I heard mention that putting on early 70's heads (pre '73 I believe) would produce more power when put on a 350 from years like mine, '77. How much of a difference would there be? Would it effect fuel mileage?

Thanks.

 

There was a set of early heads on ebay a while back and the seller had some numbers. See if you can still view ebay auction # 170092618553 If not I'll try to copy the numbers and forward them to you. John

P. S. I have a set of those heads on ebay right now, auction # 130099065310 ending Sunday evening.

 

Actually, you want 72-earlier small block heads. Your 77 heads will have 75-79 cc chambers. The early heads will have 60-64 cc chambers, which will bump compression.

There are a few things to consider, however.

First, 77-up Olds motors use 1/2" head bolts while older motors use 7/16" head bolts. You'll need to drill out the head bolt holes on early heads to use them on your 77 motor.

Second, pre-71 heads do not have hardened valve seats. Pick 71-72 heads if you want this (you probably do).

Third, while you're changing heads, you may want to have them cut for the larger W-31 size valves (that was the only difference between W-31 heads and those of lesser 350s). Of course, if you do this, you'll machine out the harended valve seats, which negates what I said above. You'll need to install press-in hardened seats, which means you can start with any year (72-earlier) heads. This is no big deal, but be sure to use Olds-specific hardened seats since the Chevy seats are sometimes too thick and can cause the machinist to hit water jacket. All the Olds performance houses sell these.