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We were getting 225 and 155lb ft on the dyno- unrestricted on the 20v motor.
That set up was 81.5 x 79.0 = 1649cc, legal for class 11 tarmac rallying in Ireland.
We were gettting huge BMEP out of this unit, and finding that with flicking back between 16 & 20v motors, we were able to cross pollenate and really home in on the engine's sweet spots, and not so sweet spots, culminating on a 1599cc at 217 on a 4-2-1 manifold- 140 torque but stupidly high up. Best torque we had on a 16v was 147 recorded installed.
The 20 valves always ran with 4-2-1 manifolds, and no doubt would have given more numbers on a racing set up with unrestricted (ie short) length side exit- or single seater length manifold- maybe another =10? on standard super unleaded at 12.2 CR.
The 4A was designed as a toyoa standard fare unit a lot earlier than the 16 valve conversion, so never really was optimised- and as usual, Toyota tried so hard in the "over engineering" department, but the thing is, the quality is there.
The need to go to a bigger bore is a bit of a red herring, as straight line acceleration is decided by cumulative torque though the rev band available via gearing choice, and change up point. I think the Puma 1700 rally motor is something like 81 x 81, and goes like stink.
The main problem with the Toyota block is the water drilling, I don't know if anyone ever came up with a way of doong away with it? I imagine one would need to liner the block, and then use a seriosuly trick head gasket with wire ring fixing to get it to stop blowing itself apart with such a spall space between cylinders.
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