Gday fellas, would there be much of a compression increase with this mod? Obviously high compression better bang. Although would the .1 of a L make that much of a difference?

Cheers
Josh

I doubt it adds much, My 4.0 ED has a 3.9 head on it and it feels stock.

Sorry
Brett

depending on what your bottom end is??
at a guess if your bottom is the eb-early ed it would have been 8.8:1 so it might go up to 9.1 or 9.3:1..
but the thing with the 3.9 head is it might bump the comp up a bit, but the intake ports are smaller ...3.9 has 39mm intake ports where the 4.0 has 41mm intake ports..
so might gain comp but lose a little flow...

EL Bottom end. But that makes sense, forgot the ports were smaller... So shaving a 4.0L head wouldn't be of any benefit either?

Or should i just drop this whole mindset

How did you come up with the port sizes??????.....I have done an EA head, and an EF head, ( port & polish )and there was hardly any difference in them.
The inlet ports/runners are very close to the same size as the gasket, about all you can do is smooth it.

I have an EA head ( '88 ), on my ED 4.0.....and there wasn't any difference in performance.
The EA was making 186rwhp, and the ED is making 193rwhp....all the same stuff has been put onto the ED from the EA......the ED has a good bottom end......whereas the EA was stuffed...( rattled a bit ).

i measured them..
even the log manifold ports are smaller than the bbm ports...