My head is spinning with all the posts and other info I have read on rpm's and ratio's. A couple of questions here; I could use a little help. 1) On my 59 F100 223, what is a reasonable rpm if I want to do 65-70 MPH? 2) What is the ratio coming out of the tail of a 3 speed with OD when in 3rd gear or OD? I'm trying to get to a reasonable rpm on the highway by changing tires or rear end or both. I have found a couple of calculators but still need a little more guidance. Thanks in advance.

 

the only help I can give is my 60 w/223 & 3 on the tree turns 2200 rpms @ 55 MPH on GPS. with that said, on some of the older OE tachometers I have seen that 2000-2500 is safe operating range. I do not know rear end ratio-but if needed I'm sure I can figure it out for you

Joe

 

Thanks Joe. I've got 4.10 gears. Even in OD, 55 mph was a stretch.

 

you're welcome, anytime. I see that these 223's redline @ 4200...I couldn't imagine revving that high though-sounds like its going to come apart @ 3500, maybe just my motor

 

you going to do gears or a 5 speed swappie?

 

Probably do gears and tires. I live in San Luis Obispo county and can't find any here. I'm not opposed to heading your way if I find something that will work. The calculator I used did not factor in OD. I'm not sure where to go from here. I'll have to be a bit patient.

 

If your F100 has the original rear end it's probably a 4.11 not a 4.10. The overdrive will reduce the engine rpm by approximately 30% so I'm not sure why you can only get 55 mph, just doesn't seem correct.. Do you feel the engine is pulling to many RPM or just not enough power to pull it faster?

I can only give you a ball park figure on what I run for RPMs but I have 3.89 gears and 31" tires. It cruises at 65-70 with no problem at approx 2250-2375 RPM from an online calculator program I used one time, I don't have a tach. I'm happy running at that RPM and fine on level ground but hills often require shifting back into straight 3rd gear to maintain 60 mph at a rpm I'm comfortable with. I'm actually geared a little to high and it puts the engine below the max torque RPM.

 

Hi Jim. Correct, they are 411's however, not original. No tach, I felt it was higher than it should be but possibly not much power also. I do know for sure the gas mileage was bad. Your ratio, rpm's and tire size sound easy enough to accomplish. I'll shoot for that combo and run a calc with 30-31" tires. I can get a Dana 44 with, I believe, are 392 gears for $150 in Fresno. Does that sound like a fair price? I have no idea. The 30% rpm reduction in OD and your rpm info was very helpful. Thanks.

 

Does you F100 have a 9" rear now? It would be easier to find another third member with a better gear and swapping it rather then putting the Dana 44 in, JMHO.

Normally with 4.11 gears and overdrive it should run faster then 55 mph.

Have you checked the vacuum advance on the distributor is working? 223 distributors only have vacuum advance, no mechanical. If it isn't working the engine will be a dog...

 

Truck is inoperable right now. When I get it back together I'll check all items before I change anything. I believe its an 8.5" I have posted pix in this forum a couple of weeks ago.

 

Go to the west coast differential web site they have calulater it will tell you your what you want to know.

 

Thank you.