2.62 gear ratio

Mine never does. The most at any time I have ever experienced for trans temps on the hottest day under the heaviest pull in my 18 spd running in direct is 130F. Most times, regular cruising, it barely even budges the needle. Oh, and it is not the gauge. I also have digital displays from another unit hooked in direct to the ECM that shows the same temps. Actually, if I go outside of direct, up or down, and run there for a while, my temps will bump up a little, 20+F like you stated. Direct has to be more efficient if we are basing solely on temps. At least it is that way in my 18 in direct.

 

That is a Kool Truck!

 

Confusing thread is confusing

 

Must have external oil cooler that seems about normal for that the I had with factory heat exchanger ran 150 to 180 depending on how heavy. Never ran for enough on direct to say if different

 

I could be of help, any questions?

 

Ok, so my question seems to simple then after reading this post. After 7 years company going owner and realized that I need help. Q? 13 vs 10 Eaton (ISX PRO STAR) but for $ best usable power without sacrificing economy. Should I look in the 3:36 range or lower? Weight range Ltl. 10K. To 36K. National otr. Thanks for any help.

 

With a 10 or 13 with a .74 OD ratio and 295/75R22.5s, you'd be cruising around 67 in the 1400 RPM "sweet spot" of the Family 1 (up to 450 hp) Cummins ISX engines with those 3.36 rears.

 

Bought a truck with 12.7 detroit, 500hp, 13 SPD 16913A, tranny, single axle, will be putting a pusher on it, tires LP22.5 255. Loaded between 38,0000 to 45,000 #
Loaded speed would be 62 empt,y 62 to 67. Would like to be in direct drive loaded 12 & 13 gear empty. What would be the best diff. ratio for the best MPG?
What is the sweet spot for RPM's for a 12.7?

 

My Detroit 12.7 60 has a ported ceramic exhaust manifold with a non waste gate BG turbo that has a blanket on it. Great exhaust flow which helps with keeping EGT's considerably lower and a little better mpg, but it wants to settle in and run right around 1425 RPM most of the time. Does real good even up to 1500. 1600 is not out of line either, but mpg does suffer a little. It doesn't like lower RPM's unless light or empty. The stock waste gate turbo will spool a little better at lower RPMS and is better for P&D work, but for regular highway stuff, the non waste gate BG turbo is a better choice.

I am running 2.64 rear ends being driven by an Eaton 18 speed. I only run in direct, 16th, at highway speed. 1425 has me around 62 and 1500 puts me at around 65 on Michelin wide based rubber. I am generally hauling steel coils, bulk ag products, etc that are around 45,000, but I do get some lighter stuff here and there. I just had an ABS sensor replaced and had them do a ECM dump to see what the numbers look like after 390,000 of owning this one. 7.83 mpg average according to the ECM. Probably a little off, so I just figure 7.5 mpg average for the life of the truck.

I wouldn't recommend this setup for everyone, but it has worked well for me. 3.55 in top gear of a 13 or 18 would be approxiately the same road speed at 1425 RPM as my 18 running in direct 16 with 2.64 rears. 3.08 would have someone doing the same road speed and RPM in 12th on a 13 or 17th on an 18. For the average generic setup and typical driver, with a 12.7 I would recommend 3.55/3.58 for the rears and a 13 speed.

 

Cowpie1, wouldn't my 7thH or 11 be direct as is your 16th gear? What you are running rpm and mph is what I want, if that is the best mpg.