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Discussion Starter · #1 ·
Hello everybody

Can somebody tell me the difference between crank HP on an engine dyno and HP on a chassis dyno? Where are the numbers of Manufacturer based on?

9-5 aero
 

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Originally posted by 9-5 aero:
[qb]Hello everybody

Can somebody tell me the difference between crank HP on an engine dyno and HP on a chassis dyno? Where are the numbers of Manufacturer based on?

9-5 aero [/qb][/b]
An engine dyno usually measures power at the flywheel; a number of methods are often used, though the most common is the eddie current method.

A chassis dyno measures power at the wheels; since there is substantial transmission and tire-friction losses the numbers are a great deal lower than the flywheel numbers. For Saabs the difference seems to be roughly 18%.

Adrian~
 

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Discussion Starter · #3 ·
Hi Adrian

What's the "eddie current method"? On a chassis dyno you measure the power at the wheels but then it is been corrected and then you have the engine power. A car for example has 200Ps at the wheels and 250Ps engine power on a chassis dyno corrected. On an engine dyno would the same car have more HPs? What's more common an engine or a chassis dyno?

9-5 aero
 

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Discussion Starter · #5 ·
Originally posted by aeropilot:
[qb]Manufacturers figures are flywheel figures measured on an engine dyno in a engine test cell. [/qb][/b]
Isn't the result the same with corrected power on a chassis dyno?
 

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Purely theoretical YES.

In reality it's not the case, depending from the dyno itself (brand, type), correction factors, cooling system (fan) and the user.

In my opinion the only use of a chassis dyno (if you dont have a engine dyno to compare the results) is to run "comparison" test's, means run one test before a change and than after the change. Best would be to run at least 3 tests each and average.
Getting "absolute" values is nearly impossible.
 

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Originally posted by Trionic:
[qb]In my opinion the only use of a chassis dyno (if you dont have a engine dyno to compare the results) is to run "comparison" test's, means run one test before a change and than after the change. Best would be to run at least 3 tests each and average.
Getting "absolute" values is nearly impossible. [/qb][/b]
I agree, and people spend too much time arguing about what "real" horsepower is; all methods of dyno-testing measure some amount of "real" horsepower.

But, IMHO, the amount of horsepower which makes it to the road is best measured by how the car accellerates on the road ...

Adrian~
 

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Originally posted by Adrian W:
[qb]But, IMHO, the amount of horsepower which makes it to the road is best measured by how the car accellerates on the road ...
[/qb][/b]
And how often and how long you can accelerate before the car gets slower
 

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and therefore the best way to measure any stage performance upgrades is to put the staged car side by side against the standard car and let rip
 

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Originally posted by philip hs:
[qb]And how often and how long you can accelerate before the car gets slower    [/qb][/b]
There's just as much, if not more, air running over the parts of the car during high speed motoring as there is in a well-built dynocell. I'm sure you can accellerate quickly for some time.

Adrian~
 

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Originally posted by Adrian W:
[qb] QUOTE
Originally posted by philip hs:
[qb]And how often and how long you can accelerate before the car gets slower       [/qb][/b]
There's just as much, if not more, air running over the parts of the car during high speed motoring as there is in a well-built dynocell. I'm sure you can accellerate quickly for some time.

Adrian~ [/qb][/b][/quote]Adrian, I think that philip refered to a on goin converstaion at one another saab board.
 

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Originally posted by Bubbles:
[qb]I thought most of the engine dyno cells in the UK use water as the power soak. [/qb][/b]
Yes, it's an eddie-current dyno. Most in the states are inertial-resistance dynos. The purpose of both is to measure the amount of weight the engine can lift a certain distance in a certain amount of time. 1 hp = 550lbs moved 1ft upward in 1 minute @ one g of graviational resistance.

Adrian W~
 

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Originally posted by Vigge:
[qb]Adrian, I think that philip refered to a on goin converstaion at one another saab board. [/qb][/b]
Pssst, don´t tell him! I´m glad he didn´t find & hijack it yet
 

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Originally posted by philip hs:
[qb] QUOTE
Originally posted by Vigge:
[qb]Adrian, I think that philip refered to a on goin converstaion at one another saab board. [/qb][/b]
Pssst, don´t tell him! I´m glad he didn´t find & hijack it yet [/qb][/b][/quote]Gee, thanks. How nice of you.


I didn't "find it"; I was directed to it by one of the major participating tuners there.

Adrian~
 

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Just joking Adrian However, you have a tendency to go a bit far off topic while explaining your point of view - that´s what I meant by hijacking.

Yours,

Philip
 

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Perhaps we can start it all off again here for those that have missed out on it.......

Perhaps without the teddy throwing....

Nah....can't see that working
 
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