3rd gear rolling road!

[mk1sooty]

Dose this count? I recently took my escort to a garage to set up the 45`s and a rolling road setup,after setting up the carbs on idle he proceeded to spin her up on the rolling road but would only go as high as 3rd gear 6000rpm,this showed 160bhp@ the wheels.Is this a true reading?

[oliwally]

nope,should use 4th gear as thats nearly always a 1:1 drive.

[Guest MK1gaz]

They use 3rd gear on dyno-dynamics rolling roads

[Fiesta Steve]

Shouldn't it make the same horsepower in any gear ??

 

A tuning shop is setting up next door to where I work, they had a new rolling road delivered Friday, might have to try it out

[mk1sooty]

Shouldn't it make the same horsepower in any gear ??

 

A tuning shop is setting up next door to where I work, they had a new rolling road delivered Friday, might have to try it out

Not sure,I no the engines good for 7500rpm and I was thinking it would be around that bhp for the set up Ive got,it was my first run on a rolling road,still ,happy with the figures

[bmxdave]

No. Itll read wrong. The only way itd read right is if you could input into the machine what your gear ratio is in 3rd.

 

Its because 3rd gear isnt 1:1 so lets say for example the gear is 2:1 and your engine makes 100lb-ft of torques then itd read 200 torques.

 

In theory anyway......

[mk1sooty]

No. Itll read wrong. The only way itd read right is if you could input into the machine what your gear ratio is in 3rd.

 

Its because 3rd gear isnt 1:1 so lets say for example the gear is 2:1 and your engine makes 100lb-ft of torques then itd read 200 torques.

 

In theory anyway......

well next job is a 5 speed box then ill take it to someone who knows what there doing,cheers all

[Wessie]

although it may rev more it doesnt neccesarily mean there will be anymore power from the engine, my brothers car makes peak power at 5700 but will rev to 6800

[jayson2.3pinto]

some cars start to wheel spin thats why 4 th gear is used in general but if some dynos got more grip 3 rd gear is ok

[bortaf]

No. Itll read wrong. The only way itd read right is if you could input into the machine what your gear ratio is in 3rd.

 

Its because 3rd gear isnt 1:1 so lets say for example the gear is 2:1 and your engine makes 100lb-ft of torques then itd read 200 torques.

 

In theory anyway......

 

that's how i see it as well

as long as the gear ratio can be added to the RR it's OK

 

The lower the gear the more torque at the wheels and as BHP is a calcucation of torque that will be higher too

Tis what a gearbox is for and why you can't pull away in 4th

[Fiesta Steve]

So where does the size of the wheels and final drive ratio come into it then if this is the case. ???

[Guest MK1gaz]

So where does the size of the wheels and final drive ratio come into it then if this is the case. ???

Run your car on some rolling roads , drive off , change your wheels and tyres to a different size , drive back on and get a different number

[Retromotorsport]

Did they pop it ionto 4th at any time ... ?

 

in 4th take the readings .. the computer can then work out what ratios you have .. ie take it to 4k in 4th ..its 1:1 and hit 'set'.. the rollers are spinning at so and so rpm while the engine is spinning at 4k .. then 4k in another gear and hit 'compute' the computer works out the gears .

 

The reason they run cars in 3rd isnt about grip.. as a car in 3rd is more likely to spin.. its the fact that the rollers cant read over a certain MPH ..

 

if your car does 140mph/4th at max revs and the rollers only read to 120mph they have to run in 3rd

[mk1sooty]

Did they pop it ionto 4th at any time ... ?

 

in 4th take the readings .. the computer can then work out what ratios you have .. ie take it to 4k in 4th ..its 1:1 and hit 'set'.. the rollers are spinning at so and so rpm while the engine is spinning at 4k .. then 4k in another gear and hit 'compute' the computer works out the gears .

 

The reason they run cars in 3rd isnt about grip.. as a car in 3rd is more likely to spin.. its the fact that the rollers cant read over a certain MPH ..

 

if your car does 140mph/4th at max revs and the rollers only read to 120mph they have to run in 3rd

So are ya saying what he did was`nt wrong and 160bhp would stand?

[mk1sooty]

Did they pop it ionto 4th at any time ... ?

 

in 4th take the readings .. the computer can then work out what ratios you have .. ie take it to 4k in 4th ..its 1:1 and hit 'set'.. the rollers are spinning at so and so rpm while the engine is spinning at 4k .. then 4k in another gear and hit 'compute' the computer works out the gears .

 

The reason they run cars in 3rd isnt about grip.. as a car in 3rd is more likely to spin.. its the fact that the rollers cant read over a certain MPH ..

 

if your car does 140mph/4th at max revs and the rollers only read to 120mph they have to run in 3rd

So are ya saying what he did was`nt wrong and 160bhp would stand?

No he just went as far as 3rd,it was also a old set of rollers.

[bmxdave]

So where does the size of the wheels and final drive ratio come into it then if this is the case. ???

Run your car on some rolling roads , drive off , change your wheels and tyres to a different size , drive back on and get a different number

 

Technically, yes.......

 

...... but im fairly sure the computer works stuff out.

 

Its probably why all @ the wheels figures are just estimates, itd be very difficult to measure exactly without using a brake dyno thing (forgot the name, sorry, its the one that bolts on the the box for engine testing) or hub dyno. Just a bit of extra tyre pressure could make your tyres bigger mucking up the equation.

 

What Retro said sounds about right.

[Guest MK1gaz]

Dyno-dynamics rolling roads read power at the wheels as the car accelerates . Their "wheel horsepower" readings are the most accurate of them all . The other dynos calculate power when you lift off = not as accurate

[Retromotorsport]

oooh no.. looks like we are back onto which ones best again ...

 

Roush technoligies have 5 engine dynos all reading within 0.5% of each other .. HT Racings engine dyno reads within 0.5% of these too .. and T&R rollers read within 0.5% of HT's and Roush's dyno's as born out by the engines from 'Rons place going to T&R and Roush's engines being run on T&R's rollers too ..

 

But ... and its a big BUT.. it dosnt matter what a Dyno reads as long as you go in and do a run, and then tweek the engine and come out with a better graph, note i dont say more power.. you want a bigger area under the graph .. thats what counts not peak "pub talk" bhp ..

 

Terry Donovan took his sprint car to a rolling road a few years back, they tweeked it and gave him a 20bhp increase.. terry drove the car and said it wouldnt pull the skin of custard .. looking at the figures he had gained peak bhp but lost all the torque..

 

The moral.. get the best torque figure and lie about your peak bhp .. or be satisfied when you 140bhp engine beats a 170bhp engine .. to coin a phrase from Gaz.. the clock dont lie

[Fiesta Steve]

So where does the size of the wheels and final drive ratio come into it then if this is the case. ???

Run your car on some rolling roads , drive off , change your wheels and tyres to a different size , drive back on and get a different number

 

Technically, yes.......

 

...... but im fairly sure the computer works stuff out.

 

Its probably why all @ the wheels figures are just estimates, itd be very difficult to measure exactly without using a brake dyno thing (forgot the name, sorry, its the one that bolts on the the box for engine testing) or hub dyno. Just a bit of extra tyre pressure could make your tyres bigger mucking up the equation.

 

What Retro said sounds about right.

 

If the computer can work out the difference in tyre size and final drive ratio I'm sure it can work out what gear your in so it won't make any difference, 3rd or 4th.

 

I have a 5 speed box fitted to my car and not one of them is 1:1

[Guest MK1gaz]

The new Dyno-dynamics rolling roads are the only accurate "wheel horsepower" chassis dynos out there today . The others are not as accurate i'm affraid .

[Fiesta Steve]

The numbers are fairly meaningless anyway, 150 bhp (might only be 130 on other rollers ) is more than capable of leaving 400+ bhp cars in its dust

 

Its average bhp between the gears that counts, not peak.

[X-pack-Glyn]

last time i was at the rollers an RS500 broke traction in third, there was torques escaping everywhere and running ammok....it was a nightmare.