Getting ready for Bonneville(rebuild)

[jl222]

Just for kicks, an analytical look at the vaunted 294 mph run:

GM F-body, 20.4 sq ft, Cd=.3, W= 4900 lb at 287 mph (average of 280 2-1/4 speed and 294 average over the mile) gives a result of 1118 hp to overcome rolling and aero drag.
Time to go from 2-1/8 location to 2-1/2 at 287 mph = 4.7 seconds.
Acceleration in gaining 14 mph in 4.7 seconds = 0.136 g.
Force required to produce that acceleration on a 4900 lb car = 730.7 lb.
Horsepower needed to produce that thrust at that speed = 559 hp.
Adding drag hp to accelerative hp = 1677 hp being expended
Total thrust being used, 1677 hp at 287 mph, = 2191 lb.
Assuming 55% weight on driven tires, required coefficient of friction = 0.81  !!

In the absence of any aero downforce, car appears to be on the ragged edge of traction available.

Terminal speed under these conditions (zero acceleration, 1677 hp devoted to drag only) = 329 mph

  WOW...Interested O...Those CD and frontal areas and weight are spot on what is entered in my BvillePRO
computer program. Only dif is 20.5 for frontal area. Did I post that some where?

  Rear weight is 66% and car weight is without suited up driver so actual race weight is closer to 5150

  We get downforce from the low pressure under our spoiler but don't know what that pressure is.
  
How is traction figured without tire width? BvillePro shows tire spin if tires get to narrow.
  BvillePro has an altitude entry but not sure of it's % of correction but entered at 4500 ft and 75 deg.

  Figuring 15% power loss at 4500 ft 1677 hp + 15% =1928 sea level hp

  We still had 2 miles to go, the boost and power was coming up and data log at 7000 rpm and Bville pro showing
318 mph at that RPM with 1'' tire growth. At 11/2'' its 324 mph pretty dang close.

  What hp do you calculate for 342 mph? Bvillepros predicted top speed for the 222 Camaro

        Thanks JL222  

  
  

[Interested Observer]

Re-running the numbers with the new weight and distribution:

Time to traverse 2-1/8 to 2-1/2 =            4.70   sec
Acceleration to gain 14 mph in that interval =                   0.136   g
Force to accelerate car =                768   lb.
Horsepower to produce that acceleration =          588   hp
Sum of drag and accelerative horsepower =         1720   hp at wheels
      Engine at Bonneville         1911   hp
      Engine at sea level                      2085   hp
Resulting thrust at ground =             2248   lb
Driven wheel weight fraction =            0.66   
Required coefficient of friction =            0.66   
Terminal speed, traction limited =            331   mph

The two “0.66”’s are just a coincidence.
The small added weight had little effect on the performance, but the increase in driven axle weight made the run more realistic and higher speeds more feasible--if it doesn’t spin first. 

318 mph x 3% slip = 308 mph    Quit dreaming that there’s no slip.

And, I wouldn’t give you two hoots for Bonneville Pro.

[JustaRacer]

That's something I do not understand.

At least for me, rear tires spinning doesn't make the car spin.  I can spin tires past 150mph in soft dirt and it goes "normal".

So I assume a loss of front tire traction is what initiates a spin.  Either by aero lift or lack of weight.

ie - If I take a car with 50/50 bias, and spin the rear tires, they cannot generate enough force to overcome the front tires (assuming 4 equal tires).

Seems that safety would dictate at least 50/50 without lift, or more with lift.

If you put 4000lb on your nose, I'd be surprised if a good driver would spin a car.  It would take too much lateral pressure.

[jl222]

Re-running the numbers with the new weight and distribution:

Time to traverse 2-1/8 to 2-1/2 =            4.70   sec
Acceleration to gain 14 mph in that interval =                   0.136   g
Force to accelerate car =                768   lb.
Horsepower to produce that acceleration =          588   hp
Sum of drag and accelerative horsepower =         1720   hp at wheels
      Engine at Bonneville         1911   hp
      Engine at sea level                      2085   hp
Resulting thrust at ground =             2248   lb
Driven wheel weight fraction =            0.66   
Required coefficient of friction =            0.66   
Terminal speed, traction limited =            331   mph

The two “0.66”’s are just a coincidence.
The small added weight had little effect on the performance, but the increase in driven axle weight made the run more realistic and higher speeds more feasible--if it doesn’t spin first. 

318 mph x 3% slip = 308 mph    Quit dreaming that there’s no slip.

And, I wouldn’t give you two hoots for Bonneville Pro.

  If I was a math expert like you I  wouldn't need BvillePro, but it works pretty good for me and comes close
to your figures.

 If i'm reading your numbers right 1720 drag hp [new]  1677 [old] =43 hp to go 2 mph faster 329mph to 331
or 21.5 hp per mile an hr not figuring increase in drag.
 Using 21.5 hp and not figuring any drag hp increase and speed at 342mph, 13 mph increase from 329=279.5 hp

 Sea level hp 2085 + low hp calk of 279.5=2364.5

  Now at this time I'll bring up bvillePro and see how much hp increase from 329mph-342 ...11:52

  11:55  Bvillepro shows 353 less hp at 329 mph from 342mph.OR 353 more to go from 329mph to 342.

  2085hp + 353=2438 AND 2435 is what is entered for hp in Bvillepro

  My 1st try at 10% less hp was a speed of 230 and time was only about a min [but didn't check] took 2 more trys.
  BvillePro is great for figuring gear ratios and rpms, inter tire size-trans ratios-rear gearing-hp and engine specs
 press TS for time slip and presto your rpms at different speeds-to low rpms- enter a higer gear-to high -go lower

  For instance, after entering specs for engine and body type, track conditions ect, and pressing TS a timing
slip willcome up showing time-distance-mph-acceleration-what gear and rpm.
 say your engine makes 600 hp at 8000rpm and the timeslip shows only 7000 you would know to try a lower gear

 In our case we don't like to rpms over 7200 [overall gearing is 1.85]  going to Bvillepro to change to 1.75 and see rpm change. TIME 12:19 OK 12:22   Bvillepro shows 341.9 at 7520 rpms with 1.85 gearing 343.7mph at
7150rpms with 1.75 gears. Just bringing up Bvillepro and changing was quick but writing down new and old took the time.

         JL222

  

  

[jl222]

That's something I do not understand.

At least for me, rear tires spinning doesn't make the car spin.  I can spin tires past 150mph in soft dirt and it goes "normal".

So I assume a loss of front tire traction is what initiates a spin.  Either by aero lift or lack of weight.

ie - If I take a car with 50/50 bias, and spin the rear tires, they cannot generate enough force to overcome the front tires (assuming 4 equal tires).

Seems that safety would dictate at least 50/50 without lift, or more with lift.

If you put 4000lb on your nose, I'd be surprised if a good driver would spin a car.  It would take too much lateral pressure.

  You taking your doctors advice?

            JL222

[JustaRacer]

Not sure my vehicle is comparable. Yeah, 4k on the nose.  3k on the rear.  Never been much past 200, but it's like driving a Camry at 55 mph on the freeway at that speed.  You can take your hands of the wheel.  It has 36sqft of frontal area, and the aero of a barn.

[Interested Observer]

JL222,
Discovered a misapplication in the terminal speed calculation.  The assumption is that the thrust applied in the 294 run was about as much as the surface friction would support.   At terminal speed, there is no acceleration so that amount of thrust is applied solely to overcoming drag.  One then simply calculates what speed results for that vehicle when the stated thrust is applied.  The earlier error was that the 294 power level was used instead of the thrust as the criterion to calculate the speed.  New data set below. 

Horsepower for 287 mph            1133   hp
Time to traverse 2-1/8 to 2-1/2 =         4.70   sec
Acceleration to gain 14 mph in that interval =   0.136   g
Force to accelerate car =             768   lb.
Horsepower to produce that acceleration =       588   hp
Sum of drag and accelerative horsepower =      1720   hp at wheels
      Engine at Bonneville      2371   hp
      Engine at sea level      2586   hp
Resulting thrust at ground =          2248   lb
Driven wheel weight fraction =         0.66   
Required coefficient of friction =         0.66   
Terminal speed =               356   mph

From this it would appear that you are closing in on a traction limit, but are probably power limited.  I also get 342 mph for  2300 engine hp at sea level and 90% driveline efficiency.

[jl222]

JL222,
Discovered a misapplication in the terminal speed calculation.  The assumption is that the thrust applied in the 294 run was about as much as the surface friction would support.   At terminal speed, there is no acceleration so that amount of thrust is applied solely to overcoming drag.  One then simply calculates what speed results for that vehicle when the stated thrust is applied.  The earlier error was that the 294 power level was used instead of the thrust as the criterion to calculate the speed.  New data set below. 

Horsepower for 287 mph            1133   hp
Time to traverse 2-1/8 to 2-1/2 =         4.70   sec
Acceleration to gain 14 mph in that interval =   0.136   g
Force to accelerate car =             768   lb.
Horsepower to produce that acceleration =       588   hp
Sum of drag and accelerative horsepower =      1720   hp at wheels
      Engine at Bonneville      2371   hp
      Engine at sea level      2586   hp
Resulting thrust at ground =          2248   lb
Driven wheel weight fraction =         0.66   
Required coefficient of friction =         0.66   
Terminal speed =               356   mph

From this it would appear that you are closing in on a traction limit, but are probably power limited.  I also get 342 mph for  2300 engine hp at sea level and 90% driveline efficiency.

  We haven't said much about much about the power but the 2300 hp was at 6200 when the vibration unpluged
the power cord. It's rear wheel hp so some % should be added for flywheel power.
  As much hp as this is there are others out there [in drag racing] with over 3500 hp and on gas.

  I have asked SCTA [its been awhile and I can't remember if it was an official request] for a spoiler length similar to prostock [15'' verses 10'']

  We can add what the SCTA calls a Gurnney flap for more downforce, and had plans to do it last year but ran out of time. Guess we better get our butts in gear
  SCTA limits the spill plates to 2'' past spoiler and gurnney flap can't go past that.
  A 3'' flap from end of our 10'' spoiler is about 45 deg. 2''would be less and 4 more angle.
  No clue on how much downforce this would add, or drag.  IO?
 
       Thanks for taking time for calks  JL222

[JustaRacer]

...
  You taking your doctors advice?

            JL222

Just rambling, so if you PM me, I'll get rid of this post.

I've spun a lot of cars and trucks.  Nearly everything I've owned I've looped, and lots that weren't mine.   I'm told I don't drive smooth enough.  Bah!

But, it was always because rotational inertia exceeded the rear tire traction available at first, then the front.

I don't think this is why Bville racers spin.  I can feel the arse end wiggling on the dirt and salt, and wanting to swap ends when the rear tires are spinning, but there is not enough rotational force to spin the car.  The fronts are planted.  

A lack of front weight/traction just makes me hit things I'm not supposed to when I'm not running LSR.

If you have no rotational inertia, and all four tires have the same available traction, you should not be able to spin a car.  When the rears break loose, you have less available traction, and you slow down.  Self-correcting.  

But, if the rears have a lot more traction than the front, and something pushes sideways on the front, the rears will force it to loop, and quickly.  This is what I believe spins Bville cars.  You are pushing the front tires sideways.  This cannot be corrected by steering.  Tires sliding sideways don't steer much.

I'm not 100% convinced that smooth front tires are safe for LSR, or rear weight bias.

Most of our safety gear is aimed at surviving a spin gone bad.  What if just a ribbed tire, or 50/50 weight stops this from happening?  Would it save lives?  

Anyhow, it's just something that keeps nagging me.  I could be 100% wrong, but I'm going by how the car feels.


PS - I run smooth fronts.  Just to avoid tech issues.

[jl222]

  The front runners we run have thread. If we ran 50 50 weight distribution we would just spin the tires. Been there done that with more than 50-50 dis.

  Has it ever entered your mind why formula 1 uses 65% on rear? with the addition of wings and much bigger
tires on rear?

  Do you honestly think that Grand National cars should add weight to front to keep from spinning?

  Spinning tires loose lateral traction thats why a car can spin.

  Try this..next time it rains stand on the gas on a sharp corner and see what happens [make sure your alone and no trees to T-bone
  Or, wet or dry.. find a vacant parking lot, low gear, floor it. The weaving back and force is from the tires loosing
lateral traction.  Carrol Smith's book ''Tune to Win'' explains alot on tire traction.

  Your car weighs 7000 lbs and 150mph. You need to lighten that sucker up

                    JL222

  PS. now i'm taking your Dr's advice and go shoot some squirrels

[38flattie]

JustaRacer, I've been following this with interest, and disagree with you on the spins. John's already addressed that, so I'm going to leave it alone.

I just want to know what car is yours? I missed it if you said earlier in the thread.

[jl222]

  Justaracer

  Would you give the same advice to the 385MPH DRM lakester. A lakester with the engine set back as far as
possible WITH skinney front tires.

 Damn, I hope I see them squirrels before they see me.

             JL222

[Glen]

JustaRacer, I've been following this with interest, and disagree with you on the spins. John's already addressed that, so I'm going to leave it alone.

I just want to know what car is yours? I missed it if you said earlier in the thread.

38 it's a diesel pick up truck, makes a lot of black smoke.

[38flattie]

Haha! Thanks Glenn- now I know who he is!

[jl222]

 Justaracer

  Would you give the same advice to the 385MPH DRM lakester. A lakester with the engine set back as far as
possible WITH skinney front tires.

 Dodge, I hope I see them squirrels before they see me.

             JL222

  Got one , at about 50yds with my new Savage .17 cal, shooting 2550ft per sec bullets [can get up to 3300]
 Major damage to squirrel and the coyotes will have a free dinner tonight.

  These are ground squirrels that ate every plum we had  [ 1 tree] the night before we we going to pick last year.
 This year they ate them while still green. Got the Walmart special of 100 shotgun shells for 24.99 and got quite a few. Used them all up and got another box. But they get smart, as soon as I crack the door open or see any movement they jump in their holes.
  Anyhow I couldln't get close enough anymore with the shotgun and bought the .17 cal , its twice as fast as a .22 cal. Fun to shoot because it doesn't kick a bit and is easy on the ears. + the ammo is 17.99 for 50.

             JL222