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Boris Badanov 
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Joined: Dec/14/2013 Location: NH USA Status: Offline Points: 4209 |
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 Posted: Oct/27/2016 at 8:15pm |
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Run it a tad rich and you will have no problems. |
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Gremlin Dreams
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Bruce Clarkson
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Joined: Feb/09/2013 Location: New Bern, NC Status: Offline Points: 538 |
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Posted: Oct/27/2016 at 8:16pm |
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I'm no expert but redid my 1967 343 4bbl. Dropped the compression to just over 9.6. I used a very close to stock cam. I normally run 93 octane but have no problem up in Maine or the midwest when I can only get 91. The only problem is that on occasion I've had to retard the timing just a minor amount if I had it timed tight for 93.
Would hire compession work OK. Dunno. I'm just passing on that mine works. Good luck Bruce Clarkson |
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Bruce Clarkson
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Ken_Parkman
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Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1814 |
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Posted: Oct/27/2016 at 8:19pm |
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One thing to note is the 68-69 390 engines have a larger deck clearance and are not as tolerant for compression. Off the shelf piston options are limited for those engines. One easy way to drop the compression is use the later 502 casting dog leg heads that are 60.1 cc's.
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Ralph G.
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Joined: Apr/06/2016 Location: Cincinnati Status: Offline Points: 185 |
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Posted: Oct/28/2016 at 6:58pm |
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Thanks to all who have replied.
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ccowx
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Joined: Nov/03/2010 Location: Yukon Status: Offline Points: 3510 |
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Posted: Oct/28/2016 at 8:44pm |
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Boris is right, a tad rich is good for keeping detonation down. Overall, I would start with rich and timing around 33-34 total, maybe 10 initial, all in by around 3500-4000. You can lean it out and advance the timing slowly until it feels good, which is safer for your engine. If you do this you should be ok with stock compression.
Chris
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