Dyno Speeds

[panic]

"HPxRPM number ain't got nothin' to do with nothin"

True - HP × RPM  is TQ × RPM × RPM, doesn't exist.
The "combination" is TQ × RPM, not TQ + RPM.

"The amount above peak HP to shift at is a function of how close the gear spread is."

And how flat the torque curve is, and how much change in resistance occurs with higher speed.
If torque falls off quickly after peak power (common in highly developed resonant systems tuned for peak power) shifting at or immediately after peak power produces better results.
If torque is high (but decaying) after the peak you can use a higher RPM figure than peak.
If torque below the peak is poor, even more RPM above peak is needed.

From a practical perspective, near maximum speed the engine must recover to an RPM level at which the power is almost as high, or the car will slow down ("the damned thing goes faster in 3rd than 4th"). Really fast cars, or peaky engines need a very close shift into high gear, and can use more "progession" (the spread in RPM drops through the gears, with the same 1st gear), which would have little value in a drag race.
An example of high progression, #1:
1st 2.50:1
2nd 1.55:1 recovers 62% from the 1-2 shift
3rd 1.10:1 recovers 71%
4th 1.00:1 recovers 91%
This is better than less progression with the same 1st and 4th, #2:
1st 2.50:1
2nd 1.65:1 recovers 66% from the 1-2 shift
3rd 1.25:1 recovers 76%
4th 1.00:1 recovers 80%
#1 has less total power under the RPM curve than #2, but is still has higher top speed, because the critical 3-4 shift is the only one that occurs when the car is aero-limited rather than traction-limited.
Why not just use all close ratios, like #3?
1st 2.00:1
2nd 1.40:1 recovers 70% from the 1-2 shift
3rd 1.10:1 recovers 79%
4th 1.00:1 recovers 91%
For some transmissions it doesn't exist, or $$$. For some, the much lower numerical 1st gear (i.e., 2.00:1 instead of 2.5:1) makes launching the car very difficult (clutch slip, converter heat problem, plug fouling, spark curve), and the engine must develop more power at low speed to overcome this.

[ack]

After many months studying torque compensated computer rotational dynamic simulations and gathering empirical data along with advanced scientific evaluation I have derived the following information which, because of my unselfishness and devotion to land speed racing I am willing to share with you all.

Put a gear on it that makes it go the fastest.

“Theoretical records are set by theoretical vehicles”
Quote by Denis Manning

[JackD]

"Yup , just like they said and said and said, a dyno might float yer boat, but it won't teach you how to sail." (me)

I wonder where Denis heard that ?

[SPARKY]

and it takes the 2nd impound trip to make it non theory--- as the  AA GL boys found out this year at SW ---5 one way trips 4 by the current record holder and 1 by me ---"just a tryin to "GET'r Done"

[SPARKY]

Panic, 

My FDRs are

1.  4.01
OD 3.13
3.  2.28  GM rear axel
OD 1.77

1.  3.77
OD 2.94
3.  2.14  GM rear axel
4.  1.67

As you can imagine I can only run the OD in direct with 26" tires as opposed to the 30"s---which I haven't tried yet---but will soon.

[revolutionary]

Sparky. I built a spreadsheet last night with inputs for tire size, rear end gear ratio, converter slippage (for autotragic cars), TE constant tire size with output info for mph based on rpm at up to 6 different gears as well as TE outputs at the rpm mentioned.  I'll bring home some dyno sheets tonight to plug in some real data to how how this whole deal works with the TE info.

I had an old spreadsheet that was similar that I used to show torque drop for shifting rpm but it's lost in the puter somewhere for now. 

I'm sure most folks here have similar spreadsheets but if anyone wants an excel copy let me know.

[SPARKY]

Rev,  I am intrested is seeing how you have set up your converter slip---I presently don't use a converter--but will when I am able to go to Texas and or Maxton---with what you have done in the past you may already have done most of this---remember what I was trying to accomplish---what combo that I can max out for a given speed---If I get to run at EL M this weekend I will be using the 30" tires with my 3.13 FDR comb to try to run 220+---I will be turning 8M +---way past my peak eng power---but will maximise my TE!!!!!!!

[SPARKY]

Rev.  Dont for get---Its eng(TQ) X (TR)Trans. Ratio X (RA) Rear Axle ratio X (T) tire

I use a value of 1 for my most commonly used tire my 30"---and .00 Adjust for any % size difference-- I am calculatin rear end thrust or Tractive effort---what is pulling the car forward --asuming it is hooking up

[Dean Los Angeles]

Dyno. A scientific device for determining engine tune up.
Bonneville. A scientific device for determining gearing. And lowering your expectations.

Determining HP on different engine setups is what a dyno is for.

Gearing is a SWAG at best. You don't know what the aero figures are going to be. Two identical vehicles with different aero are going to require different gears.

Air flow through the intake on the salt can be far different. And never in a good way.

The dyno doesn't rattle your teeth like the salt does. Has much better traction than the salt too.

As far as those 5 mile pulls at the salt, you should be doing them on the dyno. If it won't do it there, no sense in putting it on the trailer.

Having a setup that allows fast gear changes beats a spreadsheet every time.

[SPARKY]

Dean--that quick change EATs power---with different tire sizes and GM ratios with a GV OD---I can get awfully close---I need to work on AERO now!!!!!!!!

[Stainless1]

Dean--that quick change EATs power---with different tire sizes and GM ratios with a GV OD---I can get awfully close---I need to work on AERO now!!!!!!!!

Spark, Dean and all the bike guys don't have the power eating gear change problem... sprockets, fronts and rears, lots of changes, works the same for the bike motors in cars....

[SPARKY]

great point!!!!!

[Stan Back]

There's just the reason I needed to go back to work on my AA / Thomas Flyer roadster!