Heads: Can someone save me some work???
 

I'm trying to buy new pistons for the 427 I'm building to replace my 402...only problem is the heads I'm gonna use are STILL ON the original motor <doh>. I need to know what type of heads I have to get the proper compression ratio with the new piston. The heads are 1970 402 heads from a 1/2 ton GMC pickup. Does anyone know if these original heads are open/closed and what size combustion chambers they have?? If one of you experts knows the answer off the top of your head, it would be much quicker than pulling a head off and trying to find the casting number...

Mega-thanks!! JB:gmc:

what are the casting #'s off the head itself? If you have that, you can check www.mortec.com and find out exactly what you need. Just remove the valve cover and there should be a cast # right on them.

You only need to pull the valve cover to get the casting number.

Okay, pull the valve cover it is... Thanks for the info guys!

You are putting the 427 bbc in the truck in the pic? Sounds like a cool sleeper to me :D.

YUP! I bought this truck in 1994 in Harrison Arkansas then drove it to Washington DC, then here to VA Beach. It's about time I started working on it...it's all original (except the heads) and all the 33-year old parts aren't happy anymore!! I'm using this years tax refund to do the motor and start the frame-off resto. I'd like to set up a web page so you all can track my progress and laugh at how slow I'll probably be!!! I've got the block/crank/rods/pistons/cam for a 427 so I'm gonna build it and ace the 402...

Think it's overkill???

I hope so....<hehe>....

Hey JimmyBum, I'm doing the same thing. I've got a set of 290 heads and a 512 block. Both from a '69 427. The heads are most likely 101cc, but please post casting number. Maybe a call to Scoggin Dickey is in order, I have heard good things about the Mark VI Vortec heads. They are 99cc and are said to fit mark IV blocks with the right gasket. Flow way better than the old school heads, and are not much more expensive than completely R&Ring your originals. This is most likely the way I will go if all sorts out. Compression with a TRW flat top should be about 9.5;1, that's what I'm shooting for.

Thanks for the help guys!! I pulled the valve cover and got the number: 3975950. Here's what mortec.com says about them...

3975950....68-70...oval...OPEN...396, 402 Truck, 366T, 427T

Now, how can I find out the cc of the combustion chamber??

If they are open port being they are truck heads i would imagine they are big cc heads i have a set that are close to 125 or 128 cc heads.