I probably screwed the math up, but I was trying to figure out what my 4.2L (auto) 3.55 F150 would turn if it had a 4.10 rear axle.

Right now I get 1850RPM at 65MPH.
My math tells me I'd get 2150RPM at 65MPH with the 4.10.

Questions:

• Is my math right? If not, how do I calculate RPM/ratio differences?
• Does 300RPM make that much of a difference? My 4.2L doesn't even wake up until way past 2150RPM.
• How can I figure what 3rd gear is? When I watch the digital tach it looks like it jumps 800RPM or so if I hit the OD off button.
• Does the transmission still lock out the torque converter in 3rd?

So far I'm very happy with my 07 4.2L.

 

Bump?

I'm especially curious about the torque converter lockout in third gear. I sure wish I could find the "specs" to the transmission. Shift points, lockouts, ratios and stuff like that.

 

I get 287 rpm difference. Pretty close to the 300 rpm you came up with.

I think 300 rpm might be noticeable, but not extremely significant when driving down the freeway. Likely more noticeable when starting off / pulling a load.

I do believe the transmission will lock / unlock the torque converter in 3rd gear.

I think I have all the info you wanted. I just have to see if I can find it ????

Thanks and sorry for the delay. Life has been a wee bit hectic lately.

 

I'm used to car, motorcycle and even R/C car/truck magazines publishing torque/horsepower dyno charts. It sure would be interesting to see the charts for the various Ford truck engines. Just giving peak values is meaningless, IMO.