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12-26-2012 07:10:38

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Ive done all the hds on my tractors..i cut. 150 off it only makes like 5 to 10lbs of psi diff if u open hd up and grind brows out..u need to lengthen rods out to really make diff....josh blackburn has done few for 60 runs like 220psi now made huge diff but if u want to use it to farm with too i would keep it in 180 to 200 psi range

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12-26-2012 11:50:29

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 Re: JOHN DEERE 620 in reply to 2-banger, 12-26-2012 07:10:38  
I would work of volumetric efficiency and rpm before going to such high compression ratios. The rate of return on conversion of compression pressure vs combustion pressure into work is dropping by 175psi and not worth the rate of return past 200psi. That last 1-2 HP isn't worth the extra 10 octane points required in the fuel.

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Josh Blackburn

12-26-2012 15:14:11

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 Re: JOHN DEERE 620 in reply to buickanddeere, 12-26-2012 11:50:29  
Theories vs Dyno results. Had a b at 180 psi. Bumped it up to 230 psi and picked up 7 hp. No other changes at all. So in my opinion compression is your friend. Cams and cam timing is why most deeres struggle. Most tractors were off from factory and then you throw and grind on the wore out cam and gears and you are further off. Never have I had a tractor at 175 vs 220 psi only make 1-2 hp more. Yes race fuel is expensive but my 7 hp was worth the extra 4 bucks a gallon on the track.

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