4.0 Head Swap Question: manifold gasket overlapping intake ports

[CJ-8_Jim]

I'm about to start a 4.0 HO head swap and thought it best lay the manifold gasket on the head before installing it.

When doing so, I'm noticing that the gasket overlaps the intake ports by almost 1/16" along the same side of each intake port (see photo - ruler indicates side of each intake port with gasket overlap).

Questions/feedback:
1) I'm going to cut the gasket back on this side to make it flush with the intake port -- any problems with this approach?

2) Do you see any problems if I cut it back a little more (i.e., gasket underlap) so that it reveals the intake ports' edge by 1/32"-1/16"?

Thanks for the input,
Jim

 

[sfeather11]

Jim,
I think this is actually quite common. I've been reading up on this over the past few weeks and most people do the reverse of what you are proposing by grinding the head to match the gasket. This is what a "ported" cylinder head is. It smooths out the flow of the air entering the cylinder and is supposed to increase HP, although I've heard conflicting answers as to how much (Almost all say it is under 5HP gain). Unfortunately I am not at this point yet on my ride. My total project is a long drawn out affair when I can get time to work on it and do not need it in a hurry. Look around for some info and details. I think you can find some good information on DYI porting if you are interested. The whole process does not seem too hard and it sounds like you're already half way there. I'll try and find the sites I was looking at and send them your way...

Scott

 

[CJ-8_Jim]

Hi Scott,
Thanks for the reply. Yep.. I've seen the DIY porting websites where you lay the gasket on the head, trace the underlap of the gasket outline onto the head and then grind the head. Thanks for the offer, but there is no need to search for the DIY porting websites -- I'm going to skip the head grinding and forgo the extra 5 hp.

As you pointed out, I have the opposite problem... a gasket that overlaps. I was just curious if you had gotten to this point yet and if so, if your gasket was doing the same overlapping.

I suspect I have a lower quality manifold gasket that doesn't line up perfectly -- I'm thinking that cutting a little underlap (1/32") won't hurt just so that when it's installed the gasket doesn't accidentally overlaps.

JIM

 

[mtruckstuff]

The concept is to match the head to the block, not to the gasket. Clearance your gasket in order that it doesn't restrict flow. Check your gasket on the block, as well, to insure that not only there is no restriction, but also that there's adequate sealing material remaining. If you wanted to flow your head, a spare manifold gasket can be helpful, in that you could install it, torque it, remove it and have a perfect impression of both the block and head relative to each other. Then you could adjust accordingly. Your instincts are correct.
Paul

 

[frosty]

The manifold gasket doesn't have anything to do with the block, that would be the head gasket.

Trimming back the manifold gasket will be fine.

 

[mtruckstuff]

I stand corrected. I so dumb! Sorry if I caused confusion.

What I meant to say was that you want to match the manifold to the head.

The simple point is that the gasket is just a gasket. You never match anything to a gasket. You adjust the gasket to fit the porting. I just didn't want to see you out there with a grinder trying to fit engine parts to gaskets.
Paul