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Old 12-19-2012, 11:57 PM
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heat passage

Im sorta new on Pontiac engines so I have a q.I need to block off the heat riser passage in hte heads..Ive heard guys dump hot aluminum in there but there on the car so I dont want to do that til I start porting.Can I just JB weld a peice of metal in there or is there to much expansion from temp changes?Thanx in advance.

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Old 12-20-2012, 12:11 AM
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you can buy intake gaskets that block it off..
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Old 12-20-2012, 05:38 AM
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The only thing that will be permanent is to remove the heads and pour molten aluminum in the heat passages. The special intake gaskets that are blocked with thin metal plates will burn through within 100 miles.

If you block the heat passages in the heads and your car is a daily driver, you better have a hand choke or an electric choke or you will not get the car started when weather is below 40 degrees. If you have a hand choke or electric choke and you get the engine started, it will not run properly in cold weather. Blocked heat risers are for race cars only and if you drive the car on the street, it is not a race car. All the high performance engines with carburetors the automakers have produced were equipped with working temperature controlled chokes because the engine runs better with one.

I blocked the heat passages in my Pontiac heads with molten aluminum and it was the worst mistake I made. In order to get the car started in cold weather, I had to install a electric NAPA choke kit on my Rochester center carburetor and the engine still never ran correctly in cold weather.

Last edited by MouseFink; 12-20-2012 at 05:49 AM.
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Old 12-20-2012, 11:27 AM
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I dont want to use block off gaskets cuz they blow pert near instantly and I tried blocking the intake but that pushed out the gasket too.This car is not a daily driver nor does it see cold.But thinking about it,I do have a 2inch spacer that keeps the carb cool so it does help.All the Pontiac guys I know say blocking the passage should be first thing but Im thinking no big deal.Car runs pretty good cold(right at firing)so Im not worried about cold running.Plus I have the carb a hair rich cuz of the cam but I think I should just leave well enough alone.What do yall think ?Thanx again..Jeff
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Old 12-20-2012, 11:35 AM
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I´ve used those blocked off gaskets, never "blew" one.
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Old 12-20-2012, 11:48 AM
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Block if off. If you block both sides and have a low restriction exhaust you will have no problems. I use some .030 stainless shim stock glued to the head with red RTV. Install the IM gasket just as normal.
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Old 12-20-2012, 07:41 PM
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I did that..First the block off gasket then jb weld in the intake.Didnt even make it out the drive way.lol I do have a big exhaust so no prob there.The more I think about it,with the riser plate and an out of hood scoop,I should bee pretty good for a cooler charge,til...like I said,I do some head porting.Thanx for your input guys.jeff
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Old 12-20-2012, 10:04 PM
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Quote:
Originally Posted by jeffs66 View Post
Im sorta new on Pontiac engines so I have a q.I need to block off the heat riser passage in hte heads..Ive heard guys dump hot aluminum in there but there on the car so I dont want to do that til I start porting.Can I just JB weld a peice of metal in there or is there to much expansion from temp changes?Thanx in advance.
You NEED to block them or want to block them? If you drive in cold weather you might want to reconsider this and just block one side.

I have used two pieces (one for each side of the engine) of 0.035" stainless steel shim stock cut to size and slid in between the heads and intake gaskets and drove it like that for 50K miles until it was sold. Pontiac 455 w/ a Performer intake, driven in central FL year 'round. Mild (strongly magnetic) steel won't last as long.

Furnace cement is a lot better than molten aluminum IMHO. It requires a heat cure, so the heads need to go into the oven for a while. The cement expands some so you don't need to allow it to come all the way out of the port like shown on one of my heads below. A 1 to 1-1/2" plug made from this cement, placed 1/2" inside the crossover will do nicely.


Last edited by cobalt327; 12-20-2012 at 10:17 PM.
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Old 12-21-2012, 01:17 PM
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Originally Posted by cobalt327 View Post
You NEED to block them or want to block them? If you drive in cold weather you might want to reconsider this and just block one side.

I have used two pieces (one for each side of the engine) of 0.035" stainless steel shim stock cut to size and slid in between the heads and intake gaskets and drove it like that for 50K miles until it was sold. Pontiac 455 w/ a Performer intake, driven in central FL year 'round. Mild (strongly magnetic) steel won't last as long.

Furnace cement is a lot better than molten aluminum IMHO. It requires a heat cure, so the heads need to go into the oven for a while. The cement expands some so you don't need to allow it to come all the way out of the port like shown on one of my heads below. A 1 to 1-1/2" plug made from this cement, placed 1/2" inside the crossover will do nicely.

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