Dyno Speeds

[SPARKY]

Sum,
I am ALWAYS working to try to figure a combination of tire size, Overall tio that will geve me a better TE AT OR ABOVE my previous best speed---in my case I have run 276 with an exit of 279 with MT 30s and 2.28 --- around 282 my TE with 2.28s and 2.14s are the same---below 282 I have a better TE with the 2.28--

282 and above I have a better TE with 2.14s which move me back down the TQ curve by 7% which has a TQ value of greater than 7 % at 282--therfore I will have more thrust at the rear wheels with 2.14  and app. 6500 than I would have with 2.28 and 7300.---  I may be giving up some accleration at lower speeds --(MAYBE)---I have had an issue of hooking it up so far with the tracks that we have had--

[SPARKY]

If for example:  I could get to 300 then I will be better of going to my MT 26" and my OD which will give me a FDR of 1.77---I doubt without a snoot full of NO2---that ain't gona happen!!!!!!!!!!!!! except in my dreams----  LOL

[SPARKY]

Sum,  I am dealing with a similar crossover---but mine is the TE of the different  FDR and tire combinations:

 ie overall ratios multiplied by the eng torque at 100 rpm intervals on the spread sheets!!!!!!!!!!

[aswracing]

Sum, Scott is right. There is a simple mathematical relationship between torque, rpm, and horsepower. Horsepower is torque times rpm. Yeah, you divide it by 5252 to scale the result down to match what Watt's horse could do, but conceptually, you can think of horsepower as torque times rpm, i.e. the combination of the two. As I previously showed, torque and rpm are interchangeable entities that make equal contributions to performance, therefore they're weighted equally in the horsepower formula.

The 5252 scaling factor comes from the fact that Watt's horse could lift 1lb 33,000 feet in 1 minute. Well, 1 lb-ft of torque is defined as 1 lb of rotational force at a 1 foot radius. 33,000 feet is how far that 1 foot radius travels if you make 5252 rotations (r x 2 x pi x 5252 = 33,000). So 5252 rotations moves that 1 foot radius point 33,000 feet. If it has 1 lb of force on it and it does those 5252 rotations in 1 minute, it's doing exactly what Watt's horse could do and we call it a horsepower.

In any event, the important point is that the power peak rpm is always where the combination of torque and rpm are at their greatest. If you go to a higher rpm than the power peak, the torque will drop more than the rpm rises, hence you have less horsepower.

My point here is that it's physically impossible to rev the motor past it's power peak, and then with gearing, end up with some higher combination of torque and rpm. The power peak is where you want to be when the wall of air stops your acceleration, because that's where you're getting the most out of the motor. You can't get more with gearing tricks.

That's what you want to do to maximize rear wheel torque at a given rear wheel rpm. The difference between that and force at the contact patch is a function of the radius of the tire. But it scales linearly, there's no free lunch. A shorter tire reduces ground speed by the same factor that it increases contact patch force, and vice-versa.

That said, I think I misunderstood what Sparky is doing. From his later post, it seems he's really effectively adding resolution to his gearing selection by considering tire size in conjunction with axle ratios and power available on each side of his power peak. Basically, since he doesn't have infinite resolution in gear selection, there's a range of rpm he's forced to work over, he can't always gear right for his power peak. His available axle ratios and tire sizes define that resolution for him. Anytime he's not right on his power peak, he's going to have less than optimum rear wheel torque, but that may be outweighed by being able to get closer to the wall, which of course is the name of the game.

[revolutionary]

Sparky I can see where you are going with this ( I just did a little spreadsheet and pasted in some dyno numbers) but please be sure to mention that you can't blindly enter in a new torque value at the new rpm without going back to determine the correct gear ratio (or tire size) that would appropriately lead to the new and improved TE.

In other words looking at a dyno sheet here that a 434 was making 511.3ft lbs at 6000 and had a TE of 1308.9 with a 2.56 gear, 1:1 trans and a 1.0 tire ratio.  We now look at 6200rpm and the engine is now making 494.7ft-lbs.  Is that better or worse? Keeping all things equal it is worse  - 1266.4.  Yeah we can arbitrarily enter in a new gear ratio or tire ratio to inflate that number but we have to keep in mind the our new gear ratio/tire ratio MUST have the engine running at 6200rpm now in the real world.  If we don't keep the reality of an rpm change in mind then the numbers don't mean anything.  OK so now we have to reverse engineer the formula to determine the RPM of the engine.  I would recommend altering your formula to use an actual tire size instead of a multiplier to more easily determine this.  And to do that we need to take into account MPH.  

Please take this assignment home and bring it back to class tomorrow with your proof.

[Sumner]

Sum, Scott is right. There is a simple mathematical relationship between torque, rpm, and horsepower. Horsepower is torque times rpm. Yeah, you divide it by 5252 to scale the result down to match what Watt's horse could do, but conceptually, you can think of horsepower as torque times rpm, i.e. the combination of the two. As I previously showed, torque and rpm are interchangeable entities that make equal contributions to performance, therefore they're weighted equally in the horsepower formula..............................

Ok I put the 5280 down because I was too lazy to go look up the 5252.  Hey I was only off by 28 and that ain't bad when you are 63 and at least I know how long a mile is , and I've seen the HP/Torque formula tons of times. Glen and I got to ride Watt's horse when we were younger in fact.

..................In any event, the important point is that the power peak rpm is always where the combination of torque and rpm are at their greatest. If you go to a higher rpm than the power peak, the torque will drop more than the rpm rises, hence you have less horsepower.......................

Ok so let's get down to the above statement.  Here are some dyno numbers.

RPM   HP   Torque   T + RPM   T X RPM   HP X RPM
2000   138   363   2363   726000   276000
2500   181   379   2879   947500   452500
3000   227   397   3397   1191000   681000
3500   278   418   3918   1463000   973000
4000   326   428   4428   1712000   1304000
4500   368   430   4930   1935000   1656000
5000   391   411   5411   2055000   1955000
5500   393   375   5875   2062500   2161500
6000   372   326   6326   1956000   2232000
6500   337   272   6772   1768000   2190500

You said to combine the rpm and torque and I wasn't sure from another post if you meant add them together or multiply them, so I did both.  The adding together (4th column) didn't seem to work as the resulting number always got higher even when the torque was falling off at 6500.  The multiplying method (5th column) seems to make sense and at 5500 you have the highest number and that is also the HP peak.  Is this the method you use??

If I was gearing I would have probably picked about the same point based on the HP peaking there.  The 6th column show HP X RPM and if you used that column 6000 rpm would be the peak and that is probably where I would shift on the drag strip, on the salt in the first couple gears for a high HP car short shifting seems to help as you can never get full throttle in these gears anyway.

Looking at all of this I think we are all coming to about the same conclusions just from slightly different perspectives and until you have some real world results on the salt or dirt it is hard to fine tune the gearing to achieve the maximum potential of the vehicle at any set HP/Torque level.  Before you run you are doing a lot of guessing with the aero drag.

I'll add your torque/rpm to my data that I look at and also Sparky's Tractive Effort.

Thanks guys,

Sum

[tortoise]

The 6th column show HP X RPM and if you used that column 6000 rpm would be the peak and that is probably where I would shift on the drag strip

At the drags you want to shift at above the HP peak if the redline allows, and cross the line at above the peak, to keep the RPM range in each gear more or less centered around the HP peak.

[Sumner]

The 6th column show HP X RPM and if you used that column 6000 rpm would be the peak and that is probably where I would shift on the drag strip

At the drags you want to shift at above the HP peak if the redline allows, and cross the line at above the peak, to keep the RPM range in each gear more or less centered around the HP peak.

6000 was above the peak HP in the example.  The peak was at 5500, but the HP X RPM peak was at 6000.  I found that interesting as that peak goes along with the commonly accepted shift point that you mentioned.

c ya,

Sum

[tortoise]

6000 was above the peak HP in the example.  The peak was at 5500, but the HP X RPM peak was at 6000.  I found that interesting as that peak goes along with the commonly accepted shift point that you mentioned.

c ya,

Sum

I should have read you more closely. Calculating the HPxRPM peak is a prosecutable case of spreadsheet abuse, I fear. The amount above peak HP to shift at is a function of how close the gear spread is.

[isiahstites]

Glen and I got to ride Watt's horse when we were younger in fact.

[/quote]

LMAO!!!

[JackD]

Glen and I got to ride Watt's horse when we were younger in fact.

LMAO!!!
[/quote]

HORSES TO LET AND DYNOS VERIFIED
              INQUIRE WITHIN

[1212FBGS]

bla..bla...bla...
Sum put your calculator down.... go out in the garage and pick up a wrench... you got 289 days till speed week... and less if ya wanna take your lakester to elmo for a pre-speedweek shake down
love ya
kent

[SPARKY]

Tortoise --gets IT as I understand IT --we are a 4 mile drag with a 1 mile trap---almost the same---I am just using TE --trying to figure out how much to under gear.

[Sumner]

The 6th column show HP X RPM and if you used that column 6000 rpm would be the peak and that is probably where I would shift on the drag strip

At the drags you want to shift at above the HP peak if the redline allows, and cross the line at above the peak, to keep the RPM range in each gear more or less centered around the HP peak.

6000 was above the peak HP in the example.  The peak was at 5500, but the HP X RPM peak was at 6000.  I found that interesting as that peak goes along with the commonly accepted shift point that you mentioned.

c ya,

Sum

I should have read you more closely. Calculating the HPxRPM peak is a prosecutable case of spreadsheet abuse, I fear. The amount above peak HP to shift at is a function of how close the gear spread is.

I'm confused, which is it??  When drag racing shift above the HP peak or not??  You say "shift at above the HP peak"  The HP peak on the dyno run I posted was at 5500 and the point where the HP X RPM produced the highest number was 6000 RPM.  Is this not above the HP peak??

Now I didn't say use the HP X RPM method as awsracing never said to use it, I just observed that it indicates what your are suggesting "shift at HP peak".

I agree that the gear spread is critical and why I made the spread sheets on my site that show the rpm drop on gear shifts at any rpm:

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html

c ya,

Sum

P.S. Kent I've been working on the car since your post and I'm going back out there now  .

[tortoise]

Now I didn't say use the HP X RPM method as awsracing never said to use it . . .

All I was saying is that the HPxRPM number ain't got nothin' to do with nothin', and wondered what it was there for.  We've run out of stuff to argue about.

c back atcha,
tortoise