RPM @ 60??

mannytranny402 · November 5, 2002

You Dmax guys, what is your RPM @ 60 with the allison in 5th? Is there a rule of thumb for measuring this for use with larger tires? In other words, how many mph does a tire size give me? thanks

Shaners · November 5, 2002

I think your speedo will be off about 3-4% for each tire size you gain. You will be traveling faster than your speedo reads, and you will be putting less (recorded) miles on your truck between fillups, so unless you figure it in, your mpg's will appear to have declined.

bluenote · November 6, 2002

I think it's about 1600 rpm's at 60 mph??

When I drive to work tomorrow, I'll double check and come back with a definitive answer.

bluenote · November 6, 2002

The real numbers...

55 MPH = 1600 RPM's

60 MPH = 1750 RPM's

mannytranny402 · November 6, 2002

Hey thanks.

My dmax ZF runs a little higher, i think. Like 1950@ 70. Or 2500 @ 85. What would changing the tires to the next larger sixe over stock get me? thanks

bluenote · November 6, 2002

The Duramax/Allison combo turns almost exactly 2000 rpm's at 70 mph. I would think it's likely that there would be slight variations in rpm's at various speeds with the Allison vs. the zf6, but it's probably always pretty close. Of course, you have a little more control over things with the zf6, but I gotta tell ya that the Allison is a towing marvel, IMHO. Changing to a larger diameter tire will effectively lower the number of your rear end ratio (i.e., you'd probably be around the equivalent to the range of 3.4 to 3.5). However, since you've got the manual, you can always drop into a lower gear if needed. Most people I've heard from with the Allison who went to a larger tire have not had any major problems, so you should be fine. Good Luck!

mannytranny402 · November 7, 2002

Thanks.

I have yet to ride in one for longer than a mile. Test drive guy wasnt fun. Anyway, Ill have to get in one some time. Which do you think is faaster?

bluenote · November 7, 2002

Thanks.
I have yet to ride in one for longer than a mile. Test drive guy wasnt fun. Anyway, Ill have to get in one some time. Which do you think is faaster?

Faster?

Stock vs. stock, I would think the zf6 would be slightly faster if the driver knows how to shift right. However, the chips that are out right now don't seem to work as good with the manual tranny. So, if you modify 'em, I think the Allison equipped truck would be quicker.

I know I can go 0-60 in about 8½ seconds with my stock '01, how 'bout you??

mannytranny402 · November 7, 2002

Ill have to try some time. It takes some good coordination. Shifting and pressing the clock buttons. I have to fond some open road somewhere. Ill let you know the verdict...

Colorado Kid · November 8, 2002

60 is kind of a stacked deck speed for the ZF, as 4th will only reach 58 MPH!

I haven't made 0-60 runs, but the Allison has the advantage of being able to "power-brake" an build boost while standing still. I guess it depends on how the race starts...if everybody starts at idle I think the ZF is probably quicker, but if we're all aware the race is about to be on, and the Allison is powerbraking at 2,200 RPM while the ZF is waiting to drop the clutch at 2,800 RPM I think the Alli is going to get off the line better. The ZF can be shifter mighty fast but the driver really has to be paying attention to get max effort out of it...if you let it hit the governor the race is over because the boost will be totally gone before you hit the next gear. In the Allison my grandma could get consistent 0-60 times...and she's 90!

Pulling a trailer up a hill? This link tells the story. http://www.thedieselpage.com/features/pulloff3.htm

Modified? Right now I think the flywheel/clutch combination on the Duramax ZF is almost as close to its limits as the Stock Allison. Unfortunately there is no equivelant to "ATS" building a better flywheel for the D-max yet, so the ZF trucks can't be made to handle the ever increasing power levels. In fact some of us are beginning to see signs that our dual-mass flywheels are not up to handling the stock power level for the long haul.

That's the bad news, the good news is that when a fix becomes available for the weak dual-mass flywheel it won't cost anything like the $2300 premium paid to have an Allison in lieu of the 6-speed. (Let alone the $$$$ being paid by some to beef up the Allison).

mannytranny402 · November 9, 2002

Hey

Isnt that your truck? Cool. So, you dont think that the Zf's clutch would be able to handle more guts? Thats kinda a bummer. I would tend to think that a manual trans would be good for more than an auto. What is the life expectancy of a ZF clutch these days? I have written to you before. I am the guy that got my truck in Greeley. Remember? Anyway, thanks for the info. You seem to know the most about these trucks, so I pay extra attention to your posts...thanks

QUIKAG · November 11, 2002

For comparision, my 4.10 geared 6.0L 2500HD is turning right around 2000rpm at 60mph. Sucker revs pretty high compared to my dad's Avalanche and my brother's '99 5.3L Z71.