Thread: 350 / 305 head combo (what am I leaving on the table)

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Head casting numbers:

462624 ‘76-’78, 305, 58cc chamb, 1.84/1.50 valves, hardened seats, accessory bolt holes, best of the 305 heads 1.84/1.50 valves and ports too small for large cid; accepts 1.94/1.60 valves & seats

Block casting numbers:

14010207 Not sure ~ googled it and came up with ??? 4- bolt main / Truck block ???


Sold as a Take out 3K miles motor (Jasper Remanufactured) from a used Corvette purchase. New owner wanted more power and went with a speed shop built 450hp 350cid.

My intended use is in an early 80's inboard Competition Ski boat. 90% of the time I am pulling skiers at a snails pace 1800 rpm to 2800 rpm. Realistically what am I leaving on the table with the 305 heads (I'd guess top end RPM)?

What would be the best place to spend any extra $$$? I picked up this clean reman for $450 so I have some room to move. Vortec heads always seem to be highly recommended, but I think my application would classify as low rpm in the Hot Rod world.

Wish I understood more about piston / head / squish / cam design and relation to power performance, but sadly I do not.

This will be set up counter rotation, with appropriate crank seals / reverse cam / and stainless head gaskets. My last motor was a 130K miles 1990 Suburban take out ~ converted quick and dirty to reverse rotation. Still runs ok, but low comp on 1 and 5 + it uses too much oil.




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I'm going to agree with your assessment as your prop is probably worthless after 4 to 4500 rpm. So there is no reason to spin it any faster.
So those heads should work ok for this application. imho..

If you use 305 heads on a 350 you need to watch the compression ratio too. the smaller combustion chamber of the 305 heads will raise your compression at least 2 points which will cause you to run premium gas and you still may have detonation problems. back about 20 years ago stock car guys did that to get more low rpm power but they ran race gas I believe. (I'm no expert just good memory)

Thanks, Yes, the old style 13x13 brass nibral prop should be maxed out by 4400 or so. Searching the net for how to calculate compression ratio. Unfortunatly it will be a few weeks before i get it to a friends shop where i can open it up and check bore and cc the head. I'm wondering what made Jasper engine remanufacturing decide to use this combination. Only reason i see so far is cost - as these heads seem to be plentiful and cheap. I know a counter girl @ the local jasper hub who takes the shop orders. Im going to see what information she can get me from the reman tag.

Originally Posted by techinspector1

Understand this: YOU CANNOT INTELLIGENTLY CHOOSE ANY CAMSHAFT FOR ANY MOTOR UNTIL YOU ABSOLUTELY, POSITIVELY KNOW THE STATIC COMPRESSION RATIO BY MEASURING COMPONENTS YOURSELF OR HAVING SOMEONE ELSE MEASURE THEM FOR YOU.
You need 5 values:
1. Cylinder volume in cc's
2. Combustion chamber volume in cc's
3. Piston deck height volume in cc's (the volume between the piston crown and the deck of the block with the piston at top dead center)
4. Piston crown volume in cc's (a true flat top piston will have about 6-7 cc's in the eyebrows that are cut into the crown for valve clearance. Otherwise, for a dished or domed piston, the mfg will usually publish the volume). Most of the stock-type 350 pistons have a recess that isn't actually called a dish, but it is a depression across the crown, with a very thin ring of material sitting up a little higher around the bore. That little thin ring of material is insufficient for generating a good squish and you should be very careful with compression ratio and cam if you use that type of piston. The very best type to use in a street/strip build in my opinion is a D-cup dished piston. These provide a generous shelf of material that comes up against the underside of the cylinder head to generate a very good squish. If you build any kind of reasonable static compression ratio into the motor without using a good squish, there is a good possibility that the motor will detonate on pump gas.
5. Head gasket volume in cc's
If you want me to go through the entire routine and teach you how to find the exact SCR, just ask.
The camshaft will normally be the last component chosen, after everything else is nailed down for the build.

If you do end up using L31 heads, don't let anyone talk you into increasing the valve sizes. Stock, they are 1.94"/1.50" and will do a fine job on a 350. Any cutting done on an already thin-wall casting is just asking for trouble.

I found this great info from techinspector and wanted to add it to my post. I will ned this info to find my SCR.

Repeat: If you want me to go through the entire routine and teach you how to find the exact SCR, just ask.
Each and every one of us started off knowing NOTHING.

Thanks TI!

I would like to learn how to find the exact SCR.

SCR looks to be a key element in cam selection. Will I need tools beyond the basic dial caliper and lab syringe?