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Old 01-04-2011, 11:48 AM
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Putting larger valves in a set of heads questions.

I just picked up a set of 305 heads, casting number 376450, ready to run for $50.00. They have new Z/28 springs installed, valve job, planed, hot tanked, and cracked checked. The guy I got them from also pocket ported the heads, and It looks like he did a really nice job on them. I have seen some pretty trashed home ported heads before in the past. He basically gave them away because friends of his said all 305 heads are junk. However, being the junk collector I am couldn't pass up a fresh set of heads for $50.00, especially with port work done to them.

I know they are not performance heads, but I am thinking of putting them on my old 4x4 chevy truck that the engine needs redone in. The truck has a 350 in it. I think they will work well since it wont probably see over 5K rpms in its life, and the added low end grunt to get its heavy butt moving. The heads have 60cc chambers in them.

They have the standard 1.72 intake and 1.50 exhaust valves in them. I have a set of new 1.84 intake valves sitting in my garage(again me and my collecting). I know the later 305 HO heads had 1.84 intake valves in them. It is possible to get these cut for 1.84 valves? I would disassemble the heads before I would take them in, and I can put the valves back in. I am wondering what kind of cost I would be looking at for a machine shop to do this if possible?

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Old 01-04-2011, 12:49 PM
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To just cut the seats for the intakes I'd guess about $100. Its probably possible but will only know for sure after you try it. it will help but its like putting lipstick on a pig.
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Old 01-04-2011, 01:07 PM
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Unless you are lucky, chances are that the larger valves will also require additional porting on the backside to accommodate them. It may be cheaper to just have the original heads done.
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Old 01-04-2011, 01:48 PM
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If you are going to go for the larger valves and new valve job, go with a 1.94 valve.
The heads probabily/may need further porting. Especially the bowls just under the valves and the areas around the guide boss. Open up the intake flangeport opening area to a felpro #1205 gasket size, no bigger. Open up the pushrod pinch wider and taller. Do not lower the floor of the port. You cannot port this head too much.
airflow is power

To do the bowls ("bowl hog") for the new larger 1.94" valves use a old 1.72" intake valve as a guide.
Open up the intake valve bowl so the 1.72" valve just fits in the bowl. Then take the heads in for a new 1.94" valve job. 1.50 or 1.60 will work on the exhaust side.
The exhaust ports on these heads needs a lot of work. Carve two strong flow paths around both sides the exhaust valve boss in the port streamline all the valve guide bosses. The opening of the exhaust ports only need be as big as the inside diameter of the headers, (not the gaskets)
All the valves will work better with a 30deg back cut on them.
The 450 castings are not the favoured/best 305 heads....but.....
They can work well for you if done right. Pick a torky Short duration cam for your 4x4. 211 to 218 intake duration 218 to 224 exhaust duration 108 to 110LSA 1.6 intake 1.5 exhaust rockers.

comp cams Dual energy 265DEH-10 comes to mind.

Last edited by F-BIRD'88; 01-04-2011 at 02:09 PM.
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