sheriffav8r

Okay, on the 5.9 it is generally acknowledged that 1900-2100 is the sweet spot for engine RPMS while cruising. I agree. At that RPM the engine just sounds sweet. What's the sweet spot on the 6.7? Looking at both the 5.9 and the 6.7 power curves it appears that the 6.7 should be somewhere between 1700 and 2600RPM with the middle at 2000-2200RPM? Any input?...

dhe9

i would think that depends on the gearing in the rear end. my 5.9 with the 3.73 loves about 1900 RPM. have an '11 being built for delivery on 15 august the dealer tells me and i ordered with the G56 and the 3.42 gearing. i have had both 4.10 and now the 3.73 so the 3.42 will be a new animal for me.

semper fi '68 - '00. "what a long strange trip it's been."

david
socal

Blake Clark

Mine seems to be happy at around 1800 rpms.

68RE, 3.73's 35 Toyo's

That is right at 76-77 on the interstate.

ramtradxb

Gotta pretty much mirror what Blake says - it surprised me but mine seems happiest at one or two hundred under two grand - much less than my 5.9...

(w/ Auto, 3.73's, and 34's)

sheriffav8r

Interesting. The 6.7 makes 220HP/650ft.lbs at 1650ish rpm and 350HP/650ft.lbs at 2600ish rpm. The 5.9 makes 100HP/460ft.lbs at 1400 and 235HP/460ft.lbs at 2400ish rpm. I would have thought that the spot would've been higher for the 6.7 but I guess not, since the 6.7 makes HP faster on the flatter/longer torque curve.... From what I can figure, my 3.73 with .69OD in the 5.9 is about the same final drive as the new 4.10 with .625OD....

sheriffav8r

Well, I did some digging and Cummins, through their downloadable PowerSpec program says that they are looking for between 2000-2400rpm for fuel economy and power. They want 2050rpm at 65mph and don't want you to go below 1800 while cruising. With 4.10 gears in OD the Ram will turn 1827rpms at 65mph with 265/70R17 tires and 1967rpm at 70mph. Close enough for me....

sctsnpr

I've been playing with mine lately, just using the lie-o-meter and resetting it every trip. My truck with 4.10's avgs about 15.5 hwy at 72 mph or between 2000 and 2100 rpms. This is during a 30 mile highway trip to work.

Jaxom

I'd like to thank the 1st 2 posters for their service.

As well as everyone else and their families for the sacrifices.

dhe9

that's nice that you would say that, your welcomed. sure did not do it for the money in january 1968. did it for the $100 per month, 3 hots and a cot.

david
socal

BigGreen

Whats the normal gear ratio in these trucks I have a 01 and was wondering.

Blake Clark

Greeny,

You asking what common in your truck???

This is the new 4th gen HQ.

But.... Your truck should have had either 3.55 or 4.10's

sheriffav8r

The '10s have 3.73 or 4.10 in the auto with a .625 overdrive ratio. The 5.9s have 3.55 or 4.10 with .69 overdrive ratio.

Jaxom, thanks for your comment. Semper Fi.

ramtradxb

Hmmmm...now I'm worried - since often out on the country roads I'm cruising at less than 1800 rpm (w/ my 3.73's and 34's) - not much less, but less all the same. And the other day I was climbing up a long six percenter and was impressed with the pickup (ability to speed up, versus the truck) while in the top gear and accelerating up the hill at a relatively low rpm. So why would they specifically not want you to go below 1800? And why don't they say that in the manual?

Ace

I believe that would be assumed hauling or towing a load. Engine efficiency is not that big a concern running unloaded, especially when wind resistance is the overriding factor in fuel economy at anything over 65mph.

signature600

Cummins PowerSpec is for Medium Duty applications, AFAIK.

I like my 3.42's and 68RFE...seems to get better mileage than most 6.7's I've heard about, and runs darn good!

Chris