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JOHN DEERE 620

A

Anonymous-0

Well-known Member
How much can I shave off the head to raise the compression without getting in to problems. The engine is .125 over and cranking compression now is around 120psi. What pressure should i shoot for and how much power will be gained.
 
The mistake was not installing LP pistons when it was apart. Then having the cam re-ground and the followers re-faced.

You won't find a lick of difference on a dyno let alone the track. Between stock, 45, 90 and 125 over bore.
 
How many hours are on the motor? If not too many? You can re-ring/rebuild withour the worry of a ridge at the top.

If you are serious at all, you want new high compression pistons, and/or longer rods.

I have heard of .250" oe more being taken off a deere head, but the more you remove, the weaker the head gets. You may find your pushrods get too long as well.
 
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 me...my 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
 
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.
 
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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