This sounds silly,I know,but need some help with it.I bought some C heads ,bare,need to know where to measure,to see which valves they have.Seems the most outer part measures 2.07,the next seam inward measures about 2.00.I've got digital caliper,help please,Thanks guys,later,BO

 

Check the head section in "Tech" at the top of page

Big valve is 2.072 exhaust is 1.625

Small valve is 2.00 exhaust is 1.65

if the flat surface of the seat is only 2.07 and the valve sets with in that diameter then it would be a small valve head.

 

Thank you,sir.BO

 

What is the measurement where the 45 (or 30) degree angle is at.
Nothing beyond that matters.
Jim

 

Hey,Yes i'm measuring the widest flat across,not the outside diameter,but where the valve should seat.Also not measuring the narrowest inside diameter,or the first angle.Theres not much difference in 2.00 /2.07.I need valves for these heads,just need to get the right ones,thanks for any futher advisment.BO

 

Actually, the valve can seal itself anywhere across the seat, depending on the exact angle it has been ground on. Many builders will go to a 46, or down to a 44 (or 29/31), just to put the interference right where they want it. You can see this once you slap (very hard) a freshly machined valve, and seat together for the first time. It will leave a line (hopefully) right across the center of the valves machined seat angle. If this line is too low, or too high, I may adjust the angle in which I grind the valve, to center it on the valve's seat.
Remember that a 2.072 will USUALLY be on a 30 degree seat, and can create an illusion of sorts. Factory seats are easily distinguished, though.
Go by the inner diameter, you have to have material supporting the valve, or it will never seal. Around .060 (min) on each side.
The numbers you give are even a little large for the typical 2.072 intake.
The factory usually goes around 1.950-1.975 inner diameter for the big valves.
A 2.00 (actually 1.995) will be around 1.85 inner diameter, or so.
These numbers will hurt many a ego, but tis the truth. It would be beneficial for many head jockeys to use THIS inner diameter to measure true window area, not the outer valve diameter.
I think (without seeing the heads-just going by the numbers you gave me) that you have large heads.
That's how I see it.
Jim

 

Thanks JIM,yeah its alot easier to measure that way,thanks,now i know.There 1.85,so there small valve.Thats ok,I had them magnafluxed today,there good.Also the machinist needs his motercycle painted[my trade]so he wants to barter.My kind of guy!He wanted to know why i'd like the center divider brazed up flush,I dont know.I'm sure its to produce power or olds builders would'nt be doing it.You've helped alot already,but could you explain?THANKS,BO

 

OH! He also questioned cutting for bigger[2.07]valves,since the seats are touching now.So I need to document everything so he'll understand.I dont want to come off as a know-it-all,or offend him.Just explaination.He can't tell me how to do paint work,but he can explain what he wants to do,SEE?Thanks again,BO
I LOVE THIS SITE!!!!!

 

You can fit a 2.072, and 1.710 valves in there, or even better- a 2.125, 1.625 set of valves, and the seat angle should be fine.The 3rd "chamber" angles (15, or 30 degree, top cuts), might get into each other. NO BIG DEAL.
I would not bother building up the center divider unless you are filling the crossover with aluminum, also. (20 HP-guaranteed) What you are trying to do is separate all 4 center exhaust ports from each other. Due to the firing order, you have the 4 center ports under pressure while those 4 exh valves are opening one after the other- BAD for scavenging! It's also why these things sound like tugboats, IMO.
It is actually easier to mill the exhaust side of the head (rather than braze, or spray weld the center, plus it raises the exhaust port), if you are running headers,
*** but lot's of people don't like doing this if they might ever go back to stock exhaust manifolds***.
You will actually have to mill off at least .125 to get divider totally separated on most castings. That is a LOT. You can go up to about .175 safely on almost every early casting, More than .200", and you will find water-FACT!!!
.....ANYWAY...if you want to make more power, I would go as large as possible on the intake side (you can go as large as 2.125 here), and keep the exhaust side at 1.625, and the valves won't touch. The machinist will then have a LOT of material to remove from the bowl area with a 60 degree cutter, and this opens up that "window" area, before the 45 degree seat. With a valve this large, you will have around a 2.05" or so, throat behind the valve. More bowl porting can be done here, leaving around .100" length of the 60 degree cut untouched, just before the 45 seat angle. Also narrow the guide. This will be your best bang for your buck.
Yes, I would fill in the crossovers, even if I left the divider alone. It does more for the money. Run an electric choke.
Print this out for your machinist to read, instead of trying to relay this to him.
MY opinion.
Hope this helps,
Jim
P.S.....Bartering is your friend! But It's TAXABLE!

 

Hey JIM,thanks a ton!!Yes,i'm planning to fill the crossover.I'm researching all i can.I want to do all the porting work myself.Also use every means to get the best heads i can,may take me longer because moneys tight,but i'll get there.A big plus i think.To me doing things myself is more rewarding in the end.I'd like to know as much i can about these old cars.Well, back to the research,thanks again,BO