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HawkX66 01-10-2017 07:41 AM

Cometic are around $180 a pair instead of readily available Mk IV gaskets at $50-$80 or so.
Thanks for the help guys.

MILD THUNDER 01-10-2017 07:53 AM

1 Attachment(s)
Im still not understanding the hang up with using a mark IV gasket, when having a gen6 block, with gen 6 heads. Cometic will make you whatever you want, and theres plenty of gen 6 felpro options.

It clearly states, that on a gen 6 setup, the gasket must cover/block the front hole on the block, without getting a chance to circulate thru the rear cylinders as well.

Most guys here, have tens and tens of thousands wrap up in custom GEN 6 style engines , and arent going to risk overheating their rear cylinders over a gasket. It has happened , and is a legit issue.

If you look at felpros 1037, it fits mark iv, gen 5 , and gen 6 blocks. It simply has the coolant hole blocked.

Here you can see a mark 4 gasket on a gen 6 block. I can see how water can come in at the water pump inlets, go right up into the #1 and #2 cylinder areas, and out the thermostat housing.

Either way, good luck.

HawkX66 01-10-2017 08:11 AM


Originally Posted by MILD THUNDER (Post 4518066)
Im still not understanding the hang up with using a mark IV gasket, when having a gen6 block, with gen 6 heads. Cometic will make you whatever you want, and theres plenty of gen 6 felpro options.

It clearly states, that on a gen 6 setup, the gasket must cover/block the front hole on the block, without getting a chance to circulate thru the rear cylinders as well.

Most guys here, have tens and tens of thousands wrap up in custom GEN 6 style engines , and arent going to risk overheating their rear cylinders over a gasket. It has happened , and is a legit issue.

If you look at felpros 1037, it fits mark iv, gen 5 , and gen 6 blocks. It simply has the coolant hole blocked.

Here you can see a mark 4 gasket on a gen 6 block. I can see how water can come in at the water pump inlets, go right up into the #1 and #2 cylinder areas, and out the thermostat housing.

Either way, good luck.

I appreciate you posting the article. I just read it more closely and now I see where my thinking was flawed. For whatever reason I thought the issues were with the lower holes. More specifically the one that isn't machined in the Gen 6 block. After looking at things a little closer, that's not the issue. It's the upper hole. Without question, you guys are right and I have to use a Gen 6 gasket. It's a pain in the ass, but I usually want to understand the "why" and don't always take things at face value. Too many times normative practices aren't exactly right. Now I understand the why and I won't put the gasket on backwards like I might have before... Goes to show you how bad the original engine rebuilder was. He used Gen IV gaskets.

open87 02-11-2017 08:23 AM


Originally Posted by MILD THUNDER (Post 4516083)
Thats a cool engine GM came out with, for towing applications. 4.25 forged crank, vortec heads, etc. Pretty much a big brother to the old 454 L29 Vortec engines, like I have in my 1997 dually, and a bigger version of the old "tall deck" 427T engines.

http://www.gmserviceinsights.com/wp-...lock_crate.png



Am I reading correctly , that the 1996-2000 7.4 454 in the Chevy/GMC 2500/2500 is a tall block - steel crank platform?


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