403 heads on 350

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blacks78cutty

Not-quite-so-new-guy
Oct 11, 2008
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i just rebuilt my 78 olds 350 rocket. with the original heads. i just came a blown 403. thinking about having the heads redone for my 350. wondering if it would be worth it and about how much power would it bring me? any help?
 
It would give you little to no gain, it might even lower your power.
I would recomend doing the work to the 350's heads.

The 403 uses larger head bolts and they have much larger combustion chambers which would lower compression.

They MIGHT have more flow, but a good porting & polishing of the 350 heads will take care of that.
 
Early 350 heads(68-70cc) will gain you power and 1/2 point compression with Corteco gaskets. Your 3A(75cc) heads exhaust ports suck bad, get pocket porting done in the valve area and any other porting to help your exhaust side. The 403 heads would to need be milled ALOT and still would ovelap the bore with minimal flow gain. Even #8(79cc) 350 milled .010-.020 with the .028 Corteco gaskets will flow the same as the 403 heads but will need the head bolts enlarged to 1/2" and one dowel drilled. This goes for any 330 or pre 77 350 head too. The 330(60-64cc) head is decent also but needs push rod holes reamed on all but the #4 due to a different cam angle.
 
The only advantage to the 403 heads is the larger intake valves. As noted above, there are a lot of disadvantages. Keep the 350 heads and install the 2.000/1.625 valves as used on the W-31s.
 
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