i dont disagree that you may have found a set of heads that a chamber a few cc off the "blueprint" volume, heads with the same casting numbers can have chamber volumes that vary somewhat, but i havent seen a variance of four cc before, but maybe the volume on those heads is supposed to be 68, even though i thought I always saw that vortec heads should be around 64

i think your wrong about the aluminum vortec heads on corvettes, if they're on the "new" corvettes, like corvettes after 98 they for the Gen III engines, if there from 93-97 corvettes, then they are LT1 engines, so no vortec heads ever saw corvettes that i know of, since vortec heads started in 96 and only went to '00, im pretty sure they were just found on trucks, as cars of the 96-'00 saw LT1's or some in 98 and 99 saw LS1's, and then starting in '00 Gen III were everything, and now i guess that '06 is going to start the Gen IV gen

i know what you mean as far as the blueprinted head may be off a cc or so and yes i use to think the same that vortec heads was just  64cc untill i came across these and crossed the #'s over you can double check if you like but i have checked them though four diff. webs and thorough the local chevy deal in my home town and they come back as a 68cc vortec head off a 96'chevy truck the cast # is 10239906 please fill free to double check me and let me know what you find out here is a web site i use to cross most of my cast #' it is very good and it has never lead me the wrong way http://www.chevymania.com   if you find out that these are not vortec head please let me know

906 casting heads are considered vortec, i know this from previous readings, its just that GM never made a alumium vortec head that could bolt on Gen I engines

now as far as the alum vortecs i am not saying you are not on them either but i have seen a set of alum vortec and it had GM stamped on them and the guy that had them said they came off a vette of '98 but it could have been untrue but could it possible that it could be a GM preformace head please let me know what find out about the cast heads and if you like you can check on this cast know also 12558062 chp used this cast in one of there tech articles

im pretty sure that in 98 corvettes went to LS1's

im also pretty sure that GMPP has never made a aluminum head dubbed vortec

Update:  I've purchased a complete 400 motor to rebuild.  It's a 4-bolt, stock bore.  It was in the process of being rebuilt - the crank was turned and installed as was a new cam & bearings.  I think I'm going to have the block and crank checked out just for peace of mind though.

Next on my to-do list is to order the KB pistons & get a set of 5.7 rods and then drop the block off at the machine shop for machining and assembly.

I think I'm going to buy a new set of Vortecs.  S-D has a package deal that includes the heads (with upgraded springs for up to .550 lift), rockers, head bolts, intake bolts, gaskets and a Performer RPM intake (I decided against the air-gap).

Am I correct in assuming I can use stock length push-rods?

Thanks again for all your feedback.  I'll post up again as I move forward.

John Noble

in theory i suppose you could use the stock length pushrods, as long as nothing has been seriously altered from stock, of course decking the block and re-surfacing the heads changes this, but unless there was a large amount of grinding done i dont think it would change it enough to worry about

Another question: I seem to be finding differing specs on stock Vortec heads with regards to valve springs and how much lift they'll handle.  I've seen specs from .450 to .490 lift.  Will stock Vortec springs handle .480 lift?

Thanks again,

John Noble

i just read that .420-.430 lift is the max for clearance from the retainer to the top of the valve guide

but on top of that stock valve springs are matched to stock cams designed for low RPM's and that peak at as low as 4500 RPM's, springs aren't designed to handle a certain amount of lift, they exert a certain amount of pressure that can handle a certain amount of valvetrain acceleration, stock valvesprings just dont exert enough force to do this well enough and you end up losing top end performance, its a fairly cheap investment and since you have to take apart the heads anyway to machine the vavlve guides down, then aftermarket springs that the cam manufacturer prescribes (even though i wish there was a better way) is your best bet

Thanks again Gibs, I thought as much.  I'm purchasing a kit from SD that includes heads that have already been modified.

http://www.sdpc2000.com/catalog/2172/products/108807/Upgraded-Vortec-Head-Kit-Edelbrock-Performer-RPM.htm

I was just wishfull thinking I could save $100 if I could go with standard heads instead.

You've been a great help.

John Noble