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Old 11-30-2012, 09:26 PM
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stupid question about valves

Are chevy valves all that different from pontiac valves? I mean if some machine work were done to the seat, could chevy sbc valves be used in pontiac heads?

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Old 12-01-2012, 04:23 AM
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I used Ferrea 5000 Series SB Chevy SS valves in 1963 Pontiac 421 HO/1964 GTO heads. The 4.910" valve length, 11/32" valve stem diameter and valve material is the same.

My engine builder turned down the valve heads and back cuts to fit Pontiac seats. I turned down Chevy 1.940" intake valve seats .020" for 1.92" Pontiac Intake valves and turned Chevy 1.750" intake valve seats .090" for Pontiac 1.66" exhaust valves. That also required a 30 degree back angle to reduce valve head thickness behind the 30 degree intake and 45 degree exhaust face angles. It cost $6 per valve plus the cost of the valves. I had to do that because there are no "off the shelf" Pontiac SS valves that size.
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Old 12-01-2012, 07:29 AM
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SB Chevy valves will fit Pontiac heads except for the 1967-and later Pontiac large valve heads. The large valves used in Pontiac heads from 1967 - up, are 2.11" I and 1.77" E diameter and SB Chevy valves are too small. BB Chevy valves will not fit Pontiac heads in any way.
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Old 12-01-2012, 12:57 PM
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Quote:
Originally Posted by Nuck Chorris View Post
Are chevy valves all that different from pontiac valves? I mean if some machine work were done to the seat, could chevy sbc valves be used in pontiac heads?
While many things are possible, the real question becomes is it practical, when there are Pontiac valves readily available.

What is it you are wanting to do? I hope it's not that you want to put 45 degree intake seats in a 30 degree Pontiac head...
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Old 12-01-2012, 07:00 PM
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I have a pontiac 350. I got some machined 1968 lemans heads, 18 I believe, for a good price. The intake valve size is 1.96. I was told by LATech that my valves are too small to hit 210 cfm. However I am pretty sure that 2.11/1.77 will be shrouded in the P350's bore. So I was thinking to myself, well what about some 2.02 chevy valves, would that bridge the gap? Would help me get to 210 cfm?
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Old 12-02-2012, 06:27 AM
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Valve shrouding is a problem in the 350. You will notice your block has a chamfer on the edge of the top of the cylinder to help unshroud the valves as the bore is smaller.
The guy in the video you posted ran the 092 heads from a 389/421, they have the 1.92/ 1.66 in/ex valves in them.
My thought is they are fine and bigger is not better when you want torque. I would bet he did some port work on the heads to make the runners more uniform in size, without enlarging them too far for CFM as that would cause a velocity drop and torque would suffer.
That being said, his cam choice and carb mods were probably accompanied by port work, done correctly, yielding his results.
He didnt need the larger valves.
Just my 2 c.
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Old 12-02-2012, 09:51 AM
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Agreed with Lynn. Large valves on a 350 are not the hot lick. And who said you "can't get" 210 because of a 1.92" valve should not be consulted again. That valve size will support well over 250 CFM if the ports are "right". It's possible to gain a BUNCH in the Pontiac intake runner with the proper approach, and it results in very little loss of low-end. Those 18s are decent heads for the 350. A good port job is called for, though.

Comparing '64-back heads to '67-newer is apples to donuts. '65 and '66 heads are okay, but NOTHING like the good ones later.

Agreed, "bang for the buck" is better with the larger cube Pontiacs. One said you can build a bad-*** small block for the money it takes to build a strong 461. True. However, that small block would be very "high strung", and no small block can approach the level of low-end power the big Pontiac makes. Drivability in a street car is second to none with the 461 done "right", and still making BIG power (not unusual to see a 3,600 lb. 2nd gen F-body running 10s on pump gas).

Butler Performance is one of the many Pontiac specialists "out there". They are the "premiere" shop, building moslty "high-end" engines. Good people, good stuff. David is "straight up". Butlers took the "big dog" spot from us in 2010 with their ProMod (6.26 @ 227). Nobody has approached that since. There are a couple "threats" that, once they get "sorted", should be solid 5 second cars, including one nitro funny.

Jim
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Old 12-02-2012, 11:58 AM
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The only thing iffy about the Pontiac bottom end is the rods. And the large journals on the big engines if they're going to rev. Cranks are stout as-is.
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Old 12-02-2012, 12:09 PM
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You said the bottom end wouldn't be reliable. I say the crank is fine. The 350 Pontiac is totally capable of 400 ft/lbs w/stock 3.75" stroke. If the pistons are worn and the block needs reboring, buy pistons- obviously. The heads he has are capable of enough CR as-is.
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