will make a difference, put in some intake gaskets with proper stainless block-off plates then drill and tap the crossover in the intake for pipe fittings and run water through it.

My Holley carbs book by David Vizard talks about this exact subject; he did a test checking the effects of the crossover on power and the water/coolant method actually made MORE power than no crossover at all due to better vaporization as well as keeping the intake plenum floor at a more constant temperature since after the engine has warmed up the intake will ALWAYS get hot from latent engine heat anyways.

FWIW I've driven my Air-Gap equipped 360 in 10* weather in a snowstorm (drift central LOL). It was a bad idea, it took me 10+ minutes just to keep it running but I needed to get somewhere and my driver was in the shop. Crossovers are only necessary if you expect to be driving a lot in sub-freezing temps which you said you aren't anyway. IF it really is a concern get a factory dual-snorkel air cleaner with the heat riser, I run that in the colder months and it makes a noticeable difference vs. my open-element air cleaner.
 
I never tried it but Fiberfrax might be something to try plugging an intake with. It's a high temp insulation. Used in heat treating and sintering furnaces. up to 2000° F I believe.
 

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From what I have read, the best way is to pour it full of molten aluminum (scrap pistons) or zinc.
 
Fel-pro has intake gaskets just for this purpose! Both for small port (273-318) & large port (340-360) intake ports. Done.
 
Hipo65 said:
Fel-pro has intake gaskets just for this purpose! Both for small port (273-318) & large port (340-360) intake ports. Done.
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I am aware there are gaskets that block the crossover, but that does not close off the huge tunnel IN the head itself.
 
Bad Sport said:
Has anyone blocked the heat crossover in the head itself where it comes from the exhaust port?

If so, how'd ya do it?

I know it can be done between the head and intake, but I'm speaking of the whole tunnel that runs through there.
Click to expand...

If you want to permanently plug it all the way to the exhaust port bowl, you have to take the heads apart and clean them, place them on a steel bench intake face down and clamp them tight to the bench. Then you have to get some sort of small iron pot to put chunks of scrap aluminum in. Then you get a big-*** torch, heat up the aluminum until it's molten and then pick it up with big channel locks and pour it into the exhaust port from the bowl side. Once it all cools, you grind the aluminum in the bowl until it matches the contour of the iron. If your valve job, etc is ok and you didn't nick a seat, put it all back together and you're good. If not, do whatever other head work you need.

I've done this numerous times. Works great, but also, I'm in California.

On the 340 in my old Barracuda, I just made some sheet metal pieces the same thickness as the intake gasket and glued them in with silicone.
 
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