is it just the pistons, heads, and intakes that are different or is it the whole block? is it possible (realistic) to convert back and forth?

 

yep, just the intake/heads/pistons...
and possibly headers - many 18* (and less) heads come with a "stahl flange" bolt pattern. The different pattern allows you to run bigger headers (to match the intake flow!) without crimping the pipes around the header bolts.
Very possible to switch back and forth - just takes money.

 

The valve train is different as well. I know a guy with a 18* headed EFI 406. Makes about 900hp on motor. Also ran him around $30k before the nitrous setup.

p.s.- his car runs 8.60's on a 400hp shot.

------------------
-Joe
79' Z28 4-spd
http://joesmith59.freeservers.com/
*Boycott Lapeer*

 

that's right, forgot about that.
It's not the 18* valve angle (there are 23* heads that do the same thing), but they design the heads for offset rockers, lifters, etc...
This allows the makers to move the pushrod out of the way of the intake port for a straighter airflow path.

 

so would there be any machinework needed or is it just a purchase the parts and put them in kind of thing. i don't know if this is something i want to do but i just wanted to find out more info.
thanks
jeremy

 

Most 18* heads should be just a parts-swapping operation (very expensive parts, though)
Depending on the lifters needed, you *might* have to grind for clearance in the lifter valley, though - contact the people who make the lifters to be sure.