I stopped in a local performance shop the other day to see their dyno, among other goodies They stated that the dyno simply measures RPM's and from that they somehow develop HP and torque curves.

So I am wondering, If I datalog using Xcal2, could the data I collect such as engine load, rpm and whatever else, be used to compute HP?

Simply put, how does a dyno calculate HP from measuring RPM's?

thanks,

 

Hi Waterman;

I think I'd find another facility if they weren't just jokin' with you

Dynos come in (at least) three major flavours - brake, inertial, and eddy current. Plus there are chassis, engine & other types.

In the case of a chassis dyno, each of those are designed to present a load to the drive wheels; the load can be varied ( or fixed) and that is what is used to directly measure torque. HP is calculated from that. RPM is indeed integral to said calculation. I believe I have that right

That's why some dynos, particularly those at ricer facilities, are rated too low - do not provide enough load - to handle the requirements of larger vehicles like the F150 - apart from the physical fit issue.

Check out Dynojet's web site for some more info ...

As for using the X2 - I don't think so, at least not accurately. LiveWire (and the Edge) has a HP calculator but it's not meant to replace a true dyno.

There are formulas available that will take ET's, trap speed, gearing, vehicle weight, weather corrections, etc, etc to poop out a rough figure too - these can be found on Innovate's site, built into the LogWorks app.

BTW - for the purposes of datalogging you are really after A/F's at the dyno facility, as the X2 can record all the rest of the required data, as you know. Knowing HP/TQ is great but not absolutely necessary in this context.

I patiently wait to be corrected ....

Cheers
Bubba

 

I am probably over-simplifying their dyno. It consisted of two large heavy rollers for the rear wheels, the computer of course, and I think they use a tail pipe sniffer for the a/f ratios. But basically they measured the rpm's (maybe torque too).

Sounds like the tourque is the elusive item. My mechanic mentioned once that he has a portable dyno - hook it up and drive. Not sure if it measures hp or what. Mostly used to interrogate the vehicle as he's working on it.

Wondering if the "engine load" parameter logged by Xcal2 can be an indicator of torque etc?

Be interested in any websites with dyno info on how they work. I'll check out the website you mentioned.

Thanks.

 

waterman308,

Yes it can be done. You would need to know the tire diameter, gear ratio/speed and mass of the vehicle. Drive the vehicle on a flat road with minimal head wind.

From your OBDii port, this product does it all for you: http://www.autoenginuity.com/products-speedtracer1.html

 

Yup - as do the other products I referred to. But they ALL produce approximations only.

Still no substitute for an accurate dyno, but okay if you want ballpark numbers.

And none of them provide the A/F's Waterman needs ...

 

Is there anything that will let u use your pocket pc as a dynometer. I'm looking for something that gives you a read out like the edge, but don't need the programs. I got a TP xcal2. I would like to know my 0-60, 1/4, but would also like hp/tq.

 

Maybe a hawkeye guage? It's basiclly an edge without the tunes, just moniters engine temps and might also do 1/4 and 0-60 times not sure. I don't know much about it other than that but I think it's on their website, I can't remember where I saw it.

 

Dashhawk just saw it at the top of the screen on this site.....lol sorry for calling it a Hawkeye..lol

 

Yes, you can get 1/4 and 0-60 times on the dashhawk and it comes with a HP calculator. I've run some quick 0-60 tests but haven't used the calculator yet to see what it looks like vs. dyno that i did.

 

if you know the vehicles brake specific fuel consumption you should be able to get a fairly accurate estimation on the horsepower, just from seeing how much fuel/oxygen gets burned.

some handheld tuners and stuff can calculate power by measuring your cars acceleration and estimating the power used to get the mass of the vehicle up to speed, it needs to take the drag coef. into account too.

 

Hi Waterman,

The simple reality is the only way you can get a roughly accurate reading of power is to put the vehicle on a chassis dyno, which is simple to do - and preferably a dyno like ours, that has the eddy-current load cell built in, as otherwise, you are depending on a static load of (typically) only 3600 lb, and these vehicles weigh far more than that.

Even using the standard formulas to take the acceleration times of the vehicle over a known distance I don't care for, as they aren't as accurate as a good dyno - they require exact vehicle weight (and really shoudl also have things like wind resistance, rolling resistance, etc., etc.) taken into consideration as well, which is why the hand-held or other "tuner" devices (or devices like the G-Tech Pro) are not good for power numbers in terms of real accuracy, though they can be fine for getting a measurement of acceleration times.

Now the one comment about the BSFC was interesting, however, you have to realize what you have to do to even get a correct BSFC (brake specific fuel consumption) number of an engine, as well as realize that if you do something as simply as install a set of underdrive pulleys, you will change the BSFC of the motor. Getting BSFC typically requires putting the engine on an engine dyno to getting the data required (power readings, at what rpms), as well as engine displacement, etc., so you can get the actual BSFC. So again, you'd be far better off (cheaper and much easier) by simply putting the vehicle on a chassis dyno.

As far as what all the hand-held tuners allow you to do, even including the great LiveWire device or the newer GTech Pro units, while the acceleration times in those units can be very close to accurate, the power readings simply cannot be counted on as accurate.

So the long and short of it is - the way to determine power is to get it on a good chassis dyno, and that will measure torque, and then from the torque & rpm, calculate a horsepower value.

Now much of this can be argued endlessly, but that's the basics - if you want to know power, get it on a good dyno, is our advice.

Thanks to everyone for their responses!