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Hi guys,
My friend Dave Taylor, B'Ville racer , is now trying to re=create his early 50s competition coupe drag car.
He has an aluminum 12 port head which will be going on a 302 Jimmy which I supplied. I'll see the casting# tomorrow.
He is NOT computer literate! I am helping.
The head is empty and I am looking for info on the valves.
A specific set of specs rather than a application is what I am after.
They look approximately like 2.02/1.60 Sm Blk Chev valves with .341 stems, but the length is a mystery so far.
They look to be in the 5.5" range.
All help and comments appreciated (as usual) Regards, W.
49 fastback bonneville project
51 club coupe street hot rod
50 ford taildragger
flthd roadster pu
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Joined: May 2000
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Look for some used NASCAR valves. Some are extra long.
FORD 300 inline six - THE BEST KEPT SECRET IN DRAG RACING!
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Joined: Jan 2005
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You won't know the length until you repair and install the rocker shafts and arms. The contact pads will tell you the stem height, depending on the cam lobe height and rocker ratio.
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Joined: Aug 2006
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Which head is it? Horning's and Wayne's used different valves because of the chamber in the Horning. In the old days you made do with what was available; I know many used Cadillacs. If it's a Skinner I can give you the head diameter and lengths....Good Luck
216.158 MPH 12-Port 302 GMC on 70% 171.0 MPH 302 stock head on gasoline 7 years later
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Joined: Aug 2006
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Opps! Horning's and Wayne's used the stock GMC rockers and adjusted lengths with lash caps and push rods...
216.158 MPH 12-Port 302 GMC on 70% 171.0 MPH 302 stock head on gasoline 7 years later
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Well, that shortens the list of variables, but (except for parade purposes) the GMC rocker isn't up to big springs. Of course, the problem is that there isn't anything else.
Milling or shimming the stands is also a variable, but as I said you won't know until you get closer. Pushrods are the very last purchase.
Which cam does it use, stock GMC lobe positions or special?
The stock valves are:
Ex - In - In - Ex - Ex - In - In - Ex - Ex - In - In - Ex
The Fisher/Horning looks like this:
In - Ex - In - Ex - In - Ex - Ex - In - Ex - In - Ex - In
Not sure if actually made for GMC, but common 12 port layout:
In - Ex - In - Ex - In - Ex - In - Ex - In - Ex - In - Ex
These 2 last require special billet camshafts.
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Panic, IIRC Ron Golden made a set of roller rockers for his Jimmy (HA/GR car over on the HAMB) and was successful with those. Just for an idea, here's a post with a picture in it. http://www.jalopyjournal.com/forum/showpost.php?p=2298475&postcount=11
My, what a steep learning curve. Erik II#5155
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I have a copy of the original blueprints (dated 10/2/1951) for the Horning/Fisher head. It lists the intake valves as 1.875 dia and the exhaust valves as 1.625 dia. Length is 5.5 inches. In addition it lists the push rod tube length (less ends)as 10.187 inches.
Last edited by greyghostgmc; 04/10/12 12:13 PM.
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When I had Harlan Sharp make a set of custom rocker arms built for my crossflow Ford they told me they used Pontiac extrusions. I had them bronze bush the pivots vs needle bearings. Roller tips. But be forewarned it required me to make a trip to their Ohio offices with a set of blueprints of what I needed to get their attention. You must be willing to sacrifice to have a unique and technologically superior engine. That means hours of selling your ideas and up-front work on your part. 
FORD 300 inline six - THE BEST KEPT SECRET IN DRAG RACING!
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I don't know where the idea that stock GMC rockers were not good enough. There were no roller rockers in the 60's and I don't remember having any problems. We used the set with aluminum stands and welded the rockers down the split on top and tacked them on the under side. I still have a set on the stock shaft. Even with roller lifters we normally didn't have over .550" lift total. Think about it the push rods were 2" longer than stock and couldn't take it. Springs were good for about 6500 max if drag racing and lower for the lakes. Our problem was going thru valve guides since the rocker tip pushed the valve sideways because of the lift. I didn't have roller rockers until 1991 when I designed and made my own. As I remember only 3 guys had them on the west coast. Don Ferguson made his first set right at the same time I was doing mine and his copyed Joe Fontanas. Mine were a little different at 1.63 to 1 and have never failed.
I now have a set of Joes 1.75-1 and look to go over .700" lift. Gheesh when I got over .620" I thought it was phenominal for a GMC. 50's knowledge was trying new stuff and breaking it to know the limit....Just like today. To bad we can't go back and Howard J. on how much he broke going fast.
Hey have some fun, built what you like, and some day my kids will throw all the "junk" I've got hidden.....but don't count on it.
JD
216.158 MPH 12-Port 302 GMC on 70% 171.0 MPH 302 stock head on gasoline 7 years later
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