When using these online horsepower calculators, some say crank hp and some say at the wheels, yet give the same numbers. A guy at my work has dyno'd his car and ran at the track. He put his weight and mph in the calculator and he said the calculator is spot on what it puts to the wheels. So which is it actually when using car weight and mph?
Online Horsepower Calculators
- Thread starter clinteg
- Start date
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does the calculator know what transmission or rear end is in the car?
no....
but the HP at the rear wheels does not matter to the calculator what trans or rear is in it..
the calculator can only guess what the hp at the flywheel is....
that is the way I figure it..
no....
but the HP at the rear wheels does not matter to the calculator what trans or rear is in it..
the calculator can only guess what the hp at the flywheel is....
that is the way I figure it..
I see your logic and it does make complete sense. When I put my info in, it's saying I have around around 540 hp. At the crank I would think that was true. But if I say it's at the wheels, that's a big difference. To me, this number seems high. So that's why I was wondering.
Been using Wallace calc for years, its flywheel hp....this one>
http://www.wallaceracing.com/accel-calc.php
http://www.wallaceracing.com/accel-calc.php
fly wheel hp....ok
How does..the calculator know if I am running a 904 or 727?....a 727 takes more HP to turn then a 904.....
I can run almost 2 tenth faster with the 904 which shows more hp....but the engine is making the same hp with either trans...
I would assume the calculator uses a flat % of drivetrain loss regardless,,,,
dynos and calculator should be taken with a grain of salt..
How does..the calculator know if I am running a 904 or 727?....a 727 takes more HP to turn then a 904.....
I can run almost 2 tenth faster with the 904 which shows more hp....but the engine is making the same hp with either trans...
I would assume the calculator uses a flat % of drivetrain loss regardless,,,,
dynos and calculator should be taken with a grain of salt..
AGREED!.....perhaps a bit larger than a grain of salt, but yes, they are only a tool not an absolute, and yes, a dyno is just a tuning tool nothing more, its on track numbers that count as your sig says. I ONLY use the calc I gave the link for as it has been reasonably accurate on timeslips actually run by me and fellow racers cars I know the specs of currently. Other wallace calcs that give rwhp are off a long way as they only give 10% drivetrain loss as you mention. Also when trying to calc out the numbers for a Stocker, its miles out, had this discussion on Moparts.
I could give you the specs of my '69 car and what wallace said it should run against the timeslip/fly hp and it was close if your interested?
ScampMike
Despicable Damn Yankee
those things are mostly doing a general guesstimate.. don't hang your hat on the # it comes up with
No its more than just a guesstimate, you just gotta know how to use it properly, and it can be useful, not an absolute though, I've done all manner of cross references with gears/tyre combo's trap rpm's, flyhp numbers ET/mph on my cars and its more or less spot on with what my timeslips were for trap rpm/ET/mph/60's. However, 1 thing has to be a constant....and that is your car has got to be able to Hook reasonably well.....otherwise forget it, the only thing you'll get out of a car that doesn't hook is that is your mph/weight can give you a rough fly hp number for that run.....but it will also show what your ET could've been if you hooked her up and how far your off with your set up.
ScampMike
Despicable Damn Yankee
didn't I say the same thing you said just differently? perhaps a bit larger than a grain of salt, but yes, they are only a tool not an absolute = guesstimate.. ie; too many variables for an exact #.
Hmmm... I always figured they told you RWHP. Example: If a car has 1000 hp at the flywheel, but it has traction issues and runs a 10 flat. The calculators will take the weight, ET and/or MPH and come up with a HP needed to move that weight for that distance. The flywheel HP is irrelevant. What the track sees is RWHP. We have all seen just the opposite occur - a 400 flywheel HP car lay down extraordinary numbers for that HP. The track doesn't have any idea what the flywheel HP is, only what HP the rubber puts into the track. The reason I say this is because those online calculators use the numbers generated by runs down the track to compute the HP. As already stated above, they are only a guide. I will use my Cuda as another example. I know what the engine HP is because we dynoed it prior to installation in the car. I made some track runs and then plugged the numbers into the calculators and they came up about 100 HP shy of what the engine dynoed.
actually yes you did.......#-o
mderoy340
Well-Known Member
This is the one I use from Wallace Racing and IMO gets you pretty close.
Rear Wheel HP is assuming 10% drivetrain loss.
Calculates estimated HP for ET and MPH
http://www.wallaceracing.com/hpcalculatorquarter.php
Rear Wheel HP is assuming 10% drivetrain loss.
Calculates estimated HP for ET and MPH
http://www.wallaceracing.com/hpcalculatorquarter.php
Yeah if I use that calc on my numbers it says 484.01 fly hp. Now if I use my calc........
http://www.wallaceracing.com/accel-calc.php
I input 3000lb, and play around with the hp till I get what my car ran ET/mph, 10.7@125 I get, 484hp on that run, thats deff Flywheel, with no 10% loss rule which is inconsistent for every car as we know, its fly hp you wanna know for tuning purposes, who cares how much it made at the rear wheels, at least thats my philosophy, unless your running a stocker then everything matters! And that is why a dyno is pretty much useless for anything but tuning/development purposes, that you can do at the track, just takes a bit longer to find the right combo that way, but its somewhat cheaper, unless your on race fuel, but a whole lot more fun.
http://www.wallaceracing.com/accel-calc.php
I input 3000lb, and play around with the hp till I get what my car ran ET/mph, 10.7@125 I get, 484hp on that run, thats deff Flywheel, with no 10% loss rule which is inconsistent for every car as we know, its fly hp you wanna know for tuning purposes, who cares how much it made at the rear wheels, at least thats my philosophy, unless your running a stocker then everything matters! And that is why a dyno is pretty much useless for anything but tuning/development purposes, that you can do at the track, just takes a bit longer to find the right combo that way, but its somewhat cheaper, unless your on race fuel, but a whole lot more fun.
Wind resistance (pickup truck verses a corvette), how well the suspension is tuned, converter, torque (318 with 300 hp and a 360 with 300 hp will not have the same torque), none of this is asked with the Wallace, yet, they spit out an E.T. slip.
I always use the track time when people ask how fast it is. That's a sure indication of how it runs. It's those who ask how much power it makes that I don't know how to answer. Typically I just say around 550. But I try not to get too caught up in the dyno/calculator numbers much. I used the Wallace calculator that had inputs for hp, weight, gears, tire height and it came up with this:
Power to Weight Ratio: 6.24
60 Foot E.T. : 1.49
1/8 Mile E.T. : 6.77
1/8 Mile Trap Speed : 100.45
1/4 Mile E.T. : 10.72
1/4 Mile Trap Speed : 125
1/4 Mile Trap RPM : 5940
Those numbers are damn near spot on what I run except the rpm is about 1000 less than what I go through the traps at. That's guessing on my weight of 3370 with me in it too. Thanks for the input so far!
Power to Weight Ratio: 6.24
60 Foot E.T. : 1.49
1/8 Mile E.T. : 6.77
1/8 Mile Trap Speed : 100.45
1/4 Mile E.T. : 10.72
1/4 Mile Trap Speed : 125
1/4 Mile Trap RPM : 5940
Those numbers are damn near spot on what I run except the rpm is about 1000 less than what I go through the traps at. That's guessing on my weight of 3370 with me in it too. Thanks for the input so far!
Yep, but the ET/mph/60ft numbers have been more or less spot on for almost every car I've inputed and known the real numbers for, and the hp numbers have matched with what was inside those engines. I've only managed to better the 60 times given so far. If its off in some way you then use it with your knowledge to see where your off, engine or chassis, its not an absolute, you don't need to know windspeed etc., or if its a truck, you know your mph is gonna be a bit off, its a useful tool if you know how to use it properly.
Where it can go off some is for very light cars and stockers etc.
Here's my Cuda...3000lbs, 599hp, 14x32's, 4.88 gears>
Wallace says
60 Foot E.T. : 1.39
1/8 Mile E.T. : 6.29
1/8 Mile Trap Speed : 108.09
1/4 Mile E.T. : 9.97
1/4 Mile Trap Speed : 134
1/4 Mile Trap RPM : 6,895
Actually ran [email protected] with a 1.388 60ft, 7200rpm trap
and you can see the slightly better 60ft slowed it down a fraction but it picked up 1/100th which is what you'd expect.
Where it can go off some is for very light cars and stockers etc.
Here's my Cuda...3000lbs, 599hp, 14x32's, 4.88 gears>
Wallace says
60 Foot E.T. : 1.39
1/8 Mile E.T. : 6.29
1/8 Mile Trap Speed : 108.09
1/4 Mile E.T. : 9.97
1/4 Mile Trap Speed : 134
1/4 Mile Trap RPM : 6,895
Actually ran [email protected] with a 1.388 60ft, 7200rpm trap
and you can see the slightly better 60ft slowed it down a fraction but it picked up 1/100th which is what you'd expect.
So I enter 260 hp (not much of a teener), 3400lbs, and 2.76 gears and I'm suppose to run a 13.72. So virtually a 318 4bbl, dual exhaust in a Duster with 2.76 gears goes 13.72?? am I not using this calculator right? Guess I never payed much attention to calculators and dynos
Thats its p/w potential, the fact that it has 2.76 gears and probably a stock verter and therefore wouldn't launch worth a damn....it probably wouldn't run anywhere near that. But, if you put in 3.91 gears with 26" tyres that hooked, and upgrade the converter, if that motor made its 260hp at 5000rpm it could run a 13.72 shifting and trapping in the power band in top gear....yes its possible. The chassis is as important as the hp for a car to ET, as is the gearing/tyre to keep the car in the power band, thats what the calc helps you with and is exactly how I just used it.
I will give you another real world example close to that, and that was my all steel full interior street/strip '71 Cuda 340. 3600lbs, 3.55 gears 8x26" slicks, stock 2.02 heads, Hdrs., DC..484 hyd. purple, 750DP 3500 stall verter. Wallace has it at 300hp for this run>
60 Foot E.T. : 1.85
1/8 Mile E.T. : 8.41
1/8 Mile Trap Speed : 80.80
1/4 Mile E.T. : 13.33
1/4 Mile Trap Speed : 100
It ran [email protected]
I will give you another real world example close to that, and that was my all steel full interior street/strip '71 Cuda 340. 3600lbs, 3.55 gears 8x26" slicks, stock 2.02 heads, Hdrs., DC..484 hyd. purple, 750DP 3500 stall verter. Wallace has it at 300hp for this run>
60 Foot E.T. : 1.85
1/8 Mile E.T. : 8.41
1/8 Mile Trap Speed : 80.80
1/4 Mile E.T. : 13.33
1/4 Mile Trap Speed : 100
It ran [email protected]
The Wallace calculator is pretty damn close with my Dakota.
Your HP computed from your vehicle ET is 289.27 rear wheel HP and 321.41 flywheel HP.
Your HP computed from your vehicle MPH is 296.67 rear wheel HP and 329.63 flywheel HP.
Truck dynoed at 290 rwhp on a dynojet IIRC
Your HP computed from your vehicle ET is 289.27 rear wheel HP and 321.41 flywheel HP.
Your HP computed from your vehicle MPH is 296.67 rear wheel HP and 329.63 flywheel HP.
Truck dynoed at 290 rwhp on a dynojet IIRC
When i used the calculator to predict my et from my mph it was alway off!
Not because i had traction issues but because it wouldn't 60 foot.
The calculator said my car should run 13.7 but my best time was 14.10(usually 14.20s)
The problem wasn't tire slip but just the opposite. Not enough converter for the cam i was using. 60' time were it the 2.2-2.3 Calculator said i should have been 1.9 60 foots.
There can be many reasons why the calculator isn't accurate. and this is just another reason why!
Not because i had traction issues but because it wouldn't 60 foot.
The calculator said my car should run 13.7 but my best time was 14.10(usually 14.20s)
The problem wasn't tire slip but just the opposite. Not enough converter for the cam i was using. 60' time were it the 2.2-2.3 Calculator said i should have been 1.9 60 foots.
There can be many reasons why the calculator isn't accurate. and this is just another reason why!
the hp is pretty close! i would look at that and say there is some improvement in the tune(chassis/drivetrain) that need some improvements. The ET isn't showing the full potential of the HP you have.
If you focus on exact ### it will drive you crazy.
replicaracer43
Grumpy Old Man
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My take on the whole thing is that it takes basically a certain amount of horsepower to trap at a certain MPH, at a given weight. Even the old mopar engine bible had recommendations about what kind of horsepower it would take to run a certain MPH. The issue I have noticed, is that sometimes guys have engines built where they were "told" what it made on the dyno, but they run it at the track and it doesn't even come close to the MPH number it should. There natural reaction is that "calculators" are all wrong........ BUT I can tell you for sure, a REAL 500 flywheel horsepower in a 3200 LB car, will trap at somewhere around 120-125 in the 1/4 mile.
Yup there called HAPPY DYNO'S #-o
The Bottom line is if you have a car that has a reasonably good chassis that can hook, a loose-ish converter and a sensible gear/tyre combo with a motor thats set up well and runs strong you can use the Wallace calc to your advantage as a good tool for predicting its on track performance. The numbers given from your input data will be for an optimum run, and any differences from those figures against your actual time slip is where you can work out where your car is lacking, but you need a good understanding of how a Drag car works,
Here's a good example of 2 Camaros that run over here in the UK and how 1 differs from the other in the chassis dept, both have roughly the same hp.
1 is a '68 Camaro Bracket car with a 441ci SB, the other is one of the few legal "Stock" class cars we have.
The bracket car runs 9.79@137 mph with a 1.41 60ft, Wallace says that is spot on except for the 60ft which should be 1.36 so the car is down on the chassis side but the hp is there with good mph, its got potential to ET better.
The Stocker is a '69 with a 427BB and runs the same 9.79 but only at 135 mph with a 60ft of 1.27, way faster than Wallace predicts for that ET (1.36), the power is still there but its a far harder launching car which gets up the track further quicker technically has less track to build as good a mph, its maxxed unlike the bracket car. So, don't expect your street car with 2.76 gears a stock converter and treads to match anything ET wise that Wallace will come up with for your weight/hp figures, hp means nothing if you haven't got the chassis to convert it into a good ET.
Here's a good example of 2 Camaros that run over here in the UK and how 1 differs from the other in the chassis dept, both have roughly the same hp.
1 is a '68 Camaro Bracket car with a 441ci SB, the other is one of the few legal "Stock" class cars we have.
The bracket car runs 9.79@137 mph with a 1.41 60ft, Wallace says that is spot on except for the 60ft which should be 1.36 so the car is down on the chassis side but the hp is there with good mph, its got potential to ET better.
The Stocker is a '69 with a 427BB and runs the same 9.79 but only at 135 mph with a 60ft of 1.27, way faster than Wallace predicts for that ET (1.36), the power is still there but its a far harder launching car which gets up the track further quicker technically has less track to build as good a mph, its maxxed unlike the bracket car. So, don't expect your street car with 2.76 gears a stock converter and treads to match anything ET wise that Wallace will come up with for your weight/hp figures, hp means nothing if you haven't got the chassis to convert it into a good ET.
^^^ I agree... ^^^
The calculators a great tools to use to see if your combo is operating at it's fullest potential. If both the MPH and the ET are real close to what the HP should run, you are good to go. If the MPH is there, but the ET is not, then you have some chassis work to do. And vise-versa....
The calculators a great tools to use to see if your combo is operating at it's fullest potential. If both the MPH and the ET are real close to what the HP should run, you are good to go. If the MPH is there, but the ET is not, then you have some chassis work to do. And vise-versa....
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