Author Topic: 302 Compression Ratio  (Read 1604 times)

TooManyReels

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302 Compression Ratio
« on: March 16, 2011, 12:28:36 AM »
What was the factory compression ratio on a 1969 302, 10:01 or 11:01?
TMR
Eddie
63 Chevy II SS 570hp 560tq.
69 Z28 X33 Cross Ram JL8

bertfam

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Re: 302 Compression Ratio
« Reply #1 on: March 16, 2011, 12:58:07 AM »
11:1

Ed

TooManyReels

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Re: 302 Compression Ratio
« Reply #2 on: March 16, 2011, 01:03:51 AM »
Thank you...That would have been my guess, but I was just not sure...
TMR...
Eddie
63 Chevy II SS 570hp 560tq.
69 Z28 X33 Cross Ram JL8

william

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Re: 302 Compression Ratio
« Reply #3 on: March 16, 2011, 11:07:24 PM »
At the risk of sounding "techie" advertised compression in those days was the optimum possible number. All parts vary and the actual compression ratio could be lower; 10.0:1 or 10.5:1. Deck height and compressed head gasket thickness affect it. The standard speed shop "bluprint" included decking the block to reach the advertised ratio. Standard rebuild practices such as boring cylinders or a valve job can reduce the ratio.

TooManyReels

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Re: 302 Compression Ratio
« Reply #4 on: March 17, 2011, 01:05:47 AM »
So is Cam 2 fuel or higher octane required for these motors if driven on the street today..If so, that going to be an expensive ride,,,

TMR
Eddie
63 Chevy II SS 570hp 560tq.
69 Z28 X33 Cross Ram JL8

RAfbody

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Re: 302 Compression Ratio
« Reply #5 on: March 17, 2011, 02:31:14 AM »
That would depend on your cam choice.  Advertised and dynamic compression are totally different.
Russ

JohnZ

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Re: 302 Compression Ratio
« Reply #6 on: March 17, 2011, 02:16:42 PM »
So is Cam 2 fuel or higher octane required for these motors if driven on the street today..If so, that going to be an expensive ride,,,

TMR

With the stock "30-30" cam, no; its late-closing intake valve bleeds off some cylinder pressure, reducing the DCR somewhat, and any stock 11:1 302 that won't run properly on pump premium simply isn't tuned properly. Aftermarket cams always close the intake valve sooner in the never-ending quest for more power, and all bets are off with aftermarket cams.
'69 Z/28
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