Cometic MLS headgasket (please read)

[IT Manta]

I decided to go with a multi layered steel headgasket for my race engine.A friend of mine works with Cometic and Cometic already had the basic template for a 12 bolt opel head so I had a couple .036 thick gaskets made with 95.5mm bores.

There are some differences between the Cometic gasket and the Felpro gasket and I believe it is probably a “perfect” match for later heads. The differences are basically extra cooling holes for the head. The extra holes match up to passages on the passenger side of my block but the drivers side of the block does not have the openings. I was thinking of drilling holes in the head to match the holes in the gasket for added head cooling. I guess I would just do the side that has passages in the block. The other difference is that the hole on the gasket for the front most head bolt on the driver’s side is elongated. This should not pose a problem.

Here are some pictures so you know what I am talking about and comparison. Has anyone used this gasket or anyone who has had experience with later heads and the extra cooling holes? Any and all information will be appreciated.

[IT Manta]

bump for those who might have some input

[jeff denton]

I would sure like to have one in my hand to examine and play with, there's some bare blocks and heads on my workbench at all times.

[IT Manta]

Originally Posted by jeff denton I would sure like to have one in my hand to examine and play with, there's some bare blocks and heads on my workbench at all times.

Jeff, you can compare the picture of the gasket with what you have there to visualize the added holes better .

[GTJIM]

The general consensus is that the best results are obtained with only two extra holes on the manifold side of the head - directly under the centre exhaust ports each side of the head bolt between cylinders #2 & #3.

Rally Bob has done temperature tests that indicate a considerable reduction in exhaust temperature in the centre ports with just a pair of 3/8" holes in the gasket there.

More holes along that side may just upset the coolant flow through the head?

The holes along the passenger's side are for spark plug cooling - just like SB Chevy heads. I remember GM trumpeting the addition of the spark plug cooling as one of the great changes to Chevy V8 heads - way back in the 1960's ... Gee am I getting old ... or what!

[RallyBob]

Originally Posted by GTJIM The general consensus is that the best results are obtained with only two extra holes on the manifold side of the head - directly under the centre exhaust ports each side of the head bolt between cylinders #2 & #3. Rally Bob has done temperature tests that indicate a considerable reduction in exhaust temperature in the centre ports with just a pair of 3/8" holes in the gasket there. More holes along that side may just upset the coolant flow through the head?

Yes, I've found that too many holes is not good. The coolant flows from the front of the block to the rear, then up to the rear of the head and forward towards the thermostat housing. By putting the two extra holes i the head gasket a little bit of the slightly 'cooler' water is intercepted and hits the notoriously hot #2 and #3 exhaust valve areas.

These are the only two exhaust ports that have no coolant flow between them, and they also run hotter by about 200-250° F on the EGT's because they have higher exhaust flow. The two 3/8" holes add much needed cooling to those ports.

By adding holes 'everywhere', it seems to add some turbulence and interrupts the flow pattern and it runs hotter again.

Bob

[RallyBob]

PS, Happy Birthday Pete!

[IT Manta]

Thanks for the happy Birthday! You even beat my wife to it. 44 today but I feel like 34 and act like an 18 year old.

Ok I will just do the two holes and see how it goes.

What head actually uses all the extra cooling holes and the elongated hole by the head bolt?

[IT Manta]

Originally Posted by GTJIM The general consensus is that the best results are obtained with only two extra holes on the manifold side of the head - directly under the centre exhaust ports each side of the head bolt between cylinders #2 & #3. Rally Bob has done temperature tests that indicate a considerable reduction in exhaust temperature in the centre ports with just a pair of 3/8" holes in the gasket there. More holes along that side may just upset the coolant flow through the head? The holes along the passenger's side are for spark plug cooling - just like SB Chevy heads. I remember GM trumpeting the addition of the spark plug cooling as one of the great changes to Chevy V8 heads - way back in the 1960's ... Gee am I getting old ... or what!

If you look one more time at the picture of the Cometic gasket you will see that the "extra" cooling holes are not where you suggested they be. Should I just use the middle hole or the three holes on the manifold side of the head?

[RallyBob]

Originally Posted by IT Manta Should I just use the middle hole or the three holes on the manifold side of the head?

This is what I typically do and recommend.

HTH,
Bob

[tekenaar]

Took your Cometic headgasket BMP and added 2E/3E coolant hole locations . . .

[IT Manta]

Taking into account that I am already $200 into the gaskets and I do not see modifying them as an option. I think I will use the gasket as a template and utilize the three 1/4" holes in between cylionders 1/2, 2/3, and 3/4. I would estimate similar levels of coolant flow just over a bit larger area but still centered around the #2&3 exhaust ports.

[jeff denton]

Originally Posted by RallyBob By adding holes 'everywhere', it seems to add some turbulence and interrupts the flow pattern and it runs hotter again. Bob

Yes, this is just NOT something to screw with. Analyzing just exactly how coolant flows through an engine is quite the science; read Smokey's book to see how hard he worked to get the SB Chev to flow right. In that case he found that some pumps work better (flow more) than others, but his biggest breakthrough came from seperating the outputs, a moot point on an Opel, however... later he tried reversing the flow and it worked, worked so well that GM copied it on the second generation LT1..
We KNOW the two added holes work and we understand why. Myself, I am not aware of any reason to try to improve it.

Plus, HAPPY BIRTHDAY!!

[GTJIM]

Originally Posted by IT Manta What head actually uses all the extra cooling holes and the elongated hole by the head bolt?

Those holes are there from the casting process - the core that forms the water spaces inside the head has to be 1) supported during the metal pour and 2) bashed up and removed when the casting is finished.

More holes are needed for these reasons than are best used for coolant flow ... so the gasket is used to block them off. Just because there is a hole in the casting does not mean it is good to use for coolant flow ...

Looks like somebody has already had a 'better' idea and put 'steam' holes between the cylinders - like on 400 CID SB Chevys - but there is only a connecting set of holes in the block that line up with one side of them .... and no small holes at all in the head!

The two 3/8" holes located as Bob & Otto have illustrated work to improve head cooling in the critical area of the centre exhaust ports - other holes are at your risk ... go to it and let us know the good (or bad!) results.

[IT Manta]

I understand and agree with both Jim's and Jeff's last two posts, and also I have great respect for Bob's input and experience. But, If you take a look at the three holes that I wish to utilize and look at a block and head you will see my interpretation of what is available to me at this point. The overall flow that would created would be very close to the flow that 2 3/8" holes would allow. Also the area that would benefit from the cooling would be localized on the manifold side of the head in the center near the #2 & 3 cylinders as would be desirable. I am not trying to reinvent the wheel , just trying to work with what I have and what makes sense to me. Unfortunately I do not have any prior data to create an empirical discovery, but I do believe my thinking has merrit and I am willing to give it a try. On top of that I will have a custom aluminum radiator the next time the car runs so I may never have the empirical data to determine the areas where I gained ground.