Changa2

Somethings bothering me and I'm hoping you guys can set me straight.

My buddy put together a sweet running 82Z with a 454 NA Big Block (strictly drag) and I've taken a couple of his Time Slips and played with the HP Formulas, MPH and ET.

Weight (Car and Driver) = 3,420#

T/S #1
MPH 127.48
ET 10.700

RW HP (MPH) 548
RW HP (ET) 552
ET is a plus 0.7%

T/S #2
MPH 128.21
ET 10.469

RW HP (MPH) 557
RW HP (ET) 589
ET is a plus 5.7%

My mental problem is that T/S #1 seems maybe to be resonable. T/S #2 does not, in my rookie opinion.

In reading many posts I've been led to believe that the MPH number reflects most accurately on HP with the ET having to many variables. It would seem that even if you were able to achieve 100% efficency in ET that it should never reflect a HP reading greater than that for MPH.

With this in mind I'm a bit surprised that the ET would ever show a positve HP gain over MPH. What's wrong with my logic?

Our local track is not the greatest but it gets the job done. They do have all the lights and computer print outs. Track itself is just so-so.

Any thoughts on this? Could there be anything in the track equipment or set-up or is this just the nature of Formulas?

Thanks Bruce




[This message has been edited by Changa2 (edited November 25, 2001).]

AlkyIROC

Your math is slightly off somewhere.

#1
MPH 127.48 = 552.97 hp
ET 10.700 = 551.78 hp

Nothing wrong with that. It's close enough to be considered a perfect pass.

#2
MPH 128.21 = 562.53 hp
ET 10.469 = 589.11 hp

That pass tells me either the 60 foot clocks screwed up or you got some really good traction however something happened on the top end to slow you down since the MPH should have been about 130.3

What are all the interval times.
60 foot, 1/8 mile, 1000 foot and 1/4 mile. Break each one down to see where you lost or gained time.

------------------
Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block (times are for the current engine)

Best ET on a time slip: 11.447 altitude corrected to 10.99
Best MPH on a time slip: 119.42 altitude corrected to 124.86
Altitude corrected rear wheel HP: 493
Best 60 foot: 1.586

Racing at 3500 feet elevation with a typical race day over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

NJ SPEEDER

one thing i must point out is that et is a completely inaccurate way to judge hp. et's are a measure of gearing and traction, not absolute hp. yes it does take more hp to create a much lower et, but i have lesss power than a lot of guys thats are significantly slower than me.
mph is the only way to get a realistic estimate of hp from the track since it is a measure of your power to weight ratio. the formula to come up with a + or - 5% at the wheels number is
[(.00427*mph)cubed]*vehicle weight= rwhp
to see some other formulas in action you can check out www.prestage.com
it is the best automath site i have every seen.

later
tim

------------------
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nicmike85

There are other variables as well. Such as what RPM is he crossing the line at? His engine might be reved out or running out of air. This would explain no increase in MPH on the second pass. The way to find the problem is like Stephan said you need to break down the time slip and see how much time he spent in each section of the track.

Changa2

Ya Stephan, there is a difference in our calculations based on MPH. I used the following formulas:

Formula: HP = Weight * (MPH/234.74)3
Formula: HP = Weight/(ET/5.825)3

Originally I used the factor 234.0 but recently saw the 234.74 figure and I thought it was said that it complied with the NHRA accepted formula but I could be wrong. Could have been the other way around. As far as I'm concerned it doesn't matter as 234 seems to be the most commonly used. RJ uses a multiplier of .00427 which is the same as 1/234. I'm comfortable with going back to the following:

Formula: HP = Weight * (MPH/234)3

Now Stephan our numbers agree and the % variances tightened up somewhat, but the question remains.

I'll fill-in the blanks just as I saw it on the TS:

T/S #1
MPH 127.48
ET 10.700
60 Ft 1.577
Mid MPH 102.74
660 Ft 6.064
Reaction Time 5.01

My calculations based on:
MPH 553
ET 552
ET is plus 0.2%

T/S #2
MPH 128.21
ET 10.469
60 Ft 1.492
Mid MPH 103.93
660 Ft 6.662
Reaction Time 5.39

My calculations based on:
MPH 563
ET 589
ET is plus 4.7%

Nicmike raises an interesting point in that my buddy is turning 7000 at the end running a TH400 and 4.33 Moser. This bothers him to the point that he is almost sure to chage over to 4.10's this winter.

AlkyIROC

I wish your track gave 1000 foot times also but oh well.

First run.
60 foot: 1.577
1/8 mile: 6.064 : 4.487 difference from 60
1/4 mile: 10.700 : 4.636 difference from 1/8

Second run.
60 foot: 1.492 : Already a .085 improvement
1/8 mile: 6.662 : 5.17 difference from 60. Something went wrong and he lost .683 from the 60 foot mark to the 1/8 mile. Different shift rpms probably.
1/4 mile: 10.469 : 3.807 difference from 1/8. A big improvement in the last 1/8 mile. All the shifting is done before the 1/8 and brute HP pulls that last 1/8 mile.

Without a 1000 foot time to break the run down more, I'd say he had problems at the shift points between the 60 foot mark and the 1/8 mile. The better 60 foot time translates into the better ET but by shifting at too low or too high an rpm lost valuable HP for the loss of mph at the finish line. It could be that the 4.33 gears are letting the engine come up to 7000 quicker than he can react. He's either anticipating the shift or is way to slow.

One way around it is to use air or an electric solinoid on the shifter and let an rpm switch do the shifting. At 7000 rpm, bam, it shifts for you automatically. Perfectly legal in non electronics class. I also have to assume he shifts by using a shift light instead of a tach. It's a lot easier to see the light come on than trying to watch a needle on a tach. I only use a tach while working on the car or during the burnout. After that it's strictly the shift light.

Changa2

It could be that the 4.33 gears are letting the engine come up to 7000 quicker than he can react.

Another good point, he does use a light but has commented on his shifting. He's also commented on his shifter, not real comfortable with it. Not sure if it's him or his shifter, although he's no BS'er, if he thought he was falling asleep he'd say so.

Great response to my original post. This will make a good topic at our Wednesday night garage party. Thanks.

NJ SPEEDER

thsi is also very true, the number you come up with from the formula that i posted is more of an aveerage type of a number. it is somewhere between the peak hp, the hp at the shift point, and the hp when passing through the trap.

later
tim



------------------
91 Camaro RS-LO3,Auto
New Times Coming Soon!
Check Out The East Coast F-Body Nationals Home Page
www.geocities.com/njspeeder
My MAFB.ORG Home Page
www.mycar.net/mafb/registry/detail.cfm?id=299
DSI Racing Home Page
www.geocities.com/foff667