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V-8 Engine Tech

Head Gasket Slot Alignment....

Mopar Big Block Talk

by RockyUSA » Tue Feb 18, 2020 12:13 am

I had "Boiling After Engine Shutoff" (as opposed to "Unwanted Heat"), and was pretty convinced that "goop" had gummed up my head gasket slots.

According to the PO, the heads had been done during the car's refresh, but there was no denying the boiling / hot-spots in the passenger side head.

So I pulled the head, and what I found was what looks to be a significant misalignment between the slots in the gasket, and the cooling holes!

Can this possibly be the design (or an update to keep the heads at a hotter temp for emissions?), or does this look like these are the wrong gasket?

Let me know what you think. The circles in the gasket show the location of the water passages. You can see the slots are almost totally blocked, due to their position.

It looks like the passages in the heads don't align with the block.

Rocky
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by money_one_four » Tue Feb 18, 2020 9:39 am

From what I have seen and read on this forum this is how they are designed to keep the temperature up for the sake of emissions, however you can open up the slots . Somebody with first hand experience will be along shortly to tell you by how much.
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by Steve Payne » Tue Feb 18, 2020 6:48 pm

The earlier head gasket had wider slots to allow more water to flow from the block to the head, in the early 70's when emissions became a concern one of the ways they found to reduce emissions was to increase the cylinder head temperature. This with leaner fuel air ratios and it was inevitable the engines were going to have problems especially after a few years as the narrow slots started to block. I have seen some gaskets where the slots were almost completely blocked

Enlarge the slots to the pre emission level and you will notice how much cooler the engine runs. When I do this I use a Dremel and file. The width of the holes and the full length of the distance between both holes, if you use the thicker head gasket you will get the maximum of water into the head with out modifying the block.

This might make things a bit clearer.

http://members.tripod.com/mopar_roadste ... _cure.html

I would also suggest a high flow water pump and thermostat to increase the flow.

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by DPP » Tue Feb 18, 2020 9:27 pm

This is my G series 383, the engine was rebuilt in 2013 and I enlarged the holes using a hole punch.
The car has now done about 20,000 miles since the rebuild and the only time it boiled over was when the fan fuse blew.

The rad and fans are original design and the only cooling system upgrades are a high flow pump and thermostat.
My car has sat in long traffic jams on some of the hottest days in UK and not overheated.

I do think fully clearing all the crud from the water jacket ( I do this with a 150 degrees C steam cleaner) and fitting a new radiator core os also key to an engine that does not overheat.

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by RockyUSA » Wed Feb 19, 2020 12:59 am

Thank you all for the insight.

DPP - I note that you also opened the lower holes, as well as the ones connected to the slots.

This gives me some confidence to make changes.

Appreciate the insight and experience.

Thanks -

Rocky
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by RayR » Wed Feb 19, 2020 7:22 am

I had read on a Mopar site in the past that you can make the holes too big which might cause poor cooling distribution and the rear of the engine/head gets undercooled? Hopefully someone with more knowledge can confirm or not. Obviously it works for you DPP.

When I did mine I doubled the slot width and lengthened a bit also (think it was also from the Mopar site). Has been fine also for 3 years.

Have to remember Rocky is in a really hot climate!! I lived in Phoenix for 20 years and the challenges of 45C+ days are significant.

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by Philip Lochner » Sat Feb 22, 2020 3:46 pm

I also opened up those slots to the full width of the port in the block. Now I have no overheating issues on my fuel injected car.
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by RockyUSA » Fri Feb 28, 2020 3:33 am

As Phillip pointed out.... I live in a hot climate.

What is the collective wisdom regarding blocking off the heat riser in the intake manifold?

I did this on another American V-8 (Ford 351 Cleveland) with no issues. Legend has it that this can pick up a few horsepower by reducing the heat transfer to the intake charge.

Comments? Opinions? Fact-based Experience Descriptions?

Thanks -

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by RayR » Fri Feb 28, 2020 6:45 am

Rocky, I used the FelPro valley pan gasket with the heat riser blocked off on the last 2 head jobs I had to do. No adverse affects over 20+ years but wouldn't know if there was any actual power benefit.

FYI came across this old picture during cleaning. The Interceptor being pressed into service as a tow car after our regular tow car wrecked. Tucson Quarter Midget club at Marana in 2002.

Ray
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by Philip Lochner » Fri Feb 28, 2020 6:55 am

RockyUSA wrote:What is the collective wisdom regarding blocking off the heat riser in the intake manifold?


Not sure by what is meant by "heat riser". I presume you are referring to the Exhaust Gas Recirculation channel that runs between the two banks? I blocked this off on my Interceptors as well as the 350 SBC in my C10- which also runs on a Carter TQ BTW. My EFI thread in my signature should have pics of how I modified the alu intake in this regard unless dropbox killed them as well. EDIT: I uploaded the pics to JOC. Pics here: https://www.joc.org.uk/forum/viewtopic.php?f=20&t=15116&p=113746#p113746

Living in a hot climate, I felt there is enough reason to NOT heat the intake air more than what happens anyway. If there is more horses, good. I was more interested in engine efficiency and cooler air means more dense air, ie more O2 molecules going in- which is good. :D
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by RockyUSA » Sat Feb 29, 2020 1:20 am

Thanks both of you. I appreciate it and agree.

Ray – very cool picture. I just drove through Marana on my way to LA. Unfortunately, not in the Interceptor - in the Jaguar.

Rocky
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