So I thought I'd spin this one in here as I was doing a back to back test on my road dyno equipment on a car I dyno'd last Friday.

When I started road tuning specifically I didn't want to map customers cars without having a fair idea as to the improvements being made. Chassis dynos are fantastic at doing just that, showing small improvements very obviously in graph form. Particularly useful if you map rally cars with restrictors. Other software based dyno loggers have proven to be very inaccurate, I see lots of delta dash dyno graphs which have peaks and troughs of up to 40bhp at peak power, so how do you really know what it puts out?

So here it is for the debate, dyno dynamics graph, (ignore the red lines):


And the road dyno graph:



I did two runs on my dyno logger using the standard kerb weight, plus me and a full tank of fuel. 2nd gear is used as higher gears involve significant aero losses. One downside to using second gear is slower spool shown on the graph, however I can log spool in 4th gear without the need to use the dyno logger if I'm looking for spool time.

In my eyes the benefits are:

• Mobile accurate dyno graph tool for measured and repeatable improvements.
• Very cost effective compared to a dyno, very small investment.
• Easy tool for diagnosing faults and issues.
• Accuracy on WHP figures is within 1%, used correctly!

Disadvantages:

• Using 2nd gear increases spool time, higher gears can be used but aero drag takes great effect at higher velocity.
• Must have a relatively flat and bump free test road, ideally able to test in both directions.
• Not able to load car specifically in gear to load cells and measure power like a chassis dyno.
• Flywheel power is percentage estimated by user. (I use Dyno Dynamics figures transmission loss percentages).

I map on both types of dyno and would choose the chassis dyno every day of the week as it is quicker and easier to map with. However the use of this road dyno has enabled me to be just as accurate on the road.

Let me know what you think....

Graham

 

I forgot to add last night that the Dyno Dynamics graph is flywheel torque and hp, the road dyno graph is wheel torque and hp.

The chassis dyno read 237bhp at the wheels. The road dyno read 236.6bhp at the wheels.

Graham

 

I was going to ask you that but its also very close on the @wheel figures by about the same ammount, could this be also due to a slight dip/raise in ambient temperature?
Figures do look good though, can see the difference in spool, much later (200bhp@3.5k on the dyno, nearly 4.2k on the road), but sort of puts to bed that one method is better than the other with virutally no difference there, plus the dyno is a little safer unless you have a nice long runway to map on
Can you enlighten me on the way you can log the spool in 4th please?

Tony

 

I can either do a road dyno run in 4th, but with most cars you'll be running well past 100mph at redline so I try not to, or just use whatever software I'm using to log boost vs rpm.

What I mean to say, if I'm hunting for spool improvements I can use other methods than the road dyno to test.

I have to say I'm very impressed with it's accuracy so far.

Graham

 

Oh and Tony don't forget 200bhp at 3.5k on the dyno, (flywheel) is the same as 145bhp at the wheels on the road dyno! Just to confuse you. So 145bhp is at 3700rpm.

Graham

 

Doh! so its not that bad in 2nd either then

Tony

 

Hi Graham, why was the car in run 5th gear on the DD plot?.....My cars have always been run in 3rd for a 5speed and 4th for a 6speed....any reason why 5th was used?

 

Hi Jay, 5th ob a 6 speed is usually closest to 1:1 in terms of ratio vs engine rotation so gives the most accurate result on a dyno, for 5 speeds its usually 4th.

Hope this helps,

Graham

 

Good stuff