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Nov 22, 2002 | 11:07 PM

Jimbare

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From: oklahoma

gear ratios

Nov 23, 2002 | 06:54 PM

freejay

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From: Alberta

gear ratios

Ok I have a two part question here. First, what kind of usable RPM range do you get out of a 360/390? (normal driving, and I guess the 390 would be better down low because of the longer stroke) Second, I have 4.10s in my F250 right now and it is definately geared too low so im looking for input on what most guys prefer 3.73 or 3.54? I will be pulling a trailer some of the time, nothing extremely heavy. Thanks for any input:-)

Nov 23, 2002 | 07:22 PM

gtex

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From: Texas

gear ratios

[updated:LAST EDITED ON 23-Nov-02 AT 08:23 PM (EST)]My 390 runs well to 5500 RPM+, it seems pretty happy at 3400 RPM on the highway. Diamond Shamrock is also happy :-( I'm seriously considering an aftermarket OD unit.

Less than 5000lbs of trailer, I'd say 3.55s are ok. If more than that , I'd stick with the 4.10s or consider 3.73 gears. It's probably not worth the money to go 3.73 in my opinion.

Nov 24, 2002 | 07:17 AM

jowilker

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From: Creedmoor, North Carolina

gear ratios

Damn Gtex, Why are you running that ol mota that hard? At 3800 mine has used all of the numbers on the speedo (and it's more than 85).

Jay FEs like other Ford engines make their torque in the lower rpms. Ideally you want to be running the hiway at 25-2800 rpms. The 410s are too short for a big V8. 3.25 should work nicely also. IMHO of course.

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Nov 24, 2002 | 07:39 AM

jds1971

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From: Watauga TEXAS

gear ratios

That's what I'm talking about.

I'm doing 2250RPM at 60MPH with a 360, C6, 3.25's, and 31" tires. The highest I've ever had it was in passing gear at 70MPH and it was turning 3800RPM.

Joe

Nov 24, 2002 | 10:11 AM

GolferSA

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From: Texas Hill Country

gear ratios

[updated:LAST EDITED ON 24-Nov-02 AT 11:16 AM (EST)]The data plate on my truck says I have a "G" tranny and an "08" axle... that equates to a "Ford-A-Matic" tranny and a 3:50 rearend. The tranny is a 3 speed, and I believe the Ford-A-Matic was a 2 speed... Yes? No? Either way, the tranny pan has the same configurement as a C6, so I'm assuming there's been a swap at some point.

Looks like it's the original rearend, but is there an easy way to tell what's in there, or do I have to break the housing apart? I have no tach, so I don't know what rpm I'm running, but it sure seems like it shuts down quickly when letting off the gas.

Thanks!

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Nov 24, 2002 | 10:54 AM

gtex

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From: Texas

gear ratios

I've got 4.10s, and 255/70r16 tires (about 29.5 inches tall). I do have long duration cam, and bigger carb. So my truck may not be typical. At 70-75 MPH it is running around 3400RPM. Works well with the new 90 galon tank I put in the bed :-)

For towing, you want to be at highway speed at the RPM that provides the most torque. Thats why I suggested staying with the higher gears if you will be towing. I suspect the torque peak is somewhere over 3000 RPM for a typical FE. In hotter 390s it's probably closer to 4000.

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Nov 24, 2002 | 01:03 PM

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From: Brea CA

gear ratios

"G" means an auto tranny, it doesn't tell you which one. It could either be a Cruise-O-Matic (MX) or a C6 (which I think yours is).
Ford-O-Matics were the old cast iron 3 speeds and Fordomatics were the old alum. 2 speeds, confusing isn't it?

Barry

Nov 24, 2002 | 06:25 PM

#10

GolferSA

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From: Texas Hill Country

gear ratios

Well gee, Barry... thanks for clearing that up!

Any clear cut way to tell what the rear-end is, without pulling it apart and counting teeth?

GolferSA

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Nov 25, 2002 | 06:00 AM

#11

jowilker

Fleet Owner

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From: Creedmoor, North Carolina

gear ratios

One method of checking the rear gear is to count it's revs. Two very important items needed, a very level spot and a helper. Mark a rear tire at the edge of the tread, and the drive shaft as well. Have one person watch the ds rotate while the other pushes the truck one complete tire revolution. Count the turns of the ds. You will need to watch carefully for 1/4, 1/2, & 3/4 turns of the ds. I like using the garage floor, it has less resistance.

Nov 25, 2002 | 07:32 PM

#12

jds1971

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From: Watauga TEXAS

gear ratios

Just make sure you don't run over your buddy!!!! It's would suck to have to scrape his carcass from between the treads on your tires, not to mention the driveway/garage floor!

Joe