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Old 7th March 2012, 23:33   #31
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One can approximate ones engine power if you have a OBD logging tool. Its about mass air flow sensor(MAF reading in grams/sec)/0.8 . Things like timing you are running , knock retard etc will effect this calculation but still good.

jn-3-16 you cant calculate the power of your engine from max torque as max power is produced at a higher rpm than max torque.

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Last edited by Technocrat : 8th March 2012 at 01:04. Reason: Please read the note in your post carefully, thanks
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Old 9th March 2012, 22:50   #32
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Default Re: Computing h.p.

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Originally Posted by jn-3-16 View Post
tbhp gurus. I'm trying the find out the HP for an SX4 VXi. Google tells me that:

1 HP = 2pi(T)(RPM)/33,000

One site tells that:

HP = (T X RPM) / 5252

According the MUL website: T = 145 Nm @ 4100 RPM

So is '113.194973343 hp' the correct answer?

Your corrections/suggestions/thoughts most welcome.
The 5252 number is applicable if torque is in pound-feet. If in Nm, the number should be 7120. For kgm, the number is 726. More important, the maximum power is not necessarily obtained at the same RPM where max torque is obtained. The actual torque at 6000 RPM where max power is made, would perhaps be around 110-115 Nm.
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Old 29th December 2015, 19:54   #33
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Default Re: How do manufacturers calculate the engine's BHP?

Reviving an old thread. Hope this is the right place for this question. I was reading up on the crank hp vs wheel hp. From what I have read in various places, understood that most manufacturers quote the max bhp as measured at crank and a limited few quote the hp measured at the wheel.

VW, as per what I read here, quotes the Wheel HP and all other key manufacturers here quote crank HP. Is this correct?

Questions:
  1. The WHP is said to be 10-15% lower than the crank HP. Is this on an average a standard loss %?
  2. I have a Vento TSI rated at 105 BHP. A Honda City or Verna is rated at 120+bhp. Since VW measures Wheel HP, does it actually make sense to add 10-15% to get a HP for comparison (or reduce 15% from the other car's numbers)?

This question just struck me when I was reading the Baleno Boosterjet thread, lot of comparisons on the Bhp/tonne and torque/tonne. These are basically flawed when the underlying numbers are not based on the same metric.
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Old 30th December 2015, 16:27   #34
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Default Re: How do manufacturers calculate the engine's BHP?

Quote:
Originally Posted by Rajeevraj View Post
Reviving an old thread. Hope this is the right place for this question. I was reading up on the crank hp vs wheel hp. From what I have read in various places, understood that most manufacturers quote the max bhp as measured at crank and a limited few quote the hp measured at the wheel.

VW, as per what I read here, quotes the Wheel HP and all other key manufacturers here quote crank HP. Is this correct?

Questions:
  1. The WHP is said to be 10-15% lower than the crank HP. Is this on an average a standard loss %?
  2. I have a Vento TSI rated at 105 BHP. A Honda City or Verna is rated at 120+bhp. Since VW measures Wheel HP, does it actually make sense to add 10-15% to get a HP for comparison (or reduce 15% from the other car's numbers)?

This question just struck me when I was reading the Baleno Boosterjet thread, lot of comparisons on the Bhp/tonne and torque/tonne. These are basically flawed when the underlying numbers are not based on the same metric.
The power losses between the engine and the wheel are more or less of the similar magnitude in cars of same size and power range.

You can consider the effect of losses while comparing the wheel HP of one car to the engine HP of the other car. But more than just the HP figure, you need to see the engine characteristics (power vs engine rpm and torque vs engine rpm). The quoted HP is just the peak HP (and you get it at a particular engine rpm) and we do not drive the car always at that engine rpm.

A car may have lower value of peak power / torque but it may have actually better torque at usual driving rpm (1500 to 3000 rpm). We usually do not drive at 4500 rpm (typical peak torque rpm for petrol cars) or 5000-6000 rpm (typical peak HP rom for petrol cars).

So, look at the torque curve and power curve. It may not be easily available. In that case, decide after having a test drive.

Last edited by Rahul Bhalgat : 30th December 2015 at 16:29.
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Old 31st December 2015, 11:51   #35
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Default Re: How do manufacturers calculate the engine's BHP?

Quote:
Originally Posted by Rajeevraj View Post

VW, as per what I read here, quotes the Wheel HP and all other key manufacturers here quote crank HP. Is this correct?
Where did you read that?
It would be a HUGE marketing blunder for a manufacturer to publish the wheel horsepower figure while others publish crank horsepower.
Any guess why?
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Old 31st December 2015, 12:35   #36
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Default Re: How do manufacturers calculate the engine's BHP?

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Originally Posted by alpha1 View Post
Where did you read that?
It would be a HUGE marketing blunder for a manufacturer to publish the wheel horsepower figure while others publish crank horsepower.
Any guess why?
Have read it in a couple of places in this forum itself. Unfortunately do not recollect which thread it was.

From what I recall, that's VW standard way of measuring.
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Old 31st December 2015, 13:16   #37
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Default Re: How do manufacturers calculate the engine's BHP?

Quote:
Originally Posted by alpha1 View Post
Where did you read that?
It would be a HUGE marketing blunder for a manufacturer to publish the wheel horsepower figure while others publish crank horsepower.
Any guess why?
I believe Rajeev is basing that information on the various dyno graphs of VW vehicles on this forum (just before they were mapped, or modified).
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Old 31st December 2015, 16:03   #38
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Default Re: How do manufacturers calculate the engine's BHP?

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Originally Posted by lamborghini View Post
I believe Rajeev is basing that information on the various dyno graphs of VW vehicles on this forum (just before they were mapped, or modified).
Quote:
Originally Posted by Rajeevraj View Post
Have read it in a couple of places in this forum itself. Unfortunately do not recollect which thread it was.

From what I recall, that's VW standard way of measuring.
Then, it is a foolish marketing blunder by VW, because for the customers: the larger number the better.

If VW has a 100 whp car (= 120 chp) and is competing with Hyundai which has 110 chp - customers will always place Hyundai higher than VW in engine performance. Whereas, it turns out in reality, VW is better than Hyundai.

I am sure VW will have enough MBA guys in their organization to understand this.
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