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Discussion Starter · #1 · (Edited)
This may be a dumb question but I have to ask it anyway. How much hp does it take to drop 1/10th from your et's? I know that there are a lot of variables here, skill of driver, launching, 60ft times, etc. But all things being equal, is there any way to estimate how much it would take? I know that for every 100lbs you drop it can equate to .1 off your et's but is there a way to calculate the same for power? Please specify crank or wheel when answering?.
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Discussion Starter · #3 · (Edited)
That's something I heard as well but I don't see how it could be. Let's take you for instance. A stock GT runs in the high 15's right? Let's say 15.9 just for example. That's with about 160 whp. You dyno'd 308whp, and had an et of 13.4. If we went by the .1 per 10whp equation, with you being about 150whp over stock, you should have only ran a 14.4. Now this could be off by a tenth or two but you're a whole second faster than the calculation would predict. This, along with several other cars, leads me to believe that this is a false method. What does everyone else think? Do you understand what I'm saying or am I overlooking something?
 

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I see your point, but you got to understand one thing..... and that is torque. My torque of my NA GT was probably 210~215whp at its prime and probably falling off around 4500 rpms or so. Now my torque is 265 and stays even through the whole rpm spectrum. Big difference which could explain that ummm 1 sec difference between the theory calc. When adding a CSC the whole power curve changes in a different direction, had the curve stayed the same then the theory would stay the same as well.
 

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The 10HP = .1sec off your 1/4mile thing is just too give people an idea. Its nowhere near exact but it does give you an idea.

Its just like the 100lbs = .1sec off your 1/4mile!

Also a Stock GT has ran as low as High 14sec! Going by his time and following the 10HP = .1sec rule puts him at 14.9sec stock going by your 150HP over stock and 13.4 et.
 

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Discussion Starter · #6 ·
I see what you guys are saying. I was just wondering if there was some type of formula for estimates. That one just seems to be too innacurate. Anyway it's not that important, I was just curious. Good enough info for me.
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Here are other ways to calc the power... I use it just as a 'rough' guide on what I make during a pass.

http://www.smokemup.com/auto_math/hp_mph.php
HP based on trap

http://www.smokemup.com/auto_math/hp_et.php
HP based on ET

*This requires that you know the race weight of your car. Also note that this is for RWD so the HP numbers are a tad higher.

**I prefer to use Trap as an HP estimate instead of ET since ET is based on how well you drive (which I don't). ;)
 

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Another thing is that it seems hp--> 1/4 mi would be better found using an exponential curve. If you're car already ran say a 6.00 in the 1/4 mile, adding 10 horse isn't going to change anything, if say you instead add 10 horse when your car runs 14s, you could get .1 quicker, then if your car ran something to the other extreme, say 20s+ adding 10 horse would make a huge difference, since your hp number would be extremely low anyway, so the %hp your adding would be much greater. (taken in the context of our cars, 10 horse extra to a car that runs 10s will have significatnly less 1/4 miles change than 10 horse extra to one that runs 15s)

Like if your car puts down 100 hp, you add 10 hp, you're adding ~10% more power, whereas if the car puts down 1000 hp, your only adding ~1% more.
 

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kObun- the important factor is the % difference in power or weight. Both will affect your ET close to the cube root of the difference.

Example-

Original ET- 15.9
Original WHP- 160
New WHP- 308

160/308 = .519
cube root of .519 = .804
.804 x 15.9 = 12.78 ET, which is about where Rick should be if he got a good launch.


The same applies to the mph, just use 1/.804 or start by dividing 308/160.

308/160 = 1.925
cube root of 1.925 = 1.244
1.244 x 86mph(guess of stock mph) = 106.98 mph which is close to what he runs.

-Matt
 
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