More power on second Dyno run?

[oliie]

This may be an easy one.. but why does a car produce more power on the second run on a Dyno? Is it that it isn't pushed as hard on the first run?

Sorry if it there is an obvious answer... I was just looking at the Dyno printout from Janspeed and it got me thinking... :?:

Cheers
O.

 

[fUbAr]

I noticed they were all like that, more power on the second run.

my second run was 4bhp up on the first.

 

[Day]

They were not all like that, saw some where the car faired better the first time.

 

[=CatasTrophy=]

i missed the janspeed rr thread , what sort of wheel figures were the trophys making ?

 

[stu_allen]

Heat in the tyres? (if you want more power on a dyno run, put 50psi in your tyres) Oil hotter and so thinner?
Dyno figures are subject to such variation that their figures are useless really as anything other than a finger in the air before/after mods.
Its why it makes me laugh lots when people claim their car does "207.5bhp" or the ilk.

 

[Day]

If all RR's differ so much and they should be taken with a pinch of salt then what is the point of actually having them?

Soon as you post a result it gets shot down!

 

[Fred]

If all RR's differ so much and they should be taken with a pinch of salt then what is the point of actually having them?

Soon as you post a result it gets shot down!

they're very good for before/after tuning (working on a % gain system)

a chassis dyno will never bee 100% accurate


the only accurate test is an engine dyno (even these have variables)

 

[Day]

Right I'm booking that Dyno session at Janspeed...

 

[Fred]

make sure they run the car in 4th

 

[AndyC]

2nd gear makes more power on the rollers as it produces more torque at the wheels in a lower gear...

4th is used as its the closest thing to a 1:1 gear ratio....therefore theoretically giving the most accurate engine output.

 

[duffer987]

If all RR's differ so much and they should be taken with a pinch of salt then what is the point of actually having them?

Soon as you post a result it gets shot down!

they're very good for before/after tuning (working on a % gain system)

a chassis dyno will never bee 100% accurate


the only accurate test is an engine dyno (even these have variables)

I'd agree completely. Not knowing much about nothing, it was good at Janspeed to have x amount of Trophys, 182s, 172s on the rr and judge the results relative to the other similiar cars.
In isolation its just another number and pretty much meaningless.