wolfe10 wrote:gemert wrote:
I am no expert but I do know one! I have a CAT engine. He researched the serial number and gave me the original test data. The way he explained it to me, with my limited understanding is that at 1200 RPM my engine is at max torque burning least amount of fuel. for me that would be somewhere around 57 in 6th gear. You are probably cussing at me now because I didn't answer in a way that most of us would look at it. I'm pretty sure that with a new coach of the quality of yours that it would be relatively easy for you to get the same data from either your coach maker or the engine maker. I'm guessing that they are all going to be a similar speed. For me the question is how fast can I go before the mileage just completely goes to "you know what?" For my coach that seems to be around 62 mph. I determined that by watching the engine data readout for fuel mileage.
What Cat engine you have???
It's in my Sig. Brett, it's a C-12 505 HP 1550 TQ. As knowledgeable as you are you probably know the guy that looked it up. Name is Dave on the BAC.
Happy Camping.
The Caterpillar 3126 and C7 have peak torque at 1,440 RPM. C9 or larger, yes, at lower RPM.
Just do not want to mislead anyone with a different engine than you have.
bluwtr49 wrote:
As has been said the "sweet spot" correlates to peak torque rpm. In my case the cat C12 is around 1250 or so and is fairly flat to ~1500 so that range is what I consider my sweet spot. ~1450 give me 65 mph so it all comes together nicely.
Find the torque curve for you particular engine and that should help.
tinkerer wrote:
A lot depends on head winds, but with my C7 Cat it seems that 72 mph is it's sweet spot as it will cruise over the hills with not downshifting especially when I run in the economy mode on the transmission,That is around 2000 rpms.
wolfe10 wrote:
Reality is the "best MPG speed" varies with coach, gearing and terrain.
On flat ground, the lowest RPM you can hold high gear is the best "reasonable" speed. That will be right at peak torque RPM for your diesel.
When I say "reasonable" in most coaches peak torque RPM in 5th gear (MUCH less aerodynamic drag at lower speed) will give better MPG, but is excruciatingly slow!
But, that speed (peak torque RPM, 6th gear) in rolling hills will cause a downshift on each hill-- so a little higher speed that will allow you to stay in high gear is better.
Crespro wrote:wolfe10 wrote:
Reality is the "best MPG speed" varies with coach, gearing and terrain.
On flat ground, the lowest RPM you can hold high gear is the best "reasonable" speed. That will be right at peak torque RPM for your diesel.
When I say "reasonable" in most coaches peak torque RPM in 5th gear (MUCH less aerodynamic drag at lower speed) will give better MPG, but is excruciatingly slow!
But, that speed (peak torque RPM, 6th gear) in rolling hills will cause a downshift on each hill-- so a little higher speed that will allow you to stay in high gear is better.
Good question -- max torque first, then top gear, then sufficient kinetic energy to top the hills at your chosen minimum speed (I prefer 50 mph). On fairly flat terrain, that is 65 mph for me. If there are major hills, it is 68 to 70 mph.
Most of my driving is at 65 mph. But with 400 HP and 1200 ft-lbs of torque pulling 36,000# (coach with Enclave), I probably have slightly more power to weight ratio than many on this list.
Mr. Mark, your Volvo and Prevost are quite heavy in proportion to both HP and torque. I suspect you may be 2 mph higher than me based upon those parameters.
Mr.Mark wrote:tinkerer wrote:
A lot depends on head winds, but with my C7 Cat it seems that 72 mph is it's sweet spot as it will cruise over the hills with not downshifting especially when I run in the economy mode on the transmission,That is around 2000 rpms.
Tinkerer, are towing when you are going 72 mph?
MM.
24 ft car trailer with a Honda CRV and Polaris trailer. If the ground is more level I like to cruise at 65. If I am bucking a strong headwind it might be 55. I like to see my turbo boost 25 or less when crusing.
