F150 Ecoboost Forum banner

61 - 63 of 63 Posts

·
Administrator
Joined
·
11,054 Posts
I feel like your question has been answered.

Higher numerical ratios generate more of a mechanical advantage. That is, the engine turns more RPMs per revolution of a tire. Allowing the work to be easier for the engine. This comes at a cost of needing more RPMs at any given speed. Think about riding a bike. When you shift the bike to the lowest gear, you pedal pedal pedal really fast with your feet but the bicycle isn't going very fast. This makes it easy to climb a tough hill but you can't go as fast. Or it actually winds up taking you MORE energy to go at a fast speed because you're pedaling crazy fast. This would be the extreme end of high numerical ratios example. Say this is similar to a 4.10. Gives you lots of power and makes the work easier for the engine (you) but going fast is harder.

Conversely, you shift to higher gears and you have a harder time climbing a hill or accelerating, but you don't have to pedal as hard, or at as many rpms to maintain a faster speed. You get more distance out of each revolution of your pedals. This is your 3.15 example.

There is always a give and take.

Back to trucks. In theory you get better acceleration and better towing out of higher numerical ratios. I.e. 4.10 is superior to 3.55. But it isn't as cut and dry as that. Engines have power bands and "sweet spots".

My old employer had an f550 with something like a 5.13 rear end and an f350 with a 4.10 rear end. The 350 really felt stronger towing overall because the 550 would get anything moving, but then you promptly got out of the sweet spot and needed a bajillion RPMs at 65 and that engine made peak power at lower RPMs. Running down the road with the bobcat running 65, the 350 was more in its power band with the 4.10. The 550 was starting to turn so many rpms it was no longer in the meat of the power band. That engine didn't make as much power at that many rpms. On a mountain grade it might even slow down until it really got into the peak power. Then it might hold no matter how much weight was behind it.

Our engines make peak power at low rpms but do have a broad and fairly flat power band. They accommodate a wide range of gear ratios and give good performance across them all. Ford has assigned 3.55 gearing to Max Tow with 3.5 ecoboost, and 3.73 to Max Tow and heavy duty payload package.

When we start talking about the 10 speeds vs 6 speeds and whatnot, that's because what really matters is the final drive ratio. Not the rear end ratio. The 10 speed has different internal gearing than the 6 speed. A 10 speed 3.31 truck in first gear has darn near the same final drive ratio as a 6 speed 3.73 truck. This makes gear ratio selection in the rear end less important than ever.

And, my 6 speed makes it much less important than my old c6 3 speed.

So, in summation, a 4.10 will get you off the line or up a hill better than 3.73 or smaller.

3.15 should in theory get you down the road at speed at less RPMs than 3.31 or larger, using a little less fuel. There are ranges in between each of these that are a little worse on one end and a little better on the other. 3.55 is a real nice sweet spot all around for everything.

I'm not an engineer, this is my understanding. Feel free to correct anything I've stated that's wrong!

Sent from my moto z4 using Tapatalk
 

·
Premium Member
Joined
·
9,088 Posts
A 10 speed 3.31 truck in first gear has darn near the same final drive ratio as a 6 speed 3.73 truck. This makes gear ratio selection in the rear end less important than ever.
Awesome point

Sent from my SM-G988U using Tapatalk
 

·
Registered
2016 Ford F-150 XLT 2.7 Ecoboost
Joined
·
137 Posts
Discussion Starter #63
I feel like your question has been answered.

Higher numerical ratios generate more of a mechanical advantage. That is, the engine turns more RPMs per revolution of a tire. Allowing the work to be easier for the engine. This comes at a cost of needing more RPMs at any given speed. Think about riding a bike. When you shift the bike to the lowest gear, you pedal pedal pedal really fast with your feet but the bicycle isn't going very fast. This makes it easy to climb a tough hill but you can't go as fast. Or it actually winds up taking you MORE energy to go at a fast speed because you're pedaling crazy fast. This would be the extreme end of high numerical ratios example. Say this is similar to a 4.10. Gives you lots of power and makes the work easier for the engine (you) but going fast is harder.

Conversely, you shift to higher gears and you have a harder time climbing a hill or accelerating, but you don't have to pedal as hard, or at as many rpms to maintain a faster speed. You get more distance out of each revolution of your pedals. This is your 3.15 example.

There is always a give and take.

Back to trucks. In theory you get better acceleration and better towing out of higher numerical ratios. I.e. 4.10 is superior to 3.55. But it isn't as cut and dry as that. Engines have power bands and "sweet spots".

My old employer had an f550 with something like a 5.13 rear end and an f350 with a 4.10 rear end. The 350 really felt stronger towing overall because the 550 would get anything moving, but then you promptly got out of the sweet spot and needed a bajillion RPMs at 65 and that engine made peak power at lower RPMs. Running down the road with the bobcat running 65, the 350 was more in its power band with the 4.10. The 550 was starting to turn so many rpms it was no longer in the meat of the power band. That engine didn't make as much power at that many rpms. On a mountain grade it might even slow down until it really got into the peak power. Then it might hold no matter how much weight was behind it.

Our engines make peak power at low rpms but do have a broad and fairly flat power band. They accommodate a wide range of gear ratios and give good performance across them all. Ford has assigned 3.55 gearing to Max Tow with 3.5 ecoboost, and 3.73 to Max Tow and heavy duty payload package.

When we start talking about the 10 speeds vs 6 speeds and whatnot, that's because what really matters is the final drive ratio. Not the rear end ratio. The 10 speed has different internal gearing than the 6 speed. A 10 speed 3.31 truck in first gear has darn near the same final drive ratio as a 6 speed 3.73 truck. This makes gear ratio selection in the rear end less important than ever.

And, my 6 speed makes it much less important than my old c6 3 speed.

So, in summation, a 4.10 will get you off the line or up a hill better than 3.73 or smaller.

3.15 should in theory get you down the road at speed at less RPMs than 3.31 or larger, using a little less fuel. There are ranges in between each of these that are a little worse on one end and a little better on the other. 3.55 is a real nice sweet spot all around for everything.

I'm not an engineer, this is my understanding. Feel free to correct anything I've stated that's wrong!

Sent from my moto z4 using Tapatalk
Thanks! I appreciate it. And yes my question has been answered.
 
61 - 63 of 63 Posts
Top