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Location:
Melbourne
Registered:
October 2003
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Re: dynos and diff ratios
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Mon, 28 June 2004 15:21
 
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you still technically end up with the same power at the wheels.
Often when extra power is 'discovered' it is because you are able to rev higher with a higher diff ratio.
Most engines torque drops off before they reach maximum HP.
As the torque drops off, rpm's are still increasing at a rate
which causes overall power to be higher..
Assuming a very simple way of describing HP = Torque X Rpm, here's what i mean.
RPM 1---2---3----4-----5---6-----7-----8-----9----10
TOR 1---2---3.5--3.5---4---3.8---3.3---2.5---2----1.5
H.P 1---4---10.5-14----20--22.8--23.1--20----18---15
.............max torque.^.........^max HP...........
As you can see, torque drops off at just after 5rpm, but
maximum power is at 7rpm, because of the RPM factor.
On a dyno the dyno's has a certain resisting torque,
sometimes this resisting torque can now allow the engine
from being able to get to the higher HP figue. As in
say the dyno was applying a resitive torque of 4n/m,
this engine would not be able to rev past 5rpm. And
thus power would read 20hp. But with a higer diff ratio,
the toque is multiplied and it can get past that
'hurdle' Changing diff ratio's can help with this, but in what
way and how much depends on too many factors to mention.
One other point is the drag effect.
Power is power, based off the above simple HP thing,
1nm of torque X 100 rpm = 100kw OR
100nm of torque X 1 rpm = 100kw or
50nm of torque at 2 rpm = 100kw.
If your rear wheels are spinning really slow per given engine rpm, as in a high diff ratio (4:1 lets say), that means your diff is spinning slower, while transmittin still the same amount of power. That means friction losses are much less (as in diff oil is quite thick, and can add a lot of drag) -- not to mention
wheel bearings, etc etc bla bla.. mainly the diff oil though
Similary a car with a low diff ratio, say 2:1 is literaly got 4 times as 'diff drag' (since drag increases with v^2)
shit iv'e gotta go, but i hope i made sense
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| | Subject | Poster | Date |
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dynos and diff ratios
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Chris Davey | Mon, 28 June 2004 05:31 |
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Re: dynos and diff ratios
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V8_MA61 | Mon, 28 June 2004 06:52 |
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Re: dynos and diff ratios
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IRA11Y | Mon, 28 June 2004 07:19 |
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Re: dynos and diff ratios
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oldcorollas | Mon, 28 June 2004 08:05 |
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Re: dynos and diff ratios
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IRA11Y | Mon, 28 June 2004 08:46 |
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Re: dynos and diff ratios
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Rex_Kelway | Mon, 28 June 2004 08:53 |
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Re: dynos and diff ratios
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IRA11Y | Mon, 28 June 2004 09:24 |
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Re: dynos and diff ratios
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draven | Mon, 28 June 2004 09:41 |
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Re: dynos and diff ratios
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hemi twofifteen turbo | Mon, 28 June 2004 15:21 |
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Re: dynos and diff ratios
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Chris Davey | Mon, 28 June 2004 22:12 |
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Re: dynos and diff ratios
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Rex_Kelway | Tue, 29 June 2004 08:54 |
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Re: dynos and diff ratios
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Siktoy ra23 | Tue, 29 June 2004 10:07 |
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Re: dynos and diff ratios
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Chris Davey | Tue, 29 June 2004 23:51 |
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Re: dynos and diff ratios
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Norbie | Wed, 30 June 2004 00:58 |
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Re: dynos and diff ratios
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Chris Davey | Wed, 30 June 2004 02:22 |
