REV App Turns iPhone Into Performance Driving and OBDII Diagnostics Tool

How on earth can it compute instant MPG? There are apps too which also claim to show BHP -- are they mental or something? How is that possible without a rolling road?

I really do fear people are being ripped off with these apps as Apple sits by and let's it happen.

I was wondering exactly the same thing.

Bristol: It reads directly from the OBDII port, and many cars provide MPG readings through it. It's not an estimation; it's what the car is telling the device that it's getting. Also, not all readings are available for all cars through this device, so if the car's CPU doesn't read MPG, it won't display on Rev.

Quote: and the ability to clear annoying "Check Engine" lights

LOL, why would you want to turn it off? If the lights on then I would highly recommend getting it to the closest garage ASAP.

It's not meant to delete the light, but to tell you what the light means in your specific scenario.

It's very useful to be able to clear check engine codes when diagnosing a problem. For example, if you get a check engine code that is a temporary problem and fixes itself, many times the code won't clear itself even though the problem is fixed. Also if you've replaced the part that caused the light to trip, you want to reset the code and drive for a bit to make sure the code doesn't exist any more.

BHP can be estimated by using the cars weight that you read into the app, the accelartion and driveline losses. Instant MPG it gets from OBDII which all good car calculates themselfs.

You cannot get anywhere near an estimate based on weight and acceleration. That's just crap. For a start it's torque which gives acceleration and it is just as dependent on available grip and gearing. Any figure they estimate is pure fiction.

I see you're a skeptic in all aspects ;)

Horsepower can be estimated based on weight of the vehicle and velocity. HP is usually calculated based on torque as you said, but can be estimated if torque is not known, based on your speed after a certain distance - say, a quarter mile.

"it's torque which gives acceleration" by implication bhp doesn't contribute? Eh?

Horsepower = Torque x rpm / 5252 so Torque = Horsepower x 5252 / rpm

As power is a measure of the rate of doing work, if you know the weight of the car, and how fast it is moving, you can calculate how much power/torque is being used.

Force = Mass x Acceleration

That's not fiction, that's physics.

So if a car is cruising at 60mph, or accelerating, or braking, it is using the same power and torque?

If it was easy as the apps make out then who would need a rolling road?

Everyone is oversimplifying things. If I am in third gear travelling at 60mph, the engine is spinning at a different speed than if I was in second or fourth gear. And if you don't know what speed the engine is spinning at, then you can't accurately predict power or torque. It could be spinning twice as fast to do 60mph in second as it is in fourth, so you'd be at a completely different point in the power curve (ditto torque) for the same vehicle speed.

I'm not even going to mention the effect of mechanical grip on acceleration or of aerodynamics on speed and the ability to maintain/increase it.

Common sense should tell you that before you even start worrying about physics lessons.

There are standalone care performance calculators that do just that: estimate horsepower. While they might not present a reliable source of finding just how much power your car has, it sure helps in determining relative power gains from modifications. If they manage to sell the OBDII to WLAN adapter at a decent price and provide decent PC drivers for it so it can be used with other apps too, I think this might make some decent money out of this :)

Obviously the power and torque are not always the same, it depends on engine speed, that's why the formula listed contains rpm as a parameter. I only listed these to show that if you know the engine speed, then power and torque are just two different ways of stating the same thing.

But you don't need to know engine speed to calculate power/torque output, its only one way to do it. By definition power can be calculated if you can measure the rate at which work is being performed. Therefore if you know the acceleration from GPS and the mass of the car, you can calculate power.

Anyway, this is not the only app available that does this type of thing, PocketDyno is a free iPhone app that calculates power output.

I've tried it, and it works great.

So if you are worried about getting ripped off, or didn't do well in GCSE physics, then try this one first.

Yes you can calculate power in KW like that. Then i guess you convert KW to hp. But that would be very inaccurate because of gearing, wind resistance, traction, terrain. I mean if you are doing it downhill with the wind at your back with 13" wide rear tires with special 0-60mph gearing your HP would be false. In order for you to accurately calculate it you would have to be on a perfectly flat road with 100% traction, and in a vacuum, and the wheels being directly connected to the engine and spinning at the same rpm.

Ok obviously none of you have seen an OBDII reading, It tells you EXACTLY how much fuel you have to .01L in the tank, so you can start the app and it can calculate your mpg in combination with gps, distance covered/L used..Also torque on automatic transmissions is recorded at the crank this is also output into the OBDII. As keeperlit stated HP is a calculation of torque based on rpm, which would at the crank would be somewhat easy to compute, but at the wheels is another story for both torque and hp as they would vary based on the gear you are in and rpm, as the input rpm from the crank would be different than the output rpm to the wheels. I guess if they had the FINAL effective gearing for all gears including all the changes in diameters and such all the way from the crank to the wheel it could calculate effective torque and hp. On manual transmission cars this would not work, they do not record torque.

The thing with this is that if you have two stats which are notoriously hard to get right, then you can get a power stat which is an estimate based on possibly incorrect data which doesn't take account of gearing, wind resistance, mechanical grip and a whole load of other stuff radmeister mentions.

Who actually knows the accurate weight of their car? Chances are it is nowhere near the published figures from the manufacturer, as Evo regularly finds when it weighs cars it tests. And acceleration isn't that easy to measure either, which is why it's tough to get a whole loads of runs at the same time. So if you start with those being wrong -- or at best with huge tolerances -- then the highly dubious calculation to estimate BHP is going to be even less accurate.

I would never rely on this for an actual power reading -- there are just too many flaws. i agree you could use it to check on tweaks to the car to see if they are successful, but I am not sure this offers anything you couldn't achieve with a comparative timed runs.

Bristol it is hard to change anyones mind, but this does work, i personally used dynoliscios, also a ipod app. it gives power figuger within 3% of the cars qouted power. the cars weight can be 99% accurately measured with a scale or just read off the registration papers. and a roling road is just as inaccurate as you also estimate the drive train losses, and the cooling on a roling road is not nearly as effective for a car as on the open road meanint Inter coolers and radiators and cold air induction don't work as good. and not to mention that a dyno also have to be calibrated regularly.

most of the ways of trying to get a cars power figures are inaccurate in some ways. the best way is to just stick to one way and see possable improvements. this is just alot cheaper than to go to the local tune shop to have your car dynoed every time you think you added 3 bhp.

You don't have to beleive me and i don't have to sell this to you, i can just tell you that i tested similar app with an ipod and they work.

as for radmeister it works for manual cars aswell. it doesn't read torque from the OBDII, it calculates it using user input drivetrain losses and weight and acceleration from the very accurate accelerometers from the ipod touch or iphone. It is possable.

Ok so really you put in a drive train loss which we can call the "safety factor" the rest is a simple physics calculation, calculate the acceleration and the mass of the car, along with the manufacturer's coefficient of friction for the tires on a typical road and you get the Force required on the tires, based on the over all diameter of the wheel you calculate the RPM at a given speed and convert that moment force acting on the surface of the tire to HP. The only problem is like most GPS devices the data is not "real time" so your speed may not be accurate. But like i said it would give you effective hp at the wheels, so yes you could in theory use it as a benchmark/starting point to track your gains from mods as long as every time you do the test the environment is always the same. Like 3hp is nothing, a sudden gust of wind can make you gain or lose 3hp even more depending on the strength and direction. If you could do it in a tunnel that is flat it would be fairly accurate. After all physics is physics, the laws are constant, it's the testing environment that you have to worry about.

Oh and i forgot to mention, that it doesn't always give you current torque, you accually have to do a full power from standstill run to a preset distance for this to calculate your power and torque. much like you would on a normal dyno.

OBDKey is what you're looking for guys. They have WLAN, Bluetooth or simply USB output options for their OBD connectors.

The supplied program could be installed either on a laptop or on a smartphone.

I will opt for the Bluetooth+smartphone option so that I read all the OBD inputs like IAT, Boost etc on my R53 Mini. :)

Just my 0,02 $