Does anyone know what the weight /unit volume of petrol is?. The reason I'm asking is that I need to enter an accurate mass co-efficient into my AP-22 meter.

 

Does anybody also know the~

1. Cda

2. rolling resistance

3. Tilt factor

4. Roll factor

 

Would mucho appreciato any of the above for my little box of tricks...

 

Thanks in advance

 

Oops,

http://www.300zx.co.uk/rides/rock_star/run-020502.xls

max hp 121? Go in your mum's micra did you? LOL

As I said, only used 1/2 throttle.

I hope you measured the mass of your car at the same place you did the run, otherwise, due to gravitational forces changing according to location you could be wildly out

 

CheerZ,

 

Andy

 

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Originally posted by rock_star:

As I said, only used 1/2 throttle.

 

Sorry.

 

1 thing I don't understand is how it knows what gear you are in. It uses the accellaration to calc the power, but acceleratig by 30mph in 1st, will be much quicker than accelerating by 30mph in 4th, hence giving a false reading. V.

Guess i must be missing something, can anyone explain?

Jezz - these type of chassis dynamometers require you to run in the gear that is closest to a 1:1 ratio - as you have pointed out this is VERY important

 

CheerZ,

 

Andy

 

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It doesn't know/care what gear your in, it only calculates power from the readings of the accelerometer device. I said that I selected 2nd due to the fact it will select 1st automatically if you stop or accelerate down to a slow speed, is more predictable when doing something 'out-of-the-ordinary'.

 

I didn't do the test as a 0-60 etc, just blasted the car around a roundabout to see what the box will show.

Tony

I feel Andy is right.

 

Look at it like this, in first car does 0-30 in say 2 seconds, (3.5:1 ratio)

but if you were to do that in 3rd auto, 4th manual (1:1) it would take ages, infact about 3.5 times longer.

 

The accelerometer must assume that you are in a 1:1 ratio gear else the power figure will be multiplied by the ratio of the gear you did the test in.

 

Edited due to not paying attention properly and therefore talking b*llocks.

 

 

[This message has been edited by Dave Marley (edited 02-05-2002).]

Spot on Jezz - just like on a rolling road

 

Best way to test would be to put the car in the gear that most closely gives a ratio of 1:1, then set off from cruise at around 1500 rpm (who cares what the power is below 1500???) and accelerate foot down all the way to redline then off again. This will give you a very good idea of the power output (at the wheels) of your car. Some units calibrate themselves for drag coeff by putting the clutch in and letting the car decelerate... the rate of deceration can be used to calculate the transmission drag etc...

 

CheerZ,

 

Andy

No, i don't think so.

 

What I think...Could be bolocks but sticking to it until convinced otherwise.

 

The G force in 1st is going to be higher than in 4th due to gearing. So you have to divide the g force in 1st by the ratio of 1st gear before you can use the 'G' value to calc the BHP figure.

 

Like a RR, you have to do it in a 1:1 ratio with the correct rolling radius of tyre.

So you are saying when they rolling road your car Jezz, they need to test it in 4th gear?

 

 

Yeah, or 3rd for an auto. Which ever is 1:1

How it actually calculates the figures from the data it collects is described in some detail on their web site.

http://www.race-technology.com/WebPage/Products/Accelerometer/MeterTech.html

Originally posted by Jezz_S13:

Yeah, or 3rd for an auto. Which ever is 1:1

 

Shit, that means when the guy dynoed my car last week he did it in 3rd gear of my manual.

Does that mean I got an inaccurate figure?

 

It would certainly not be a direct comparison with another car that was dyno'd in 4th.

'fraid so Mark. It'll have read high by something close to the 3rd gear ratio (engine and gearbox friction comes into play and that doesn't change from gear to gear).

 

I agree with others that you need to test it at a 1:1 gear ratio. However, doing this takes you up to around 130 mph in an auto and something similarly high in a manual (never driven a manual that fast as they're crap and can't get to 130). At 130 mph, drag is a major factor and will give a much lower bhp reading.

 

To get closer to accuracy, the unit would be better calibrated to first gear ratios and then the test run in first. But then you'd get wheel spin and traction control screwing up the figure.

 

At the end of the day, not a terribly accurate toy. But still a bloody good one and I wouldn't say no !

 

Dave

Mr Hairs.....

 

Surely a 1:1 ratio is a 1:1 ratio so the speed at redline would be the same

 

Don't forget the unit takes the drag into account (it uses the Cd of the car). Furry muff this is only drag caused by air resistance but I think you'd get a far more accurate figure this way than you would by adapting it for different gears...

 

One other point - the unit takes samples at set time intervals. If you do a run in 1st gear then the run only lasts a few seconds and there are so many samples taken. If the run is done in 4th (or 3rd for caravaners ) then the number of samples taken in the run will be far greater so you'll end up with a more accurate result...

 

Discuss.....

 

CheerZ,

 

Andy

 

PS Marc - where was your run done?

 

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Originally posted by andyduff:

Mr Hairs.....

 

Surely a 1:1 ratio is a 1:1 ratio so the speed at redline would be the same

 

 

Now come on Mr Duff - surely you're not really expecting me to take facts into account in the manual / auto debate ? They'd all call me a poof !

 

Hadn't realised that it takes into account the drag coefficient. Pretty clever stuff. Mind you, it does reinforce your earlier points that there's a hell of a lot of settings to get wrong ...

 

Still like the idea of the kit though. And what it WILL do is allow true comparison of real performance of the same model of car.

 

Would be great to see back to back logs of a manual and an auto !

 

Dave

Did the dyno have the Speedhole calibration kit?

I mean if not then its horribly inacurate.

 

At the end of the day your all talking crap and manuals are far better.

Hairys theory is all wrong as he is not taking into account that he thaught this all up while 2000 feet in the air and therefore the rolling road velocity spigot bearing, has a ratio of 1:11/2.

It was done at a rolling road in Dorking, forgot the name, he was using a DynoPlot rolling road. ah well, when I get a few more mods on the car, I'll take it to were you boys took your cars in that Jap Mag.

Sold your TreVoR yet Hairsy? The pain of getting married eh!!

lets start another Manual vs Auto debate.

Autos are WANK!! rofl

Hit 140 indicated down the mad mile yesterday night my new record! shit my pants though as the brakes started to fade when breaking for the roundabout!

Waz, that's why I'm such an expert on Speedholes - I spend my weekends inside them(cue dodgy comments ...)

 

Marc, yes sold it a while back and now have a Shogun (rear seats removed so I can fit more speedholes in). As you say, pains of getting married. And living just north of Cardiff now.