Dyno discussion for modern big blocks

[ohiorider]

I looked at the dyno chart on the attached link https://www.guzzitech.com/forum/downlo ... &mode=view showing that the stock 1200 Sport dyno'd approx 70hp at the rear wheel. This is lower than I would have expected to find, in light of Guzzi posting factory specs of 95hp at the crank. My 1999 K1200RS was advertised by the factory to output 130hp at the crank. Most of the magazines that dyno'd this bike saw rear wheel figures in the 109 - 112hp range. Say 110. So if we divide 110/130, the result is a loss of approximately 16 percent hp at the rear wheel.

70/95 is a 27 percent loss. That is quite a bit of hp loss between crankshaft and rear wheel.

Question - Any thoughts? Is Guzzi using a different method to arrive at hp at the crank? Or is there something else that influences the numbers?

Bob

 

[Mi_ka]

Re: cam choices for norge?

Depends on the dyno.
If it is an inertial dyno then all measurements are approximate and highly relative, that is useful for comparison but must be compared to similar data.
Given the high inertia of the the Guzzi engine-transmission system, if the inertial dyno takes no account of approximation factors depending on bike type, then 70hp on this dynamometer may well be around 85hp on a brake dyno (and the rest missing hp can easily be the friction losses through the transmission and rear tyre as well tyre-roller slippage).

Todd, is it a braked dyno run?

 

[GTM®]

Re: cam choices for norge?

It is an eddy current/load cell Dynojet 250i dyno.

I have a library of dyno run files that goes back over a decade. Many factors go into results of every dyno run; miles on the motor, ambient air temp, barometric pressure, altitude, correction factors, etc, etc, etc.

Stock '00-05 1064cc V11 Sport engines consistently produced mid 70's at the rear wheel. They had far less stringent emissions to contended with, so anywhere in the 70's rwhp is typical IMO for the 1200S in stock trim (which I have documented runs of on numerous machines), which this one was.

Hope that helps.

 

[Mi_ka]

Re: cam choices for norge?

Reputed Brake dyno and user so mid 70s it is - thanx Todd!

Maybe 3-4 extra ponnies lost into tyre slippage (usually 2%-6% depending on dyno set up) or tyre deformation under tie down strap forces.
If we account 3-5% lost in the gearbox & primary transmission and that shafties have supposed loses of 12% or so we can say total transmission losses hover around 16%.
So, 75hps + 16% = 87hps plus tyre losses = around 90-91 at the crankshaft which is pretty close to the 95hp Guzzi publishes.
If the dyno operator did not warm up properly the bike so the various engine-gearbox-shaft oils become properly thin or if he overwarmed the bike so the fuel tank became too warm, this can very easily be the reason the lost hps are not there.
Or he may have overtightened the bike on the dyno and too much tyre deformation occured or he undertightened the bike and excessive slippage occured or he had the tyre underinflated or overinflated and so on...
That is why a Dynamometer is not a magic machine and requires a user that knows his trade.
Otherwise you end up with a lot of head scratching guys (or even worse very expensive thin air moded bikes...)
===
Maybe (just maybe) a dyno numbers poll thread could show what different numbers cann be expected between different brand dynos, in particular inertial dynos for stockish bikes.
U know, something that will eventually come up like X(DJ) = Y(Fuchs) = Z(SuperFlow) etc.

For guys using other dynos, please make sure what "Rear Wheel Power" is supposed to be according to each manufacturer.
DJ says RWP of what FUCHS & MAROLO entitles as ROLLER POWER and given the great difference the brands count the ponies, the numbers are not directly comparable.

 

[ghezzi]

Another factor which needs to be taken into consideration regarding "the stock 1200 Sport dyno'd approx 70hp at the rear wheel". I've noticed that more stringent emission regulations are applied in the USA, causing some bikes to have a big hole in the midrange, compared with the same models sold in other markets.

 

[Bisbonian]

While the numbers can't be trusted to be exactly accurate you can definitely see the big dip in the powerband. You have to look hard as the lines are dim.

This was on a completely stock bike with few miles on it.

 

[Mi_ka]

(Thanx Todd for the new thread.)

A NOTE TO ALL GUYS:
PLEASE TRY NOT TO MAKE THIS AN OILLESS OIL THREAD

It is not uncommon around here to have guys mocking each other for having 154 vs 149 hps for dyno runs on different dynos or even bikes and then filling the respective mechanic's head with complaints over what is a normal and expected 2-4% inaccuracy between different climate days runs (SAE/DIN etc climate correction formulas does not mean the bike's EFI responds flawlessly linearly over the entire climate spectrum).

 

[ohiorider]

Biz - this is more in line with what I would have expected to see, as your printout reflects a decrease of 13+% between factory dyno numbers at the crank, and RWHP dyno numbers. All academic, anyway .... I just found the topic interesting, and a 27% difference curious. Also forced me to look up how to calculate percent increase and percent decrease, which I'd totally forgotten.

Percent decrease 95 to 70 =(95-70)/95 = 26.3% decrease
Percent increase 70 to 95 = (95-70)/70 = 35.7% increase

Or as represented on your readout.
(95-82)/95, or a 13.6% decrease or difference in published vs RWHP on a dyno.

Bob

 

[Mi_ka]

I suppose you are referring to RWHP as being reported by Dynojet? (which is not the same across other brands).
Bisbonian's printout is for a DYNOMITE dynamometer and I do not know if its numbers compare to DJ (highly improbable).
Is this an inertial or brake dyno? (VERY important for the numbers you get vs bike's rotating inertia).

 

[ohiorider]

I suppose you are referring to RWHP as being reported by Dynojet? (which is not the same across other brands).
Bisbonian's printout is for a DYNOMITE dynamometer and I do not know if its numbers compare to DJ (highly improbable).
Is this an inertial or brake dyno? (VERY important for the numbers you get vs bike's rotating inertia).

Michail, I don't know the type of dyno Biz's shop used. One of these years (probably not in my lifetime) it would be nice if the speed shops, bike magazines, etc, etc, etc, would adopt what in the accounting profession is known as GAAP. What does it stand for? Generally Accepted Accounting Practices. Maybe we need GADP or Generally Accepted Dynamometer Practices. I do suspect that the dyno used with Biz's bike must be similar to those used by the motorcycle magazines, who typically report a 15% decrease in manufacturers' reported hp at the crankshaft vs hp at the rear wheel for shaft drive bikes.

Regards,

Bob (Ohiorider)

Note:

Regardless, I had a wonderful afternoon on Sunday and today, riding my (either) 70hp or 82hp Moto Guzzi 1200 Sport

 

[Mi_ka]

One of these years (probably not in my lifetime) it would be nice if the speed shops, bike magazines, etc, etc, etc, would adopt what in the accounting profession is known as GAAP.

Unfortunately some type of GAAP would only by applicable on brake dynos and again there would be (much smaller) differences among brand for various secondary reasons, not to mention the dyno manufacturers relactance to come and implement some type of standarisation agreements - no,no,no each one is the savior of the holy grail himself and no other exists!

With inertial dynos in particular, things are much more complicated than just adding a fixed percentage as "losses" (which also is also somewhat different even among same type transmissions).
With inertial dynos not only the dyno's drum rotational inertia (not mass) is different among dyno brands but, much more importantly, the different inertia of drum+bike rotational system makes acceleration different which makes the combustion conditions different so the same engine comes to produce different power on different brand inertial dynos.
This is what each manufacturer tries to "equalize" each one with his own set of correction parameters.
This equalization cannot be the same for different engine-transmission inertia bikes but how the heck can the manufacturer know what different inertia corrections to apply for each bike?
However elaborate the correction calculations are, there will always be differences in measurements unless you know exact data for the specific bike under test.

Then, and vastly importantly, braked power output may directly relate to top speed or other high load conditions but it is less related with acceleration behavior of engine systems under low load or sudden acceleration or sudden load condtions we often encounter in normal city/rural/mountain riding.
An engine with less hps as the Guzzi's or MT-01's may be vastly superior for canyon climbs than a higher hp 600's engine depending on road shape or the 600's output in in-city "traffic race" accelerate/deccelerate condtions may be much faster than a V2 same power bike while a V2 will do a better city dragster (if the V2 rider knows how to use his accumulated rotational inertia even if he has less hps, like here: http://www.youtube.com/watch?v=jXsoAdh5P5g#t=5m38s , ok weight distribution affects grip also :whistle: )

No dyno provides for some standard type of bike's system inertial measurement units in order to compare bikes on this important field. The only comparisons that can be made are for distance or speed/time it took to get there.

And of course, high power output under steady accleration or load conditions may show nice numbers but what about throttle variation conditions?
How can someone come with a standard acceptable and feasibly implemantable way (for the normal shops) to measure variying load and throtle conditions like this? : http://www.youtube.com/watch?v=clT_jCSnYQ8#t=55s

Regardless, I had a wonderful afternoon on Sunday and today, riding my (either) 70hp or 82hp Moto Guzzi 1200 Sport

Agree, best dyno is the butt-dyno. Wish I was in you shoes! B)

 

[davem]

Another factor which needs to be taken into consideration regarding "the stock 1200 Sport dyno'd approx 70hp at the rear wheel". I've noticed that more stringent emission regulations are applied in the USA, causing some bikes to have a big hole in the midrange, compared with the same models sold in other markets.

Same dip in the Euro models most noticeable in the torque curve between 3500 and 4500.
Dyna Pro shows 75hp and 60ft/lb for a 1200 2v Breva. Guzzi quote 65kw/90CV or to us 88bhp.
That to me is about a 15% drop off which seems about right.

 

[ohiorider]

I'm only beginning to understand the variations in dyno types, and that there's many different parameters that affect dyno hp and torque figures. Mi_ka, thanks for your patience. I'm beginning to understand that what is important is the hp and torque differences as measured before and after modifications, when done on the same dyno, under the same conditions. I understood there were differences between dynamometer brands and types, but am just now beginning to realize these differences could be major, right down to the algorithms used to calculate hp and torque.

Again, thanks to all who helped me with this topic.

Bob

 

[Mi_ka]

Always make sure the weather station is properly calibrated & you use the same SAE/DIN/ECE95.1 etc climate corrections or else you will not have comparable data between graphs.
The bike must be properly warmed up (not only coolant wise but also oil-wise, which takes riding under load),
the cooling fan airstream must not mess with airbox input not to alter barometric pressure measured by the EFI vs what the dyno reads on its weather station or push warm air from the engine to the airbox input, the fuel tank must not have become too warm hampering fuel performance, the tyre must be in good condition, properly inflated and of usual road type (not superglue slick or wood hardened by age), possible strap-downs used must be properly tightened or else wheel spin may chew power, cooling must be properly provided (strong fans may overcool the bike) and the check list goes on...
Maximum power is usually achieved between 3rd-5th attempt when everything has warmed up properly and power absorption by the tyre slows down and it provides better grip and the fuel has not become too warm.
Never trust a dyno or a lambda sensor blindly - a lot of though must be used assesing the data you measure or you may not have the results you expected to.

Mods may improve throttle responce/rideability without achieving more horsepower.
To measure this you must follow as precise as possible throttle opening at certain rpm/load conditions and look at different values like time needed to achieve certain velocity graphs.
Or you may notice same peaks but less "fat" valleys as the injection pressure pump goes south aging or the injectors eventually gather up muck over thousands of miles/kilometers etc.

Other mods like lighter wheels or flywheel may show zero difference on a brake dyno while they register horespower increase on an inertial dyno and the bike feels faster in the canyon/city but achieves the same maximum speed or mid to high speed acceleration. It is just a rotating inertia differnce providing snipper performance but less torquey feel on lower engine speeds or load increases.