Landracing Forum

Introductions => Formulas => Topic started by: Stan Back on April 06, 2010, 06:56:28 PM

Title: Hp needed for % of Speed Increase
Post by: Stan Back on April 06, 2010, 06:56:28 PM
What's the formula(s) for when you can go 160 on 500 HP, how fast you can go with 600 and/or if you need to go 180, how much increased HP you need.

You know -- the square of the increase(?) is half the angle of the dangle or whatever?

Help!!!

Simple Stan
Title: Re: Hp needed for % of Speed Increase
Post by: racer x on April 06, 2010, 07:19:04 PM
I found this one
http://robrobinette.com/top_speed.htm

170.025mph on 600hp need 715 hp to get 180mph
Title: Re: Hp needed for % of Speed Increase
Post by: sabat on April 06, 2010, 07:33:05 PM
Here's Sumner's calculation Excel sheets, including the one you're looking for. 

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html#Horse%20Power%20Needed (http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html#Horse%20Power%20Needed)
Title: Re: Hp needed for % of Speed Increase
Post by: Stan Back on April 06, 2010, 07:41:31 PM
The Robinette one gave some unbelievable figures -- and as usual I couldn't access Sumner's spreadsheets.  I guess I'll have to depend on the Shearers for the best answer.

Stan
Title: Re: Hp needed for % of Speed Increase
Post by: Cajun Kid on April 06, 2010, 07:43:47 PM
Stan,

Just mash the gas pedal and hang on.....I am sure you have all the power you need.

Charles
Title: Re: Hp needed for % of Speed Increase
Post by: racer x on April 06, 2010, 08:08:04 PM
I think it goes... all the power you can afford dose not go as fast as you want.
Title: Re: Hp needed for % of Speed Increase
Post by: desotoman on April 06, 2010, 10:31:43 PM
Stan,

Send me the numbers and I will crunch them for you.

Tom G.
Title: Re: Hp needed for % of Speed Increase
Post by: Milwaukee Midget on April 06, 2010, 11:58:18 PM
I think it goes... all the power you can afford dose not go as fast as you want.

Here's the formula - it's corollary is based on boat ownership -

($ x APR) + 5W = S x .99, where

$=$
APR = variable
5W = lodging
S = speed
.99 = "I'll be back next year" coefficient

 :cry:
Title: Re: Hp needed for % of Speed Increase
Post by: Stan Back on April 07, 2010, 11:35:09 AM
Payback is hill.

Stan
Title: Re: Hp needed for % of Speed Increase
Post by: Geo on April 07, 2010, 11:49:10 AM
Did you want that formula to work forwards or backwards?  :evil:

Geo
Title: Re: Hp needed for % of Speed Increase
Post by: Stan Back on April 07, 2010, 11:50:29 AM
Yes
Title: Re: Hp needed for % of Speed Increase
Post by: desotoman on April 07, 2010, 01:36:22 PM
Stan,

Send me the numbers and I will crunch them for you.

Tom G.

Stan,

Are you sure those are the right numbers you sent me? I come up with a minus 7. Sorry.

Tom G.
Title: Re: Hp needed for % of Speed Increase
Post by: jacksoni on April 07, 2010, 01:48:30 PM
If you are only going 160 on 500 hp you need a different car- 'less you are driving a freightliner or something!  :cheers:
Title: Re: Hp needed for % of Speed Increase
Post by: bvillercr on April 07, 2010, 03:28:10 PM
If you are only going 160 on 500 hp you need a different car- 'less you are driving a freightliner or something!  :cheers:

it's called a rolling brick :-D
Title: Re: Hp needed for % of Speed Increase
Post by: 64avanti on April 08, 2010, 12:38:33 AM
The power is proportional to the speed.  To find the power take the ratio of the two speeds and cube that number.  180/160 = 1.125,  1.125 cubed =1.438  so 500 hp x 1.438 = 712 hp, rounded up

So how big is this car?  It has one heck of a CdA!
Title: Re: Hp needed for % of Speed Increase
Post by: sheribuchta on April 08, 2010, 12:53:34 AM
check your calculator --or your typing                                       willie buchta                                                   
Title: Re: Hp needed for % of Speed Increase
Post by: jl222 on April 08, 2010, 12:55:05 AM
 Salty Dog... I mean Stan :evil:

  From Carroll Smith's book [Tune to Win]  Drag HP=  CD X Frontal area X ( Velocity in mph) to the 3rd power divided by
                                                                                                 146,600

  His example  Drag HP = (.65) X ( 17 FT) x (180 mph) to the 3rd power OR 180 X180X 180
                                                  --------------------------------
                                                             146,600                                                     =  439 HP


                           JL222 :cheers:
Title: Re: Hp needed for % of Speed Increase
Post by: jl222 on April 08, 2010, 01:08:08 AM
 With out putting a lot of time in, Bonneville Pro came up with 166 mph but thats at 4500 ft

                    JL222

  Smith was using a formula 5000, car dropping the weight from 2350 to 1200lbs the speed was 170
Title: Re: Hp needed for % of Speed Increase
Post by: Stan Back on April 08, 2010, 11:33:07 AM
We're not talking about any specific car, here.  Nor any Cd.  There's a formula that sez that if you get the car (bike, whatever) to go, say 180 with, say 200 HP, how fast you'll go with 250 HP.  I think that Avanti comes closest, but I think it has to do with the square of the percentage of increase, not the cube.  I don't need anyone to figure it out for me -- I'm good with formulas -- I just don't have that one.

Stan
Title: Re: Hp needed for % of Speed Increase
Post by: jl222 on April 08, 2010, 12:39:48 PM
  
 There would have to be a specific car [ cd and frontal area] it takes less HP to make a small slippery car go faster than a big dragey one.


              JL222
Title: Re: Hp needed for % of Speed Increase
Post by: Stan Back on April 08, 2010, 02:46:22 PM
No, no, no.

There's a formula that sez that if you get the car (bike, whatever) maxed out to go, say 180 with, say 200 HP, how fast you'll go with 250 HP.

In other words -- but not so different -- "I went 180 MPH best with 150 HP after years of trying, doing my best.  If I had 200 HP, how fast would I go?"

Stan
Title: Re: Hp needed for % of Speed Increase
Post by: bbarn on April 08, 2010, 03:03:18 PM
http://craig.backfire.ca/pages/autos/drag (http://craig.backfire.ca/pages/autos/drag)

Stan,

Look down the page to the "Acceleration and Top Speed" section, there is a formula below that. I have an Excel spreadsheet someplace that has a simpler formula already in it but I can't find it.
 
Title: Re: Hp needed for % of Speed Increase
Post by: jacksoni on April 08, 2010, 05:07:01 PM
DRAG goes up as Square of velocity. HORSEPOWER goes up as CUBE.
Title: Re: Hp needed for % of Speed Increase
Post by: 4-barrel Mike on April 08, 2010, 05:48:07 PM
Or a Sum summerized in the explanation to his spreadsheet, to go twice as fast, you need eight times the horsepower.

Mike
Title: Re: Hp needed for % of Speed Increase
Post by: Stan Back on April 08, 2010, 06:59:07 PM
There you go!

Now if I could only read the spreadsheets.

I'm about ready to give up on this.

But I think that the percentage of increased HP cubed is equal to the percentage of increase in velocity squared -- right?

Stan
Title: Re: Hp needed for % of Speed Increase
Post by: Stan Back on April 08, 2010, 07:01:00 PM
Really -- I'm thankful of all the offers of where to find the formula and how to plug it in here and there -- but I don't have a passport (or machine) to get there.  I just wanted the formula.

Stan
Title: Re: Hp needed for % of Speed Increase
Post by: 4-barrel Mike on April 08, 2010, 07:26:43 PM
What's the formula(s) for when you can go 160 on 500 HP, how fast you can go with 600 and/or if you need to go 180, how much increased HP you need.

You know -- the square of the increase(?) is half the angle of the dangle or whatever?

Help!!!

Simple Stan

180 mph / 160 mph = 1.125 times faster
1.125 cubed (1.125 x 1.125 x 1.125) = 1.423828125
500hp for 160 mph * 1.423828125 = 711.9140625 hp for 180 mph

Mike

Assuming that I entered and copied everything correctly
Title: Re: Hp needed for % of Speed Increase
Post by: interested bystander on April 08, 2010, 07:32:21 PM
F=MA, E=MC2

In all seriousness, the Sten Block machine has a realistic shot at the Dirty Two Club, if the Inkrez predictions are correct!

Phone me in Atlanta if ya do!
Title: Re: Hp needed for % of Speed Increase
Post by: Stan Back on April 08, 2010, 09:03:23 PM
Now that I've got this cubic foot of enriched unobtainium, how do you lean it out? 
Edsel = Motor Cars for 2?

Stan
Title: Re: Hp needed for % of Speed Increase
Post by: 64avanti on April 09, 2010, 02:37:38 AM
It is proportional to the cube of the speed.  The force due to drag is proportional to the square.  To get power you have to multiply by the rate.  Therefore the power is proportional to the cube of the speed.

If it takes 100 hp to go 100 mph then to go 200 it is the ratio of (200/100) cubed times 100 hp or 800 hp.

The calculator works fine.
Title: Re: Hp needed for % of Speed Increase
Post by: SHughes on April 09, 2010, 11:05:35 AM
Not to high-jack the thread, but this is a great topic and I LOVE the formulas.  IF they are accurate, I need far less power to meet my goals than I previously thought.

And power is certainly not the problem I have...it's money to make the truck safe to drive that's the problem.
Title: Re: Hp needed for % of Speed Increase
Post by: agrassfidf on May 12, 2010, 11:28:00 PM
Is there a formula that involves weight, or does that not matter when you already have hp and top speed? Is there a reasonably accurate formula for motorcycle?
Title: Re: Hp needed for % of Speed Increase
Post by: LSR Mike on May 13, 2010, 12:49:32 PM
Dr Mayfield,
Mayf, for all the Listers, has a site with many specifics including the Cd, frontal area etc... of many production cars and trucks,
along with simple explanations...

http://www.mayfco.com/dragcoef.htm
Title: Re: Hp needed for % of Speed Increase
Post by: 1212FBGS on May 13, 2010, 03:55:59 PM
theoretical vehicles set theoretical records every theoretical time.....
Kent
Title: Re: Hp needed for % of Speed Increase
Post by: Seldom Seen Slim on May 13, 2010, 04:04:09 PM
Kent, you should add that you're speaking theoretically, I theorize.
Title: Re: Hp needed for % of Speed Increase
Post by: Peter Jack on May 13, 2010, 05:24:21 PM
But it's so true! :-D :-D :-D

Pete
Title: Re: Hp needed for % of Speed Increase
Post by: desotoman on May 13, 2010, 10:30:55 PM
Dr Mayfield,
Mayf, for all the Listers, has a site with many specifics including the Cd, f :evil:rontal area etc... of many production cars and trucks,
along with simple explanations...

http://www.mayfco.com/dragcoef.htm

Mike,

He forgot Roadsters!!!!!!!!!!!!   :evil: :-o :-D

Tom G.
Title: Re: Hp needed for % of Speed Increase
Post by: Peter Jack on May 13, 2010, 10:59:31 PM
And he runs one ------------ just a little newer than the rules allow!!! :? :? :-D :-D

Pete
Title: Re: Hp needed for % of Speed Increase
Post by: LSR Mike on May 24, 2010, 07:15:54 PM
Interestingly enough Tom, I stole an old method from my high school Photography instructor to calculate the frontal area for #300. He was a Air Force Photo Intelligence Interpreter.

Shoot a pix of the of the intended vehicle with a known value object in the frame. From there you can calculate the frontal area of the vehicle. In Vietnam they knew what the bore of rifle the VC was carrying, therefore he could tell you what size shoe he (the VC) was wearing.

I have since lost the excel file I was working with to approximate the HP necessary to put that brick over the record, and we really never knew how much HP we were producing because the LSR tires would never hod traction on a chassis dyno. but alas, we know what happened to that engine...I still have some (very broken) parts of it in the "offering to the gods of speed" section of my LSR chapel.
Title: Re: Hp needed for % of Speed Increase
Post by: thecarfarmer on August 18, 2012, 12:26:19 PM
DRAG goes up as Square of velocity. HORSEPOWER goes up as CUBE.

Really?

Maybe someone can explain how this works...

If most of the drag on a car at speed (like >100 MPH) is aero, and aero drag goes up as a second power function of the increased velocity, how come HP needed would go up as a third power function?

In other words, if air resistance is the largest single factor in drag, and if it goes up 4X when I double the speed... where's the other "horsepower vampire" hiding here? 

Just tryin' to understand...

-Bill
Title: Re: Hp needed for % of Speed Increase
Post by: hotrod on August 18, 2012, 12:59:17 PM
Quote
In other words, if air resistance is the largest single factor in drag, and if it goes up 4X when I double the speed... where's the other "horsepower vampire" hiding here?

Just tryin' to understand...

The speed itself is the 3rd factor.

If you could drive in a vacuum the power required to go faster would go up directly in proportion to the speed. With air resistance you also increase drag at the square of the speed. speed squared x speed = speed cubed

Larry
Title: Re: Hp needed for % of Speed Increase
Post by: panic on August 18, 2012, 06:44:39 PM
In Vietnam they knew what the bore of rifle the VC was carrying, therefore he could tell you what size shoe he (the VC) was wearing.

Plus or minus 100%...
Title: Re: Hp needed for % of Speed Increase
Post by: Jack Gifford on August 19, 2012, 12:43:42 AM
Bill- what you were missing is that power is force times velocity.
Title: Re: Hp needed for % of Speed Increase
Post by: tallguy on March 11, 2024, 02:26:24 AM
We're not talking about any specific car, here.  Nor any Cd.  There's a formula that sez that if you get the car (bike, whatever) to go, say 180 with, say 200 HP, how fast you'll go with 250 HP.  I think that Avanti comes closest, but I think it has to do with the square of the percentage of increase, not the cube.  I don't need anyone to figure it out for me -- I'm good with formulas -- I just don't have that one.

Stan

Aerodynamics is not the only thing that plays a role here.  There are other frictional things coming into play.  But based simply on aerodynamics -- which is probably the major biggie --, the horsepower required increases as the cube of the speed.  Of course, available power is not the only important thing.  Appropriate gearing is also critical to success.
Title: Re: Hp needed for % of Speed Increase
Post by: Stan Back on March 11, 2024, 12:16:17 PM
I said that 14 years ago?  Yikes!!!  I musta stole that from someone else.