How much compression on jd a

[Michael Bay]

How much compression is to much compression on a 51 John deere A
 

[buickanddeere]

Depends.
You will ahve to supply some info such as cam duration, fuel octane, rich or lean mixture, coolant temp, all fuel or gasoline manifolds, rpms, ignition advance and air temperature.
 

[spareparts-45]

If you go much over 200# it will not lug down like it needs to.Had an A that was 12 to 1 it didn't start good ,would blow the petcocks out and didn't lug down.
It is now 10 to 1 no problems and pulls much better an will live a lot longer
 

[Michael Bay]

We got it all together and were pushing 180/150 with petcock open
 

[Kelly N.]

Michael, I can offer what I know from experience. I have an A that is stock stroke and has M&W aluminum pistons of 125 over bore. I installed a flat head on it and it is ALL I want since I haved to use 110 octain fuel in it. Did it give me more power. Oh hell yeah! but I'm sure it would have been cheaper and would have made alot more power to have had it stroked. But since I have no shop to work in and do all my work outside in the driveway, a crank removal and crankcase modifications were impossible for me. Its your decision.
 

[Kelly N]

I think I may have given the impression that I'm not pleased by what I have done with my tractor by installing the flad head. ON THE CONTRARY! It makes gobs more power and Im pleased with my expendatures. Compression is ALWAYS more power. All I have is 'seat of the pants' dyno time, but i know it makes atleast twice the power it made in totally stock form.
 

[buickanddeere]

At least twice as much power?
Depending how worn the old bores and pistons were and the engine being way below rated HP and making perhapes 20HP.
Then sure with round bores,minimal blowby and 11 to 1 compression instead of 5.6 to 1. Maybe 42 HP.
Factory was 37HP.
 

[Kelly N]

It was the all fuel, 4 something to 1 compression motor and yes it was welll used. Now it has 125 over with the M&W style aluminum pistons and is probably close to 10 to 1 with the flat head. The bigger valves and the better ports help alot also. It would bogg down in the 4500 class pretty easy without spinning out. Now it doesnt bogg in the 5500 class and does spin out. Would use garbage fuel in the beginning but now needs 110 octain to pull. So, yep i'de say it is about 50hp or more with no sweat.
 

[Kelly N]

This is numbers taken from tests done on the old tractors way back when:::
(Drawbar power (max): 26.20 hp [19.5 kW] }