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Old 01-29-2009, 08:33 AM
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305 stock piston cc?

I got a sbc 305 from a 76-79 car, casting number 460776. Anyone know the cc's of the stock dish pistons? Or the deck clearance? stock internals, hasn't been decked either. Thanks any info will help

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Old 01-29-2009, 08:44 AM
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I`m not sure what cc dish the pistons have. However, the deck clearence is "supposed" to be .025, but usually isn`t. It`s often the decks are tipped. The only way to find out is to bring the number 1 piston to TDC, and check the clearence. You can do so with a basic dial micrometer or with a feeler gauge. Next you check the number 2 cylinder at TDC, then cylinders 7 and 8. Record the measurements and it`ll tell you how much the decks are tipped.
Some cases I`ve seen them vary by .002 which isn`t bad, but in other cases I`ve seen the front be dead zero and the rear be as much as .040.
I usually find the piston to be in the hole around .028 or so. But as said, it depends on how much the decks are tipped. Another thing to keep in mind is are the pistons factory pistons or aftermarket "rebuilder" pistons. Rebuilder pistons have .020 off the compression height. The factory piston has a comp. height of 1.560, the rebuilder piston is 1.540. So if it`s measured using rebuilder pistons it can be as much as .050 in the hole.
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Old 01-29-2009, 08:57 AM
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Thanks very much for the info. i have one in my car and a set of ported 434 heads sitting around so i might swap them in. just want to get the compression right cause he 434 have 60cc chambers. people have told me DCR of 8-8.5 is good for street application on 91 octane or better. also the squish should be ".035 to .045" any truth to this?
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Old 01-29-2009, 09:27 AM
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If the piston is the concave dish design you can`t get any quench action from them. With a 305 being small on the cubic inch side I would want at least 9.5:1 compression. So using a thin head gasket would be a step in the right direction. The only 434 casting on heads I could find is a pontiac made small block chevy head for race applications. If these are the heads you have don`t waste your time bolting them on to a 305.
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Old 01-29-2009, 09:44 AM
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I haven't pulled the head yet, the guy gave the motor to me and said he rebuilt it with stock pistons. the casting number is 354434. The sbc casting number book i have says they are 75-76 off of a 262. with 1.72 and 1.5 valves. The were fully ported from my dads friend down into the bowl. Why would it not be worth bolting these on?
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Old 01-29-2009, 11:53 AM
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The valves are too small. (unless someone installed larger ones.) the 305HO #416 heads have larger valves and the ports are larger too. (1.84x 1.50)

In order to get a decent cr on a 305 with a dished piston, you'd want a 52cc head. For best power on a 305 you want a 1.94x 1.50 valve set.
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Old 01-29-2009, 12:08 PM
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This engine by no means is going to be a high performance high output motor. I just want to get what i can out of what i have. Probably won't turn over 6000. I have another set of heads on a 76-79 305. i will post the casting number when i am back home friday night.

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