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Discussion Starter #1
I thought it might be intersting for performance minded Saaber's on this forum to do some on road (but legal) dyno testing using a video camera and stopwatch. Using this method to compare to a rolling road is a fruitless venture as you could never makup for the differences is rolling reistance, wind resistance, and other conditional changes. But assuming (and we'd be on the honor system here) that everyone tapes the speedometer on a level surface it should be comparable.

Here's how it goes, you get a videocamera if possible (if you don't own one you might try to con a friend into letting your borrow his/hers) and get a stopwatch. Find a way to get the stopwatch and instrument cluster in focus at the same time. You only need to be able to see the speed. Then videotape a run to redline in 2nd gear or higher.

Obviously this usually ends up being 2nd as 3rd would require some fairly illegal speeds anywhere but the 'bahn.

Then if you can get the tachometer into the tape find the two frames 200 rpm or so on either side of where the max hp should be. Because I couldn't get the tach into the shot on my camera, I just found what speeds those points were at beforehand. Then find the time between the two points. In my case the two points were 82 and 92 mph, and the time between the two was 1.71 seconds. Then find the mean speed. (82+92)/2 = 87 mph

Here are the formulas that will be needed (most you may already know):

hp = weight (in pounds) x accelleration (in g's) x speed (in ft/sec) / 550

accelleration = change in velocity / time

1g = ~32 ft/sec/sec

1 mph = 1.466 ft/sec

1 kph = ~.62 mph

For my test here is how the calculation follows through:


92-82 = 10 mph

10 mph = 14.66 ft/sec

(14.66 ft/sec)/ 1.71 sec = 8.573 ft/sec/sec

(8.7573 ft/sec/sec) / 32 ft/sec/sec = .268 g's

87 mph x 1.466 = 127.54 ft/sec

hp = (3560 lbs) x (.268 g's) x (average speed of 127.54 ft/sec)/ 550

= 221 hp @ 87 mph

I'm not sure what the wind resistance would be at 87 mph, but I imagine it would be pretty significant and this method does not take it into account. I would do this test at about 50-60 mph where I know the resistance is about 15 hp or so. But then the Viggen wouldn't be running full boost, which would mean it's not running full power.

If anyone wants to see pics of the instrument cluster at the two times I do have them. Just let me know and good luck! Would be kind of insteresting to see what cars that have been dynoed do with this sort of test. Perhaps because of cooler/denser air etc our cars make more power out in the open than they do crowded into dyno rooms. Also it should be noted on the street you are accellerating considerably slower so less hp is lost to accellerating things like all of your ancilliary devices, and flywheel and wheels and brakes etc. On a dyno it's accellerating so quickly it takes a lot of power to move those parts ... might account for the discrepency if there indeed is one.

Have fun and be safe!


Yours Truly,
Dubbya
 

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Adrian,

It wouldn't work on mine as there would be too much wheel spin in 2nd and 3rd to get an accurate engine power figure.
 

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Discussion Starter #3
Even at the top end of 3rd gear? As long as you baby the car until then you should be able to keep the tires firmly planted on the pavement. You don't need to give it full throttle till 3500-4000 rpm. If you boot the gas going too slow, by the time you reach full power your intercooler is starting to get kinda hot. So it helps either way.

Might just be worth it to see how quick it goes even with a little tire spin just for comparison's sake. I'd love to watch the speedo go if it's got that much power.


Cheers,
Dubbya
 

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Even at the top end of 3rd gear?  [/b]
Yes


Just got back from Emarald RR session.

283.1 bhp @ 5109rpm (112mph)
311.9 lbft @ 3723rpm (81mph)

(225.9bhp at wheels)

See a plot appearing soon in the Emerald RR topic

Andrew
 

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Discussion Starter #5
Sounds like you had fun. I do think you should give this method a go if you want. Because of the increased load you may see even higher numbers. (Which never hurts )

I did the math and most Saabs can get at least over .50 g's of accelleration. Pretty typical for a FWD traction limit.

To accellerate at .50 g's at 90+ mph would take over 400 wheel hp!!
You might wanna give it a shot. Of course, only if you want to and feel it's safe. But it sounds like you had enough fun on the dyno to not need any further testing.


Cheers,
Dubbya

edit: Just looked at the dyno graph. Looks like fun.
 

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LSD .... wow...limited slip differential I'm assuming..

Haven't seen a set up for one of those..and looking for one on my NG900.

Do you notice an improvement over the pegleg..?

DC
 

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Discussion Starter #8
Abbottracing has the quaiffe unit for the NG900 and 9-3 I believe. Doesn't help traction much in a straight line, or any time the weight is evenly distributed on the front two tires. But is infinitely helpfull coming out of corners etc!

DC, you should be warned, when Saab was asked on the Viggen why they chose not to fit the limited slip they said because it exacerbated torque steer. Now I remember you saying you had the better steering rack clamp, but when you get the LSD you may want to look into some of the other parts for the VRK .. as the force of the torque steer will increase. Just a reccomendation though, not really "necessary" or anything.

Cheers,
Dubbya
 
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