1. Do you have any idea what torque converter you have? That will help determine if you truly have an M Code engine. (6/6/2012-Read the post that follows regarding '71 Torque Converters used on M Codes).
No idea, all I know is the partial vin# on the engine matches the dash Vin# which is M code. So how do I determine what torque converter I have?
Well, you can take it out and read the numbers on it. I don't know if you can remove the access plate that allows you to remove the flywheel bolts and read the numbers, although you might get a camera at a decent angle.
Or, if you have a tach, you can get a ball park range. (You do have an automatic, correct?):
1. Place your vehicle in a spot where you have LOTS of room in front of you, like a football field's worth of room.
2. Put your foot on the brake and push like mad.
3. While watching the tach, start to SLOWLY press on the accelerator pedal.
4. As the motor increases in RPM, the torque converter is increasingly locking the crankshaft/flywheel of the engine to the shaft of your transmission. At some point, regardless of how much you press the brake your car is going to want to move.
If the RPM at this point is less then 2000 RPM, then it would suggest the engine was not originally a 4V, or someone removed the 4V converter(Rare) and replaced it with a 2V. If it went over 2000 RPM, then I would believe the engine was originally a 4V. Someone could have installed an aftermarket converter(very popular to those of us who were teenagers at the time and didn't have a clue about what we were doing). But, I don't think it is likely someone would change out the torque converter when doing these other changes.
I posted torque converter specs on this forum a couple of weeks ago as printed in the 73 Ford Specifications Supplement. If you can't find it, I will post again. I think 2V had a spec of 1500 RPM, where the 4V had 2500-3000, enough of a difference that the test suggested above should work. You should also understand that the wrong torque converter may be the reason people feel their 4V's are dogs on the low end. Instead of allowing the motor to rev up to it's sweet spot of 3000K off the line(which the proper torque converter allows), their torque converter may keep the motor at 1500 RPM. I think everyone agrees the 4V has a hard time making torque at that RPM...but of course it doesn't stay there for long.
By the way, I like how you think outside the box.
It is the Polish in me.
