Rolling roads and autoboxes.

Rolling roads and autoboxes.

Author
Discussion

Vixpy1

42,620 posts

263 months

Sunday 7th June 2009
quotequote all
I was spending more time fking around with cars than doing a proper job, I tried to buy a tuning firm which fell through, was sitting in the pub one friday night shortly after and it was suggested I open an independant Rolling Road.

The rest is History, Almost 5 years, 23,000 dyno pulls and over 3000 cars, some run many times. Lowest BHP is around 30bhp, highest 1017bhp. Current record for number of pulls belongs IIRC to a Supra which has had 210 dyno pulls.

LHDisbest

17,000 posts

186 months

Sunday 7th June 2009
quotequote all
scratchchin

One assumes there is decent money in it?

Well, enough to sink all your hard earned into an E34 M-fünf.

I'm contemplating another career change....

Vixpy1

42,620 posts

263 months

Sunday 7th June 2009
quotequote all
There is decent money in it, however I would not open a tuning firm or Rolling Road now, the market is saturated, add in the fact that there are many rip off merchants, criminals and people who have no idea what they are doing and its not the nicest industy to work in, having said that, I bloody love it!

LHDisbest

17,000 posts

186 months

Sunday 7th June 2009
quotequote all
It's just a thought. I get bored easily. biggrin

I can't think of anyone up here who does such a thing.

I'm kept busy enough just now between the cars and the clothes business.

TheEnd

15,370 posts

187 months

Sunday 7th June 2009
quotequote all
Grab a stool, this will be a long post.

for a manual car, normally you'd pick a gear closest to 1.1, as that cuts out losses in the gearbox, but it's not always possible as some older RR's will reach their speed limit before then, so a lower gear is needed.

On an inertia RR (cheapo set of just heavy rollers and a speed sensor on them) technically you can use any gear, and the coastdown will cancel out everything else. You will need to sync the wheel speed with the engine rpms so the roller computer can figure out what rpm the engine was doing at a specific wheel speed.

The calculations run like this-
first off you sync the roller pc to the engine rpms, so it can record the engine speed compared to the wheel speed.

you'd hold it to about 1500-2000rpm, and then nail it, and the computer measures the acceleration of the drums.
press the clutch in, and let the car coast down to idle speed again.

it already known the inertia of the drums, so it can work out the wheel torque applied to accelerate them.
wheel torque is then calculated into wheel bhp from the roller speed.

the coast down drag is then added to the wheel power to give engine power (which is flawed, due to stuff like gears meshing on the other less used sides on the teeth etc, but the only way to measure it easily)

engine power is then calculated back into engine torque.

to get engine power and torque, you need an accurate measure of rpm, which is where many autoboxes fail as they will change gear, or slip through the convertor etc as they aren't solidly linked. You can knock it out of gear, but if the torque convertor was slipping a bit during the run, the rpms will be higher than what the pc measured and the data will be plotted in the wrong spot.

you can however always do a Australian type run where wheel power and torque are plotted against road speed.

I've seen dyno operators pull tricks like not dipping the clutch so engine braking gets recorded as something it had to fight against, and gets added to the engine power, and even as far as some actually feathering the brakes to bump up the drag figure.


If you have method of locking it into one gear, or a dyno with an OBD2 link, you can get accurate wheel power figures, but you'd probably need to calculate engine power on paper instead of letting the computer do it.

Vixpy1

42,620 posts

263 months

Sunday 7th June 2009
quotequote all
Good post that, I would only point out that the maha type and dasktek rollers are pretty much the only systems to still use coastdown losses, most others either don't give flywheel figs at all, or use a computer program to estimate it (such as the DD dynos)

300bhp/ton

41,030 posts

189 months

Monday 8th June 2009
quotequote all
Vixpy1 said:
Good post that, I would only point out that the maha type and dasktek rollers are pretty much the only systems to still use coastdown losses, most others either don't give flywheel figs at all, or use a computer program to estimate it (such as the DD dynos)
What make of dyno to you use? I have to admit to finding the whole topic rather fascinating.

A DD dyno just uses the age old 15 or 18% transmission loss doesn't it? Or at least there abouts.

As for dyno'ing an auto I know some cars have torque limiters in 1st gear so don't give such a high reading as others. Not sure how they do it in the states though as loads of people seem to dyno high HP auto's successfully over there. They tend to use inertia Dynojets or eddy current Mustang Dyno's for the most part from what I've seen.

The Wookie

13,909 posts

227 months

Monday 8th June 2009
quotequote all
My GTS was on Vixpy's rollers a couple of years ago. It looked problematic at first, it has a manual override, but it also has a kickdown switch at WOT that overrides the manual override, meaning it kicked down into 2nd about half way through a pull. I can remember standing behind it watching it cresting the front rollers eek

The next few attempts got some solid runs out of it which gave realistic WHP figures, and when I was there recently with the Evo he told me that he's had another couple of 928's on the runs and has mastered the art!

AGWC

5 posts

72 months

Thursday 12th April 2018
quotequote all
Hi speaking of autos on rolling roads.

I'm trying to test a Jag XF with tiptronic. Leaving it in 3rd but every time I get up to 70mph it changes up to 4th. It's in sports mode with 3rd selected with the paddles. Have tried it with WOT before changing the speed up on the dyno but just changes down to 2nd, I change back up to 3rd and it hits 70mph and the car changes up to 4th.

Anyone had similar issues?

Cheers,

DR