Understanding Dynos...

[AndysR]

In my opinion/experience a dyno run is better at highlighting a problem and disappointing an owner than it is at producing accuarate power outputs. I took from my rolling road session that the AFR's were safe the boost was consistantly solid as soon as it hit full boost and the power graph was as smooth as you could ever want, the later being something I expected by the way the car drives, after all the car is auto so the power reading will never be correct. Even before the run I did know that it's very good at putting what power it does make to good/effective use, a fact that was later highlighted when I ran the car down the 1/4 mile at Avon, in fact I was more shocked at the results it achieved over the 1/4 than I was at the rolling road day. I don't think I will be rushing to get to another rolling road day as I see little benefit in them other than providing ammunition for boasting rights and pub conversations.. Just my opinion on the subject of rolling roads... lol

[LiamT4]

In my opinion/experience a dyno run is better at highlighting a problem and disappointing an owner than it is at producing accuarate power outputs. I took from my rolling road session that the AFR's were safe the boost was consistantly solid as soon as it hit full boost and the power graph was as smooth as you could ever want, the later being something I expected by the way the car drives, after all the car is auto so the power reading will never be correct. Even before the run I did know that it's very good at putting what power it does make to good/effective use, a fact that was later highlighted when I ran the car down the 1/4 mile at Avon, in fact I was more shocked at the results it achieved over the 1/4 than I was at the rolling road day. I don't think I will be rushing to get to another rolling road day as I see little benefit in them other than providing ammunition for boasting rights and pub conversations.. Just my opinion on the subject of rolling roads... lol

Probably the way i look at them to be honest. Fault finding, good afrs, smooth power curve, etc...... dyno days make for a good day out though.

The looks on some peoples faces as there car is screaming towards the red line is priceless lol

[AndysR]

Probably the way i look at them to be honest. Fault finding, good afrs, smooth power curve, etc...... dyno days make for a good day out though.

The looks on some peoples faces as there car is screaming towards the red line is priceless lol

Agreed! I love a good dyno shoot out from a viewing perspective, I was at one today, but as for running my own car on the dyno again I doubt I will bother tbh..

[LiamT4]

Agreed! I love a good dyno shoot out from a viewing perspective, I was at one today, but as for running my own car on the dyno again I doubt I will bother tbh..

Not even to check for any possible issues?

I'd like to do one in my car, just to see how smooth the curve is and how that compares with turbo'd cars.

[stephenevans99]

Stuart Sanderson who wrote the article has 60+ other Tuning articles available to download as PDF's on his site.

Motorsport Developments Technical Articles Link

[V70 Graham]

The looks on some peoples faces as there car is screaming towards the red line is priceless lol

Don't know what you mean Liam

[wegal]

A Dyno is a useful tool to compare things with, not car Vs car, but on your own car, so long as you use the same dyno and the same operater. Run the car, make a change run the car again, make a change etc etc. It will give you an indication of what difference ( if any) your mods have made.

Beyond that its just a number on a bit of paper

[smithy]

I've just read the last page of that article and that will give something to think about .

[stephenevans99]

The article mentions the Coast Down method.....

"Most systems use the coast down method. This system has the operator depress the clutch and allow the transmission to come to a halt on its own while the system measures its resistance to rotation. The system measures this resistance and creates what you might call a negative bhp graph. This resistance is then simply added on to the power we measured at the wheels/hubs and given to us as flywheel power. As an example, if we make 200 bhp on the power run, and our rollers measured that the transmission consumed 30 bhp when slowing down, it would give you a power reading of 230 bhp at the flywheel. Simple..."

He then goes on to mention how figures can be manipulated by gently touching the brakes during the coast down to give greater resistance and increase the predicted flywheel power.

Anyone heard of a dyno operator doing this?

[mitchyboy01]

A Dyno is a useful tool to compare things with, not car Vs car, but on your own car, so long as you use the same dyno and the same operater. Run the car, make a change run the car again, make a change etc etc. It will give you an indication of what difference ( if any) your mods have made.

Beyond that its just a number on a bit of paper



Yeah this exactly. It's a great tool for comparing your own figures to gauge how well new mods are working and as a diagnostic tool to ensure everything is as it should be.

[Wobbly Dave]

For better or worse I have always used the same dyno - as I am primarily interested in the delta value, the changes I have made.

The dynojet at HLM has both inertia & load cell functions & the single roller has only a single tyre deflection. I've used it on all my major modifications on the silver sh_1t box since I've had it.

[smithy]

For better or worse I have always used the same dyno - as I am primarily interested in the delta value, the changes I have made.

The dynojet at HLM has both inertia & load cell functions & the single roller has only a single tyre deflection. I've used it on all my major modifications on the silver sh_1t box since I've had it.

I use the same rollers but for comparison reasons I will go to merlon motors on there maha rollers next time the is a dyno day

[AndysR]

Not even to check for any possible issues?

I'd like to do one in my car, just to see how smooth the curve is and how that compares with turbo'd cars.

I'd consider it as an option if I felt the need but it wouldn't be my first port of call if there was one...

Being a V8 and auto the torque curve should be smooth and flat as a witches.....

[jdavis]

Only ran at one rolling road. That was in my 2.0 zetec'd mk3 fiesta and despite a dead throttle position switch and a major misfire it produced a lowly 130bhp. Not sure of whp. Operator wanted to abort the run due to misfire but told him to carry on. A standard 106 gti Got 140+bhp at the same session yet my fiesta wiped the floor with it on the road. In my opinion. The opinions above capture it great, rolling roads are good for diagnostics and pub ammo. That's about it. Want to know how fast your car is go to a 1/4 mile or the track.

[turbo-tuner]

This topic has come up many times over the years. A couple of people have already mentioned that it's a tool best used for measuring changes between modifications, and you can minimise the variables by sticking to the same dyno. But here are a few other summary points to take into account -

1. Single roller dynos have less tyre drag than twin roller dynos, therefore single roller dynos normally show significantly higher WHP.
2. WHP + Drag losses = Engine Power (normally measured at the clutch). This applies to ALL chassis dynos. However, results can vary due to many other variables. Drag losses increase exponentially with increasing speed / rpm.
3. Other variables also affect your power, including load, fuel type, ambient temp. Ambient temp can be factored into the final readings using a standardised correction formula.
4. Dyno loading can be a problematic variable to deal with (load is normally applied using eddy-current retarders). Too little load and the engine doesn't work hard enough (not enough boost) to generate max torque and power. Too much load and you get excessive intake temps which cause the ECU to reduce the power by lowering boost and/or increasing the fuel mixture more than normally required and/or retarding ignition timing.
5. The size of the dyno fan makes a significant difference to the peak power. The larger the fan, the better it is at keeping the intake temps down during the dyno run.

Diesels tend to perform much better on dynos than petrols, because they are not as sensitive to high intake temps.