[Aero]

I've just bought an AC-22 performance meter and I am trying to set it up as accurately as I can.

I need to calculate my car's CdA and rolling resistance. I've tried coastdown timings but these are difficult to time accurately giving dramatically variable results.

I would have thought that the CdA would be 'known' statistic but I can't find any info anywhere. I've found that the car's Cd is 0.31, but can find nothing for CdA. My car's a 9-3 Aero, which would be similar to a Viggen aerodynamically (I guess).

Any info (or educated guesses) would be most welcome

Straight out of the box which apparently should be accurate to about 2-3% I got the following results:-

'02 9-3 Aero (stock 205BHP, 280NM) 0-60mph 7.11s and a 1/4 mile 15.78 @ 93.?? mph. (I did a 7.00s on a slight decline, and 7.58s on the way back up). I also did some shabby 8 seconders, as well as aborting one or two runs due to excessive wheel-spin an uncontrollable torque-steer

By comparison, the same AC-22 in my mates Audi S3 (225BHP, 280NM, 4WD, 6 speed) gave a best time of 7.3?s on the slight decline, so I don't think my timings are over-optimistic). He was severely hampered by having to change into 3rd to get to 60mph. The S3 should be sub 7sec.

 

[cdcarlsson]

Hi Aero.

I've asked the CdA question in an attempt to set up my AC-22 a couple of times now. It seems that our friends knowledge base is lacking here... Oh, well I s'pose even Bill doesn't know everything

I've used 0.87 when testing /johns modded 2.0 HOT SE. This gave a wheel hp of 205 with his Maptun ECU which wasn't far away from the figures later recorded at Emerald (admittedly with a different exhaust fitted).

The best use of these meters is for your own comparison when improving the vehicle, as absolute figures mean little, it's the improvement measured that really matters. Make sure you test with the same amount of fuel on board (easiest to have it brimmed), the same passengers weight etc, on a level piece of road. Don't even think about trying a bhp graph when it's at all windy, it really mucks it up. With a little knowledge of Excel a graph of Bhp and torque is readily achieveable as well as overlaying previous traces to show the improvement.

Have fun.

Nick.
9k Aero + mods.

 

[Aero]

Thanks Nick

I've just this minute set the CdA to 0.8 based on an average of my very variable coastdown runs, so this might be about right comparing to the figure you used for /john's car. I think the Aero body-kit is a little less 'wind-challenged' than the HOT. Incidentally I thought /john had a Speedparts ECU?

I know I need to take the absolute figures with a pinch of, but I have read some reviews of the AC-22 (& AP-22) which have implied remarkable accuracy. I'd like to believe it's accurate

Is yours the AP-22 Nick? Isn't that the one which allows you to download to your PC? The AC is upgradeable to an AP by downloading the appropriate software from the website. Perhaps I'll do this if things get serious

What has amazed me is how difficult it is to do decent, consistent launches. I'm having a whole load of fun learning though!

Thanks again

 

[California Saab Tuner]

I think the wind resistance on the Viggen was .32 . Should be about the same as the Viggen. Seems yours works more or less the same as the g-tech, and you're getting numbers that are more or less what one would expect from that car. I hardly think the g-tech was over optimistic with the Viggen either. It was dead on when I took it to the quarter mile. And when it was warm out it was even what it was supposed to be on 0-60. Just that all the magazines test during the day, when it's above 65 degrees. Car is MUCH faster with the stock plugs when it's below 55 degrees. Also if that 9-3 Aero has pltinums change it! I bet money it'd go faster without em if it's at all warm out. Anyway ... good luck with your testing and ENJOY. It's always fun to go testing. Especially when you start making upgrades.

 

[john]

Originally posted by Aero:
[qb] Incidentally I thought /john had a Speedparts ECU?
[/qb][/b]

Yes - but I have two other ECUs which I can make comparisons from

 

[Skiddins]

That AC-22 device looks interesting, I just might6 have to buy one, provided I still have some money left when I get back from hols!

Skiddins

 

[cdcarlsson]

Hi Aero,

Yes it is the AP-22 and at the very least it is very repeatable, figures are within hundredths for each run (unless I've been tweaking that is )
As far as absolute accuracy goes I think it is a mile better than using a stopwatch so in that sense it is very accurate. The bhp calculations it performs are quite revealing especially if you have the 'AP' and can download the data from a continuously logged run for a graph.

The hardest thing (as you say) is the measurement of the coastdown times as the speedo in car is not really suited. I've thought of using a digital bicycle speedo as this will have 1mph resolution, making it easier to take times from. Thinking of fitting the magnetic 'sender to the inner rim of the wheel and the pick-up to the front suspension strut, if that is near enough...

Have fun, I certainly do.

Nick.

PS. Just been out for a run with some new settings, and am now getting around 212 hp at the wheels. 40 - 60 in 2.34s (2nd Gear) 3.62s (3rd Gear), 50 - 70 3.60s (3rd) 60 - 80 3.73 (3rd)

 

[Aero]

Originally posted by cdcarlsson:
[qb]The hardest thing (as you say) is the measurement of the coastdown times as the speedo in car is not really suited. [/qb][/b]

.....not to mention trying to find a flat stretch of quiet road!

Originally posted by cdcarlsson:
[qb]PS. Just been out for a run with some new settings, and am now getting around 212 hp at the wheels. 40 - 60 in 2.34s (2nd Gear) 3.62s (3rd Gear), 50 - 70 3.60s (3rd) 60 - 80 3.73 (3rd) [/qb][/b]

I'll have a go at these timings, should be revealing. 212hp @ the wheels (

) - what would that be at the flywheel? Can I assume certain transmission losses to calculate approx flywheel hp?

Originally posted by cdcarlsson:
[qb]Have fun, I certainly do.
[/qb][/b]

I will

Thanks.

 

[California Saab Tuner]

I remember reading somewhere that @ about 95 mph most cars take roughly 40-60 hp to keep moving. When playing with my little friend g-tech, I was seeing about .23g's in 3rd gear at redline (about 100 mph). Also watching my video it works out to roughly the same accelleration when timing the time from 90-100 mph in 3rd. Anyway ... the car has two people in it in the video, with a weight of roughly 3520 lbs. Th equations are designed for mass, but if you put in g force instead of accelleration in ft/sec/sec the constants cancell out.

10mph x 1.466(ft/sec)/mph = 14.66 ft/sec

14.66 (ft/sec) / 2 secs = 7.33 ft/sec/sec

7.33 (ft/sec^2) / 32 = .229 g's

(.229 g's) x (3520lbs) x (98 mph) x (1.466 ft/sec/mph) / 550 = 211 hp @ the wheels @ 98 mph.

If you assume at 98 mph you're losing at least 40 hp to wind resistance (or somewhere near that) you'd get 251 hp. 252 might not be all the far off the mark. *jumps for joy* Of course the speedo isn't half as accurate at measuring accelleration as the g-tech's accellerometer is. But if I were to go by the accellerometer I get the same results, sometimes more. I think the speedo is just sluggish. If you calculate times using the speedometer you don't always get the same accelleration the accellerometer says you're getting. Unfortunately I've not had the opportunity to use the g-tech to calculate 50-70 times or anything like that as my model does not have the capacity to do so directly. However, as in 3rd gear I've seen consistent accelleration readings at .33 g's (sometimes higher) that would put my 50-70 around 2.77 seconds. Which doesn't seem at all consistent with what other owners report for their Viggen's, which leaves me at a loss. But I guess I will indeed just have to wait untill I can reach a dynomometer.

Cheers and ciao

 

[Aero]

Adrian, one of the advantages of the AC/AP-22's is that you can account for mass, rolling resistance and aerodynamics to improve accuracy. It even has a tilt setting to account for the rear end of the car 'squatting' under acceleration.

However, the g-tech looks the part compared to the AC-22

 

[California Saab Tuner]

lol You can account for mass in the g-tech. But not wind resistance, or car squat. Fortunately, while the Viggen does squat some, it isn't too attrocious. Especially in the higher gears. I imagine the Viggen's front end lifts about an inch under hard accelleration, and the rear squats about the same I'd imagine ... hmmm ... *calculates*

If the car is roughly 15 ft, or 180 inches long ... and the combined angle change is due to 2 inches ...

inverse sin(2/180) = .64 degree difference

If the car were accellerating in 2nd gear at about .45 g's perpendicular to the accelleration due to gravity ...

[(.45)^2 + 1^2]^(1/2) = 1.097 g's

inverse sin (.45) = 26.7 degrees from vertical (The angle of the accelleration vector @ .45 g's away from the vertical axis)

26.7 degrees + .64 degrees = 27.34 degrees

sin (27.34) degrees = .4593 g's ...

That's about 2% of accelleration due to squat. Since that's about 2 inches, you can assume it's roughly 1% per combined inch of squat. Hard to say what the relationship will be like when you have less squat, but also less accelleration. Seems not too terribly significant. But it would be nice if the g-tech accounted for it.

Oh well. It's cheap. Can't beat the price. YOu're welcome to take 5% off the hp rating the g-tech gave me if you want to add 10 hp due to wind resistance. Hehehe .... doesn't quite cancell out, but I guess someone thought it would aye?

Ciao

 

[Aero]

Excellent post Adrian, I think you're better at doing sums than me . I happen to have my 3rd year (age 13) maths book on my desk and I don't understand any of it! Bizarre thing is I got most of it right at the time

Anyway I was messing about today with the AC and I don't think I've set things up well at all. Max power on one run was 203hp (at the wheels) which is quite remarkable as the flywheel power should be 205 max! I need to reconsider weights and RR's and CdA's. I also did a 6.76s 0-60 bettering my previous times

Is there any chance that just as you get the odd duffer of a car that doesn't perform as expected that you also get the occasional better performer? I ask this 'cos my car feels quick. It's easily as quick (if not quicker) than my friends Audi S3 (which has more horses and the same torque). Mushdaffer has exactly the same car as me and in this thread he describes how the power used to tail off around 4000rpm until he got it chipped. I get none of this, my car boosts hard and consistently up to the redline. When I drove the new 9-3ss Aero I was bitterly disappointed because the boost tailed off noticeably compared to mine. I've often wondered if it was chipped before I got it - but I don't see how as it was as good as new (pre-registered). I spose I need to take it on a rolling road.

Cheers for your input

 

[California Saab Tuner]

I seriously just think the new Saabs, especially the '02s for whatever reason it seems, are HEAVILY underrated. Could have a number of reasons, but I have no clue what they are. To me 203 hp sounds reasonable considering your 0-60, weight, and similar traction issues to my car. Also like you said about your car boosting hard to redline, my Viggen does more or less the same thing, though above 5500 it does taper slightly. Perhaps the software was updated before the 02 model year? Remember the Trionic System for the 9-5 Aero was updated to "250" hp ... I suspect a revision was made to all the software, but that for insurace and licensing reasons (and because on warm days the power is probably what it's rated at) they just left the original numbers. Oh well ... it's all just theory. Who knows? Who cares? You've got 203 wheel hp!!!

 

[California Saab Tuner]

Oh ... AND ... to go along with the updating the power but not the figures theory. Look in the front of any 02 9-3 SE or Aero. It's got the Viggen crossflow intercooler. The others didn't (Actually I think the 01 had it too). So the power was obviously increased, but not the figures. Seems logical to assume it has more power than the figures would lead you to believe.

 

[john]

Originally posted by Adrian W:
[qb]  Look in the front of any 02 9-3 SE or Aero.  It's got the Viggen crossflow intercooler.  The others didn't (Actually I think the 01 had it too).   [/qb][/b]

I can't speak for the US market, but here in the UK all diesel models, HOT models (ie: 200bhp and more) and models from M00- had the Crossflow intercooler.

The 98-99 154bhp and 185bhp 9-3 model and the GM900 turbo models had the more restrictive intercooler.

 

[California Saab Tuner]

Perhaps that's what it is. Alas I am indeed at a loss. Maybe Aero and I just lucked out and got real performers?

 

[cdcarlsson]

Originally posted by Aero:
[qb]  212hp @ the wheels (  

  ) - what would that be at the flywheel?  Can I assume certain transmission losses to calculate approx flywheel hp?

[/qb][/b]

Well, it seems from other posts that 16% is about right for a 9000 but, If I remember correctly /johns' 9-3 had around 200 wheel hp and a dyno calculated 248 flywheel hp (I have been known to be wrong though, just ask the missus

)
What I definately remember from /johns printout from Emerald is that at the top end the flywheel power was climing gradually but the wheel hp was static as the transmission losses were mounting significantly. As it's the power at the wheels that actually does the job then you have to be carefull of headline figures, but hey, we all love 'em don't we?

Nick.

 

[wrighar]

My Aero has always been about 18-19% in the loses stakes at the high rpm's from 3 different RR establishments.

Best figures were 202w/248f

I do need a retest now though

Andrew

 

[john]

Originally posted by cdcarlsson:
[qb]Well, it seems from other posts that 16% is about right for a 9000 but, If I remember correctly /johns' 9-3 had around 200 wheel hp and a dyno calculated 248 flywheel hp
Nick. [/qb][/b]

I have just taken a look at the data. Power at wheels peaked at 197.5bhp at 105.3mph. Flywheel Power was 246.2bhp.

Flywheel power peaked at 248.8bhp at 118mph. Power at wheels was 190.3bhp.

 

[Skiddins]

Ok, so I've been looking at the pages for the relevant loggers and accelerometers (AP-22, AC-22 & the 2 G-Tech devices)

Does anyone have any recomendations as to which would be best?

Race Technologies data logger is simply too expensive, and the AP-22 looks the best of their other devices (£160).
However, the G-tech looks as though it would be more like a datalogger for half the price (£200 or so after shipping and VAT)

What do you all think?