Dyno balance

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Re: Dyno balance

Post by dp26 »

jlv wrote: Sat Feb 20, 2021 2:15 am I have heard that some factory bikes aren't very fast. Basically the advantage they have over stock bikes is they only have to last for an hour or two. So they probably let them rev a little more and run a little closer to the edge on compression ratios. It's not going to make 25% more power. When the difference is that big it's probably someone comparing crank HP to wheel HP.
Biggest difference comes on lighter weight of the engine, due to the materials they use in the engine, and the engine Brake is much smoother (less engine brake) adding rear grip and control on braking bumps and corner entry. Also a little more top end power.
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Re: Dyno balance

Post by jlv »

dp26 wrote: Sun Feb 21, 2021 3:17 pm Biggest difference comes on lighter weight of the engine, due to the materials they use in the engine, and the engine Brake is much smoother (less engine brake) adding rear grip and control on braking bumps and corner entry. Also a little more top end power.
Have you ridden factory bikes? Do you mean the lighter engine parts add power or just make the bike lighter? Weird that the engine braking is different. Is that because of something like a slipper clutch or is it a valve timing thing? You'd think that if they're running higher compression as you'd expect, there would be more engine braking.
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Re: Dyno balance

Post by dp26 »

jlv wrote: Mon Feb 22, 2021 2:19 am
dp26 wrote: Sun Feb 21, 2021 3:17 pm Biggest difference comes on lighter weight of the engine, due to the materials they use in the engine, and the engine Brake is much smoother (less engine brake) adding rear grip and control on braking bumps and corner entry. Also a little more top end power.
Have you ridden factory bikes? Do you mean the lighter engine parts add power or just make the bike lighter? Weird that the engine braking is different. Is that because of something like a slipper clutch or is it a valve timing thing? You'd think that if they're running higher compression as you'd expect, there would be more engine braking.
Yes i have ridden factory bikes. At the end the overall weight is lighter than a stock because all the components are lighter, like forks wheels etc. But for instance, honda,ktm and husqvarna factory crankcase are magnesium so the engine is a step lighter. It affects more the mass weight feel , rather than the power. So the bike stops and handle better and its more easy to control when bouncing arround.
For the power , yes there is higher compression, but engine brake is balanced out with re-mapping ecu and with the factory exhaust, both helping on less friction in the engine when throttle off. No slippery clutch. ( Stock engine brake is mapp for the average rider level, often unhappy when the bike is too free off throttle )
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Re: Dyno balance

Post by jlv »

dp26 wrote: Mon Feb 22, 2021 10:11 am Yes i have ridden factory bikes. At the end the overall weight is lighter than a stock because all the components are lighter, like forks wheels etc. But for instance, honda,ktm and husqvarna factory crankcase are magnesium so the engine is a step lighter. It affects more the mass weight feel , rather than the power. So the bike stops and handle better and its more easy to control when bouncing arround.
For the power , yes there is higher compression, but engine brake is balanced out with re-mapping ecu and with the factory exhaust, both helping on less friction in the engine when throttle off. No slippery clutch. ( Stock engine brake is mapp for the average rider level, often unhappy when the bike is too free off throttle )
Thanks for the insight! What's your estimate on the power compared to stock? If stock is 40 HP, there's no way factory is 55 HP on the same dyno, right?
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Re: Dyno balance

Post by Andy_Hack »

jlv wrote: Tue Feb 23, 2021 1:35 amThanks for the insight! What's your estimate on the power compared to stock? If stock is 40 HP, there's no way factory is 55 HP on the same dyno, right?
Here's a comparison between a stock 2017 250SX-F and the same bike equipped with the DCR Factory Engine Package.
Image
The increase is quite remarkable when you consider it's only camshafts, ECU, a pipe and everything set up correctly (although this dyno run seems as it was done at perfect conditions).
I don't want to go too deep and in this case i'll concentrate on MX2 GP bikes, but I wouldn't be surprised if they made even more than 55HP at the rear wheel. They usually shorten stroke and increase bore on japanese bikes, not sure about KTM, but I wouldn't be surprised if they did the same (KTM even runs as little as possible of oil in their engines).
Cosworth's KX250F engines peak at 16500rpm, have DLC coated internals (even their pistons are DLC coated).
Compression on a stock KTM 250SX-F is 14,4:1 and they run well over 18:1 on factory bikes, which is obviously a lot. Like Daniel said, everything is lighter, better materials, less tolerances, less vibrations, less power loss at the clutch, much less internal friction and therefore loss in power etc. ...they don't really have much in common with stock bikes.
If you look at the crème de la crème of naturally aspirated race engines like the 2006 spec F1 2,4L 90° V8s (300cc per cylinder), they're at 320HP/liter at ~20.000RPM and a max compression of only 13:1 (more compression isn't possible due to bore size and keeping a good combustion chamber shape + a narrow valve angle)
Now if you look at 160HP/liter in stock mx bikes, there's a huge gap to those 320HP/liter. Can you compare both? Yes and no, the F1 engine has a very narrow powerband and almost no torque, something you very much need in a motocross bike, especially with stock bikes for the average rider.
Pros however can deal with a narrower powerband, hence they increase intake diameters, RPMs etc. which results in more air flow and more ignitions per minute -> more peak HP. I don't want to go much deeper and i don't want to start with calculations, but 55HP is definitely no miracle these days for full factory bikes.

But that's what I meant when I said I'm afraid of such a big increase in power on 250Fs and what it would do to the game, the fact that even in real life 250Fs sometimes had faster lap times than 450s, shows that it's not just a problem we could face in Sim. Like you mentioned before, you could fix that by simply less traction, but in the end people will just increase it again. If you ask me, if you increase power, it shouldn't be by 15HP. I think such a big increase would hurt the game, but that's just my unimportant opinion.
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Re: Dyno balance

Post by Andy_Hack »

dp26 wrote: Sun Feb 21, 2021 3:17 pm Biggest difference comes on lighter weight of the engine, due to the materials they use in the engine, and the engine Brake is much smoother (less engine brake) adding rear grip and control on braking bumps and corner entry. Also a little more top end power.
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Re: Dyno balance

Post by jlv »

That DCR dyno is impressive, but it's not exactly an unbiased source coming from their own dyno. If you can do that with just a cam, ECU and pipe why aren't the stock bikes doing that?

Do they really run 18:1 in MXGP? I thought FIM fuel was 100 octane. Hard to believe you could do that on 100 octane.
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Re: Dyno balance

Post by Wilson156 »

jlv wrote: Wed Feb 24, 2021 1:49 am I thought FIM fuel was 100 octane. Hard to believe you could do that on 100 octane.
They probably aren't even running 100 octane. Higher octane helps detention but how people are building power with fuel is oxygenation.

Take a look at the tables from, vp. A highly used race fuel for motocross/supercross is pro 6 or pro 6 high temp. You can see they have a low octane but they're oxygenation makes up for it.
https://vpracingfuels.com/master-fuel-tables/
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Re: Dyno balance

Post by jlv »

Wilson156 wrote: Wed Feb 24, 2021 2:17 am
jlv wrote: Wed Feb 24, 2021 1:49 am Do they really run 18:1 in MXGP? I thought FIM fuel was 100 octane. Hard to believe you could do that on 100 octane.
They probably aren't even running 100 octane. Higher octane helps detention but how people are building power with fuel is oxygenation.

Take a look at the tables from, vp. A highly used race fuel for motocross/supercross is pro 6 or pro 6 high temp. You can see they have a low octane but they're oxygenation makes up for it.
https://vpracingfuels.com/master-fuel-tables/
I was referring to the 18:1 compression ratio. I don't think that'd work with only 100 octane.
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Re: Dyno balance

Post by dp26 »

jlv wrote: Tue Feb 23, 2021 1:35 am
dp26 wrote: Mon Feb 22, 2021 10:11 am Yes i have ridden factory bikes. At the end the overall weight is lighter than a stock because all the components are lighter, like forks wheels etc. But for instance, honda,ktm and husqvarna factory crankcase are magnesium so the engine is a step lighter. It affects more the mass weight feel , rather than the power. So the bike stops and handle better and its more easy to control when bouncing arround.
For the power , yes there is higher compression, but engine brake is balanced out with re-mapping ecu and with the factory exhaust, both helping on less friction in the engine when throttle off. No slippery clutch. ( Stock engine brake is mapp for the average rider level, often unhappy when the bike is too free off throttle )
Thanks for the insight! What's your estimate on the power compared to stock? If stock is 40 HP, there's no way factory is 55 HP on the same dyno, right?
Increase power from stock to factory on a 250f is between 3 an 6 HP depending on the brand.
If you are considering on making a factory 250f Dyno version, that has pretty much the step there is in reality I would suggest:
-3/4 HP more
-Just a very little Lighter bike (1.5 kg) or engine weight reduced ( 0.7 kg )
-less engine brake
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Re: Dyno balance

Post by ddmx »

jlv wrote: Sat Feb 13, 2021 1:34 am So basically factory versions of each bike where the power at each RPM is equal to the highest torque out of all the bikes at that RPM?

I.e. torque(rpm) = max(crtorque(rpm), kxtorque(rpm), rmtorque(rpm), sxtorque(rpm), yztorque(rpm))
Didn't bother reading any of the rest of the posts (sorry). I would take a similar approach.

This image is really old, however, I would create a scale factor to equalize all brands max HP/Torque. For this image, RM factor would be 43.7/39.5 = 1.1. At each RPM step, multiply RM HP by 1.1. You'd want to keep the powerband characteristics unique to the brand (I would think).
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This is a really interesting concept by the way, I like it.
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Re: Dyno balance

Post by Andy_Hack »

jlv wrote: Wed Feb 24, 2021 1:49 am That DCR dyno is impressive, but it's not exactly an unbiased source coming from their own dyno. If you can do that with just a cam, ECU and pipe why aren't the stock bikes doing that?

Do they really run 18:1 in MXGP? I thought FIM fuel was 100 octane. Hard to believe you could do that on 100 octane.
Yeah, that's why i said that dyno run was probably done at perfect conditions, but even then the gap is quite remarkable.
First of all we're talking about a stock engine, a stock engine is basically just a bunch of mass produced parts and although quality of mass produced parts is quite high these days, there's still a big difference to a proper race engine that has each and every part finely machined to match each other component. In a stock engine, you must consider every tolerance and therefore limit it's performance to a point where everything runs reliable enough. ECU mapping of a stock engine is also very conservative, because it has to be able to run at -30°C just like at 45°C, wet weather,dry weather(yes it has EFI, but a stock mx bike has a very basic EFI system so it still uses existing data independently from prevailing temperature and weather) ... fast rider or slow rider aswell as every part is unique and therefore behaves differently in a whole package. In fact each single engine is different and would need it's very own mapping to react to that. Since that's virtually impossible aswell as pretty much pointless in a production bike, they give it a map, that works good on everything. It's also worth mentioning that a stock mapping also has to be able to deal with different pipes, modifications to the intake system (yes even an air filter changes that) and mechanical wear, aswell as different oils.
It still amazes me that even the smallest changes often have a huge impact.
How do I know? I have a degree in technical engineering and i literally work in that industry, just like my whole family.

The performance gain by a camshaft is usually limited by something called "valve float". If the cam lobe profile is too aggressive/sharp or the engine revs too high, valves begin to "float", meaning they're not controlled correctly anymore and aren't dampened when they hit the valve seats. To compensate that it's important to find a good mix between lift and lobe profile, but since that's already a given factor these days, people use harder valve springs which have a quicker reaction time. It's often said that stiffer valve springs result in larger mechanical losses, but that's not always true. The engine needs more power to compress those springs, but once the valves close, the springs expand and actually somewhat help to drive the camshafts. So it evens that out a little bit. More aggressive camshafts also mean your bike will be more prone to damage through heat when idling due to "sharper" valve timing, that's why you always have to rev race engines i.o. to get more fresh air in and cool it down. A stock bike can be bought by everyone, no matter what knowledge they have so it has to withstand idling for much longer hence it's not that big of a deal on a stocker (althought I still wouldn't recommend it to run longer than 5 minutes idling).

However, those engine speeds, more aggressive cams and engine mapping has it's price, DCR and many other tuners say you can run stock springs and that their tuning doesn't take a toll on longevity and reliability, but more boom means more stress and more stress simply decreases durability.

The manufacturers usually only add power, if they were able to get more durability out of their parts, be it because of better materials or better design, in KTM's case, that's achieved by getting lots of parts produced by an industry leader like Pankl to smaller tolerances.

I don't know exactly what ratio which brand and team runs, but like I said compression usually decreases with bore diameter and the need for a reasonable combustion chamber shape. The FIM mandated limit of fuel is 102 octane(RON), which actually allows a very high compression ratio without knocking. A higher octane number is the most meaningful sign for more knock resistance, but i'd not fully rely on it either, since there are a few more significant factors aswell (combustion chamber shape, spark plug and it's position, piston crown shape, temperature ...)
All in all modern fuel and engine design is so good, that you can achieve quite high compression ratios with rather ordinary fuel.

Nevertheless, I wouldn't take those power gains too serious, peak HP is one thing, but usuable power for the average Joe a whole different story. There are GP 125 2 stroke engines which peak at 53HP @ 12500RPM, but it would be nearly impossible to ride it on an MX track. That said, realistic or not, 55HP 250Fs in this game wouldn't be a good idea in my opinion. I'd support what ddmx said.
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Re: Dyno balance

Post by jlv »

dp26 wrote: Wed Feb 24, 2021 8:07 pm Increase power from stock to factory on a 250f is between 3 an 6 HP depending on the brand.
If you are considering on making a factory 250f Dyno version, that has pretty much the step there is in reality I would suggest:
-3/4 HP more
-Just a very little Lighter bike (1.5 kg) or engine weight reduced ( 0.7 kg )
-less engine brake
Yes, that's close to what I'd have expected. Thanks again.

If I do the factory versions, it'll be more of a spec racing thing than an attempt to accurately model a factory bike. Lighter might be a good idea but the most important thing is everyone agrees it's a fair platform that improves the racing. So if anyone else has an opinion on this idea speak up!
ddmx wrote: Wed Feb 24, 2021 8:10 pm Didn't bother reading any of the rest of the posts (sorry). I would take a similar approach.

This image is really old, however, I would create a scale factor to equalize all brands max HP/Torque. For this image, RM factor would be 43.7/39.5 = 1.1. At each RPM step, multiply RM HP by 1.1. You'd want to keep the powerband characteristics unique to the brand (I would think).
Image

This is a really interesting concept by the way, I like it.
That would give an unfair advantage to the slower torquier bikes. If you scale the KX up to the same peak as the SX, it would hold the peak power from 10-13.5k. You'd have to account for area under the curve somehow.
Andy_Hack wrote: Thu Feb 25, 2021 12:33 am I don't know exactly what ratio which brand and team runs, but like I said compression usually decreases with bore diameter and the need for a reasonable combustion chamber shape. The FIM mandated limit of fuel is 102 octane(RON), which actually allows a very high compression ratio without knocking. A higher octane number is the most meaningful sign for more knock resistance, but i'd not fully rely on it either, since there are a few more significant factors aswell (combustion chamber shape, spark plug and it's position, piston crown shape, temperature ...)
All in all modern fuel and engine design is so good, that you can achieve quite high compression ratios with rather ordinary fuel.
OK. 18:1 sounded more like something you'd run with 110 octane to me. I didn't think 102 was that high. I get that you could probably back off the squish band to control knocking but that's going to have some trade offs.
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Re: Dyno balance

Post by Timo Van Dyk »

I like the idea of a factory dyno, but what about being able to change the max rpm? This would be cool to tweak it on every track. Like more rpm has a disadvantage on some tracks while less rpm can be usefull on a different track ( im not trying to go in depth, i think this would be a cool feature too mess around with. Just something new for us to learn)

Or make the rpms of the factory dynos higher then the " stock " dynos.

I really like the " factory " dyno idea. This would make the game more interesting.
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Re: Dyno balance

Post by Quinten »

I'm not sure what the idea of adding a "factory dyno" is going to do. Everyone is just going to run that dyno over the stock dynos because it's lighter, more hp, etc. What's going to make this idea any different from any other dyno update in the past?

Adding "factory dynos" is going to turn stock dynos obsolete, just saying. I do think the 250 needs substantial fixes but not sure adding a 250 factory dyno is the fix to the problem.
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