Feel good story about the L8T towing heavy

Ray Pickle · January 17, 2022

I have towed that route and had no problem maintaining speed far above what TFL accomplished. Clearly the truck will perform much better than their representation. No one that knows anything about towing would allow their truck to lug like they did in their test. Understanding the desire to test uniformly, thus leaving the truck in drive, the ultra conservative tuning by GM caused the poor result. Another poster alluded to thermodynamic characteristics of small block being the reason for this tuning. My own experience indicates normal operating temps for coolant and trans temps ascending that grade at higher rpm. Further I see no significant differences in cooling capacity between the big three that would require the GM trucks to limit engine speed under those conditions more so than the competition. I would sure be interested in a more in depth reason for the tuning parameters GM has chosen to use in this truck. I don't see where a 10 speed would change the result much with the tuning parameters GM is presently operating this engine under.

the wanderer · January 17, 2022

15 hours ago, kenny_r said:

You don’t go up a mountain 3 minutes faster than the competition having an extra 29hp and 10 ftlbs. Transmission/gear ratios played a huge role in the outcome of that race. I’d be far more worried about transmission problems in a 10 speed vs 6 speed though so maybe they just need to option a 4.10 with the 6.6 for those folks who don’t care about getting an extra 1 mpg.

Gear ratio doesn't come into play in that test. Power comes from RPMs, not gears. Gears (both transmission and rear end) simply allow you to change what RPM you get at what speed, but as long as the truck has room to downshift then gear ratio is unimportant.

The truck had room to downshift, but didn't. They should have manually forced a downshift and the power would have come back on strong.

swathdiver · January 17, 2022

23 minutes ago, the wanderer said:

Gear ratio doesn't come into play in that test. Power comes from RPMs, not gears. Gears (both transmission and rear end) simply allow you to change what RPM you get at what speed, but as long as the truck has room to downshift then gear ratio is unimportant.

The truck had room to downshift, but didn't. They should have manually forced a downshift and the power would have come back on strong.

Foot ponds of torque and force in newtons at the wheels does indeed both come from engine power and gearing.

4.30 gears in my little 5.3 truck will be nearly the same torque at the differential and force in newtons at the wheel as a 2500 6.0 with 3.73 gears.

sheath · January 17, 2022

I thought the trailer was about 1 ton heavier for the Chevy as well, since it was a "Super Ike" test.

I'd have to go back and watch them again, but I thought the Ford and Dodge trailers were just over 14,000 lbs, and the Chevy a bit over 16,000 lbs.

If that is correct, that would definitely skew the results in doing direct comparisons. But definitely fits the theme of the "Super Ike" test.

I like the way they do the testing, as it represents kind of a "worse case" scenario.

Edit to add:

went back to watch the videos.

Ford and Chevy same weight, same trailer. Only real difference was Ford was run on a very cold clear winter day, where Chevy was a warmer spring day. So air density, would slightly influence to the Fords favor (not three minutes worth... lol)

Dodge pulled a 14,300lbs trailer with a clean roof, so not comparable (imo).

Edited January 17, 2022 by sheath
Correct previous information

the wanderer · January 17, 2022

30 minutes ago, swathdiver said:

Foot ponds of torque and force in newtons at the wheels does indeed both come from engine power and gearing.

Yes it does, but there's a catch; Rear end gear allows you to increase the torque that you would have in each transmission gear, but the flip side of the coin is that you need a higher transmission gear number now at that same speed (otherwise you're redlining). So you lost your torque advantage because you upshifted.

If two otherwise identical trucks are running at the same speed/mph, and the same rpms, then they are putting down the same power. It doesn't matter what gear ratio they have, or what gear number they're in at that point; they will have the same final gear multiplication.

So keeping that in mind, you can have a 5.10 or a 3.21 rear end, as long as your transmissions are in a gear that ends up putting both trucks at 4000 RPMs at 40mph, then both trucks are putting down the same power at that speed.

Edited January 17, 2022 by the wanderer

sheath · January 17, 2022

Something else to consider, for those of us cheap bastages. Chevy tows max capacity on 87 Octane. Ford tows max capacity on 93 Octane. That is a big difference in cost, when you also look at the lower fuel mileage.

I'd be happy to find a gear that lets the Chevy cruise in the 4-5K rpm range on a heavy climb, and what ever speed that equates to, is how fast we'd go.

All said, the Ford is one heck of a truck. Huge respect! :cheers:

the wanderer · January 17, 2022

Interesting, I didn't know that about the octane. That certainly makes a difference.

I think the 7.3 is probably a beast, and it's probably an advantage to some buyers over the 6.6. I suspect that after GM bumps up the power output on the 6.6 then Ford will simply turn a screw somewhere and do the same, with that much difference in displacement there has got to be a ton of room left on the table.

The problem with the 7.3 is not the 7.3, it's everything else holding it off the ground.

swathdiver · January 17, 2022

1 hour ago, the wanderer said:

Yes it does, but there's a catch; Rear end gear allows you to increase the torque that you would have in each transmission gear, but the flip side of the coin is that you need a higher transmission gear number now at that same speed (otherwise you're redlining). So you lost your torque advantage because you upshifted.

If two otherwise identical trucks are running at the same speed/mph, and the same rpms, then they are putting down the same power. It doesn't matter what gear ratio they have, or what gear number they're in at that point; they will have the same final gear multiplication.

So keeping that in mind, you can have a 5.10 or a 3.21 rear end, as long as your transmissions are in a gear that ends up putting both trucks at 4000 RPMs at 40mph, then both trucks are putting down the same power at that speed.

I don't think so. I've made a calculator to look at the differences. The first is my LC9 with 3.42 gears, then with 3.73s compared to our Sierra with 3.73s which has a 6.2 motor.

the wanderer · January 17, 2022

24 minutes ago, swathdiver said:

I don't think so. I've made a calculator to look at the differences. The first is my LC9 with 3.42 gears, then with 3.73s compared to our Sierra with 3.73s which has a 6.2 motor.

What "don't you think so"? This is a mathematical certainty:

Quote

You can have a 5.10 or a 3.21 rear end, as long as your transmissions are in a gear that ends up putting both trucks at 4000 RPMs at 40mph, then both trucks are putting down the same power at that speed.

Edited January 17, 2022 by the wanderer

swathdiver · January 17, 2022

11 minutes ago, the wanderer said:

What "don't you think so"? This is a mathematical certainty:

Only if they have the same engine power.

Torque at the differential is calculated as using engine torque times the final drive ratio (transmission ratio x axle ratio). So since the 6.2 makes more power, it puts down more torque at the same rpms. Force at both wheels is calculated by dividing differential torque by tire radius.

The LC9 puts down 689 foot pounds of torque at the differential in 6th gear at 2000 rpms. The L9H puts down 980 foot pounds of torque at the differential in 6th gear at 2000 rpms. Both vehicles with same driveline in this example, just different engines.

The 5.3 puts down 45 Newtons of force at 2000 rpms in 6th gear. The 6.2 puts down 64 Newtons, again both have the exact same driveline in this example.

My calculator has not been reviewed, if I'm wrong, I'm all ears, show me.

the wanderer · January 17, 2022

23 minutes ago, swathdiver said:

Only if they have the same engine power.

Yes, that was the assumption in my example. I forget how you and I got to this point and I'm too lazy to look, but somebody somewhere implied that the TFL test of this truck would have went better with a higher gear ratio, but I was just saying that gear ratio doesn't affect this specific test. As long as you have room in the transmission to downshift, then the axle gear ratio won't change anything as far as getting up the IKE quicker.

The transmission gears and axle gears do the exact same thing. You don't have to change the rear end to make more power, you can also change the transmission gear; that's exactly what it's there for.

Edited January 17, 2022 by the wanderer

the wanderer · January 17, 2022

I've you've ever pedalled a mountain bike it becomes very obvious; I have a 21(?) speed, but I don't have 21 unique gears. There is an incredible amount of overlap depending on where the front and rear gears are sitting.

I can change the front gear and change the rear gear at the exact same time, make a lot of noise and fuss, and if I pick my change correctly.... end up right where I started in terms of pedalling rpm vs wheel rpm.

swathdiver · January 17, 2022

9 minutes ago, the wanderer said:

Yes, that was the assumption in my example. I forget how you and I got to this point and I'm too lazy to look, but somebody somewhere implied that the TFL test of this truck would have went better with a higher gear ratio, but I was just saying that gear ratio doesn't affect this specific test. As long as you have room in the transmission to downshift, then the axle gear ratio won't change anything as far as getting up the IKE quicker.

That's the nice thing about lots of transmission gears, you can run a truck like it was equipped with 4.10s by shifting to 5th or 6th instead of running around in 10th. Yep, agree all the way. Heck, still nice even in the 6-speeds over the old 4-speeds!

Ray Pickle · January 17, 2022

3 hours ago, sheath said:

I thought the trailer was about 1 ton heavier for the Chevy as well, since it was a "Super Ike" test.

I'd have to go back and watch them again, but I thought the Ford and Dodge trailers were just over 14,000 lbs, and the Chevy a bit over 16,000 lbs.

If that is correct, that would definitely skew the results in doing direct comparisons. But definitely fits the theme of the "Super Ike" test.

I like the way they do the testing, as it represents kind of a "worse case" scenario.

Edit to add:

went back to watch the videos.

Ford and Chevy same weight, same trailer. Only real difference was Ford was run on a very cold clear winter day, where Chevy was a warmer spring day. So air density, would slightly influence to the Fords favor (not three minutes worth... lol)

Dodge pulled a 14,300lbs trailer with a clean roof, so not comparable (imo).