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Discussion Starter #1
I see this mis-information being spread around all the time! This is for the people trying to make their minds up on which one to buy, if pulling power is on their lists of "things I need". Or for the people that think just because the 855d is a diesel, then it automatically has more "low-end grunt" than the 825i. They aren't even close, in performance(pulling power), and I've made several different charts to show you the differences of the two.

First, there is the basic horsepower and torque comparison, based on RPM. As you can see below(red is 825i, green is 855d), the 825i has more TQ and more HP than the 855d at every RPM! Even down at where clutch engagement first occurs(roughly 1500 rpms), the 825i has more TQ than the 855d does at peak tq rpm...
825i power stops at 6000 RPMs, and the 855d stops at 3600.







And here is where things get interesting, and show the true potential of each vehicle, as I have accounted for Primary/Secondary gearing and the Differential ratios in each vehicle. Motor TQ x gear ratio x differential ratio = wheel TQ. And that is what we feel accelerating us. Acceleration = Force divided by mass... so the more force you have, or the lighter you are, the faster you accelerate(The harder you can pull!). I did not account for CVT power losses because I'm not positive what they are on the gator setups... I've heard there are 30% losses from the engine to the rear wheels, but excluding them doesn't change our comparisons below. I will show a couple hypothetical "what if" graphs after the first one, for the people who always say "but but but... what if?!?!"... trying to uphold the lowly diesel. :D This isn't meant to hurt anyone's feelings, just to show the actual numbers behind the performance!


This graph depicts the wheel torque of both vehicles in their stock configurations, being held at wide open throttle. 825i shifting ~5500 rpms stock, and the 855d shifting around ~3400 rpms stock. The most notable difference is around the 10-11 mph mark. You can see that the 855d is making around 850-900 ft-lbs of wheel tq, while the 825i is making nearly 2100! This means that at that mph, the 825i has OVER DOUBLE(233%!) the amount of pulling power(wheel tq) than the 855d does! Up near the top speed of the 855d, it has ~300 ft-lbs of wheel tq, while the 825i has ~700... still a hair over double the amount of pulling force.

Another way to look at the following graphs, is pick a number on the TQ side of the scale.... say 1000 lbs. If you follow it out to the blue line of the 855d, you can see that it intersects with the 9 mph mark on the bottom scale... this means that when the 855d is pulling with 1000 lbs of wheel TQ, it is going 9 mph...in comparison, the 825i is pulling with the same force at roughly 21 mph! There is no comparison of pulling power anywhere throughout the rpm band in their stock configurations.






And now for the hypotheticals(to show the people with excuses and illogical reasoning)... The scenarios that would call for re-clutching of the CVT system, or really bogging the machine down with major loads, to achieve the wide-open throttle RPMs that follow...



This graph shows the differences if each vehicle was re-clutched to operate at their respective peak torque RPMs when at full throttle. 825i @ ~3000 RPMS and the 855d at ~2500-2600. The 825i still wins in this department. A lot of people think peak torque RPM is the place to be for CVTs and other vehicles, but pick a few points on this graph and compare the wheel TQ to the graph above to see how inferior "peak torque shifting" really is. Please don't ever do this(in ANY vehicle!).




This graph retains the same clutching setup as above for the 855d, with a 2600 wide-open throttle shift point. But shows a completely neutered 825i setup and simulates an equivalent shift RPM of 2600... to show a direct comparison for the "but my diesel has more low-end grunt" people! Even with the 825i churning along at these comparative, near-idle speeds, it still has roughly 50% more wheel TQ than the 855d.




To finish off this write-up, I'll show a comparison of the 855d shifting at 3400 RPMs(stock) versus a re-clutched version of the same machine that would shift at the peak torque RPM of ~2600. The peak of the blue line you see is the peak torque in "first gear"... the lowest ratio on the CVT pulley setup(1350 ft-lbs is the absolute max this machine could ever make...but still nowhere near the peak wheel tq of the 825i). As the RPMs increase, the wheel TQ would finally hit the point at the top of the red line. After that, AT NO GIVEN MPH would the wheel tq ever be higher than at the shift RPM of 3400(stock). Looks like a 10-15% difference at all MPHs.





To conclude:
1. If you're needing max pulling power, get an 825i. The 855d isn't even remotely close!
2. If all your machines are diesel, then maybe I'd recommend getting an 855d...but only to simply fuel demands.(And only then!)
3. The last chart shows that, for ANY MPH, maximum wheel torque is ALWAYS made at higher RPM(preferably peak hp RPM).
4. The fastest, AND HARDEST PULLING(because that's what wheel TQ equals) cvt setups are the ones that shift at peak HP.(Only exception is peak TQ rpm in low gear)
5. I'm really surprised the 855d isn't setup to shift at the max rpm, since the wheel TQ is kinda low. (Needs all the help it can get)

If you don't fully understand these charts, or have any questions at all, ask away!
 

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Discussion Starter #4 (Edited)
You really must hate the diesels. But why? To each their own....
I don't hate the diesels. Just trying to inform the people who think the diesels have more torque.

I'd hate for someone to buy the 855D, if what they really wanted was the one that pulled heavy loads the best. :)
 

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You really must hate the diesels. But why? To each their own....
:hi: Where can we find the below used graphs in the internet elsewhere, who leaded the measurement? And, the graphs compare apples w/ oranges because of the different hp.
 

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People automatically equate ALL diesels to the engine in the Kenworth truck on the highway,,, :dunno:

My personal search showed for similar horsepower, the small diesel did not have more torque,,:flag_of_truce:
 

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People automatically equate ALL diesels to the engine in the Kenworth truck on the highway,,, :dunno:

My personal search showed for similar horsepower, the small diesel did not have more torque,,:flag_of_truce:
My 2009 Jetta TDI that was bought back from me by VW.

2.0l Turbo Diesel Engine = 236 ft-lbs torque

My 2015 Subaru WRX that replaced the TDI

2.0l Turbo Gas Engine = 258 ft-lbs torque

Not talking truck engines but even in cars it is the case. Same displacement engine and both turbo charged but the gas engine produces more HP and Torque. The two cars also weigh about the same, around 2200-2300lbs but the WRX is AWD and puts the power to the ground much better.
 

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Discussion Starter #8 (Edited)
:hi: Where can we find the below used graphs in the internet elsewhere, who leaded the measurement? And, the graphs compare apples w/ oranges because of the different hp.
If you meant to quote me, I made the graphs using the horsepower and torque numbers, at all RPMs, from the manufacturers of each engine. And then used the primary/secondary CVT gear ratios and differential gear ratio to find axle torque for each machine, at every RPM and MPH. A bunch of math in excel, and you have some nice graphs like the ones above:cheers:
 

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I don't hate the diesels. Just trying to inform the people who think the diesels have more torque.

I'd hate for someone to buy the 855D, if what they really wanted was the one that pulled heavy loads the best. :)
I definitely understand what you are saying. I looked at similar charts before I settled on a diesel. In fact, the #1 fear I had was that the diesel Gator might be under powered --especially considering the HVAC and the extra weight R models.
I pretty much wanted to know if the diesel would be adequate for my needs.
The diesel does seem to be powerful enough. The gas model is stronger, but one thing I noticed is that the engine is always screaming and reving, whereas the diesel just lumbers along. It feels more pleasant to operate.
If you live on a farm and have other diesels around it makes sense, plus it will be cheaper to operate.
If you like running down the road at 45, and screaming around, then the gas is the way to go.
I would like to see a 35HP diesel, but the EPA kinda screwed that up.
 

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Discussion Starter #10
The diesel does seem to be powerful enough. The gas model is stronger, but one thing I noticed is that the engine is always screaming and reving, whereas the diesel just lumbers along.

If you like running down the road at 45, and screaming around, then the gas is the way to go.
I actually put the weights and spring from the diesel's Primary clutch into my gas gator. MUCH more pleasant to drive around now! No more of that 4000 RPMs junk just to get going... :banghead:

I would like to see a 35HP diesel, but the EPA kinda screwed that up.
What did the EPA do, regarding that?
 

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What did the EPA do, regarding that?
Since 2012 (or there about) any diesel over 25 HP has more stringent emission standards. They would end up having some combination of DEF injection, EGR, and DPF.
Possibly all 3.
 

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It is interesting that this is even controversial.

There are so many design factors that contribute to an engines torque and power curves. Too many to fit into a short post, especially one written by someone who is far from an expert. Suffice it to say that *it is possible* to design a diesel with greater torque that a comparable displacement gasoline engine just by increasing the stroke. This limits RPMs, but they're limited with a diesel anyway because of the higher compression.

It's not the fuel, it's the engine design.

Al
 

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It is interesting that this is even controversial.

There are so many design factors that contribute to an engines torque and power curves. Too many to fit into a short post, especially one written by someone who is far from an expert. Suffice it to say that *it is possible* to design a diesel with greater torque that a comparable displacement gasoline engine just by increasing the stroke. This limits RPMs, but they're limited with a diesel anyway because of the higher compression.

It's not the fuel, it's the engine design.

Al
As mentioned though, the real limits are going to be 25hp limit from the EPA. Go above that and you need room for lots of other crap. That adds weight and cost.

I would agree with others that the main driving factor this engine is farm use. There is a demand for running as much as possible on diesel. Many people will just assume that it runs on Diesel so it is a torque monster.
 

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Discussion Starter #15 (Edited)
There are so many design factors that contribute to an engines torque and power curves. Too many to fit into a short post, especially one written by someone who is far from an expert.

Suffice it to say that *it is possible* to design a diesel with greater torque that a comparable displacement gasoline engine just by increasing the stroke. This limits RPMs, but they're limited with a diesel anyway because of the higher compression.



Al
How do you know I'm NOT an expert?! :dunno:

Besides... you're talking hypotheticals, while I'm comparing the two actual engines in these two vehicles. That's what we're limited to, here.
 

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I think that in many cases a typical diesel will have more torque than a gasser of the same horsepower.
The reason of course is diesels usually make their rated hp at a lower RPM.
If there was a 54 hp diesel gator, I don’t think there would be a mystery of which one had more torque!
 

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I think that in many cases a typical diesel will have more torque than a gasser of the same horsepower.
The reason of course is diesels usually make their rated hp at a lower RPM.
If there was a 54 hp diesel gator, I don’t think there would be a mystery of which one had more torque!
I would agree to that. Going back to the comparisons between my previous car and current.

TDI 16.5:1 compression ratio 140 HP and as mentioned before 236 ft-lbs

WRX 10.6:1 compression ratio 268 HP and 258 ft-lbs

So while they are both 2.0 liter engines and the WRX has more torque it also has almost double the HP that results in only 22 more ft-lbs more. Of course the WRX revs a lot higher. I think the TDI redlined around 4500 RPM and the WRX 6000 or so.
 

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Horsepower is a funky thing. It’s a measurement based on torque times RPM divided by 5252. It’s just math. Torque is an actual measurement while HP is a mathematical calculation.

Let’s say you have two engines, one gas, one diesel. If they both are only allowed to run up to 3600 RPM and they both make 50HP, then their output is exactly the same. Once again, HP is calculated by torque times RPM divided by 5252. Now the torque curves can be different with the gas engine peaking at 3600 while the diesel could be a relatively flat curve with even a peak at a lower RPM.

Let’s look at that math again. Since HP = torque x RPM / 5252, all we need to do is raise the RPM to create more HP with the same exact engine as before.

So now let’s take our same hypothetical engines and raise the rev limiter to 6000 RPM on the gas engine without raising its peak torque we found at 3600. We now have an engine that makes substantially more HP. The major difference is you have to rev the engine up to those much higher RPMs to get that HP. But limit the engine back to 3600 and you get the same HP as the diesel.

See how this works? Lots of auto manufacturers play the HP game and raise the output of a newer car simply by raising the rev limiter a few clicks and POW! More power and a cooler number to brag about. You feel awesome about getting more power, but who the heck drives around with the tachometer bouncing off the rev limiter? I don’t.

This is why gearing is so important. You want your engine to be comfortable when cruising as in enough torque available to do the job without having to down shift to raise the RPMs to get more HP.

Torque is a measurable twisting force while HP is measuring how much work can be done in a certain amount of time. So torque is a great thing, but where in the RPM range is it? How flat is it? Do I need to scream my engine to get it?
 
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