66HP at rear wheel
- Thread starter cbertozz
- Start date
G
Grant
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mauricejota7604
Hero member
- Location
- Victoria Australia
No pulling the clutch in on the closed throttle.
Dellortoman
Hero member
- Location
- Tasmania, Australia
Thanks for the link Lothar.
I understand what they are doing, but still believe it won't give an accurate measurement of transmission loss. Although it might be useful to compare different final drive chains.
You mention your discussions with 3 different operators of Dynojet machines, which makes sense because Dynojet machines are inertial dynamometers. You can't do the kind of slow down measurement you refer to on a brake dyno.
An inertial dyno, as the name implies, uses the inertia of the dyno to measure HP. Basically, the dyno's computer measures the acceleration rate of the dyno roller, then works out the force imposed on the roller by the tyre to produce that acceleration. Knowing that force, it can calculate torque, and the rotational speed gives the HP. It also works the other way exactly as you say - deceleration rate will give a measure of the resistance the dyno is feeling from the tyre and transmission. But without also knowing the inertia of the bike's rotating components, neither the acceleration nor the deceleration measurements will be accurate. If the dyno roller is heavy enough, the bike's rotating masses could be treated as insignificant in comparison, but it would have to be a heavy roller indeed. I looked up the specs of a Dynojet motorcycle dyno, and it weighs just over a ton. Maybe a good proportion of that weight is the roller.
Inertial dynos have their limitations. For instance, an inertia dyno can't measure steady state HP. Meaning that you can't hold an engine at a fixed speed and measure the HP. If the drum isn't accelerating or decelerating, it doesn't see any power being transmitted.
Most other dynos are the brake type, which apply a resistance (or brake) to the roller and use a load cell to measure the torque. A brake dyno measures HP directly, and doesn't need to know anything about the bike's rotating machinery. But in the case of a chassis dyno (as opposed to an engine dyno) it can only measure RWHP.
It's not possible to do an inertial slow-down test with a brake dynamometer. That only works with the inertial type. That's why there's no clutch pulling in most dyno vids, such as the one Carlo posted. Presumably Carlo's bloke has a brake dynamometer.
An inertial dyno is very simple. It's just a big roller and a speed measuring device. The speed sensor is connected to a computer that works out everything from the rate of change in drum speed.
A brake dyno is more complex because it has to have some kind of braking system on the roller. The 'brake' is usually a hydraulic turbine or an electro-magnetic brake. It has a load sensor on the brake as well as a speed sensor on the roller. It also has a computer to translate the input from both sensors info into HP.
I'm showing an engineering bias here, but it's my opinion that a brake dynamometer is a real dyno which gives real HP readings, whereas an inertial dyno is a cheap way of making a crappy substitute.
You'll find a lot of negative opinions on the internet about Dynojet. People talk about 'Dynojet HP' as distinct from 'real HP'.
I understand what they are doing, but still believe it won't give an accurate measurement of transmission loss. Although it might be useful to compare different final drive chains.
You mention your discussions with 3 different operators of Dynojet machines, which makes sense because Dynojet machines are inertial dynamometers. You can't do the kind of slow down measurement you refer to on a brake dyno.
An inertial dyno, as the name implies, uses the inertia of the dyno to measure HP. Basically, the dyno's computer measures the acceleration rate of the dyno roller, then works out the force imposed on the roller by the tyre to produce that acceleration. Knowing that force, it can calculate torque, and the rotational speed gives the HP. It also works the other way exactly as you say - deceleration rate will give a measure of the resistance the dyno is feeling from the tyre and transmission. But without also knowing the inertia of the bike's rotating components, neither the acceleration nor the deceleration measurements will be accurate. If the dyno roller is heavy enough, the bike's rotating masses could be treated as insignificant in comparison, but it would have to be a heavy roller indeed. I looked up the specs of a Dynojet motorcycle dyno, and it weighs just over a ton. Maybe a good proportion of that weight is the roller.
Inertial dynos have their limitations. For instance, an inertia dyno can't measure steady state HP. Meaning that you can't hold an engine at a fixed speed and measure the HP. If the drum isn't accelerating or decelerating, it doesn't see any power being transmitted.
Most other dynos are the brake type, which apply a resistance (or brake) to the roller and use a load cell to measure the torque. A brake dyno measures HP directly, and doesn't need to know anything about the bike's rotating machinery. But in the case of a chassis dyno (as opposed to an engine dyno) it can only measure RWHP.
It's not possible to do an inertial slow-down test with a brake dynamometer. That only works with the inertial type. That's why there's no clutch pulling in most dyno vids, such as the one Carlo posted. Presumably Carlo's bloke has a brake dynamometer.
An inertial dyno is very simple. It's just a big roller and a speed measuring device. The speed sensor is connected to a computer that works out everything from the rate of change in drum speed.
A brake dyno is more complex because it has to have some kind of braking system on the roller. The 'brake' is usually a hydraulic turbine or an electro-magnetic brake. It has a load sensor on the brake as well as a speed sensor on the roller. It also has a computer to translate the input from both sensors info into HP.
I'm showing an engineering bias here, but it's my opinion that a brake dynamometer is a real dyno which gives real HP readings, whereas an inertial dyno is a cheap way of making a crappy substitute.
You'll find a lot of negative opinions on the internet about Dynojet. People talk about 'Dynojet HP' as distinct from 'real HP'.
Laverdalothar
Hero member
- Location
- Germany
laverdas said:
yes, to close throttle once you have pulled the clutch... Or - to avoid different speed of clutch- and transmission side, keep the revs up at around 5.000, wich helps to increase the chance the push-rod does not completely weld together...
Laverdalothar
Hero member
- Location
- Germany
Dellortoman said:
Hi Cam,
that might well be, however, if you read the comments, most of them seem also to mix RWHP with Clutch power (f.e. there are a lot of comments, that Dynojet dynos show 15 - 16 % more power than brake type ones. Well - yes... that is the transmission loss correction in my eyes...). 8) These type of dynos are very common over here. I let Dynojet talk themselfes...:
http://imageftp.dynojet.com/CMD/Truth_Lies_Dyno%20Runs_Final.pdf
I can confirm that my 1000 SFC was measured on two different Dynojet innertia type dynos on two different days, 600km appart from each other with an altitude difference of 800 Meter, different temperature and humidity, different operators. The values were within 0,3HP and within 0,2 for each run we did and just 0,6HP away from what the factory claimed them to be.
accurate enough for me at least...
At the end, dynojet runs are good for 2 things: 1) measure if the bike runs clean under repeatable conditions and 2) to measure results of setup-changes or tuning. I also do not want to defend one or the other system, I just want to point out that there are different ways of measuring the power (clutch, RWHP, SAE etc. etc.) and they are not really all comparable. Many claim they have 70 or 80HP "at rear wheel" just because the bike was measured with the rear wheel turning a drum. No talks about correction values, dyno type etc. etc., which makes such a value useless, as you do not know what to compare it to. Just like in this case - 66HP sounds shockingly low at first. But then you need to know that there are losses in transmission and that the factory claimed power was crank or clutch power, not RWHP. this puts things in perspective; knowing that, 66HP could be a good value (on a A11 equiped 3C at least).
The value itself says nothing until you know what to compare it to. That was all I wanted to point out.
There is a German saying that might not translate well enough into english:"Wer nicht wei? was er mist, mist Mist!" (maybe best translated with: "who does not know what he measures, measures crap").
markQLD
Hero member
- Location
- QLD Australia
Factory standard Jota Series 2.Laverdalothar said:
After riding it south of the border 1,000 km down to the race festival at Eastern Creek, Sydney.
I told the bloke only to take it to 8,000 RPM and he suggested I get on and run it.
Miss J spun up the roller with 85 HP (bigthumb) A good girl :-*
And the next day, rode her back home again, and collected another speeding ticket. 8)
Ya Gotta Luv Ya Lav!
G
Grant
Guest
Comparing Carlo?s with Mark?s the biggest difference is that one tails off after 6000rpm and the other revs through and makes good power.
My money os on the pod air filters strangling it as it seems clean enough at lower air flow, just choking when Jotas should be getting into their stride.
My money os on the pod air filters strangling it as it seems clean enough at lower air flow, just choking when Jotas should be getting into their stride.
lavgert
Hero member
- Location
- Vienna, Austria
... air restriction is a bad thing for our old Breganze ladies
Ciao, Gert
Ciao, Gert
Laverdalothar
Hero member
- Location
- Germany
Mark, I recommend you do NOT read the "PDF in the link above, as it points to the faults with the Mustang Dynos and especially their operators... 8)
A factory Standard Series 2 Jota without any modifications will have a hard time producing 86HP... Factory never delivered with 4/C as a standard, it was always A11 or A12 from the factory. So - the normal factory value would be something like 80HP at almost 8.000RPM. But that would be clutch or engine power, not RWHP... But then it shows "Engine Power", so there must have been some kind of correction entered to get from a rear wheel measuring to engine power. Maybe they enter a percentage to get from RWHP to Engine power? Not sure how it is done on a Mustang dyno...
What is the handwritten Nm mean? it showed 55 on the paper and someone wrote 77 aside of it. Where should the extra 20Nm (which would be 40%...) come from? or is that factory values against measured values?
A factory Standard Series 2 Jota without any modifications will have a hard time producing 86HP... Factory never delivered with 4/C as a standard, it was always A11 or A12 from the factory. So - the normal factory value would be something like 80HP at almost 8.000RPM. But that would be clutch or engine power, not RWHP... But then it shows "Engine Power", so there must have been some kind of correction entered to get from a rear wheel measuring to engine power. Maybe they enter a percentage to get from RWHP to Engine power? Not sure how it is done on a Mustang dyno...
What is the handwritten Nm mean? it showed 55 on the paper and someone wrote 77 aside of it. Where should the extra 20Nm (which would be 40%...) come from? or is that factory values against measured values?
D
Davo
Guest
Laverdalothar said:
Really?
Laverdalothar said:
57 ft/lb converted to 77 n/m
markQLD
Hero member
- Location
- QLD Australia
ay Carlo, do us all a favour and pull the pharken meshes out of the velocity stacks and toss 'em. ffs :cbertozz said:
I reckon Grant and Gert know the score. Engines need to breathe. They gulp lots of air at high RPM.
And all the best with finding a bit more 'cheap' power. There's gotta be more lurking in there somewhere?
cheers, Mark
markQLD
Hero member
- Location
- QLD Australia
Try using brute force and ignorance.
That usually works for me.
That usually works for me.
Tippie
Hero member
- Location
- Dr?bak, Norway
And make sure the mains jetting is correct. If it was right with pods it?ll be too lean with open.
Back in my dynoing days bikes who replaced original setups with pods had to jet down. We told the owners that meant less power and efficiency but they just wanted those cool looking pods.
If an air filter system is more restrictive than without, get a better filter system.
Back in my dynoing days bikes who replaced original setups with pods had to jet down. We told the owners that meant less power and efficiency but they just wanted those cool looking pods.
If an air filter system is more restrictive than without, get a better filter system.
