Some interesting thoughts on dyno transmission losses...

[gradeAfailure 0]

Think we all ought to read this...

 

Some rolling roads quote 35%+ for transmission losses?! I don't think so... Even VW themselves reckon about 15% - it's near the end of the article...

 

I've read several articles written by tuners about the transmission loss con but this seems to sum it up best; but they all quote similar figures...

 

Always happy to be corrected on stuff like this, but if my car was putting out 100bhp at the wheels and I was being quoted anything between 135 and 150 at the flywheel (as I have seen in magazine RR shootouts) then I'd be a little suspicious to say the least! :)

 

As it stands, my car was RR'd at 101.2bhp at the wheels which translated to 124.9 at the flywheel so I'd say that's fairly accurate, maybe even still a little high...?

 

What do y'all reckon on this?

[stevemac 0]

Why not just pay attention to what you have at the wheels - that's what matters. Use of transmission loss estimations to get a "at the flywheel" bhp are always just that - estimations.

 

Bhp at the wheels is what matters in the real world - bhp at the flywheel is just "pub talk".

[gradeAfailure 0]

Oh, I'm more than happy to just use the wheels figure, but it seems that no-one else likes doing that as it's never as high a number as we're used to seeing! :lol:

[stevemac 0]

Like I said - flywheel bhp is just for people "bigging it up" in the pub.

 

The only power that you feel on the road is what you have at the wheels - that's all I'm interested in & that's all the r/r can measure accurately.

 

I don't want a car that sounds fast on paper - I want one that is fast on the road. :rambo:

[Joe M 0]

Heres a post I copied from another forum about the same subject apparently wrote by Vince from Stealth.

 

Hi Guys

 

Thanks to all who attended the RR shoot-out last Sunday, was a good day and a good turnout.

 

First of all on the Subject of intake temps, VR6 engines are very heat sensitive and can loose up to 10bhp between a cool run on the rollers and a hot run.

 

The intake temp figures we put in to our RR software for horsepower correction are as follows.. Start temp set at ambient and end temp about 3-5 degrees higher, this takes into account the intake air temp rise during the power run. Rolling road testing is not carried out in a totally controlled situation to achieve 100% accurate figures, close or very near close is the best we can hope to achieve.

 

Force inducted cars by their nature create much higher intake temps, on these cars we generally monitor the actual temp through the diagnostic port during the run then input that figure into our RR software.

 

 

 

Flywheel BHP vs Wheel BHP..

I read the Puma racing coast down losses a few years back (shortly after purchasing our dyno) interesting read and I agree with most of what is written..

 

BUT

 

Since then I’ve had 3 yrs + dyno experience on VAG cars and this is what I have found.

 

Totally standard Golf 2 16V, VAG say 139bhp Stealth measure nearer 145bhp, we all know VAG engines just get better with age.

 

Totally standard VR6 OBD 1 VAG say 173bhp: Stealth measure under 180bhp (but high 170’s)

 

Totally standard VR6 OBD 2: Stealth measure 185bhp-192 bhp. VW quoted BHP same as OBD1 but you only have to drive one to realise straight away the OBD2 is quicker.

 

Corrado VR6: VAG say 193bhp, Stealth measure 190bhp-195bhp

 

There is always the exception to the rule, I’ve seen some standard cars produce way over standard spec BHP, maybe a Monday morning engine? I know I used to have a Friday afternoon 16V Golf, poo power horrible to drive no matter what I did to it tuning wise.

 

Note: All of the above are Flywheel figures……

 

 

The above figures satisfy me that our rollers produce a reasonably accurate flywheel figure when compared to what VAG state, if I did not think that this was the case then I would change it.

 

 

OK, now down to power at the wheels. I’ve had long drawn out conversations with some customers about this over the years and one guy in particular, he was adamant he was right and the figures I gave him were wrong. (he kept referring to what he read on Puma Racing) His argument was that only a power at the wheels figure was the one which had any real meaning, anything else was crap!!

 

This prompted me to do some testing of my own, and in front of said customer..

 

Figures I am quoting below are simplified for ease, (mainly because I can’t remember the actuals). You should get the idea though

 

 

Took a car and carried out power test.

 

Wheel bhp: 100bhp.

Transmission loss 40bhp

Flywheel figure 140bhp

 

Took same car and put tracking out by 6mm then back on rollers for power test.

 

Wheel BHP 95bhp

Transmission loss 45bhp

Flywheel figure 140bhp

 

From this my assumption is that no matter how inaccurate a “Rolling Road Flywheel” figure may be, in my opinion it can calculate any discrepancies in the transmission losses therefore showing a repeatable flywheel figure. There are lots of things that can affect losses, Wheels/tyres, brake disc weight, driveshafts, etc.. change any of these and you will affect your power at the wheels bhp, if however measured on our rolling road then your flywheel figure will remain the same but will be calculated differently..

 

On RR days there is one thing that you all suffer from, that’s high-ish Transmission loss figures.. Why???? Most of you have all your bonnets open trying to get your engines to cool down and get rid of that dreaded heat soak, and why not, everyone wants to see good power from their car.. I then get the car on the rollers bring engine up to a safe temp to carry out power run but your gear oil is stone cold and very thick, just another contributing factor to a lower power at the wheels figure, my dyno measures this though and adds this higher loss to the power measured at the wheels and gives me a repeatable flywheel figure.

 

I’m happy with the way our Dyno works and with the figures it gives me at the flywheel, (my preferred way of measuring) I feel the accuracy is close enough to be comparable with what VAG say their cars do. Like I said I’m happy but I would change it if it were not the case..

 

Hope this answers some questions for you?

Although I’m really crap at explaining things so you’re probably more confused now than before?

 

Sorry to go on

 

Regards

 

Vince

[gradeAfailure 0]

Interesting reading, cheers Joe M! :)

[Supercharged 2]

To make it easier to read...

 

++++++++++++++++++

 

Hi Guys

 

Thanks to all who attended the RR shoot-out last Sunday, was a good day and a good turnout.

 

First of all on the Subject of intake temps, VR6 engines are very heat sensitive and can loose up to 10bhp between a cool run on the rollers and a hot run.

 

The intake temp figures we put in to our RR software for horsepower correction are as follows.. Start temp set at ambient and end temp about 3-5 degrees higher, this takes into account the intake air temp rise during the power run. Rolling road testing is not carried out in a totally controlled situation to achieve 100% accurate figures, close or very near close is the best we can hope to achieve.

 

Force inducted cars by their nature create much higher intake temps, on these cars we generally monitor the actual temp through the diagnostic port during the run then input that figure into our RR software.

 

 

 

Flywheel BHP vs Wheel BHP..

I read the Puma racing coast down losses a few years back (shortly after purchasing our dyno) interesting read and I agree with most of what is written..

 

BUT

 

Since then I’ve had 3 yrs + dyno experience on VAG cars and this is what I have found.

 

Totally standard Golf 2 16V, VAG say 139bhp Stealth measure nearer 145bhp, we all know VAG engines just get better with age.

 

Totally standard VR6 OBD 1 VAG say 173bhp: Stealth measure under 180bhp (but high 170’s)

 

Totally standard VR6 OBD 2: Stealth measure 185bhp-192 bhp. VW quoted BHP same as OBD1 but you only have to drive one to realise straight away the OBD2 is quicker.

 

Corrado VR6: VAG say 193bhp, Stealth measure 190bhp-195bhp

 

There is always the exception to the rule, I’ve seen some standard cars produce way over standard spec BHP, maybe a Monday morning engine? I know I used to have a Friday afternoon 16V Golf, poo power horrible to drive no matter what I did to it tuning wise.

 

Note: All of the above are Flywheel figures……

 

 

The above figures satisfy me that our rollers produce a reasonably accurate flywheel figure when compared to what VAG state, if I did not think that this was the case then I would change it.

 

 

OK, now down to power at the wheels. I’ve had long drawn out conversations with some customers about this over the years and one guy in particular, he was adamant he was right and the figures I gave him were wrong. (he kept referring to what he read on Puma Racing) His argument was that only a power at the wheels figure was the one which had any real meaning, anything else was crap!!

 

This prompted me to do some testing of my own, and in front of said customer..

 

Figures I am quoting below are simplified for ease, (mainly because I can’t remember the actuals). You should get the idea though

 

 

Took a car and carried out power test.

 

Wheel bhp: 100bhp.

Transmission loss 40bhp

Flywheel figure 140bhp

 

Took same car and put tracking out by 6mm then back on rollers for power test.

 

Wheel BHP 95bhp

Transmission loss 45bhp

Flywheel figure 140bhp

 

From this my assumption is that no matter how inaccurate a “Rolling Road Flywheel” figure may be, in my opinion it can calculate any discrepancies in the transmission losses therefore showing a repeatable flywheel figure. There are lots of things that can affect losses, Wheels/tyres, brake disc weight, driveshafts, etc.. change any of these and you will affect your power at the wheels bhp, if however measured on our rolling road then your flywheel figure will remain the same but will be calculated differently..

 

On RR days there is one thing that you all suffer from, that’s high-ish Transmission loss figures.. Why???? Most of you have all your bonnets open trying to get your engines to cool down and get rid of that dreaded heat soak, and why not, everyone wants to see good power from their car.. I then get the car on the rollers bring engine up to a safe temp to carry out power run but your gear oil is stone cold and very thick, just another contributing factor to a lower power at the wheels figure, my dyno measures this though and adds this higher loss to the power measured at the wheels and gives me a repeatable flywheel figure.

 

I’m happy with the way our Dyno works and with the figures it gives me at the flywheel, (my preferred way of measuring) I feel the accuracy is close enough to be comparable with what VAG say their cars do. Like I said I’m happy but I would change it if it were not the case..

 

Hope this answers some questions for you?

Although I’m really crap at explaining things so you’re probably more confused now than before?

 

Sorry to go on

 

Regards

 

Vince

[stevemac 0]

There are lots of things that can affect losses, Wheels/tyres, brake disc weight, driveshafts, etc.. change any of these and you will affect your power at the wheels bhp

 

Vince

Which exactly proves my point - "at the wheels" figures are the ones that matter.

 

In reality - if you want to compare the true "on the road" power of a vehicle - surely the power must be measured including the running gear, etc & not just the engine itself.

[willwoll100 0]

I agree with you Steve, there's no way a RR can accurately consistently measure flywheel bhp. Every single car of the same make and model are different and would only be the same if all the components were blue printed which they are not. Have a read through this http://www.dynamometer.fsnet.co.uk/index.htm I think you'll find it interesting.

 

Cheers

[Kevin Bacon 5]

I liked Vince's tracking trick, very clever.....not many RR operators would deliberately add transmission loss to prove his Flywheel figures are repeatable, so hats off to him.... he knows his sh1t that man.

 

Gear oil temperature was another point worth raising and not even Redline helps that. I've seen some tests done in America where redline reduced the transmission losses by 1 to 2hp at the most during coast down.

 

The Americans, incidentally only ever quote whp figures too as it's your 'final' figure, if you like, taking into account your chassis mods.

 

It's all horsesh1t at the end of the day anyway, if the car feels quick on the road, then it is.... some people just get hung up on the numbers.

 

Do more with what you've got, fit a low ratio box and you'll accelerate the same as an identical car with standard gearing and 50hp more!

[Henny 0]

peak numbers are all irrelevant anyway... it's how the car gets to the figures and where in the rev/gearing the torque appears that makes a car fast/slow or accelerate quickly or slowly on the road... I know I'd rather have huge bags of torque from down low with gearing to match than an engine which just revs way up high to get high BHP figures... And yes, I do know the relationships between torque, BHP, acceleration and speed... :roll: :lol:

 

That's a fantastic letter from Vince... nice to see someone who'll put his reputation to one side and PROVE that his figures are repeatable and as accurate as possible... 8)