Farmall m - whats up?

[north puller]

atached is a graph showing the pto torque curve of 2 farmall super m motors. The bottom is a pure stock, somewhat worn out 264 inch super m. The top is a somewhat built up 281 inch motor with higher compression and a cam.

Can anyone tell me why the torque takes a dive the way it does in the circled area? What might be going on here?

The tractors were dynoed on the same dyno, the same day. A M&W slide chart was used to calculate HP, then the HP and PTO speed were used to calculate torque.

I dynoed 3 other tractors that day, (not farmalls)and no other tractor experienced this dive in torque at 400-450 pto rpm which makes me think that it is nothing to do with the dyno.

Any idea what might be going on with these super m motors?

 

[Aaron SEIA]

Just my SWAG but is it the way the Farmall gov is working?
AaronSEIA
 

[Ed Carlsen]

Just a thought carbs on farmalls frosting or was the same fuel used in the farmall tractors (high octain?)not enough compression to burn that fuel?
 

[johns]

I think the cam has the biggest effect on the torque curve and where it climbs and drops. Surprising it is in about the same range on both tractors.
 

[Roger in Iowa]

Sticky advance mechanism in distributor?
 

[CLIFF S]

My SMTA would Change like that too But it was the time the Gov Opened up all the way!

I Changed the Gov Spring to a Stiffer One and it Helped make the Gov Smoove Out and Gained about 2 Hp at 540 on the pto!

Cliff S
 

[north puller]

It is not the gov. For the sake of the dyno test, the 281 had a very stiff spring. Likely would give 2500 rpm or higher. I loaded the motor up at part throttle, then opened the throttle up all the way. I then baked off the dyno till rpm's cam up to 700 pto. I didn't want to let it go any higher and didn't feel the need as I run slower than that at a pull. The gov was for sure wide open all the way.

The dist in this tractor has a 40 deg plate in it - could it be something to do with ignition timing and a change in the advance at that rpm? Would a dist with a 30 deg or 25 deg plate be a better choice?
 

[CLIFF S]

The More Compression the Less timing advance to Loug well!

I would Try a Distubitor with Less Advance and make Shure it works Smoove on the Advance and not hanging up!

Cliff S
 

[High Octane]

north, use stiff advance springs, or lock it up all together like a mag. itll help.
 

[MLPANKEY]

main thing is cams advanced to much. distributor needs advanced lockout and timed for initial timming . my two cents
 

[north puller]

How may motor rpm's will the tq curve shift with 1
deg change in cam timming?
 

[MLPANKEY]

[Dodgeit]

[MLPANKEY]