Calculating power under the curve and applying it to the trans **** poitns

J

JasonCzerak

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All this speak of power under the curve. From what I gather, it's how "wide" your curve is not how tall/sharp it is.

So, I'm assuming one can calculate the area on the graph between the RPM's that the trans shifts though. Could we not have a new top number with the peak numbers? "The most average hp under the curve" or something.

I see peak numbers now being debated as uncorrected and corrected numbers. So yeah, more dramma for folks to argue about.

i've stared at many different graphs and I think I have the concept down, but short of getting my truck dynoed and remembering to bring the graph with me to the track and driving by it (something I forgot to do last time!!!)

so I ask the professionals, how do you do that? how do you read the graph so that you can figure out exactly where you need to grab the next gear? Care to get creative with mspaint and draw some lines and write some explanations?

I'm sure MANY folks will be very grateful for this information. Power is useless if not applied correctly so what's the trick.

How many folks attempt to dyno in 1st, 2nd, 3rd, 4th (5th and/or6th) individually, or continuously to figure out if different gears do infact have a different curve to comply with.

Is this topic were the secrets begin or will anyone spill the beans on what works for them, and what DIDN'T WORK for them.
 
JasonCzerak said:
So, I suppose the folks that went to college should show how well their mom and dad's money was spent. LOL
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Hey, easy easy lol. I had to take those wonderful classes but honestly couldn't apply what I learned to deciphering area under the curve. I haven't used that stuff once since working my job for 6 years now lol.
 
ok, lets spark this conversation some more here. The key here is exactly how many RPM's your motor drops on each shift. each gear isn't a direct "xxxx" rpm difference.

Download this: SpeedCalc

Use U.S And Metric Tire Size Information Calculator to determine you tire circumference

And use google to translate that into "mm" for the program

For the NV5600 and using my 285/70/17 tire in the math I have:

this is at the 3600rpm for these numbers

Top Gear gives 35.738 MPH/1000 RPM and a top speed of 128.656 MPH at 3600 RPM

Engine speeds in top gear:-
30 MPH = 839 RPM 40 MPH = 1119 RPM 50 MPH = 1399 RPM 60 MPH = 1679 RPM
70 MPH = 1959 RPM 80 MPH = 2239 RPM 90 MPH = 2518 RPM 100 MPH = 2798 RPM

(useless, not used)
Top Speed in 1 gear = 16.682 MPH
And changes into 2 gear at 2161 RPM dropping 1439 RPM

Depending on the mood, we could start off in 2nd, however, I have a DoubleDisk now..... Shift from 2nd to 3rd are extreamly slow, others not so bad.


Top Speed in 2 gear = 27.787 MPH
And changes into 3 gear at 2173 RPM dropping 1427 RPM
Top Speed in 3 gear = 46.039 MPH
And changes into 4 gear at 2453 RPM dropping 1147 RPM
Top Speed in 4 gear = 67.568 MPH
And changes into 5 gear at 2590 RPM dropping 1010 RPM
Top Speed in 5 gear = 93.919 MPH
And changes into 6 gear at 2628 RPM dropping 972 RPM
Top Speed in 6 gear = 128.656 MPH





For 3200rpm, where my power falls off.

******************************************************************************************


Top Gear gives 35.738 MPH/1000 RPM and a top speed of 114.361 MPH at 3200 RPM

Engine speeds in top gear:-
30 MPH = 839 RPM 40 MPH = 1119 RPM 50 MPH = 1399 RPM 60 MPH = 1679 RPM
70 MPH = 1959 RPM 80 MPH = 2239 RPM 90 MPH = 2518 RPM 100 MPH = 2798 RPM

Top Speed in 1 gear = 14.828 MPH
And changes into 2 gear at 1921 RPM dropping 1279 RPM
Top Speed in 2 gear = 24.699 MPH
And changes into 3 gear at 1931 RPM dropping 1269 RPM
Top Speed in 3 gear = 40.923 MPH
And changes into 4 gear at 2180 RPM dropping 1020 RPM
Top Speed in 4 gear = 60.060 MPH
And changes into 5 gear at 2302 RPM dropping 898 RPM
Top Speed in 5 gear = 83.484 MPH
And changes into 6 gear at 2336 RPM dropping 864 RPM
Top Speed in 6 gear = 114.361 MPH
******************************************************************************************



See attached Graph. I've printed a few copies out to take home today to look at and scan in later with some markings. However, for 3rd and 4th, I don't have any real data there because if you shift at 3200 it falls well short of the data on the graph. Even in some of the higher gear is appears if I hold to 3350rpm where I'm still over 500hp, I'll shift into 500hp as apposed to shifting into under 500hp. however, that's right where the torque peaks. when I dyno next I'll besure to have more detail on the graphs.

attachment.php



Am I on the right track here? any suggestions?
 
One thing's for sure. getting near 750hp for a 32.7" tall tire truck, 3200rpm's "in the power band" isn't enough anymore, I'll run out of gear in the 1/4. more rpm's that make power are needed big time.
 
My inexperienced opinion is this:

-Get on Excel and plot the engine speed vs. vehicle speed for each gear. This will show the speed @ rpm overlaps between each gear.

- As for shift points, I would shift at an rpm that is somewhat higher than the power peak than the difference between your two gears.... like if the gear separation is 500rpms, you shift at about 300ish rpms higher than the hp peak, so when the shift event is over you are slightly below the peak, but coming back into it.



just a thought
 
hmm - seems to me that if one wished to catch the best torque numbers per shift, and the dyno graph said ex. "1027 ft lbs" at ex. 2950 rpm then one would rev past the known truck (yours) shift rpm drop of say "650 rpm", in order to be right on top of the best torque once in the next gear

reality? = seat of the pants meter, cuz it can tell better where the truck likes to be under power n shifting and you can immediatley tell if it fell on its face or really liked it - not something a dyno or a graph can do - thats because the dynamic load is constantly changing from external factors like drag, wind, friction, temp, air quality etc etc
 
If you were going to get serious about this this is what i'd do. Get all gear ratios of the trans, tire size, and rear end ratio. Create an excell sheet which would allow you to enter horsepower at various rpms through a range. For instance, you could start with 1900, 2000, 2100, 2200, 2300, 2400, 2500 and call that one range. The next range could be 2000, 2100, 2200, 2300, 2400, 2500, 2600 call that the second range. The following could be 2100, 2200, 2300, 2400, 2500, 2600, 2700 call that the third range. So and and so forth but making sure to keep the x-axis input to seven total values with 100rpm spacing each time to make sure the info is consistant. The excell sheet would then output the average horsepower made throughout each range entered. The range with the maximum average horsepower would dictate the rpm window you want to spend the most time in. Now, after defining that rpm window adjust your shift to spend the most time within the rpm window resulting in the highest average horsepower.

The above method would rely heavily on a dyno reflecting real world output (questionable with dynoes used frequently today for these 6000+ lb behemoths).

Further, you may find that more then 7 values for a given range would need to be entered so you could play with that as well.

This may get you close but as said before, would rely heavily dyno numbers correlating to what actually happens when the full load is applied to the motor.

Not only that but would rely heavily on ones ability to read the horsepower at a specific rpm precisely.
 
You could also play around with the gear ratio calculators to determine the typical rpms between shifts to dictate what rpm span you create for your calculator. I.e. if rpms drop between the 1/2 2/3 3/4 shift an average of 800rpms then you would have 8 x-axis entries if you used 100rpm increments.
 
Does anyone have the gears, all four of them, ratios for a 47re? A link to all trans gear ratios would be helpful.
 
31 mph = 3209rpm 1st gear
31 mph = 1899rpm 2nd gear
rpm drop = 1310 rpm

53 mph = 3248 rpms 2nd gear
53 mph = 2240 rpms 3rd gear
rpm drop = 1008

76 mph = 3212 rpms 3rd gear
76 mph = 2216 rpms OD
rpm drop = 996 rpm drop

average rpm drop between all gears = (996 + 1008 + 1310)/3= 1105 rpms

Looks like you should shoot for 1100 rpm window.

The above was generated with a tire size of 32.6" diameter and 4.10 gears with the above trans ratios.
 
NickTF said:
31 mph = 3209rpm 1st gear
31 mph = 1899rpm 2nd gear
rpm drop = 1310 rpm

53 mph = 3248 rpms 2nd gear
53 mph = 2240 rpms 3rd gear
rpm drop = 1008

76 mph = 3212 rpms 3rd gear
76 mph = 2216 rpms OD
rpm drop = 996 rpm drop

average rpm drop between all gears = (996 + 1008 + 1310)/3= 1105 rpms

Looks like you should shoot for 1100 rpm window.

The above was generated with a tire size of 32.6" diameter and 4.10 gears with the above trans ratios.
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That looks right. I would recommend focusing on the lower end instead of the upper. Don't fall too much under the peak or turbo lag gets in the way.
 
joefarmer said:
That looks right. I would recommend focusing on the lower end instead of the upper. Don't fall too much under the peak or turbo lag gets in the way.
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I agree 100% and with this big s468 I run it's no wonder I didn't et a bit better. I honestly had no idea I was seeing rpms that low, hard to keep track of everything when running the truck. And honestly, I don't hink I shift at 3200 in any gear change making lower rpms even more important. This is why i'm very excited to get back to the track with the quick spool flange as the turbo light way faster!!!
 
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As already stated this all relies heavily if the dyno is accurate. I dont put much stock in engine dynos other than a fun toy and bragging rights. I would rather spend a few weekends at the dragstrip getting the shifts right and knowing its making me faster.

On the other hand for something to do when your bored. I would make an excell sheet that calculates what your rpms are in relation to mileage and gear ratios, then look at where your peak torque falls and make your truck fall just below that everytime depending on the curve and where your tq falls off. (lots of variables here) You will need to take into account where your tq peak occurs and how long it holds max tq, trans gears, axle gears, tire size, vehicle configuration, etc.
 
How about Riemann sums?

Print the dyno sheet on graph paper and count the little squares?


The vehicle that puts the most little squares to the ground in a given amount of time will travel farther in that amount of time. Right? Provided it weighs the same as the other vehicles and also has the same coefficient of drag?
 
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Simpson's rule would work to get a close approximation of the area under the graph.
((ending rpm-beginning rpm)/3*# of intervals)*(f(x0)+4f(x1)+2f(x2)+4f(x3)+2f(x4)+.......+4f(xn-1)+f(xn)
But you would still have to come up with a good way to use that information.

In the end I think you'd end up having to determine what works best it at the track anyways. Could be interesting for a dyno competition though
 
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Begle1 said:
Print the dyno sheet on graph paper and count the little squares?

The vehicle that puts the most little squares to the ground in a given amount of time will travel farther in that amount of time.
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You've stumbled upon a little-known horsepower secret used by some of the Top Shelf race teams - just print the dyno graph on 1/8 grid-ruled paper instead of 1/4 grid and you can QUADRUPLE power production with minimal tuning or track time... cheap HP by any measure! :woohoo:

However, don't try this "under the shade tree" if you're not experienced... for example, zooming the scanner to print more area under the curve could easily break tranny parts, or blow the tires away over the 60' :rules:
 
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