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Old 05-15-2004, 02:00 AM
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mark VI heads to mark IV head swap?

why is it, the more books I read on 454's, the bigger the mistakes i make.,
Some books say ,,,,with the mark VI block I can swap in older mark IV heads without any trouble and some books say NOOOOOOOOOOOOOOO!

Anyone know for sure?
I have peanut port heads on my 1996 Mark VI in my 1973 blazer and it has great low end torque , but the edelbrock performer plus cam and intake get all choked up at above 3000 rpms

I have all kinds of Mark IV heads and would love to swap to the large oval port heads.

I posted a thread earlier today on this subject and cannot find it!
greenhorn looser!

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Old 05-29-2004, 05:38 PM
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The gen VI block can use either early or late style head. It also has a plastic timing cover thats the fastest way to recognise a gen VI block.

The gen V block can only use the later style heads. It has a steel front cover and 1 piece rear seal.

The mark IV blocks can only use the early style heads. Has a steel front cover, water passages in deck surface are smaller than later blocks & heads, and it uses a 2 piece rear seal.

If the heads have large pipe plugs in the ends its a mark IV head, if they have no pipe plug its a late style head.

Hope that helps you some.
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Old 05-31-2004, 06:53 AM
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a couple of things

yes , thanks!
in salee chevrolet they talk about the mark 6 or mark VI 1996 and newer , as having changed water ports,....blah blah.....
My mark VI, and all that I have seen,has a 6 bolt aluminum timing cover that does not allow a double roller chain.
I have found a chevy single roller HD that comes with the crate motors that have a roller cam.........mine does not have a roller cam but at least this chain is a roller and the sprockets are not nylon.

I have peanut ports and I live in central america , and there are no mark VI big oval port heads anywhere here, so I was hoping for the older style large oval port heads,,, we have tons of these!, and I think that I can swap ,,BUT ! until someone says they have done this swap , and all i need is a gasket from the 1996 mark VI and whatever else that would be involved ,,,,I am to chicken to try!

If there are 454 people who would know ....what would best if this swap is possible .......tell me which would be better---101 cc closed chamber heads or 118 open chamber heads , with the original 1996 pistons

I believe my 96 motor has 8.25compression and from what I read the 101cc heads would give me around 9.5 to 1 .......or would the closed chamber heads cause problems with the flat dished pistons???????
surely not!!!!??????
anyone made this mistake and learned form it?
If this reads wierd I blame it on spanish!
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Old 06-03-2004, 11:22 PM
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true head torque settings please?

Anyone know the head bolt torque specs for the mark IV , and mark V , mark VI motors???????
I have torqued my long bolt to 75lbs , and the short bolts to 60lbs on my 1996 mark VI 454, but after, I read the bolts need sealant for the threads , and also the mark VI motors had a torque setting of 100lbs in 3 intervals. runs fine so far??????!!!!!

Is this motor a pain in the arse or what?

I have to re-torque the head bolts, add sealant, put a single roller chain and gears, change the valve springs , and then I can put back together to later change the heads over to some large oval heads of the early type.

I know I should get another Mark VI 454 book but I am scared of more conflicting info.

Thanks alot

Oh by the way in case anyone else cares I just saw 4 427 tall blocks torn down and shipped to the company that melts them down to make cast iron drainage pipes under the roads here.
I think it has to do with the gas being $2.50 a gallon here.

Very sad to seethese motors getting trashed when the cranks go for $200-600 on E-bay
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