Engine torque
After the engine in our '09 V10 6.8L F250 'sploded 3 days ago, we ended up with a new-to-us replacement '12 GMC 2500HD that we were able to find on very short notice. The V10 6.8L was rated 362HP w...
Forum Discussion
myredracer wrote:
IIRC, the V10 was running near or at 6K rpms at 65 mph, and maybe a little more. The new tires are 31.1" dia. They're a 70 profile compared to the OEM spec 75 and rmps would be a wee bit higher.
The 2500 was struggling on the inclines heading west out of Kamloops and again heading west out of Merrit. The 8% grade I believe is on the section heading east from Hope and up through the snowshed. The V10 easily made it up the 8% grade section.
Odd that when the grade wasn't as steep (like around 6-ish %), the 2500/V8 kicked into a lower gear and ran at higher rpms okay and could maintain 65 mph. But on steeper grades it didn't change gears and I really slowed down - presumably in part because it was putting out lower HP at the lower rpms.
That sounds high for a V10. But let's say it's between 5 - 6k rpm, I think the V8 simply needs a downshift.
I was thinking the GM 6L90 is geared poorly, but its 1 - 3 ratios are nearly identical to the 5R110W:
http://gmauthority.com/blog/gm/gm-transmissions/myd/
http://www.dieselhub.com/trans/5r110w-torqshift.html
Using a gear calculator, you should be able to hold 52.3 mph at 5400 rpm in 2nd. Perhaps force a downshift?
At 4000 rpm, you're either 60mph in 3rd (which may be difficult), or 39mph in 2nd - sounds like your case on the 8% grade?
I feel all small blocks should have 8 speeds. At 7k lbs, my Hemi has no issues holding 100 kph. My V10 with the ancient 4 speed is forced to chug along at 80kph in 2nd at 2800 rpm...
