Sweet Spot ???

[randco]

In January we purchased a new to us DP. It has a Cat 3126E diesel with an Allison 6 speed transmission. I have read several posts by individuals talking about their engines sweet spot. They claim that is where the maximum efficiency of the engine is.

My engine spec sheet shows Peak HP - 330 hp at 2,400 rpm and Peak Torque of 860 lb*ft @ 1,440 rpm.

So at what RPM is my engine operating at it's recommended efficiency? Or what is the sweet spot?

[wah864]

I have had two Cat's, both 330's. The sweet spot is between 1500 and 2000 rpm. The oldest one got 10mpg (an 01 Discovery) the newer on got 9mpg (an 07 Discovery) 62 miles per hour was right at 1750 rpm. When I pulled the long grade in Colorado outside of Boulder heading west I saw all sorts of folks overheating on the side of the road. That is about a 7-8 mile grade, I kept the tranny at 2000 rpm using the arrows and climbed right up without the temp gauge rising. Sorry to see Cat pull out of the rv industry.

[randco]

When I drive the Interstate I set the cruise control at 62. My tach reads 1650. We tow a 4,200 lb Buick Rendezvous as a toad and on our last trip to north Georgia and Charleston we got right aroung 9 mpg. I know the road in Boulder Canyon you are speaking of. We haven't driven our coach out that way yet, but I was raised in Colorado and went to school in Boulder. I had many great times out in that area.

[RCtime]

My driving mirrors the two previous posts.
cruise at 62-63 @ =- 1700 rpm, I use the mode button on the shift pad on economy as I prefer its shift points.
Any long grade I manually select gear 5 to 4 to raise the rpm =- 2000 rpm and have never seen my temp. gauge past the halfway mark.
Mileage 8.5 is probably a good average, however I have seen tankfulls much higher.

[Theberrys]

We have a 300hp Cat with an Allison six speed in a 1999 Tradewinds. The coach has @ 55k miles on it. Our best mileage is 1700 rpm which is 63 mph. We get between 9 and 10 mpg with the "Mode" light on. I also prefer the shift pattern with the "Mode" light on.

Dick

[randco]

Thanks to everyone for your response.

[Paladin]

I am sure wah864 was referring to the long climb on I-70 west of Denver (outside of Golden not outside of Boulder). West of Boulder (Boulder Canyon, etc.) would not be fun in a large motor home; i.e., you might need several changes of underwear plus while driving the motor home you couldn't enjoy all the scenery. I have a 350 hp Cat and I drive on cruise control @ 60 mph on interstates and on cruise contoll @ 55 mph on good 2-lane highways.