Cant dyno a merc?? Hmmmmm

[ChrisA]

Where's dieselman when you need him.

He's stuck at Celtic Tuning showing them how to dyno a Merc :bannana:

 

[ChrisA]

Chris your a spoil sport I thought I had gained some bhp from nothing

HAHA....if it were 25% all the MSL Monster builds would be close to 800bhp

 

[Mrhanky]

HAHA....if it were 25% all the MSL Monster builds would be close to 800bhp

Well just get a sticker made up and it will make it so. Well that's what most of pretenders do around my way.

 

[Leabrooks]

Power losses through a drive train are massively overestimated by dyno operators as it makes their figures look better! The biggest killer of 'transmission losses' isn't the clutch/gearbox/rear axle at all, its the tyres running on steal drums!! Even on an auto the same is true. A rolling road (chassis dynometer) is NOT a real tarmacked road, as AMGeed says, the only figures worth comparison from a dyno are the before and after figures, as single run results aren't worth anything in the real world (unless you have a 'penis size' problem or read Maxpower) If an autobox losses were true (which they aren't) they would drink fuel. yet most owners will tell you a modern autobox is MORE effecient than a manual 'box. Daft figures like 18%, 25% losses or whatever are just that, daft figures plucked from thin air from a guy trying to flog you double glazing!
How about this scenario: the old 5 speed 722.6 was fitted from anything from 100hp engines to 400hp plus, are you percentage guys honestly saying the losses are 25hp (from a 100hp engine) are then 100hp (on a 400hp engine) from the same 'box at the same revs???? :fail

 

[BFT]

And for that reason above the dyno at MSL in Birmingham WHP is quoted so we don't all get (too) excited.

The gain is the difference before and after.

If you have a decent braked and/or sync'd dyno, no issues dynoing Mercs.

 

[ChrisA]

:fail

Looks like the only Fail is from your total lack of understanding of Power losses through drivetrain ....

The total power lost between combustion and forward motion is specific to each vehicle and therefore no single rule, percentage or fixed number, could possibly apply to all vehicles. Even on the most superficial level, this is easy enough to understand because an all-wheel-drive Subaru obviously has a lot more driveline components to spin (front, middle and rear differentials along with front and rear driveshafts and two prop shafts) and a beefier transmission to hold all that turbocharged torque, so it's naturally going to suffer from greater drivetrain losses than a Honda Fit with its much smaller and less robust transmission, smaller and lighter driveshafts (and no prop shaft) and single differential.

Breaking down the different types of losses that occur within a vehicle's drivetrain, steady-state losses occur while the vehicle is cruising at a steady or constant speed, where average angular acceleration is zero because no additional torque is being called upon to accelerate the drivetrain's rotational mass. Within the drivetrain, steady-state power losses occur from the following components: the transmission torque converter (in the case of automatic transmissions), the transmission oil pump, clutch pack drag, one-way clutch drag, seal and bearing drag, gear windage and friction, and final drive losses.

It's also worth noting that the more powerful you make your engine, the greater the thrust force and angular acceleration it's able to exert on the drivetrain, generating even more friction and heat in the process. But because both steady-state and dynamic friction vary depending on engine speed, engine load and the efficiency of the engine and drivetrain's design (how well they limit friction and the associated thermal conversion of torque to heat), there's no way to apply a universal percent loss to it. Nor is it possible to apply a fixed drivetrain loss figure to your car (say 100 whp from my CLS 55 example), because as you modify the engine and increase its output, its ability to generate thrust force and angular acceleration also increases (though not in a linear fashion).

Bottom line is, 18% is actually a fairly conservative figure

 

[merc85]

Power losses through a drive train are massively overestimated by dyno operators as it makes their figures look better! The biggest killer of 'transmission losses' isn't the clutch/gearbox/rear axle at all, its the tyres running on steal drums!! Even on an auto the same is true. A rolling road (chassis dynometer) is NOT a real tarmacked road, as AMGeed says, the only figures worth comparison from a dyno are the before and after figures, as single run results aren't worth anything in the real world (unless you have a 'penis size' problem or read Maxpower) If an autobox losses were true (which they aren't) they would drink fuel. yet most owners will tell you a modern autobox is MORE effecient than a manual 'box. Daft figures like 18%, 25% losses or whatever are just that, daft figures plucked from thin air from a guy trying to flog you double glazing!
How about this scenario: the old 5 speed 722.6 was fitted from anything from 100hp engines to 400hp plus, are you percentage guys honestly saying the losses are 25hp (from a 100hp engine) are then 100hp (on a 400hp engine) from the same 'box at the same revs???? :fail

Just to add Some are HUB dyno's also

 

[John]

This thread is exactly why I go to the professionals to start with - regardless of distance.

 

[frostbite]

I suppose that at the end of the day, the figures are all irrelevant anyway, except the ones involving the stopwatch and/or the speedo. Even then they become irrelevant when you dial in the grin factor...

 

[ChrisA]

Smiles per Gallon is what it's all about

 

[E55BOF]

Bottom line is, 18% is actually a fairly conservative figure

Oh Ferk! I've just re-insured my E55K, on the basis of 14%losses, as unmodified. It produced 414 bhp on the MSL dyno, which using 18% losses gives 504 bhp at the flywheel (well, torque converter drive plate, but you know what I mean...), whereas MB quote 476 bhp as standard, and 14% losses = 481 bhp - near enough to stock, I think. 504 bhp isn't, and in the event of investigation it might be tricky to convince the insurers that it was just well-run-in....

Two questions, if I might. Firstly, will a quick Star session reveal if it's a standard MB map, and secondly, is there any definitive (enough to persuade an insurance company) data on transmission losses available?

 

[daveenty]

414bhp at the wheels equates to 488.52bhp at the crank according to my calculations, which isn't a great deal over standard?

No definitive calculation for drivetrain losses as there are too many variables to take into account, which is why there are so many different figures floating about, though most of the MB people tend to go with the 18% figure. Oh and yes, a competent operator could find that there's a different map on it, though without all the data would have no idea if it's designed for performance, economy or anything else.

 

[E55BOF]

Thank you, Daveenty, but are you sure your calculations are right? If what reaches the wheels is 414, and that is 82% of the flywheel figure, then I make 100% - the flywheel figure - as 504.878.

Like Rolls and Bentley used to do, I would describe the power output as 'sufficient' - well, more than sufficient for me, actually - but I wouldn't like to find myself uninsured just after mowing down a queue at a bus stop... Looks like a Star session might be in order, just to be sure.

 

[daveenty]

The way to calculate it would be to multiply by 1.18. This gives you the original figure of 414 which is 100% at the rear wheels. The 0.18 factor gives you the extra 18% which is the estimated loss. Same as working the VAT out on something really.

£100 + VAT = £120. To get the VAT amount, you'd multiply by 1.2 as it's a difference of 20%. When it was 17.5% the multiplication factor was 1.175. To go the other way, i.e. crank to wheels (or what the VAT is on something), it's divide instead of multiply.

Hope I've explained OK, shattered today.

 

[AMGeed]

Thank you, Daveenty, but are you sure your calculations are right? If what reaches the wheels is 414, and that is 82% of the flywheel figure, then I make 100% - the flywheel figure - as 504.878.

Like Rolls and Bentley used to do, I would describe the power output as 'sufficient' - well, more than sufficient for me, actually - but I wouldn't like to find myself uninsured just after mowing down a queue at a bus stop... Looks like a Star session might be in order, just to be sure.

I'm afraid the calculation Dave showed is correct. STAR will show if you have a stock ECU, but I don't know about BHP.
As it happens , its irrelevant now anyway

 

[E55BOF]

"The way to calculate it would be to multiply by 1.18. This gives you the original figure of 414 which is 100% at the rear wheels. The 0.18 factor gives you the extra 18% which is the estimated loss. Same as working the VAT out on something really.

£100 + VAT = £120. To get the VAT amount, you'd multiply by 1.2 as it's a difference of 20%. When it was 17.5% the multiplication factor was 1.175. To go the other way, i.e. crank to wheels (or what the VAT is on something), it's divide instead of multiply.

Hope I've explained OK, shattered today."

Thank you for that, but...

I can't fault your arithmetic, but I don't think you are starting from the right baseline figure. Logically, if the transmission loss from flywheel to rear wheels is 18%, what you get at the rear wheels is 82% of what you had at the flywheel. That gives a 100% figure of 504.

Say you start with £100, and spend 20% of it. That leaves you with £80 - 20% less. If you take 20% of £80 out of your baby son's piggybank to make up the difference, you still won't have £100.

What you have done is taken the wheels figure as 100%, which logically, it is not, and added 18% to it. If that's the way it is done, fair enough, but it's not logical.

I don't care what the actual power is, but think I'll have to have a Star check done to establish if it is a standard map.

On the other hand.... If anyone on here happens to read this, and has had an MSL dyno run done on a standard E55K, perhaps pre-modification, would he/you/they care to say what the 'before' figures were?

 

[daveenty]

Appreciate your logic, though the only baseline figure which you have from the dyno is the wheel one, hence the reason I work it from there backwards. All the AMG guys on here use the same method, as does Acid @ MSL

 

[AMGeed]

On the other hand.... If anyone on here happens to read this, and has had an MSL dyno run done on a standard E55K, perhaps pre-modification, would he/you/they care to say what the 'before' figures were?

I can do that. You'll be pleased to know your car is putting out a little more than mine is stock.
On the MSL dyno, mine was showing 405.58 at the wheels and 483.84ft lbs torque.
That calculated to 478.58 BHP and 570.93 ft lbs torque which is well above stock 507ft lbs stock.

 

[ChrisA]

And this is an after mod run

617.57 rwhp x 1.18 = Smiles per Gallon

http://www.mbclub.co.uk/forums/attachment.php?attachmentid=51605&stc=1&d=1435521490

 

[Bobby Dazzler]

Appreciate your logic, though the only baseline figure which you have from the dyno is the wheel one, hence the reason I work it from there backwards. All the AMG guys on here use the same method, as does Acid @ MSL

That may be the way the way people approximate power at the flywheel on AMGs, but that's a drive train loss of 15.25% if you believe that the power at the wheel is 414 BHP and power at the flywheel is 488.52 BHP

That's not to say it's the (right or) wrong way of approximating the power at the flywheel though. In fact my C32 was measured as 296 BHP at the wheels, and approximating the power at the flywheel in the same way (296*1.18) gives 349 BHP, or 354 PS which is precisely the published figure for that model.