Dyno Numbers

[DocWalt]

Originally Posted by Stonehorsw

Copied from a post from William Knose on Facebook. Again, 50 hp increase.
I will wait until I get more pumped up, but seems like car is doing very well.

Take ~5% off and the numbers fall more in line with what we'd normally see on a dynojet. Seems like a solid 20-25% gain for most dynos I've seen

[Baldeagle]

Originally Posted by ZDan

Nah, gearing (within reason!) doesn't affect trap speed much. 2013 BRZ did 95mph in the 1/4 with 4.1 diff, 2017 BRZ (with 5 more hp) also did 95mph with 4.3 diff, got there one tenth quicker... Trap speed is (pretty much) power/weight. Small advantage of 4.3 gearing at most speeds is negated by having to upshift sooner resulting in a huge disadvantage at some speeds.

Respectfully disagree. To accomplish the same amount of work with 4.8% less torque multiplication means it needs about 4.8% more torque/hp. Using the original HP value from the formula, the 2022 BRZ has 234.4hp. 4.8% is 11hp. What would that equivalent of 11 hp do? If you added 11 hp to 234 hp, you obviously get 245 hp. If you plug 245 hp back into the formula, trap speed should increase from 101 mph to about 102 mph.

A 2022 BRZ with a 4.3:1 final gear should trap at 102 mph versus 101 mph with the 4.1:1 final gear. We can debate if 1 mph is meaningful or not, but it is related to gearing and equates to about 11 hp given the same gear ratios.

[ZDan]

Originally Posted by Baldeagle

Respectfully disagree. To accomplish the same amount of work with 4.8% less torque multiplication means it needs about 4.8% more torque/hp.

4.3 gears vs. 4.1 don't give you 4.8% more torque at the wheels *at all speeds*. In 1st gear, they'll give you that until you have to upshift to 2nd gear, and then you'll have WAY LESS torque to the wheels for a couple/few mph. Same every upshift, you have to go to a taller gear sooner, and briefly suffer much taller gearing. On *average* it's the same.

Gearing does not give you more power! It might gain you a bit from 0-30mph, but beyond that it's a wash.

1/4-mile ET is sensitive to gearing, but mph, not so much...

Using the original HP value from the formula, the 2022 BRZ has 234.4hp. 4.8% is 11hp. What would that equivalent of 11 hp do? If you added 11 hp to 234 hp, you obviously get 245 hp. If you plug 245 hp back into the formula, trap speed should increase from 101 mph to about 102 mph.

That is not how it works...
Again, gearing does not magic you more power at the wheels! You get an advantage until you have to upshift sooner, then you are at a disadvantage.

A 2022 BRZ with a 4.3:1 final gear should trap at 102 mph versus 101 mph with the 4.1:1 final gear. We can debate if 1 mph is meaningful or not, but it is related to gearing and equates to about 11 hp given the same gear ratios.

Gearing is a massively overrated mod, and this basic misunderstanding is why. If I replaced my 4.3 gears with 4.88, it would not make my 205hp car act like it had 233hp. It would surely improve 0-30mph times, but 1/4-mile trap speed would suffer as I'd have to be in 5th gear for a goodly portion of the big end of the track. Power/weight is power/weight. Diff gearing doesn't do anything magical, it gives you slightly more thrust at the wheels at most speeds but a whole lot less at some speeds.

[Baldeagle]

Originally Posted by ZDan

4.3 gears vs. 4.1 don't give you 4.8% more torque at the wheels *at all speeds*. In 1st gear, they'll give you that until you have to upshift to 2nd gear, and then you'll have WAY LESS torque to the wheels for a couple/few mph. Same every upshift, you have to go to a taller gear sooner, and briefly suffer much taller gearing. On *average* it's the same.

Gearing does not give you more power! It might gain you a bit from 0-30mph, but beyond that it's a wash.

1/4-mile ET is sensitive to gearing, but mph, not so much...



That is not how it works...
Again, gearing does not magic you more power at the wheels! You get an advantage until you have to upshift sooner, then you are at a disadvantage.



Gearing is a massively overrated mod, and this basic misunderstanding is why. If I replaced my 4.3 gears with 4.88, it would not make my 205hp car act like it had 233hp. It would surely improve 0-30mph times, but 1/4-mile trap speed would suffer as I'd have to be in 5th gear for a goodly portion of the big end of the track. Power/weight is power/weight. Diff gearing doesn't do anything magical, it gives you slightly more thrust at the wheels at most speeds but a whole lot less at some speeds.

Are you sure about this? Consider this logic:

With a 4.1 final, at 7,500 rpm:

1st goes 37 mph, 2nd goes 64 mph, 3rd goes 88 mph and 4th goes 120 mph

With a 4.3 final, at 7,500 rpm:

1st goes 36 mph, 2nd goes 61 mph, 3rd goes 84 mph and 4th goes 115 mph

At 30 mph in first gear, the rpm with the 4.1 final would be 6,040 rpm and with the 4.3 final it would be 6,335 rpm. At 30 mph, there is a 295 rpm difference in first gear. Once out of first gear, for any given speed (outside the 3-5 mph overlap around each shift point) the rpm remains between 230 rpm to 345 rpm higher with 4.3 final than with the 4.1 final.

For example at 90 mph with the 4.1 final, the BRZ would be in 4th gear at 5,606 rpm and with the 4.3 final it would also be in 4th gear but at 5,880 rpm, a 274 rpm difference. Doesn’t the engine produce more HP at 5,880 rpm than at 5,600 rpm? If two identical BRZs were travelling at 90 mph, and one was at 5,880 rpm and the other at 5,600 rpm, wouldn’t the one at 5,880 rpm accelerate just a tiny bit faster?

But now for the big question, what is that effect of the extra rpm on HP? Based on the DT dyno, it seems that at 5,880 rpm, the 2.4 produces about 165 whp and at 5,600 rpm it produces about 153 whp. That is a 12 whp difference or 7.8% at 90 mph in 4th gear. For balance, 40 mph in second gear translates to 4,716 rpm with the 4.1 final and 4,946 rpm with the 4.3 final. At 4,946 rpm the 2.4 produces about 138 whp versus 134 whp at 4,700 rpm. Now the difference only 3% at 40 mph in 2nd gear.

Doesn’t this in some way show that at any given speed for the BRZ, the extra rpm associated with the shorter gear ratio results in 3% to 8% more power at that given speed? That was always my understanding of how to apply changes in gear ratios. I’m not saying it will produce a profound difference in trap speed. But that extra rpm (HP) will make some difference, if only one mph in this case.

[Frost]

Originally Posted by Baldeagle

Are you sure about this? Consider this logic:

With a 4.1 final, at 7,500 rpm:

1st goes 37 mph, 2nd goes 64 mph, 3rd goes 88 mph and 4th goes 120 mph

With a 4.3 final, at 7,500 rpm:

1st goes 36 mph, 2nd goes 61 mph, 3rd goes 84 mph and 4th goes 115 mph

At 30 mph in first gear, the rpm with the 4.1 final would be 6,040 rpm and with the 4.3 final it would be 6,335 rpm. At 30 mph, there is a 295 rpm difference in first gear. Once out of first gear, for any given speed (outside the 3-5 mph overlap around each shift point) the rpm remains between 230 rpm to 345 rpm higher with 4.3 final than with the 4.1 final.

For example at 90 mph with the 4.1 final, the BRZ would be in 4th gear at 5,606 rpm and with the 4.3 final it would also be in 4th gear but at 5,880 rpm, a 274 rpm difference. Doesn’t the engine produce more HP at 5,880 rpm than at 5,600 rpm? If two identical BRZs were travelling at 90 mph, and one was at 5,880 rpm and the other at 5,600 rpm, wouldn’t the one at 5,880 rpm accelerate just a tiny bit faster?

But now for the big question, what is that effect of the extra rpm on HP? Based on the DT dyno, it seems that at 5,880 rpm, the 2.4 produces about 165 whp and at 5,600 rpm it produces about 153 whp. That is a 12 whp difference or 7.8% at 90 mph in 4th gear. For balance, 40 mph in second gear translates to 4,716 rpm with the 4.1 final and 4,946 rpm with the 4.3 final. At 4,946 rpm the 2.4 produces about 138 whp versus 134 whp at 4,700 rpm. Now the difference only 3% at 40 mph in 2nd gear.

Doesn’t this in some way show that at any given speed for the BRZ, the extra rpm associated with the shorter gear ratio results in 3% to 8% more power at that given speed? That was always my understanding of how to apply changes in gear ratios. I’m not saying it will produce a profound difference in trap speed. But that extra rpm (HP) will make some difference, if only one mph in this case.

I'm no expert here but doesn't your calculation hinge on the fact that while your gearing is the variable, the engine can seemingly produce horsepower required at the RPM you are calculating to as opposed to locking in the horsepower?

[PhatFreshPrince]

Originally Posted by Baldeagle

If two identical BRZs were travelling at 90 mph, and one was at 5,880 rpm and the other at 5,600 rpm

The first one left Chicago traveling south and the second one left Atlanta traveling north. Which one would reach the mid-point first?

Answer: D) Not enough information

[ZDan]

Originally Posted by Baldeagle

Are you sure about this?

YES!

[quote]At 30 mph in first gear, the rpm with the 4.1 final would be 6,040 rpm and with the 4.3 final it would be 6,335 rpm. At 30 mph, there is a 295 rpm difference in first gear. Once out of first gear, for any given speed (outside the 3-5 mph overlap around each shift point) the rpm remains between 230 rpm to 345 rpm higher with 4.3 final than with the 4.1 final.

Thing 1: You *can't* just throw out the overlap! That part counts!

Thing 2: Being at higher rpm doesn't always mean you're making more power! At 33mph, the 4.1-geared car is at 7000rpm, peak power, and the 4.3-geared car is at 7350rpm and power has fallen off.

And at just over 34mph, the 4.3-geared car is at 4550rpm in 2nd gear while the 4.1-geared car is making vastly more power at 7200rpm.

For example at 90 mph with the 4.1 final, the BRZ would be in 4th gear at 5,606 rpm and with the 4.3 final it would also be in 4th gear but at 5,880 rpm, a 274 rpm difference. Doesn’t the engine produce more HP at 5,880 rpm than at 5,600 rpm? If two identical BRZs were travelling at 90 mph, and one was at 5,880 rpm and the other at 5,600 rpm, wouldn’t the one at 5,880 rpm accelerate just a tiny bit faster?

You are cherry-picking speeds to favor th 4.3 gears!

Have a look at what happens at 103mph.

You can't just ignore the regions where 4.3 gearing is *worse*!

Doesn’t this in some way show that at any given speed for the BRZ, the extra rpm associated with the shorter gear ratio results in 3% to 8% more power at that given speed?

NO!
Look at 32-35mph, 53-59mph, 76-85, 97-107.

[Dzmitry]

Originally Posted by Baldeagle

Are you sure about this? Consider this logic:

With a 4.1 final, at 7,500 rpm:

1st goes 37 mph, 2nd goes 64 mph, 3rd goes 88 mph and 4th goes 120 mph

With a 4.3 final, at 7,500 rpm:

1st goes 36 mph, 2nd goes 61 mph, 3rd goes 84 mph and 4th goes 115 mph

At 30 mph in first gear, the rpm with the 4.1 final would be 6,040 rpm and with the 4.3 final it would be 6,335 rpm. At 30 mph, there is a 295 rpm difference in first gear. Once out of first gear, for any given speed (outside the 3-5 mph overlap around each shift point) the rpm remains between 230 rpm to 345 rpm higher with 4.3 final than with the 4.1 final.

For example at 90 mph with the 4.1 final, the BRZ would be in 4th gear at 5,606 rpm and with the 4.3 final it would also be in 4th gear but at 5,880 rpm, a 274 rpm difference. Doesn’t the engine produce more HP at 5,880 rpm than at 5,600 rpm? If two identical BRZs were travelling at 90 mph, and one was at 5,880 rpm and the other at 5,600 rpm, wouldn’t the one at 5,880 rpm accelerate just a tiny bit faster?

But now for the big question, what is that effect of the extra rpm on HP? Based on the DT dyno, it seems that at 5,880 rpm, the 2.4 produces about 165 whp and at 5,600 rpm it produces about 153 whp. That is a 12 whp difference or 7.8% at 90 mph in 4th gear. For balance, 40 mph in second gear translates to 4,716 rpm with the 4.1 final and 4,946 rpm with the 4.3 final. At 4,946 rpm the 2.4 produces about 138 whp versus 134 whp at 4,700 rpm. Now the difference only 3% at 40 mph in 2nd gear.

Doesn’t this in some way show that at any given speed for the BRZ, the extra rpm associated with the shorter gear ratio results in 3% to 8% more power at that given speed? That was always my understanding of how to apply changes in gear ratios. I’m not saying it will produce a profound difference in trap speed. But that extra rpm (HP) will make some difference, if only one mph in this case.

As Frost is hinting at, it's a bit different than what you're thinking.

The simple answer is, you're not wrong, but you are negating additional factors that would go against your situation of gearing. You are using speed as the comparison of what RPM you are at. But you are not considering that the time in each gear or shifting varies. With the taller gear ratio, you are in the gear longer, and therefore go through the peak powerband for a longer period of time prior to shifting. It's honestly too difficult to write it all out and explain the details... that or I just don't feel like it as per usual.

But here's a video that can help you understand without having to give a very technical answer

And this is considering quite a large gear ratio difference in comparison to what we are discussing here. What you notice is the shorter gear ratio gets ahead at the PEAK RPM of EACH GEAR (similar to what you were talking about). But by the time the shift occurs, the taller geared car basically catches up.

Now I understand that the big piece we're missing with this video is how far ahead one car is from the other. The 4.88 car might pull very slightly ahead as it gets up to higher MPH a bit earlier than the 4.1 does. But regardless, this shows pretty clearly that a trap speed would come out very similar.

So to clarify again, you are technically correct about what you said. But you are only picking out points in time at a certain speed and basing your result on what your RPM is at. The part you are missing is how this differs at different points in time, particularly where a shift has to happen earlier with the shorter gear ratio and how the taller ratio gets to stay in gear longer.

[timurrrr]

Whenever there's a discussion around final drives, my suggestion is to plot wheel torque vs wheel speed in each gear for all FD options.

There you can easily see at what speed ranges each FD is faster or slower.

Ultimately it's about how close your power curve can get to the optimal "wheel torque = constant * peak power / speed" curve that CVT provides.

Here's how those graphs look like, e.g. at 7:22

[ZDan]

Originally Posted by timurrrr

Whenever there's a discussion around final drives, my suggestion is to plot wheel torque vs wheel speed in each gear for all FD options.

Here's 4.1 vs. 4.3:

[Baldeagle]

I certainly appreciate all this. ZDAN, thank you. Dzmitry, excellent video recommendation. I get how being in the powerband for longer has a benefit. That is essentially what Zdan said too, regarding shift overlap. And Timurr, thanks for your video. A good learning experience for me. Thanks to all.

[Jianlun]

Originally Posted by Stonehorsw

https://www.delicioustuning.com/2022...k_Dyno_Results

[Blighty]

Originally Posted by ZDan

??? What you mean "28% better?"

Oh, just your formula.

(101/93)^3 = 1.28

I'm really just pointing out here that even C&D have varied runs, and a small 2mph difference adds up to quite a bit according to that.

In the end everything is just more data for us to reflect on.

[nikitopo]

Originally Posted by ZDan

I'm matching 1/4-mile trap speeds with peak power numbers. Not times. Why? because 1/4-mile trap speed strongly correlates with (cube root of) power/weight.

No, power is what matters. Torque, by itself, tells you NOTHING. Torque doesn't tell you the whole story. Power does. If you know a car's power and weight, you can pretty well tell what it will do in the 1/4. If you only know torque and weight, you really have no idea...

Maybe. For sure the new car makes significantly more power, on the order of +20%. But definitely not 34% more...

Lol. Peak power is just a single POINT in the power curve. It doesn't work like this in reality for 1/4-mile trap speed. It might be a very rough estimation of what you 'll get, but nothing else. What it really matters is the power you have in the complete rev range and this is also dependent to torque. Don't you like the word torque I said? Just change the word with power under the COMPLETE power curve.