Anyone do a "street dyno" test??

[Wil Ferch]

Hi:

I remember reading about...and testing...a procedure to see if you actually made real hp improvements by using a street dyno test. For non-turbo cars it goes something like this.
-- find a flat, relatively untravelled highway...you're in 3rd gear and slightly below 3000 rpm ( crawling !)...now punch it and start a stop watch as the tach swings past 3000 rpm...and stop it when it swings past 6000 rpm ( 90+ mph maybe...so watch it).
There are a couple of "gotcha's"-
- the road better be absulutely level. I've seen a lot of data scatter when there is a slight incline or drop.
- the tach swings past 3000 rpm quickly...making the "start" time accurate...but in our itch to trigger the stop watch as it sweeps past 6000 rpm ( more slowly)...you can get a big variation in time because you "want" to record a faster time after mods! Try for consistency here to stop the watch at exactly the same point for multiple runs.

I have a 3.2 slightly modded that is now still in winter hibernation, so I can't do this now...and Bruce anderson once did a stock car like this in 10.5 seconds or so. I've averaged anywhere from high "8"'s to low 11's before I got the hang of how to do this. My last runs were typically around 9 or less about a year ago after a few things were done to the car.

Anyone else try this... or care to report back findings? Especially interested in nearly stock 3.2's.

Turbos, i think would need a different gear and rpm targets since their engines load up differently.

---Wil Ferch

[Eric86Red911]

Sounds like a measurement that's fraught with error. I can't imagine you could correctly measure the effects of incremental hp improvements due to the large error band. Just my $.02

[69911e]

For $150 you can buy a "road dyno". It is basicaly an electronic storage device which stores rpm vs time. Then download to a pc and use provided software. Good only for relative performace numbers. They seem to work well if set up correctly, and give very consistent results in one mode of operation. I hooked it up to a frequency gennerator to measure accuracy, this is where I found some modes did not work with sufficient accuracy.

[Chuck Moreland]

Do a search on "Street Dyno" . There is software that will collect the data via the microphone input to laptop and crank all the calculations for you. Lot's more accurate than watching the tach and stopwatch.

[Eric86Red911]

This is pretty much the entire purpose of the GTech Pro. It plugs into the cigarette lighter and monitors the alternator's voltage to determine the engine RPM (based on your calibration for your car). Of course you must input the correct weight for your car. Its accelerometers start its internal stopwatch. Thus, it calculates hp. I've been thinking about picking up one off Ebay (if that's even possible) just to toy with for a while.

[tsuter]

You can get as fancy as you want. I use software that reads directly off my HD motorcycle sensors. Record the data and then estimate Dyno curves, 1/4 mile times using the data logs on and on. Of course the laptop strapped on the Tour Pak looks a little strange.



Need a relatively fast CPU to pull the data fast enough.

[island911]

at speeds, there's more going on than just F=ma. Specifically drag. (wind & rolling) If you incorp a roll-down test (get decel data from coasting) you should be able to get fairly good numbers.

I checked out Chucks suggested Street Dyno . . . .pretty cool.
They have you enter in drag coef's and tire pressures to get approximate (calculated/theoretical) drag numbers.
Since most 911's have an electronic speedo, I think it would be better if the program could use that as an input. . . . it would allow you to do roll-down tests to calibrate the drag portion of the eqn.

[tsuter]

Definitely right about that. With the variables you can get any result you want if you cheat in a few places.
The good software will have at least these.

[NYSCAR]

Downloaded the street dyno software, created the voltage divider circuit, and used it to record my coil firing on a few runs. Had to play with the thresholds and delays a bit. Posted my results before and got something like 171 rwhp:

Street Dyno results

Brad

[KTL]

A street that travels a significant amount of distance for your dyno fun is not very likely to be level.

The street has to have a semblance of grade to it in order to drain. Sure, the crown in the street does the draining to the shoulders. But there still has to be some grade lengthwise ( a good road should have a min. grade of about 0.5% ) to drain the shoulders- even if the road drains to ditches and not curb & gutter.

Most seemingly "flat" roads will have 0.33% to 0.5% grade on them. I dunno how much this affects the dyno simulation. I just know a flat road is virtually nonexistent.

[Todd Simpson]

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I think this is only on the latest "competition" version.