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Old 10-06-2001, 03:56 PM
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Mr.Mopar Mr.Mopar is offline
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Default 340 Rebuild

I want to rebuild my 72 340 to 71 specs. The pistons, of course will be different, but the question is, if I use the stock 10.25:1 cast pistons with my 72 J heads that have been shaved .040 (cc'd at 64cc), will that bring the compression up to "premium gas only" use and will detonation be a problem? It's not a daily driver but it would be nice not to have that dreaded ping on regular pump gas. I'm using a Comp Cams Xtreme 268 cam with .477/.480 lift. Any problems with valve to piston clearance? Maybe I should just go with the MP performance 9:1 pistons and be safe. Someone has to know the answer....I hope.
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Old 10-06-2001, 08:53 PM
DAVE JONES DAVE JONES is offline
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Over 10 to1 CR, Iron heads.................Premium plus possible additive depending on timing and other variables. You will still have to be aware of pinging and detonation . The high compression pistons you are talking about will stick out from the deck aprox .02.
The J's are 915 castings and if they have been CC'd and verified that they are 64 cc now, then you will probably be ok and not have interference.....I did say probably. You will still need to check the clearence out. It will also depend on if someone has decked the block and the final gasket thickness you run. I think the worse case is that the valve reliefs will need to go slightly deeper to obtain the clearence if you need more. I have a positive deck highth of .02 and have run J's and 587's both that have been shaved to obtain 65 cc's. No matter what, you'll need to check and always run premium at a minimum.......Dave

You also may want to consider 2.02 intake valves if you're not running them now. You're obviously looking for more power.
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Old 10-07-2001, 05:29 PM
Darn Dart Darn Dart is offline
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I am running a 70 340 in my 73 Dart Sport with .040 overbore and TRW 10.5 pistons. I also use the 915 J casting heads milled .050 and cced to 63cc to bring me to a true 10.5 ratio. It is a strip only car and I have been running Amoco gold pump gas for 2 years with no problems. You will like the 268 extreme cam(I use it in my wifes car) it makes awsome power from 1500-5800rpm.
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