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Old 16th March 2009, 22:59   #1
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Default How do manufacturers calculate the engine's BHP?

hello everyone . i have seen many manufactures quote the bhp of a car say X. yet when its dynoed its 20% less than X . i know the dyno measures the horsepower at the wheels.! my doubt is why cant all manufactures just quote BHP at the wheels . i think if all manufactures do this it will at least reduce many confusion among general people and tuners alike !i mean what is the use of engine horsepower if it is the Wheel horsepower which decides how fast a car goes!.

my other doubt is how do the car companies actually quote these engine bhp values of a car..? obviously they are not dynoed normally or not dynoed at all there must be some other way.

i know i am asking too many questions. just my ignorance in certain fields.

PS: i tried searching for it this topic coudnt get to a appropriate thread. if there is any thread that already exists about the above query please close this down and i will be glad to continue the discussion there.
THANKS
RAVI
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Old 17th March 2009, 11:25   #2
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amulu10,

There is a chassis dyno - which you are referring to. The car's driven wheels are placed on large rollers (in the floor) and it measures horsepower at the wheels.

The figure you get is the HP at the engine(crank) minus any losses incurred through the drivetrain and transmission (the losses are usually estimated - and hence not great for getting absolute horsepower, but they are fairly constant on the same car - so they serve the purpose when comparing your car to itself after engine modifications etc).

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The other type of dyno (which manufacturers use) is an engine dyno.

This is connected directly to the crankshaft of the engine. Naturally, this is the purest way to check the power the engine produces - and ofcourse, the engine cannot be inside a car when this is done.

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In addition to the above info, manufacturers do not dyno every car they produce. They probably do the tests on a few engines at the begining of production, and then maybe checks after fixed intervals of units have been produced. Im sure some other members could shed more light on this.


Source of pictures & some more types of dynos etc : DYNO-mite Dynamometer - Engine Dyno & Chassis Dynamometer...


cya
R

Last edited by Rehaan : 17th March 2009 at 11:26.
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Old 17th March 2009, 11:56   #3
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Hey Rehaan. Thanks for that info. I have a few doubts on the same. The manufacturers mention the BHP in the specs, is this calculated by the engine dyno or the chassis dyno?

The petrol swift is 87 BHP. Is this figure at the engine?
If yes, then the power transferred to the wheels is less by how many HP approximately??
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Old 17th March 2009, 12:05   #4
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each and every engine is checked thoroughly and tuned by the manufacturer. there is a test rig which checks all the engine parameters like noise,compression vibrations BHP etc. the result sheet is printed and attached to the individual engine with its serial no for the QA people in the factory to approve.
if at all there is deviation from the tolerances of each value specified the engine is tagged as defective and reworked.
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Old 17th March 2009, 12:07   #5
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all manufacturers give figures based on engine dyno results. don't know the exact difference in HP b/w the two, maybe someone who's got their swift dyno'd can tell!
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Old 17th March 2009, 12:56   #6
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Quote:
Originally Posted by Rehaan View Post
....Im sure some other members could shed more light on this....
So i stand corrected on that part - i guess all engines produced are dyno'd at the manufacturer. However - is the dyno run as extensive for all engines? Or do they do a more extensive quality check once in every X engines produced?

Quote:
Originally Posted by swift8847 View Post
....The manufacturers mention the BHP in the specs, is this calculated by the engine dyno or the chassis dyno?...
Engine.

Quote:
Originally Posted by swift8847 View Post
....The petrol swift is 87 BHP.... then the power transferred to the wheels is less by how many HP approximately??
As speed0mania mentioned, if someone has chassis dyno'd their stock switft - the difference in the manufacturer claim and the chassis dyno result would be a good guage of the percent losses.


The "general" figure used for losses is ~15%. See my related post below from another thread :

Quote:
Originally Posted by Rehaan View Post
<except from http://www.team-bhp.com/forum/gadget...tml#post929297 (Dynolicious : Want to Dyno your car? Get an iPhone.) >

....
As you said, in general people say losses could range anywhere from 10-20%. (Actually some even say 2-3%)
But that is a topic for much interesting discussion. (I would like to start a seperate thread on that soon).

However, what really matters to the cars performance is the wheel horse power (WHP) - which is the power that is actually put down on the road (measured with a chassis/rolling-road type dyno).....
Also heres another thread which touches upon engine and drivetrain losses : http://www.team-bhp.com/forum/techni...in-engine.html

cya
R

Last edited by Rehaan : 17th March 2009 at 13:01.
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Old 17th March 2009, 17:45   #7
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@ rehaan thanks man . your explanation did clear quite a few doubt's of mine . so technically speaking if we take any engine from a new car(not talking about used cars) and dyno it in a engine dyno(if we manage to get hold of one) it should put the same hp as claimed by the auto company?

thanks
-ravi
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Old 17th March 2009, 19:49   #8
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More or less. You could have differences of around +/- 3-4 bhp, not more.
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Old 8th November 2009, 13:50   #9
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Smile Have i gained more BHP?

Have almost completed my stage one mods on my drive. Now how do i do the actual test of knowing how much Bhp has gained, and what the current Bhp of my drive. Is there specific outlet with the right equipments in Bengaluru to do these test.
Found this link, but it looks very complicated.
[COLOR=#008000]Car BHP calculator, Check ur car's horsepower - HTML / Javascript Tutorials[/COLOR]

Hope i am not here.

Last edited by Sportsmind : 8th November 2009 at 13:56.
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Old 8th November 2009, 14:47   #10
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BHP/Torque figures keep changing based on altitude, temperature etc.

The closer you are to sea level, the better the engine performs. Its said that you can lose upto 3% of engine power for every 1000ft increase in altitude.

So its possible for a 100bhp car tested at 5000ft to produce 115bhp (15% increase) when tested at sea level.

This can also be seen in the cylinder compression. A stock VTEC in B'bay reads 200psi where as a stock VTEC in Blore (3000ft) shows only 185psi (7.5% loss).

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Old 8th November 2009, 22:50   #11
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Quote:
Originally Posted by Shan2nu View Post
BHP/Torque figures keep changing based on altitude, temperature etc.
And age of the car too. For eg a brand new 100BHP car may not be a 100BHP car after 5+years or so..
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Old 9th November 2009, 00:10   #12
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Quote:
And age of the car too. For eg a brand new 100BHP car may not be a 100BHP car after 5+years or so..
Thats only for engines that haven't been maintained well. If you keep a check on the engine components and replace them when needed, it shouldn't lose out on power.

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Old 9th November 2009, 00:49   #13
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Quote:
Originally Posted by amit_mechengg View Post
each and every engine is checked thoroughly and tuned by the manufacturer. there is a test rig which checks all the engine parameters like noise,compression vibrations BHP etc. the result sheet is printed and attached to the individual engine with its serial no for the QA people in the factory to approve.
if at all there is deviation from the tolerances of each value specified the engine is tagged as defective and reworked.
No boss. I have been on a few assembly lines. And the roller is just a basic run in for the car. No sensors attached anywhere.

Quote:
Originally Posted by amulu10 View Post
@ rehaan thanks man . your explanation did clear quite a few doubt's of mine . so technically speaking if we take any engine from a new car(not talking about used cars) and dyno it in a engine dyno(if we manage to get hold of one) it should put the same hp as claimed by the auto company?

thanks
-ravi

Well, if you are lucky, you might even have a few more.
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Old 10th November 2009, 18:23   #14
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Quote:
Originally Posted by Sportsmind View Post
Now how do i do the actual test of knowing how much Bhp has gained, and what the current Bhp of my drive. Is there specific outlet with the right equipments in Bengaluru to do these test.
There is a very simple way of knowing the current increase in the power/torque of your car..

What you just need to do is take your car and do a 1/4 mile on a empty stretch (a few runs and take the lowest time of all) then compare it with a stock car..

AND / OR

Take your ride to its top speed under full throttle (Pedal to the metal ) and compare to the stock, typically a 3% increase in power results in 1% increase of top speed (Testing conditions being the same, I mean at similar place and at similar time),

And please post your figures (Top speed and 1/4 time) with your current mods, lets see how much your ride has gained..

Keep revving..

Last edited by bblost : 10th November 2009 at 18:31. Reason: Only 2 smileys per post. Please refer to the rules section.
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Old 19th February 2010, 23:56   #15
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Most of the bigger engines undergo 100% dynamo meter test based on certain specified test cycles.
But some of the high volume production lines producing smaller engines does not test the with the dynamo meter. Instead they do the "Cold Test". Cold test is nothing but driving the engine using a prime mover and check certain aspects like leak, noise, temperature etc.
It is up to the manufacturer to decide whether to go for cold test or hot teat.
In both the cases some engines are taken to the test beds at certain pre-determined frequency for a full cycle testing.
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