Calculating HP from 1/4 mile time and weight...
Calculating HP from 1/4 mile time and weight...
(OP)
MG Maestro 1/4 mile speed is 12.48 sec and 127 mph - I estimate the weight to be 2200lb.
Please can someone give me a hp calculation and workings out.
Thanks
Regards...
Please can someone give me a hp calculation and workings out.
Thanks
Regards...





RE: Calculating HP from 1/4 mile time and weight...
RE: Calculating HP from 1/4 mile time and weight...
I will run the numbers for you tomorrow when I have more time
Regards
pat
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Calculating HP from 1/4 mile time and weight...
v*v= 2*a*d (V squared = 2* acceleration*distance)
you have v=127 mph and d=1/4 mile, so you can find "a"
We all know that F=m.a where F is force and m is mass. You now have "a" and "m" and you will have F. This is the average force that engine produced in 1/4 mile drag.
Total work done in this distance is W=f.d. If you divide this work into the time (12.48) you will have work done in each second, which is POWER. Then remember that 1bhp= 736 watts (if I remember correctly !! ).
I wish it helps.
Cheers
You can live in your car, but you can't drive your House!
RE: Calculating HP from 1/4 mile time and weight...
RE: Calculating HP from 1/4 mile time and weight...
The simple method, while not perfect, is more accurate than you might expect.
1) Zimbali's statement does say AVERAGE power, so change in power during the race is not relevant to that statement.
2) Our car launches at 5000 rpm, and finishes at 8000 rpm, but it accelerates very quickly (about 1.6 seconds I think) through low gear to 8000 rpm it only drops to 6500 on the change, so it is close to maximum power for 90% of the trip.
3) If it is set up right there is not much tyre slip, but the torque convertor does slip and loose energy to heat. It should be corrected for.
4) Driver reaction time is not an issue as the timer starts as the car moves, not as the green light lights up. We could sit at the starting line for a minute, lose the race by about a minute and still record an 8 second run if that is what the car actually did.
Regards
pat
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Calculating HP from 1/4 mile time and weight...
RE: Calculating HP from 1/4 mile time and weight...
RE: Calculating HP from 1/4 mile time and weight...
Anyway, I have no idea what sort of car you are talking about, nor how much grip it has, but trying to match up those numbers, it would have to have the best part of 300 rwhp to pull that kind of speed. And if it really is that light, it seems to launch fairly poorly.
RE: Calculating HP from 1/4 mile time and weight...
MPH=10 + 221 x cube root(HP/WT)
If we solve for HP from MPH we get 315 HP
From ET we get 183 HP but this is not accurate unless suspension is ideal.
Ideal relationship of ET to MPH is
ET=1.05 + 1102.79/(MPH-10)or 10.48 sec.
RE: Calculating HP from 1/4 mile time and weight...
What I suggested was a simple method to find an estimate of the range of engine power. As patprimmer said it is an AVERAGE, and there is "no way" that you can find the maximum hp from its average, if you don't have the hp curve itself!!
It was also assumed that air resistance is low enough to be neglected, but it's not a good assumption especially after 50-60 mph. And about the the transmission loss and other things like that, I may say that we try to measure (or estimate) whp which is wheel horse power, and is the same if you take your car to a dyno shop. It is some few hp less than engine bhp which that LESS is a function of bhp and how efficient the transmission is.
And PSlem,
do you have any idea where your formula comes from?
Cheers
You can live in your car, but you can't drive your House!
RE: Calculating HP from 1/4 mile time and weight...
RGR=(RPM x TD)/(310 x MPH) for getting ideal rear gear. Again I forget what RPM you should cross finish at as related to HP and TQ curves. And lastly LGR=(TWXMPH)/HP for manual and LGR=(TWXMPH)/(1.8xHP)for autos where LGR is low gear ratio and TW is tire width. 1.8 allows for torque multiplication in convertor. Use 60% of tread width for treaded tires.
RE: Calculating HP from 1/4 mile time and weight...
Yeah, I'd say the MG in question launches rather poorly!!!
Rod
RE: Calculating HP from 1/4 mile time and weight...
Rod, you'll be glad to know the Maestro was released with the A series engine in, bored and/or stroked to just under 1.3 litres. You had to wring it out to make it fly, but the good chassis made it reasonable fun through country lanes.
My performance model says it would need about 350 hp at the flywheel, but it doesn't handle standing starts gracefully so i've no idea how accurate that is.
Cheers
Greg Locock
RE: Calculating HP from 1/4 mile time and weight...
This is the car in question - the reason for my original post was that I am very sceptical about this vehicle. on 2 fronts.
1 - I find it hard to comprehend that a front wheel drive vehicle of this minimal complexity could use 400bhp.
2 - They are only using a rover k-series....
RE: Calculating HP from 1/4 mile time and weight...
So the average engine power is 216bhp.
My assumption for the maximum power is not more than 290bhp as long as you only cover the whole RPM range in gear ONE and when you change the gear you come somewhere in 3500-4000RPM and you have at least 4 times more power than in 800-1000RPM. So the maximum is not roughly 2 times more than average and my feeling says the maximum shouldn't go further than 300bhp.
I did all this calculation to say that maybe the car is not that powerful (400bhp) as you might have imagined. And remember when this car was introduced to the market the "motto" was that it can beat a Ferrari!!! so it shouldn't be a very simple car.
Cheers
You can live in your car, but you can't drive your House!
RE: Calculating HP from 1/4 mile time and weight...
RE: Calculating HP from 1/4 mile time and weight...
RE: Calculating HP from 1/4 mile time and weight...
This works for us:
ET= the cube root of (WEIGHT/HP) x 5.825
POWER OR WEIGHT FROM ET
HP= weight/(ET/5.825)cubed
WEIGHT=(ET/5.825)cubed x HP
MPH= the cube root of (HP/WEIGHT) x 234
POWER OR WEIGHT FROM MPH
HP= (MPH/234)cubed x WEIGHT
WEIGHT= (234/MPH)cubed x HP
RE: Calculating HP from 1/4 mile time and weight...
Your figures work for me, and come pretty close to a known example
Regards
pat
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Calculating HP from 1/4 mile time and weight...
Have Fun,
Sam
RE: Calculating HP from 1/4 mile time and weight...
surprisingly close. Isky, Bell Auto Parts, Automark all printed them.
at 2200 pounds and 112 mph it shows 260 hp.
The et compared to the mph shows to me I think that this is a result of the front wheel drive....the car might have the potential...at that mph at least, to have a lot better 60 foot times and run in the 11's even with FWD.
The mph is what the clocks show...scepticism aside...but are the clocks correct and was that just on one run or a more 'realistic" best of 2 or 3?
RE: Calculating HP from 1/4 mile time and weight...
it does a 1/4 mile in under 11.9 secs
also, a Rover 200 style car, also owned by AN-racing, has done the 1/4 mile in the low 12's with about 465bhp
RE: Calculating HP from 1/4 mile time and weight...
http://www.maxracesoftware.com/race_car_physics.ht...
it will give you ET, MPH, GForces, etc every 10 Ft of distance
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
RE: Calculating HP from 1/4 mile time and weight...
hp= (mph x .00426) cubed x weight
this would result to about 350 hp
i like this formula because it doesn't take into account reaction time or e.t. which vary much more than mph does
if you make a disasterous run.