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Author Topic: HP Needed for Speed...AT A DISTANCE ?  (Read 4082 times)
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« on: August 05, 2016, 03:58:22 PM »

Does anyone know how to calculate the distance you reach a certain speed?  I am heading out for my first time this year, trying for the 150 club.  I've run 1/2 and full mile events on pavement, used the 'HP needed for speed' sheet that says my theoretical top speed...but can I hit 155 on salt in two miles?  In another event (Big Bend Open Road) the car reached it's tech (168 mph) on pavement but I did not measure how long it took.  Thanks, appreciate any assistance.
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bearingburner
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« Reply #1 on: August 05, 2016, 06:58:52 PM »

A lot will depend on rear end gear. With too high a number gear you can be wound out tight before the first mile. To low a number your engine may not be able to pull it in high gear.
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55chevr
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« Reply #2 on: August 05, 2016, 07:38:51 PM »

what was top speed achieved on paved mile?

JOE
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« Reply #3 on: August 05, 2016, 09:25:28 PM »

Thanks guys.  Top speed on a paved mile with a passenger (230 lbs) was 143.  Obviously no passenger on this run.  At the wheel it is 410 hp and tq.  Here's the "final drive" (trans gear X axle ratio) for the 6 speed w/3.92:
2.97 11.64
2.10 8.23
1.46 5.72
1.00 3.92
0.74 2.90
0.50 1.96

4000 lb. Challenger. 155 on the salt in 2 miles?

Thanks!
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Stainless1
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« Reply #4 on: August 05, 2016, 10:28:59 PM »

You'll know in September...  shocked

Actually if you car is capable of doing 155 at 6000 ft+ DA then you should be OK, there is less traction than pavement, but you have 2 miles to get there and then another quarter to be timed.  The big difference is no hard launch and altitude to deal with.
Good luck with your quest, see you at the WoS.  cool
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Stainless
Red Hat 228.039, 2001, 65ci, MSA Bockscar Lakester with a little N20 
MSA Bockscar Lakester #1000 my fastest mile 245 and change, 84 ci turbobusa motor... but Corey's 233 MPH H/BFL record is still 3MPH faster than mine.
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« Reply #5 on: August 05, 2016, 10:57:59 PM »

Choice of tire is huge on the salt. You don't run a wide ice tire & you need to approach the salt the same. I think there's two people on the forum that think the opposite is true so expect a rebuttal from them. evil
  Sid.
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trimmers
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« Reply #6 on: August 06, 2016, 06:23:34 AM »

Check out the formulas here:
http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html#Horse%20Power%20Needed

You'll probably need to know your Cd and frontal area to get a good answer.  Weight counts too, as although it sounds like you've got plenty of room, you run out of it PDQ.

I've done it, and I can tell you that it ain't as easy as it sounds!  The DA could be as high as 7000' feet, so I think if you're running a newer car with EFI and an ECU, you'll have a better shot.   When my kid and I made it (in a daily driver 350Z, with only a couple minor mods), there were a lot of pretty serious cars there that couldn't get the job done.     

On one of my runs, I missed a shift (got 5th instead of 3rd!) and it cost me about 4 or 5MPH.  So, there not much wiggle room.

The bottom line is that they don't call it the "Big, white dyno" for nothin'!  Just show up and run to get your final answer.
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nrhs sales
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« Reply #7 on: September 09, 2016, 03:39:59 PM »

if your car is normally aspirated you will lose somewhere between 10-15% of your power if it is a hot day at Bonneville compared to sea level so I have a feeling it will be be close to whether or not your car can hit 150 at the salt.
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« Reply #8 on: September 10, 2016, 11:41:02 PM »

Thanks everyone, first two passes were at 156...


* x70.jpg (109.66 KB, 795x513 - viewed 115 times.)
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rouse
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« Reply #9 on: September 11, 2016, 05:10:13 PM »

If the aerodynamic of you car is high and a lot of frontal area, you may run fast at Bonneville than you would at sea level.

Kind of works like this, you lose 10-12% HP and also lose 12 -14% drag due to altitude. Net results a little fast.

Rouse
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Johnnie Rouse
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« Reply #10 on: September 11, 2016, 05:46:24 PM »

Since the power potential for an NA engine is proportional to the air density, and the aerodynamic drag is also proportional to the air density, going between two elevations should be a wash.  Where do you get your numbers?
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rouse
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« Reply #11 on: September 12, 2016, 07:35:39 AM »

Without getting into a protracted discussion as to why, the math will do that for you, you gain slightly more on aerodynamics than you lose on HP. That's just how it is, NA sure wont have the gains that supper charging has, but there is some.

Rouse
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Johnnie Rouse
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