A friend has a Gen VI 454 square port heads and square port dual plane intake.He came to me saying after he fitted this in place of a small block he was 3" too high to close the floor area.I gave him a low rise oval port intake from a Mark IV and sent him off to fit it.He has just phoned to say it won't fit,basically that it sits too low in the valley.I'm real confused and can't understand it.I have also just pulled the same intake from a Gen VI 454 with oval port heads.Anybody know why?

Oval port heads runners are a lot smaller than rectangle port heads. You have to use an intake that matches the heads. Also Mark IV and Gen VI usually can't swap parts without modification.

Unless you are racing using a oval port intake on rect heads is quite okay and rect port Mark IV intakes fit Gen VI rect port heads just fine.Anybody have an answer?

If the block is a Gen VI 454/502 block, they're dimensionally the same as a Mk IV and Gen V. The only difference is there won't be the additional bolt above each pair of intake ports but that won't hurt it. Now on the other hand, if the block is tall-deck Bowtie, Dart or Merlin, that would account for the difference in spacing. You can use adapter plates to solve this problem. To identify, take a look at where the ovals for the water pump mounts are cast into the front of the block. If the ovals come right up to the block's deck, it's a 9.8 block. If there's almost a 1/2" gap, it's a 10.2 block.

The top of the port is above the manifold- wont seal with some gaskets.........Ken

Thanks Chris.Definitely a standard 9.8 Gen VI.I sold it to him.Ken are you saying gaskets are the answer.When he called he said that there was a gap and he could see into the intake ports above the manifold.I was sure it would fit straight on.

fast,
Are you sure he isnt seeing the cooling area around the exhaust crossover and confusing it with an intake port ? If the intake bolts go in, then the intake should be aligned properly.

Any chance of him getting some pictures that you can post ?

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Yeah i might have to go have a look.