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Author Topic: 3917291 sbc heads 2.02's or 1.94's  (Read 3620 times)
pjbizjak
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« on: January 23, 2010, 06:27:18 PM »

The 3917291 heads come in two types, one comes with 2.02/1.60 valves and the other comes with 1.94/1.50 valves., both are 64cc.Does anyone know if the castings are the same and they are just ground for the different size valves?

Pete
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jonboy1216
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« Reply #1 on: January 23, 2010, 06:47:40 PM »

i think they are the same .production castings didnt vary alot due to the fact that thousands were built with the same patterns and molds
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RAfbody
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« Reply #2 on: January 23, 2010, 07:01:02 PM »

The castings are the same.  The combustion chamber on the 2.02 heads have some machine work done to unshroud the intake valve.  It is fairly easy to have the 1.94 heads machined for the 2.02 valves and be correct.  A lot of the time the original 2.02 valve heads have had a valve job or more and the seats are deeper in the head so a rebuilt 1.94 is more desireable.
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Russ
1968 Z28
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« Reply #3 on: January 24, 2010, 12:10:19 AM »

The castings are the same.  The combustion chamber on the 2.02 heads have some machine work done to unshroud the intake valve.  It is fairly easy to have the 1.94 heads machined for the 2.02 valves and be correct.  A lot of the time the original 2.02 valve heads have had a valve job or more and the seats are deeper in the head so a rebuilt 1.94 is more desireable.
X2 on this idea....I replaced the heads on my Z28 with a good used set of 291's with the 1.94/1.50 valves.....even found the right cast dates.  Had the machinist  replace the old valves with new 2.02/1.60 valves and had him to unshroud the intakes.  Those heads looked like new ones when I got them back.
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Jerry G.

Z28-1968-07C-Norwood
Ermine White, Red Std. Interior
2nd. Owner, 38,000 miles
68Zproject
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« Reply #4 on: January 24, 2010, 02:05:25 AM »

X3
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68Z28
pjbizjak
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« Reply #5 on: January 24, 2010, 10:30:03 AM »

Thanks guys, i'll now concentrate on the casting dates now, I need late March 68's.
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jims68z
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« Reply #6 on: January 24, 2010, 11:42:46 AM »

X4.  When I bought mine, it had 2.02 valves shoved in them but they did not fit right and I didnt pay that close of attention.  The machine shop ground them to fit the 2.02 valves for me.
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JohnZ
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« Reply #7 on: January 24, 2010, 09:08:16 PM »

Photo below is a 461 chamber with factory 2.02/1.6 valves, showing the unshrouding cut adjacent to the intake valve; if you have 1.94" valves and have the heads machined for 2.02's and don't have the unshrouding cut done, they'll flow less air than the 1.94's did.
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'69 Z/28
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pjbizjak
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« Reply #8 on: January 25, 2010, 12:40:36 PM »

Thanks again...I assume 291's that came with 2.02's had the unshrouding done at the factory?
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Stingr69
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« Reply #9 on: January 25, 2010, 02:12:55 PM »

Thanks again...I assume 291's that came with 2.02's had the unshrouding done at the factory?

All of the "double hump" or "fuelie" style heads that were originally factory fitted with the larger 2.02"/1.6" valves will have the intake valve unshrouded like that picture John posted.

-Mark.
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