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Logical question(s). Appears you have a 3116... is that correct? I ask cause in my 3116 with same gears as you and I can't even reach 64mph.... 59 MAX is it with tires at 85ish PSI and 225hp
I would like lower engine speeds around 65-MPH. The CAT 3116 hits peak torque around 1,560-RPM(same with the DT466 I plan to replace it with when it finally goes). No reason to push it beyond its mechanical comfort zone. I plan to be running Goodyear MV/T tires at specified 90 PSI on aluminum wheels with rebuilt axles. Not trying to do anything crazy here. If a tapped out motor bouncing off the governor at 65 MPH works for you that's great. Not my cup of tea though.
i have 3.07 ratio and my truck shifts to 7th at just over 45 mph (GPS verified). That's with "Normal" 395 Goodyear tires. There's a huge difference somewhere and I, too, would like to know what it is. Top speed is untested. Cruise at 55 is comfortable. At that speed the engine is at low enough speed that the fan turning on does not wake the dead. Tires are too out-of-round for higher speeds.
I have a 290HP 3116 out of an M1083 in my M1078A0. I changed the engine before the gears, so I don't know what it would do with a stock 225HP engine. I can hit about 72MPH on level ground. I keep it at 65MPH (which is just after the shift into 7th gear at 60-62MPH [GPS verified] for me), mostly because the tires aren't rated for that much speed. At 55PSI (HWY mode on my CTIS) the Load Range G - Goodyear MV/T's are only rated for 40MPH, when fully loaded! I'm not sure how that number changes when at about 1/2 rated load.
With the 2.87:1, 65MPH may be with the engine screaming at the top of 6th, not low in 7th. And you're dropping your torque a further 5%. You gain a little bit of fuel economy, because you're running at a lower RPM where the engine is presumably more efficient, but you're also going faster and air resistance goes up squared (exponentially). Running at 65MPH, low in 7th gear with my 3.07:1, I gained about 0.5MPG over my previous mileage when running maxed out in 7th at 58MPH with 3.90:1.
That's interesting. Mine would barely be in 6th gear at 45MPH (with 3.07:1 gears). Mine has always been that way (original 225HP engine, new 290HP engine, 3:90:1 gears, 3.07:1 gears, even after relearning the shift points in between each of those changes). Mine has WTEC-II, not III.
If you shift into 7th at 44MPH with stock gears, you would be shifting at ~56MPH with 3.07:1 gears.
https://en.wikipedia.org/wiki/Rockwell_International
somewhere in here is the dip switch settings that need to be changed.
Do you have a write up on how you did it exactly or could you write up what you did?
