[Junkyard Dawg]

Just curious on what rpm they're good up to? (stock unported with stock 2.06/1.72 valves)

I hear most closed chambered big block heads are good up to 6000 rpm....

[sschevellefan]

well I guess it would depend on your valve spring. I was always told that if the rpms are going to stay under 6500-7000 then ovals are the way to go. My buddy had a 427 with stock valved 702 castings and would rev it to 6500 with a comp 280 cam. Did`nt seem to be low on power at all.

[Junkyard Dawg]

Yes the rpms would stay below 6500-7000, I know from the factory these heads were on an engine with a 5500 rpm redline but I don't know if that means that's about as high as they made them breathe to (I'm sure the redline just means that's where the engine is not built to operate)...

I thought I heard someone once say those heads (3964290) are good to 5700 rpms and after that you are better off with rectangular ports....

[bracketchev1221]

It also depends on how big the motor is also. But under 454 ovals will be fine to 7000. The 408 I built goes to 7000 with 781 ovals like it was meant to. Unless the motor is real big or goes past 7000 continuously rect ports are not needed.

[Junkyard Dawg]

It didn't seem like they'd be good for much over 6000.....and as mentioned someone else said they'd run out of breath at 5700....

[sschevellefan]

well they have the same runner size as the 049/781 heads that everyone loves but they are closed chamber which hurts the intake flow but probably not enought to notice. I think you`ll be fine up to 6500 easy. You could always do a little porting to them to get some extra flow from them. You could also go with a bigger intake valve. there are plenty of guys here running similar heads with great results.

[Junkyard Dawg]

Actually I've been told on a 396/402 it's not worth the hassle of going to a larger valve because the small bore shrouds the valves.

[sschevellefan]

well the factort L78 375hp 396 had 2.19 valves in a square port hear that isn`t suppost to be good for a 396 either. there are guys still running the smaller valve and runnign hard as well, just trying to make a point. You need to talk to Chad. His screen name is 67supersport I think. He replied to one of your other threads. He has done alot of work with roller cams and stock type pistons and small valved heads,ect.

[sschevellefan]

here is a link to Chads website

http://www.rev.net/~harris3/

[70 beater]

From the Car Craft/Chevy Hi Performance cylinder head database:

http://www.carcraft.com/techarticles...cc/index1.html

GM Iron 290 Oval Head

This is a representative closed-chamber oval-port head. Even with its 50cc larger port volume, the small valves hurt airflow. This head continues to flow well beyond 0.700-inches of lift, which leads us to believe that larger 2.19/1.88-inch valves would help especially on the bottom end and across the rest of the board.




I love these guys.

[Junkyard Dawg]

Originally Posted by sschevellefan

well the factort L78 375hp 396 had 2.19 valves in a square port hear that isn`t suppost to be good for a 396 either.

From what I've heard the L78 blocks were set up to unshroud the 2.19/1.88 valves....I wanna say it was some sort of machining away the edges of the bores or something.....someone said it but no one has been able to verify exactly what it was......

Interesting that chart shows those heads still flow past .700 lift yet no rpm numbers....?

[sschevellefan]

I was just trying to make a point. They may have notched the cylinder to unshroud the valves but you could do that as well. Your heads will be fine up to 6500. even if they run out of air at 6000, your not going to feel to much of a difference if anything. If your worried about it do some port work to your heads and you`ll be fine.

Think about it, your motor isn`t much different from a 406 sbc besides the rod length and the extra weight. A 255cc runner that flows 260cfm for a 406 sbc would be a pretty big head and would`t run out of air at 5700rpm. I really think your worried for nothing. your heads will be fine.

[70 beater]

Originally Posted by Junkyard Dawg

Interesting that chart shows those heads still flow past .700 lift yet no rpm numbers....?

That's flow bench data,just a head by itself,and with a piece of exhaust pipe.