Anybody know anything about these heads? I just got a set of manuals for the '91 caddys. The manual for the Allante has a little different wording than the others. It says "Swirl port design cylinder heads are used on this engine.", which the other manuals with the 4.9 don't say.

It also says the swirl port heads can be identified by a machined rib in the center of the head between the exhaust manifold and rocker arm cover, and by a large letter 'S' cast into the head visible with the rocker arm cover removed.

I'm thinking these could be a good upgrade and be more resistant to detonation being swirl type heads. May be good if you're planning forced induction.

Anyone know anything about these?

Edit: I should have said 4.5 Allante in the subject. I'm looking to use these on a 4.9 though.

--Dan

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[This message has been edited by houlster (edited 11-22-2003).]

Interesting. Anyone?

I've never heard that before.

All 1990-1992 4.5 engines used the same head casting as the 1991-1995 4.9 engines.

The casting number is 1645820

All of these 1990 and newer 4.5 / 4.9 engines used the same 1.770 intake valve and 1.500 exaust valve.

The Allante did have a stronger rocker arm pivot support made of steel.(pn 1641338) The 4.9 rocker arm pivot support is cast aluminum.

The Allante also used a different valve spring ( pn 1646891) that has a higher seat pressure and a longer free length than the 4.9. This valvespring has since been discontinued by GM. It is nothing special, but it did allow a maximum 5200 RPM compared to the standard 4.9 valve spring.

You gain nothing by swithching bare heads. Again the castings and ports are the same.

If you have a 1989 or newer Allante or access to the parts, a desirable combination would be a 4.9 longblock with Allante upper and lower intake manifolds, An afternarket cam such as one of the Delta regrinds, Allante rocker arm pivot supports, and good aftermarket valve springs.

Kerry

[This message has been edited by Kerry (edited 02-04-2004).]