KW99

Hi all,

Not sure if I am missing a trick here or something but recently purchased the Torque app and a OBD2 bluetooth adaptor to display realtime stats on my android mobile.

Most of the stats are great however the torque and horsepower ratings are way too low approx torque 125 and HP 140.

The car has a few mods and is a 231ps version.

You have to input weight and engine displacement, for which I have used both 1.3 and 2.7l for engine (neither makes a huge difference, not sure which to use) and the Kerb weight + driver and fluid weight for overall weight of car (this was estimated as best I could - my weight obviously accurate).

I realise that this is only an estimate and not a true dyno calculation, however I would have expected a bit more accuracy (I have been told the car should be running more than stock hp).

Anyone have any ideas or have used Torque and bluetooth OBD2 before?

I have just looked at the app again before posting and noticed a calibration for the phone's accelerometer in the postion you leave it. I did not calibrate before so I will give this a go and see what diff it makes.

In meantime any help would be appreciated and which weight and HP to use for the car details?

Thanks in advance

reddozen

iTrader: (1)

There is no replacement for an actual dyno pull.
That being said, the cars typically are 180~210 HP depending on tuning and engine build quality.

GeorgeH

iTrader: (2)

Weight depends on year and/or specification. I suspect you can find the data somewhere on this board for the weight of your car, but it's probably in the range of 3,000-3200 lbs. Then, add weight for you, and anything you may have done to add weight, such as a subwoofer, heavier wheels, etc.

Accelerometer calibration will be important.

Make sure and find a level, straight road for testing.

drifthappens

weight is also on the door sticker.

Don't forget to account for yourself and fuel weight.

And the 231ps (or 238hp or whatever) wouldn't be at the wheels, which is what the program would measure. Also, beating a dead horse here, again (because, why not, the noises are funny), they were overrated from the factory pretty heavily.

laythor

Here's how to solve your problem.

Download the "Draw" app, type in 232 in the biggest font that will fit. Problem solved

In all seriousness don't get hung up on HP, especially from a phone app. There isn't a single app that will come close to what the car's HP actually is and one run from another will vary wildly.

The torque app is the best app out there and I use it myself. Great for seeing some extra info and with the custom PID's it's even better. Using it for HP is just a waste of time IMHO.

drifthappens

do you happen to have a list of the custom PIDs? I know I have quite a few laying around here, but i want to see if i'm missing any. lol

Actually, if you want to figure out the horsepower, have a friend in the seat next to you with a stop watch, from a fixed point, measure exactly 1/4 mile. From a dead stop, accelerate until you hit that 1/4 mile mark (as soon as you do, have him stop the stopwatch), then apply some maths and there you go.

maths:
HP = weight/(ET/5.825)^3

GeorgeH

iTrader: (2)

That is the "Gross Vehicle Weight" which is NOT how much the car actually weighs.

http://en.wikipedia.org/wiki/Gross_v..._weight_rating

The actual weight is usually less than the GVH. Case in point, my door sticker says 3800 lbs, but my car weighs a bit over 2700 lbs with a 1/4 tank of gas (but no driver).

drifthappens

There should be more than just the gross vehicle weight in there (i guess i could go look. I know it was that way in my other cars).

EDIT: I stand corrected. I just checked and it is only GVW (3809lbs, haha). Well, I guess a trip to the truck scales is in order.

8upbad

iTrader: (3)

I have Dynolicious for the iPhone and it was within one hp difference from a real dyno. I enter the weight and about 15% drivetrrain loss.

KW99

Does anyone actually have exact car weight with full tank and fluids minus driver? Before anyone says yes I realise each car will differ, and however we are talking approximate here.

8upbad - how do you add the 15% drive train loss? Does dyno have an option or do you simply add extra weight?

What info have others used to set up their rex on torque?

Sounds a daft q but does it make any difference which gear you are in when testing hp of a car? I realise the higher the better with regards to strain on gearbox, however purely from a calc point of view?

überschnell

The best way to get a semi-accurate weight is on truck scales, or even better on corner-weighting scales ($$).

To get a figure with 15% drivetrain loss, take the "crank hp" number and multiply by .85. Alternatively, take the "wheel hp" number and divide it by .85. Simply maths, here.

The best gear to be in for a true dyno pull is the one with a 1:1 ratio. I don't know about the RX-8 specifically, but it's probably 5th...assuming 6th is an overdrive (higher than 1:1 ratio). I doubt you'll want to go that fast, and your app won't figure in air resistance at speed, so...the slower and safer, the better. Yet another problem with these apps, as you will always lose some momentum from a shift.

You're spending a lot of thought and effort on getting a number that won't really mean anything at all. Why not cough up $50 or so and do a few pulls at a local dyno day? Then you'll have a reasonably accurate number.

RIWWP

iTrader: (2)

I would question the accuracy of truck scales. I've seen comments from scales that have the error margin noted as "2,000lbs or 2%, whichever is higher".


This could lead to some pretty wild values for our 8.


https://www.rx8club.com/purchasing-financing-insurance-56/spec-decks-color-charts-pricing-each-year-2005-2011-a-200591/

3,029lbs was the 2006 weight.

drifthappens

2,000 lbs or 2%. holy cow. I didn't realize they were that bad. we always have to weigh the race cars at the track during the event.

RIWWP

iTrader: (2)

They are designed to weigh trucks, usually 12 tons to 60 tons, with a standard truck scale capacity of 100 tons, some heavy duty scales go up to 150 tons, so a 1 ton variance isn't much. Considering they also have to support that weight while it's rolling, they have to be pretty robust. The number of trucks rolling across it is actually part of the rating, due to the rolling stress.

Accuracy at weights under what a truck could possibly weigh isn't a critical design factor

überschnell

A lot of the pick-n-pull/pull-a-part places will let you use their scales in off-peak hours, as well. They're probably going to be more accurate, as they're used for cars in the first place. Free is nice, too.

I had no idea truck scales had margins of error like that.

REDRX3RX8

My Scan guage II has hpr x guage that showed 259 hp @ approx 7k rpm (07 6spd auto) with the car fairly new.

After the BHR ign at 23k miles it showed 269 hpr.

Now at 27k miles, it shows 235 hpr ( was a 100 deg day and maybe dirty filter).

So just before next track day in Sept, I'll put in plugs and air filter for first time.

The point is: I know the 269 hp is optimistic, but I can tell that I'm loosing about 12% power, and time for maintenance of plugs and filter.

KW99

REDRX 269hp?

Is this a fully stock RX8 or do you have a supercharger or turbo fitted.

From what I hear 236hp or whatever Mazda claimed the 8 was outputting was pretty optomistic and from an Auto, very unlikely!

I understand that you were just highlighting the % diff though (although if it is stock, the accuracy is more than questionable).

Another question..........how are people finding the accuracy of MPG on these Apps?

wcs

iTrader: (2)

15%! Wow that's optimistic ...

I believe most people consider drive train loss to be closer to 21% - at standard operating temperatures.

Eric Myer would be an excellent source for this .... I know he has figures (dyno) showing how drive train loss improves as the tranny and diff fluids get hot.

However I would be willing to bet that even at this optimum operating temperature .... you are still losing at least 15% ....

Day to day driving .... gotta be closer to 20 or more.

edit:
Oh I'm basing this on the Manual transmission .... have no idea what the Auto would be

REDRX3RX8

I guess I didn't explain well.

Scan guage has an xguage you can program for hpr on some cars.

Some people with 8's discounted it as unreadable because way too high.

I see it as consistant, but high.

So that 269 hp @ 7k rpm ( 6spd auto ) should be about 170-180 hp:

269 - 33 % ( approx ) = 180 wheel hp when running right.

It also found my bad tune 235 - 33% = 157 wheel hp, and I couldn't really tell.

paimon.soror

iTrader: (15)

I am not really sure why some of you are hung up on HP numbers from OBD data. The applications that do this are using a simple formula:

0.5 * weight/grav * (5280/ WheelRotationPerMile)^2 * (ChangeInSpeed / ChangeInTime) / 550

Basically the only requirement from you is to put in the weight of the car, while the rest is calculated through OBD2 parameters. However, the software makes various assumptions, with wheel rotation being one of them (considering that this is different for almost every car out there once you factor in wheel size, tire size, tire wear, tire width, etc)

Also, taking a number like "33%" as your average energy loss is really missing a lot of key factors like drag, altitude, humidity, temperature, etc.

I suppose that it would be useful to a select few people who are looking to monitor any anomalies in the calculations over time .... but time may be better spent monitoring things like timing advance, cat temp, fuel and oil pressures to ensure the overall health of the spark, oil, and fuel delivery efficiency. All of which can be monitored on the scangauge.

laythor

Why look at actual information when you can stare at some program that's telling you you're car is putting out more HP then it really is? That's crazy talk Paimon!

To digress, if you like looking at the HP numbers (no matter how far off they are), then go for it. If you actually want to do something useful, keep an eye on temps, afrs, all the stuff Paimon mentioned.

Can an app give you HP numbers that are close to what a dyno would show, yes. Is there anything useful to be taken from that number, not really, no.

And FYI if you have a 6 speed auto and you're seeing anything over 200HP from your device, NEVER PUT YOUR CAR ON A REAL DYNO... you'll be a very sad panda.

REDRX3RX8

My 8 only has 26k miles in 4 years, and I forgot that: I track on cool spring or fall days at about 600 ft elevation, while I checked it last week with the temps over 100 @ 3000 ft elevation.

I was wondering why I always see 259-269 hp on the track, but can't get it out here.

When it cools off in a month or two, I'll check the hp, then, change the plugs, and check again on the same day.

Just before track day, I'll check the same way by changing my air filter.

REDRX3RX8

The 6spd engine puts out the same hp as the manual @ 7k rpm, but yes the auto might have more drag.

I can see lots of guys dyno charts that show 170hp @ 7k rpm.

Whatever it is it is, but my hp # on the Scanguage is consistant to compare changes on the same day.

I always ran 259 at that track, but as soon as I put on the BHR ign, it would consistanly run 269 hp at that track, and I'm still on the first plugs (will change soon and check again).

Highway8

iTrader: (11)

Official California Truck Scales are calibrated accurate to within 10lbs using 20K lbs of weight. Thats a lot more accurate then 1-2%. You just have to ask if they are in fact calibrated. If they dont calibrate the scales you can expect them to be off by 1-2%, with a 3000lbs vehicle thats only 30-60lbs.