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Old 06-01-2009, 04:20 PM
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cobalt327 cobalt327 is offline
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Originally Posted by Plaintoast
lots of trucks came with casting 991 heads which was a 1.72 intake valve. there are other castings that did too, but thats a very common one.
Indeed there were- like to have fell out when I pulled the 350 SBC from a ca. '77 Blazer and found 1.72" intakes and 3/8" stem 1.5" exhaust valves- what you might expect to see on a 20-30 Series truck. I don't recall the c/n, darn it!

This engine seemed to be the original to the Blazer- had never-removed exhaust manifold bolt locking tabs, the OEM thread lock still on the bolts that hadn't been removed before, all original ground straps everywhere, etc.

Found this HERE:

1971-77 heads w/casting numbers that end in 882, 993, 487, 336 can have the 3/8" exhaust stems. 20-30 Series truck use.

Both small 1.72" intake and 3/8" stem exhaust valve on c/n's 261, 624 (likely one of these was on the Blazer I worked on).

Also 1987-'95 center bolt v-cover-type head c/n 14102191 can have the 3/8" exhaust valve.

EDIT- This could be a good engine to use the Vortec head on- it does require a different intake, but since you're already using a poor intake (IMO) an intake swap would help in any case.

There are $140 (new) intakes available for the Vortec heads from Professional Products, heads cost about $150 used (give or take), require some inexpensive mods to use w/lifts over .450" or so.

You can do a search on this forum for more info on the Vortec swap.

Last edited by cobalt327; 06-01-2009 at 05:34 PM.
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