Dyno reclass?

[RockLobster]

Yeah Jason, that's why i bowed out of this conversation. We could put up equations till our fingers bleed, being actual degreed and licensed mechanical engineers both of us. The armchair engineers will just pull out the ivory tower argument (even though we've both built championship winning cars).

 

Carry on all. Don't let physics or results get in your way.

[speedengineer]

You were smarter than me Chad - I should have realized how this discussion was going to go, and never chimed in in the first place.

[troyguitar]

There is a bit of gain to be had by skipping the need to shift since you have so many RPM of constant power. I have measured this both analytically and empirically, and it's good for an average of ~0.05 seconds per skipped shift, depending where on the straight the shift would have occurred. In my car, there'd be about about 3 skipped shifts at Mid-Ohio, so take off another 0.15 seconds. Pretty small gains. I actually don't rev my motor out unless I really, really need to. The lap time gain isn't worth the extra wear and tear on the motor.

 

I'd be really curious to see that - I know shifts are very slow in my car (Z06 with street type clutch/flywheel) and would have guessed closer to 1-2 tenths per shift. I know the 3-4 shift itself takes half a second on average (measured in my car), but obviously the car is still moving forward while that's happening. Is coasting really 90% as fast as accelerating?

 

That's also assuming absolute perfection in every downshift too, right? I know in real life I do better in braking/cornering when I don't also have to downshift, maybe I just suck.

[speedengineer]

There is a bit of gain to be had by skipping the need to shift since you have so many RPM of constant power. I have measured this both analytically and empirically, and it's good for an average of ~0.05 seconds per skipped shift, depending where on the straight the shift would have occurred. In my car, there'd be about about 3 skipped shifts at Mid-Ohio, so take off another 0.15 seconds. Pretty small gains. I actually don't rev my motor out unless I really, really need to. The lap time gain isn't worth the extra wear and tear on the motor.

 

I'd be really curious to see that - I know shifts are very slow in my car (Z06 with street type clutch/flywheel) and would have guessed closer to 1-2 tenths per shift. I know the 3-4 shift itself takes half a second on average (measured in my car), but obviously the car is still moving forward while that's happening. Is coasting really 90% as fast as accelerating?

 

That's also assuming absolute perfection in every downshift too, right? I know in real life I do better in braking/cornering when I don't also have to downshift, maybe I just suck.

 

You're correct that slower shifts will result in a bigger difference in lap time. And there's definitely something to not needing to downshift helping you stay consistent. Though, strangely enough, my car behaves weirdly when I enter a corner with the revs screaming >8k compared to when I'm in one higher gear. I wonder if the additional engine braking at the rear wheels is changing the balance of the car at turn in??

 

Below is some real data from my car with a 0.6x second shift. It's about a 0.03 second delta. Normally I don't shift this slowly, and the delta would be a bit smaller. The delta may be smaller yet in a higher hp car - since vehicle speed is higher, integrated time loss over a given distance is smaller. Though, there are other factors at play too, such as drag being higher, causing greater loss in speed while you're not applying the power. Difference could be larger too, if the shift occurred earlier on in the straight, and you had TONS of constant power rpm to use yet.

 

[speedengineer]

Another example, this time where the shift occurs earlier in the straight. Would have been about 0.024 seconds, but the shift on the blue lap was faster than the shift on the red lap, so by the end of the straight it was 0.039 seconds.

 

Now, if my motor could keep going and making constant power all the way to 9krpm, we'd be in business! Then it'd probably be a full tenth!

 

As you can see, botching the min speed in the following corner by 8 tenths of a mph had a bigger effect on laptime than the shifting did.

 

[troyguitar]

That's really interesting - although I'm thinking the difference should be larger in a higher powered car. We have both higher acceleration rates under throttle and higher deceleration rates when coasting. It should be more than enough to make up for the higher speeds but I have admittedly not run any actual numbers on it. I'm pretty curious now though so I'll put together a quick estimate and post it sometime this week.

[speedengineer]

That's really interesting - although I'm thinking the difference should be larger in a higher powered car. We have both higher acceleration rates under throttle and higher deceleration rates when coasting. It should be more than enough to make up for the higher speeds but I have admittedly not run any actual numbers on it. I'm pretty curious now though so I'll put together a quick estimate and post it sometime this week.

 

Very interested to see your data, Troy! Remember, it's really only valid with a constant hp tune, otherwise you've got other effects coming into play.

 

I've thought of another way to easily calculate the benefit that anybody can do, without simulation or data. I've you've been near another similar car on track, and you shift while the other car doesn't, pay attention to how much the other car gains on you. In a miata, I notice about a 1/4 car length position change due to a shift, say 3.25 feet. At 80mph, 3.25 feet translates into 0.028 seconds.

 

For kicks, I doubled the hp on my miata, simulated a lap. Delta still seems to be only a few hundredths for each shift.

[Greg G.]

You were smarter than me Chad - I should have realized how this discussion was going to go, and never chimed in in the first place.

Jason and Chad, don't worry, some of us understand math and physics just fine--hence, the lack of a Max Tq rule in TT, PT, ST. I gave up arguing with the leaders of the other race classes that use the "common sense" approach to math/physics a long time ago. What they have works for the most part, because all of their engines are similar to begin with, with the exception of the F/I versions. But, we have small bore, large bore, rotary, F/I, diesel, hybrid, and maybe electric soon to deal with. I would have loved to have put a "Max area under the usable Dyno HP curve" rule a long time ago, but with the number of folks that can't seem to negotiate the basics of addition and subtraction figuring out PT/TT mod points, I figured that Calculus was a definite non-starter. Also, I have considered such remedies as using a few HP data points (spread over the RPM range), averaged, instead of the Max HP, but again, it is just too complicated for our purposes. For those with a Dyno Re-class where it appears that there is some magic under the curve, the re-class reflects it. For our higher classes, it is build to your content anyway with suspension, etc., so it might as well be with engines also. (TT1/2/3).

[RockLobster]

Totally understandable. In a round about way that was kinda my point. I should clarify to say that the fact that reclasses are being handed out based on a dyno chart among other considerations (displacement, FI, etc) rather than just a 3 digit number has been a huge step forward.

[wm577]

The way I see it there are 4 main reasons to get a dyno classification:

 

1) Your car or engine / body combo does not have a base class (ie engine swaps).

 

2) Your car is 100+ over the base min. weight, so it’s a way to get more points to use on mods. Ideally all base min weights should be easy to achieve by removing simple stuff like spare tire, jack, ect.. but for many cars in the TT rules this is just not the case.

 

3) You added a bunch of mods that do little to nothing for power and are too lazy to remove them.

 

4) You want a higher base class so that your super wide tires amount to less points. This one is sort of a loophole that can remove tire width points on cars that have jumped several classes from HP mods.

[ILIKETODRIVE]

The way I see it there are 4 main reasons to get a dyno classification:

 

1) Your car or engine / body combo does not have a base class (ie engine swaps).

 

2) Your car is 100+ over the base min. weight, so it’s a way to get more points to use on mods. Ideally all base min weights should be easy to achieve by removing simple stuff like spare tire, jack, ect.. but for many cars in the TT rules this is just not the case.

 

3) You added a bunch of mods that do little to nothing for power and are too lazy to remove them.

 

4) You want a higher base class so that your super wide tires amount to less points. This one is sort of a loophole that can remove tire width points on cars that have jumped several classes from HP mods.

Add mine to it, too.

 

5) You have a swap BUT its whp is really like your base class BUT you're hundreds of pounds under it SO you class up 1 class to not only keep weight/power simple but also to gain points on your undersized high point tire compound

[speedengineer]

6). You feel that your car isn't favorably base classed, and can improve on lap time by using a dyno reclass.

7). This is kind of like reason 3, but often people wish to run cars built for another race series in TT/PT and this is the easiest way to do it.