tvis head

[totta Crolla]

Is it possible to fit the tvis head onto a later engine block that originally had the small port head (AE92) ? Would the higher compression help to increase power ?
Why ??
Because the regulations I have to run to for road rallying in the U.K outlaw modifications to the inlet manifold/plenum, my engine currently does about 400 miles per litre of oil

[Ivan141]

I really have no idea what you mean....the TVIS head doesnt have higher compression AFAIK. The head will probably fit on the high comp block.

[Darkstar]

The early type TVIS head will fit on a AE92 block. The benefit from this is higher compression ratio compared to the standard engine, and more flow from the 86 head (with smaller intake velocity tough, because of the bigger intlet ports). Also, the 92 block is stronger than the 86's, and uses oil squirters. I suppose the best shot would be to use it as a high power NA screamer, which should be good for an outlaw rally car. Good luck with it!

EDIT: It's not the head that makes the comp. ratio on the AE92 higher - the pistons are different.

[totta Crolla]

thanks Darkstar, just the answer I was looking for. Do you think there would be any benefit in using the AE92 cams as well ? When you say early tvis head I assume that would be the one from a 3 rib block ?

[AEsuperG]

ae92 cams are slighty smaller than ae86 cams. like 10 deg and like .2mm...something so little that you would not even notice.

some ae92 did come with tvis and low comp 3 ribs. i dont know if that is the case in EU.

[Ivan141]

I have an AE92 TVIS 3-rib engine in my car at the moment. And as darkstar's edit says, it's the pistons that create the higher compression, not the cilinder heads. Bigport heads are basically crap...but if regulations dont allow you to re-weld the non-tvis manifold, or the use of an adapter plate for a bigport manifold then yes, you're condemned to fit a bigport head.
May I ask what causes the oil consumption you mentioned? I dont see what it has to do with the manifold.

[PetzK]

I have a smallport block with largeport head (milled 0.5mm) and largeport cams - this should give best power with least modifications.

[Darkstar]

As someone earlier said, the cams in the early type 3-rib 4AG have slightly longer duration, and - if I remember correctly - the lift is just a bit higher. Using the AE92 cams may lower the power, especially in the bigport head. I think it should be possible tough, considering that you can put AE86 cams in the AE92 head.

EDIT: There are lots of things that can cause high oil consumption... Have you checked anything yet?

[totta Crolla]

Not sure about the oil consumption, no leaks and no black smoke from exhaust. Could it be the head filling up with oil ? I've heard this can be a problem on early engines. How much oil is likely to be lost by this happening ?

[Ivan141]

The oil problem only occurs in long corners..The cilinderhead doesnt have adequate drainage to let the oil flow back down and thus it gathers in the head. In long left-hand corners the oil builds up in the head and then gets sucked into the inlet manifold through the crankcase ventilation. This effect is easily demonstrated by driving a few fast circles (turning left). The car will lay a smokescreen if you keep it up long enough.