Why is it so (Dyno)

[DivHunter]

Quick question that will hopefully get a straight answer. How does the gear a car is run in effect the power output?

[BI6TIM]

If it does at all it would only acount for a mnimal difference of say 1 or 2 horse power.
The only real difference between gears on a dyno is the speed that your rear wheels reach on the dyno.
However, having said that, it is best to run a car, on the dyno, in the gear that is closest to a 1:1 ratio. Then you are purely testing engine power at the wheels.
But like I said the difference is so small it's not worth worrying about.

[Ghiadude]

on a turbo car it can load the car lower in the rev range giving you a false torque hence power curve

[DivHunter]

Load the car?

How do you explain a stock (187kw engine, not mine) R33 GTS-T getting 182rwkw in 3rd gear? That's around 40rwkw too high. What about a modified one with 200rwkw in 4th over 240rwkw in 3rd? Those were on different days, different dynos.

[jonbays]

Originally Posted by Fairmont99

Load the car?

How do you explain a stock (187kw engine, not mine) R33 GTS-T getting 182rwkw in 3rd gear? That's around 40rwkw too high. What about a modified one with 200rwkw in 4th over 240rwkw in 3rd? Those were on different days, different dynos.

Your assuming that all dyno's and all days are the same and they are not.

Variance between them is huge. Its not so much the gear as the dyno and operator.

[DivHunter]

a 187kw car can't get 182rwkw though surely? That's almost no drivetrain loss. I think I confused you with the last bit I meant the 2 cars were on different days the one with 200 then 240 was on the same dyno same day.

[superpursuit83]

true measurements are made in a gear with 1:1 ratio, normally 4th. Any lower gear creates a mechanical advantage thus increasing torque etc.

[jonbays]

Originally Posted by superpursuit83

true measurements are made in a gear with 1:1 ratio, normally 4th. Any lower gear creates a mechanical advantage thus increasing torque etc.

Not true the dyno is getting more torque applied to it for sure but it is supposed to calculate the power from the nm force and the rotational speed. It does make a difference as I have seen cars run back to back with just a change from 18" to 15' wheels make more power but it shouldn't its all about correction factors in the dyno.

[LTDHO]

Originally Posted by superpursuit83

true measurements are made in a gear with 1:1 ratio, normally 4th. Any lower gear creates a mechanical advantage thus increasing torque etc.

exactly

[Black XR6]

geez, 15' wheels, freeking HUGE rims. He musta rolled the guards im betting.

[xdclevo]

I done many runs with my 3 sp auto, in 2nd and 3rd and it makes 1 or 2 hp difference maxx. Like stated, the dyno can tell with the different wheel speeds.

[Walkinshaw]

Originally Posted by xdclevo

I done many runs with my 3 sp auto, in 2nd and 3rd and it makes 1 or 2 hp difference maxx. Like stated, the dyno can tell with the different wheel speeds.

As it should be. There are a few dynos arround that seem to add 20rwkw when tested in a lower gear. Ie testing a manual in 2nd gear to claim 180+rwkw

[buickman]

[QUOTE=Black XR6]

geez, 15' wheels, freeking HUGE rims

.

They were back in the 70's & early 80's

[xdclevo]

Originally Posted by buickman

.

They were back in the 70's & early 80's

15'
Are you driving a monster monster truck. haha

[bazzalong]

was the dyno in shootout mode? if not the figures can be played with.....


eg a 100hp engine could be made to look like it is a 200hp engine...

next time look at the dyno screen, and see if it says "shootout mode",
if not, they could be having you on

[superpursuit83]

Sorry looks like i am all torque

[sfr rob]

so basically, dynos are lying pieces of crap, and are usless apart from when tuning.
I am sure there are ways to exploit dynos with diff ratios etc, probably what the dyno queens do.
hahaha

[Walkinshaw]

Originally Posted by sfr rob

so basically, dynos are lying pieces of crap, and are usless apart from when tuning.

Any tuning house worth a grain of salt will agree with this.

[jonbays]

Originally Posted by sfr rob

so basically, dynos are lying pieces of crap, and are usless apart from when tuning.
I am sure there are ways to exploit dynos with diff ratios etc, probably what the dyno queens do.
hahaha

Yep you got it right. In a nutshell YES.

[outback_ute]

I would say only a small power difference due to the faster turning tailshaft, diff centre, axles & wheels absorbing a bit more power. 18 vs 15 inch rims will be heavier with the weight further from the centre so they will actually take more power to accelerate.