Rolling road & Dyno’s

[JP.]

Well what about these, which ones are good and give true figurs.
We have experiance with brake rollers and dynamic (Dynojet) rollers now and we have found out that there is a lot of difference between them in read outs. To us it seems that braked rollers give higher readouts than dynamic rollers which calculate their figurs by acceleration.
We know it all depends on several factors including the weather (hot, cold, moister etc.) but
to us it looks that you never can compare readouts between each other only if you have been to the same rollers at the same day.

Well you’ve probably all see our dynosheet in the dyno topic but we still don’t know what to think about it. The comment of the Dynojet guys was that it was spot on and didn’t bother to give it more runs to see if there was probably only a few more horsepower to be found as it always depends on things like the weather. So they could setup our engine perfectly for today which coul’d be differend by tomorow. Well I won’t argue with that but what are your commends and idea’s about readouts versus dynamic rollers and braked rollers.

No we don’t bother about the highest readout, we only care about a good running engine but how can we compare readouts from each other if there are so many factors which have influence on our expectations so to speek.

[Alley Kat]

Not run a car on a dyno, but found big variations with my bike. E.g. in 1070cc form it made 139 rwhp. On its 1260cc build, on another dyno it read 133 rwhp. Yet I had to gear it up massively just to keep the front wheel down - made more power & shedloads more torque than 1070 guise. Still wheelied at walking pace after. Seemed like it was best to pick one dyno & always stick to that, rather than worry about what the numbers were.

[kev_the_mole]

Dynamometers or rolling roads are really only good for comparing setups ie "have I made an improvement with this new cam or not"? But accuracy absolutely depend on all factors being the same between runs. Parameters such as temperature and barometric pressure and tyre pressures should always be the same else you will get differences that you will not be able to take into account. If the guy operating the rolling road ties the car down tighter that the last time you will get greater transmission losses and having the wheels running on two relatively small diameter rollers gives you two contact patches and then the tyre acts very differently than being on a flat road.

Just a few disjointed rambles.

Confused? I am.

Cheers,

Ian

[katanaman]

A proper engine dyno is about the only one that is trustworthy and even then the figures can be scewed. Rolling roads can be fooled so easy it isn't funny and should only be uses to compare your own figures. Because it works via acceleration changing your wheels and tyres for lighter ones will make it look like you have more power. Course we all know it isn't that easy its simply there is less mass to accelerate. Same goes if you change your diff or even your prop for something lighter in fact a lightened flywheel and clutch will do the same. Doesn't mean they are bad as they are measuring what they are supposed to it just means you cant compare figures with your mates cars accurately.
Bill if you changed your gearing on the bike you effectively changed your final drive ratio (same as diff on a car) so the figures you saw were accurate. that's why anything accelerates quicker on a low final drive, it multiplies the torque. Where high final drive decreases the torque so it accelerates slower. The dyno you used should have had correction factors set in to compensate for this so I am guessing they didn't put the figures in properly.

[Alley Kat]

Marki, I raised the gearing after dyno'ing. It was dyno'd just after running in, then modded gearing to tame it. It was bonkers at the 1260 stage yet read less hp than the much tamer 1070 tune before. Best thing was getting the fuelling right though, regardless of numbers, money well spent.

[katanaman]

It shouldn't have shown the figures it did then but yes its still money well spent.

[Mark]

The Emerald rolling road (Dave Walker) is meant to be spot on and consistantly reads at least 15bhp less than the Power Engineering rolling road as proved by my old escort RS2000/2.3 which made an extra 16 bhp after I had sold it on the PE dyno without any extra mods?

While bikes are in the topic
Shameless plug for my bike on Ebay

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 0052539534

Mark

[katanaman]

Will get back to you re the bike I know someone who might be very interested in that. Only trouble is if he buys it I will have to do something serious with my EXUP as I just cant let him beat me lol.