Gear Ratios for 68RFE...according to the gear speed calculators I have found, and the transmission ratios

Gear
1 --- 3.231
2 --- 1.837
3 --- 1.410
4 --- 1.000
5 --- .816
6 --- .625

35's, 3.42's and 6th gear would put you about 1450RPM Way too low for my tastes.

If I had thought about it, I would have got 3.73's and put my 285/65R18's on it, and gave me about the same as 3.42's...just because I had them from my 98



BTW RJ, 315/70R17 and 3.73's would give you the same Effective final ratio as my 265/70R17's and 3.42's
Chris

 

Chris,
Rechecked my math..... made a mistake above.
But... 1600 rpm @ 70 mph in 5th gear, with 265's (31.8") and a 3.42 rear end, calculates to a .67 ratio. No?
I confirmed the math HERE

.67 make sense, to me. Where are you getting your figures? Are they published anywhere?

RJ

 

I have a gear speed calculator that I use...list's the ratios and calculates tire size based on the metric sizing, or known diameter.

Also found THIS

And This...from Automobile mag...
6-Speed HD Automatic 68RFE Transmission - $1,575
Automatic six-speed transmission with lock-up, electronic control, shift lever on column, 3.231:1 first gear ratio, 1.837:1 second gear ratio, 1.410:1 third gear ratio, 1.000:1 fourth gear ratio, 0.816:1 fifth gear ratio, 0.625:1 sixth gear ratio and 4.444:1 reverse gear ratio 68RFE; Automatic drive indicator on dashboard; Front seats cup holders fixed; Requires: [ETJ] 6.7L High Output Cummins Turbo Diesel Engine; Excludes: [DGQ] 5-45RFE 5-Speed Automatic Transmission


HERE is my gear speed calculator

Chris

 

OK! My error
Tried different on line calculator!
3.42's on 31.8" tires with final drive of .625....and at 70 mph = 1,581 RPM. Like you all said!

I'm getting old. Only took 5 months (this year) be be wrong for the first time.
(You believe me, don't you?)

RJ

 

Sure do...

Chris

 

Nobody really build a decent RFE68 transmission. Nothing over 700-800rwhp seems to pan out. The same thing on the G56 stick transmission. Depends on how badly you need that extra power.

 

Will Don M.'s injectors work in the 2010?
I paid little attention before, but just realized his Flux injector page discusses nothing newer than 07's??

RJ

 

He probably can do a set of nozzles for the engine. Rumor is that the injector has to go back into the same cylinder that it came out of. Each injector body is calibrated to the ecm for each hole. There are a few good choices out there beside Don, just in case you buy a truck. This is based what I've read, I have yet to try it out.

I'm keeping my injector stock until the smarty comes out and someone builds a decent RFE68 transmission. My new 10 is just for pulling my RV, in stock form it works pretty good for a stock truck. The older 2nd truck isn't great for hauling a family plus all the junk that comes when you go camping. You probably can run stock injectors/single CP pump and get close to 700rwhp. To bad the stock RFE68 transmission will hate you. Suncoast has a transmission supposily rated for 750rwhp but...

I wonder what dodge/cummins boys are thinking right now with Ford and chevy engines closing in on the advertised engine power of 400HP and 800ft*lbs.... The 10 CTD engine in stock form is 350HP and 650 ft*lbs, of course you can bomb the heck out it and dig out some that big power.

 

I know mine will run right with my Brother's 09 LMM Chevy...and that thing will walk an 06 CR Dodge with a 60hp tune on it, a Stock 2010 6.4 Ford, and a stock 09 6.7L Dodge. For being stock, it's not bad...and my new 2010 will run with it.

Loaded, the two truck drivers of ours that have taken my truck says it's got a lot more grunt than his, but they run about the same...just less RPM on the Dodge I'll take torque at 1500-3000RPM instead of an extra 50 ft lbs from 2500-3500RPM...but that's just me!


I really kinda think the 3.42's are helping the Cummins load up and make the torque it should...but that's just a theory
Chris

 

Well, I decided to go with the 3.42 gears and have put approx 4k on my pickup in the last month...... Empty it is where it should be in my opinion at highway speeds ( between 1500-1800 rpms not 1800 to 2200 rpms that my previous pickup would run at). I did tow a ~ 7 k trailer for 1000 of those miles. running down the road at 70 was a decent load, but the pickup wouldn't downshift until the steepest of grades. Once again if I pull a 15 k trailer i would just run in 5th @ maybe 65 mph or so.

Great vehicle so far. I'm at maybe 16 mpg empty right now and hope to improve to 18 after more of a break in. Thanks for all the replies you guys were a great help.

 

You can always tow your trailer in a lower gear. Even with my 3.73 gears, I manually kicked down the transmission a gear to climb a hill. The tow/haul button seems to firm up the transmission shift some. During hard braking, I kick a gear down or two just to get some rpm's for the exhaust brake to do its job. Mine doesn't shift down right for me during braking. Hopefully someone can write a program to do this automatically. The computer does do the down shift, but it’s not that aggressive.

 

5400 miles and counting...truck is back at dealer today to replace the battery in the key fob, and make sure the trailer brake controller is working correctly.

Mileage is decent, about 16-17mpg depending on driving...towing mileage kinda sucks, about 10mpg. I guess I'm just used my 95 that would still get 12-14mpg towing

I've happy with the truck...really impressed with how it handles a load. 72mph with the cruise set, in 6th, pulling hills at 23K GCVW at 1650RPM...I'm sure the tranny will hate me for it, but the engine was fine with it!

Chris

 

you are pulling approx. 15-16k and complaing you are getting 10 mpg? that really isnt too bad.

 

Yes, yes I am...because my 95 with MORE power will do it on less fuel. Also, will do it without having to downshift...ever

But the new engine is more efficient....
Chris

BTW, I'm not complaining about the new truck...but I am complaining about the EPA's definition of efficiency

 

Really? What do you think medium duty and OTR big rigs tow? What do you think they get for fuel economy?