Mix 'n' match

[Ivan]

After being a dumbass and burning up my engine on Red, I acquired a 2H7 engine to transplant.

I have a cylinder head off a 4R0 that is in the process of getting ported, and new valves.

Will the late model cylinder head with the big valves run on the early model pistons without interference?

[Guy_b_g]

Yeah, but you'll lose some compression ratio Ivan. Works better with a set of Wiseco pistons, you still lose a bit of compression, (not as much) compared to stock.

[Ivan]

I thought the compression ratio was different from the dome of the pistons. Doesn't the wiseco kit lower the compression on the 78-79 and raise it on the 80-82?

I thought the heads were basically the same, but different size valves.

I could be mistaken. I was once before, but it turned out I only thought I was.

[Guy_b_g]

The Wiseco pistons dome height come in right between the later model XS11s and the early ones.

If You switch to the Wiseco setup on the '78 you get a slightly higher C/R.

On the Later engines it's about a wash from what I understand (due to the bigger bore).

The later heads have larger valves, but of you look at the head, they had to inset them deeper into the head to avoid clearance problems, that lead to a lower compression ratio, so they made it up with higher domes on the later pistons.

C/R from high to low would be:

'78 head/ '80 pistons (not sure if there would be interference here)
'78 head/ Wiseco
'78 head/ stock
'80 head/ stock
'80 head/ Wiseco
'80 head/ '78 Pistons

I believe this is the right order...maybe someone else can chime in?

[DGXSER]

Ivan, I'd look for a post by Dan Hodges. I know he has built these things thoroughly and went through all this.

I know the valve sizes changed in the 80 heads. I also thought the head chamber was increased due to more dome on the later model pistons. Which would mean lower compression using early model pistons and later model head.

[dbeardslee]

I wonder if using the 2h7 intake cam with the 81 head might help compensate for the lower compression. The earlier cams had more lift and duration, so you'd be packing more 'mixture' into the cylinders, even though it wouldn't be compressed as much. Or you could scavenge some domed pistons from a later model motor. To quote John Wayne, I'm just spitting out words to see where they splatter .