Rpm range?

[Brock]

(03-14-2017 )Waterloo Wrote:  871, 3.36 gears 18spd, I find the sweet spot right around 1350 - 1400. I haul very light, normally just a few skids in a 53' dry box, and rarely leave Michigan. When I am heavy, I try to keep the rpm's up, she does not like to be lugged, especially with those lousy gears I am cursed with. And yes, I do use the cruise control, and I do have an occasional pull here in Michigan on a few roads I frequent. I will drop out of that and downshift to keep the rpm's up at that 1400 mark. Oh, I don't know how to double clutch, I have forgotten how to do that. ;-)

I love my 3:36 gears in my pete. I haul 140k with them but I have tall 11r24.5 rubber too. At 65mph I am at 1250rpm in top gear or 1500rpm in 17th. I like this gearing because 17th has more grunt to it due to it being a direct gear so I slow down on hills way less! So I always run in 17th, 18th is my "gettin home" gear. At 62mph I'm at 1400rpm which is a decent spot to be at with my cat.

[389driver]

(03-14-2017 )Rawze Wrote:  This bullS$it maximum 1500 rpm or less crap I see over and over...

Best advice I've read so far. The easiest way to explain it is to look at it like the automatic transmission in your family car... The farther you push the accelerator pedal down the higher the RPM range the engine operates in. The isx is no different. Low torque/demand: 1200-1400 RPM is ideal. High torque/demand: 1500-1650 RPM is ideal.

[Chamberpains]

Im curious if instead of looking at the RPM's for a "sweet spot" for fuel mileage. I've looked at it as don't take it over 10 psi boost with a 15-20 psi max. That way if 15 psi won't get you over the hill drop a gear and repeat till your up and over. But I've also been trying to see how it feels to watch the TPS position, sort of like Rawze says he keeps his foot at no more than 1/3 throttle which should equate to 33 TPS out the 100. But I just started this monitoring and finding it very hard to keep TPS that low without rapidly downshifting and losing all speed to a ridiculously slow speed in every climb. I find never exceeding 70 TPS with a fading throttle pedal (gradually letting up on the pedal) to keep it under my goal 15-20 psi boost at the same time seems to get me up and over most hills without literally crawling at 5mph over every hill.
The way I look at it if you gear yourself so that the engine load never goes above say 50% or less then it shouldnt matter how steep or long the hill is or how heavy the load, your getting maximum fuel mileage for whatever codition your faced with. The engine doesn't know its on a hill it just knows its being requested to work and how much is asked of it dictates how much fuel it needs.

The less you demand from the engine the less fuel it takes to get the job done.

Any thoughts or problems looking at it this way?

I guess I should add that I am a step deck flatbed operation pulling anything and everything anywhere at any time. Except California Canada and Mexico. And weight never exceeding 84000 pounds with a 10 speed 3.55 rears

[berrytrucking94]

Driven cats, much different than any isx ive driven.. a cat can take lugging better than an isx in my opinion. Hauling heavy with 3.90s my isx is happiest between 1600-1900 while going through gears. Truck will turn 2200 which gives plenty of room for using rpm to advantage on hills, hard pulls etc.

Lugging my isx will give high turbo temps and too much vibration. Higher(but safe) rpms are friendlier than some ppl think :big_smile2: