Tow Test - New Chevy & Ford

[More Power]

Chevy -Vs- Ford (http://www.thedieselpage.com/duramax/2007PullOff.htm)
Tow testing the new emissions LMM Duramax and 6.4L Power Stroke
A recent pickup truck ad I saw on television said: "Truck guys will tell you taking off with 10,000-lbs ain't no picnic. Stopping 10,000-lbs ain't no picnic either." We agree. Towing tests are few and far between in the automotive media. Most of what we see are dyno results, 1/4-mile elapsed times, and generalized reports about on-road capability. Those types of tests can provide some clue about what we might expect to see while towing a heavy trailer, but they fall short of a real towing evaluation. Part of what most potential GM & Ford buyers really want to know is how the newest diesel pickups stack up against one another in a real-world towing test on a real hill while towing a trailer that weighs at least 10,000-lbs. That's what this test was all about.

[Willcoc]

What is the MSSRP for each of the truck's tested?

To bad you could not find the truck in the ad to test with.

[More Power]

What is the MSSRP for each of the truck's tested?

To bad you could not find the truck in the ad to test with.

Yes, MSRP might not have been a bad idea - I'll do it next time. Though I don't know many Chevy & Ford truck owners who buy a new truck based on MSRP...

If you're referring to the lead-in ad quote in the article about a 10,000-lb trailer, it was a Toyota TV ad.... Would have been fun to run a new Tundra in the mix... Unfortunately, they aren't offered with a diesel... yet. ;)

JIm

[More Power]

No one has mentioned it yet, so I thought I'd ask.....

How is it possible for the Ford to achieve a combination of 3000-rpm and 60-mph? The gearing chart is included in the article for both the Chevy & Ford. I've plugged the numbers into a couple of different gearing calculators, and can't come up with 3000-rpm at 60-mph.

At least one Ford owner has suggested the new Torqueshift is splitting gears... I doubt it, but I dunno.... Maybe an unlocked torque converter is skewing the ratio. If so, it would build heat rapidly.... Any ideas?

Jim

[OC_DMAX]

How much is it off by? Maybe the Ford really does not have a 3.73 Axle Ratio. How about tire size?(guess you have that one pictured in the article - too bad GM is still using 245x16)

I'd run the numbers with a 4.10 Axle ratio. Does it come closer?

[More Power]

The factory tire sizes are listed in the article (both trucks had stock tires) along with the transmission ratios for both the Allison & Torqueshift.

The rpm & mph numbers match pretty well when calculating the Chevy - using tire size, Allison gear selection and rear diff ratio. The Ford, on the other hand is way off, with either a 3.73 or 4.10 diff ratio.

The Duramax was running in direct at 60-mph. The Ford was running in a lower gear. It's a puzzle....

Jim

[JohnC]

My ford had a 3.53 or something close....

(A few minutes later) 3.55, yeah that's what it was, 3.55....

[DarylB]

Good article here on the 2007 trucks

http://www.pickuptruck.com/html/2007/shootout/hdshootout1.html

Not quite apples to apples comparason but the DMAX/Allison combo was definitely on or above par with the others. It appeared to be an unbiased test with a lot of good data.

[Colorado Kid]

Interseting observation Jim, I hadn't caught it but I agree with you. In 3rd-locked the Ford should have been turning about 3500 RPM and in 4th locked about 2300 RPM, both far from the power peak which happens to be at 3000 RPM.
60 MPH, 3000 RPM, 33.16" Tire diameter and 3.73 implies 1.32 tranny ratio. (3rd is 1.55, 4th is 1.00). I would certainly expect that 32% slip with over 600 ft-lbs on the input in the torque converter would warm up the tranny fluid PDQ.

Assuming the tranny is in 4th with the converter locked would lead to an estimated rear end ratio of 4.88 . . .Hmmmmm. A ringer seems unlikely, but it COULD happen.

What's the T-case ratio? My guess is about 2.7:1. 2.7x0.71 (5th gear) = 1.91, that's not it (unless the T-case ratio is about 1.9:1. I don't do 4x4's, does anybody know?).

I think the most likely explanation is that the Ford is in 4th with the converter unlocked, but that's a LOT of slip.

[DmaxMaverick]

......What's the T-case ratio? My guess is about 2.7:1. 2.7x0.71 (5th gear) = 1.91, that's not it (unless the T-case ratio is about 1.9:1. I don't do 4x4's, does anybody know?)

The transfer case ratio doesn't mean anything unless it is in 4 low. High range is 1:1, in all of them.

[More Power]

How much is it off by? Maybe the Ford really does not have a 3.73 Axle Ratio. How about tire size?(guess you have that one pictured in the article - too bad GM is still using 245x16)

I'd run the numbers with a 4.10 Axle ratio. Does it come closer?


Neither the 3.73 nor 4.10 differential ratios used by the 2008 Ford F250/350 trucks fit the 3000-rpm & 60-mph combo as seen on the dash. I was told this truck had 3.73s. This truck was 100% stock.

Not a big point, but one worth mentioning, is that to almost equal the LMM in top speed, the Ford needed the torque multiplication advantage of a lower gear. Also, even though the 6.4L PSD is technically governed at 3700-rpm, it shifted well below that during this full-pedal run.

Jim