SXI - Matt
Member
Registered: 8th Jul 07
Location: Leicestershire Drives: Corsa C SRI
User status: Offline
|
Sorry to sound like a tw*t but how does it work when your car is put on a dyno is it taken to the limiter in every gear? Sorry just not to up to date to how it all works?
|
Dave A
USER UNDER INVESTIGATION - DO NOT TRADE
Registered: 10th Dec 03
Location: County Durham
User status: Offline
|
different engines/gearboxes will e run in different gears. you select the best gear to do the run in and start from around 1k rpm and rev it until the power starts to peak and drop off, or until you get to the limiter.
|
Lucky B
Member
Registered: 7th Apr 02
Location: Lunatic asylum. Drives: Hard & Fast.
User status: Offline
|
A Rolling road measures power/torque @ wheels and then calculates power @ flywheel, an engine dyno measures engine power/torque due to the engine not being in a car at the time.
Normally 4th gear is used on a RR as its nearest a 1:1 ratio.
[Edited on 19-02-2008 by Lucky B]
|
Warren G
Member
Registered: 14th May 06
Location: Kent
User status: Offline
|
what happens if the gear ratio isnt 1:1, will this then give an inaccurate reading ie read high if a high ratio box and lower if fitted with a stupidly low ratio box?
|
deano87
Member
Registered: 21st Oct 06
Location: Bedfordshire Drives: Ford Fiesta
User status: Offline
|
Hmmm I can barely pull away in 2nd at 1krpm.
|
SXI - Matt
Member
Registered: 8th Jul 07
Location: Leicestershire Drives: Corsa C SRI
User status: Offline
|
Ah ok making sense now so if i was to mine on one would start it 4th and finish when the power drops do you not go through any gears? And does the rolling road push the car or does the car push the roling road if you no what i mean?
[Edited on 19-02-2008 by SXI - Matt]
|
deano87
Member
Registered: 21st Oct 06
Location: Bedfordshire Drives: Ford Fiesta
User status: Offline
|
I guess they might go through the gears to get it going, then switch on the actual graph.
No idea though 
|
AndyCorsaSport
Member
Registered: 12th Feb 06
Location: Horsforth, West Yorkshire
User status: Offline
|
quote:
Originally posted by deano87
Hmmm I can barely pull away in 2nd at 1krpm.
Why would you want to 
|
Lucky B
Member
Registered: 7th Apr 02
Location: Lunatic asylum. Drives: Hard & Fast.
User status: Offline
|
quote:
Originally posted by warren.g
what happens if the gear ratio isnt 1:1, will this then give an inaccurate reading ie read high if a high ratio box and lower if fitted with a stupidly low ratio box?
On an older RR yes it probably would, a new/modern RR would probably be ok.
|
SXI - Matt
Member
Registered: 8th Jul 07
Location: Leicestershire Drives: Corsa C SRI
User status: Offline
|
quote:
Originally posted by Lucky B
Normally 4th gear is used on a RR as its nearest a 1:1 ratio.
[Edited on 19-02-2008 by Lucky B]
That why he asked
|
Lucky B
Member
Registered: 7th Apr 02
Location: Lunatic asylum. Drives: Hard & Fast.
User status: Offline
|
quote:
Originally posted by deano87
I guess they might go through the gears to get it going
|
SXI - Matt
Member
Registered: 8th Jul 07
Location: Leicestershire Drives: Corsa C SRI
User status: Offline
|
Ah ok i see so get to 4th at 1k switch on graph and away you go?
|
Lucky B
Member
Registered: 7th Apr 02
Location: Lunatic asylum. Drives: Hard & Fast.
User status: Offline
|
Something like that yes.
|
Dave A
USER UNDER INVESTIGATION - DO NOT TRADE
Registered: 10th Dec 03
Location: County Durham
User status: Offline
|
it isnt about 1:1 gear ratios. a car will often make the same power in 2nd, 3rd and 4th gear.
its down to acceleration rates in each gear. The dyno applies a load against the tyres (the brake in 'brake horse power) and the dyno measures the turning force that the engine can apply to that brake. this is measure in torque.
BHP is worked out from the torque and is a measurement of the speed that the engine can produce the torque. as a general rule:
an engine with lots of torque but low bhp will have lots of pulling power and can tow heavy loads but will not accelerate through the revs quickly i.e a tractor
an engine with lots of bhp but low amount of torque will accelerate through the revs quickly but not be able to do so when a weight is applied to it. i.e a motorbike
the above explanations are a gener rule, gear ratios play a large part as well to how the torque or BHP is transmitted to the wheels.
|
deano87
Member
Registered: 21st Oct 06
Location: Bedfordshire Drives: Ford Fiesta
User status: Offline
|
quote:
Originally posted by AndyCorsaSport
quote:
Originally posted by deano87
Hmmm I can barely pull away in 2nd at 1krpm.
Why would you want to
i.e. when you're slowing down and are going quick enough for 2nd. Have to dip the clutch and brake slightly but are still moving, I tried to lift the clutch and give it some revs, with nothing happening.
Either lack of 12v torque or nackered clutch. I figured it was the torque, 'cause the car has always done it.
|
Dave A
USER UNDER INVESTIGATION - DO NOT TRADE
Registered: 10th Dec 03
Location: County Durham
User status: Offline
|
quote:
Originally posted by SXI - Matt
Ah ok i see so get to 4th at 1k switch on graph and away you go?
different dynos work differently, generally there are 2 types:
Inertia dynos dont have a brake to apply the load on the wheels, they use a big heavy roller drum and that works as a brake. not a very accurate method of measuring power but was the only real option years ago. The level of load applied to the wheels cannot be adjusted and the computer systems are very primitive and have to rely on mechanical workings to produce a power graph.
An eddy current retarder dyno uses a large electromagnet type setup to apply the load or 'brake' to the wheels. its fully computer controlled so that the level of load can be varied and adjusted to suit the vehicle that is being run. They are far more accurate at measuring power, torque, RPM's etc... and have minimal mechanical workings. Some older types have pickups from the dyno only every 100-300 rpm. Others such as Dyno Dynamics can measure up to 40 channels of data 3000 times per RPM and up to 30,000 times per second! this makes for a far more accurate and repeatable system, especially when mapping as you can hold the engine at any throttle position or RPM that you want to just by flicking a switch.
|
Dave A
USER UNDER INVESTIGATION - DO NOT TRADE
Registered: 10th Dec 03
Location: County Durham
User status: Offline
|
some dynos have a built in weather station to calculate power losses/gains for the conditions on the day, i.e intake air temp, ambient air temp, barometric air pressure, humidity etc.. so the conditions on the day will not be affected by any outside factors. Wether the car is run in the middle of winter or the hottest day in the summer the results will be calculated to show the engines true power.
Another benefit of the dyno dynamics machine is the method used to tie the car down, the car is not anchored but allowed to move freely on the rollers. it uses a traction tie-down system the does not hold the car back at all during the power runs, it pulls the car down into the dyno. Usually this would be a bad method as the more force pulling the tyres into the rollers = more resistance and more of a power loss! howvever the dyno actually measures this tie-down pressure and the weight of the vehicle on the dyno and removes these factors from the final result.
|
deano87
Member
Registered: 21st Oct 06
Location: Bedfordshire Drives: Ford Fiesta
User status: Offline
|
Will they start the car in 1st, run it until ready to go into say 4th, and then take it to the red line?
|
SXI - Matt
Member
Registered: 8th Jul 07
Location: Leicestershire Drives: Corsa C SRI
User status: Offline
|
quote:
Originally posted by deano87
Will they start the car in 1st, run it until ready to go into say 4th, and then take it to the red line?
|
Dave A
USER UNDER INVESTIGATION - DO NOT TRADE
Registered: 10th Dec 03
Location: County Durham
User status: Offline
|
if its an eddy current dyno then there is no load on the wheels until they want there to be so the rollers will spin freely so they can pull away in 3rd if they wanted to. then get the engine to a stable rpm, usually 1000-1500 rpm, flick the load switch and put the foot flat to the floor, at this point the engine wont be allowed to rev no matter how much you put your foot down, hold foot on the floor and release the brake and the engine will accelerate to the peak revs smmothly and evenly.
a less powerfull engine will have less load applied by the brake, and the opposite for a more powerfull engine.
then theres the ramp rate, which is how fast the engine is allowed to accelerate. you dont want it so slow that the engine explodes by the time it gets to the peak revs, and not so fast that the engine gets from 1000 rpm to 7000 rpm in 2 seconds as you wont get a reading that is accurate.
|
