Torque curves

I read an article about the Dynotech inertia dynos which said in effect - that after they built the first dyno, they simply put a Yamaha Vmax on it and introduced a fiddle factor to make the dyno read the right number. Most power calibrations depend on a calibrated load cell and a dead weight tester

acotrel said:

If I put my bike on the dyno, does it matter what gear is engaged when measuring torque ?

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I believe that doing dyno pulls on an inertial dyno in higher gears is to avoid the greater drive losses in the lower gears. Top gear or near top gear are at (or near) lock up and that is where the least gear box losses are. Furthermore (and I speculate here), using a higher gear gives greater sampling duration (ie. takes more time to spin up the inertial mass).

Glen yes some do
My race motor was on avgas when I dynoed it, stinking hot day, just off the track after a race while the engine was hot
I currently run it on 98 pump gas, although need to dyno again soon to see what difference I am getting if any
Regards Mike

Inertial dynos are for bragging rights at motorcycle social events.

Hi Guys, I note there is quite a distain for any sort of dyno testing among some of the members, I hope I am wrong.
There are a great tuning tool, whether you get 1 HP or 100 HP, 2 ftlbs or 80 ftilbs, isnt it best to use all the tools available to get your motor running right.
They are also great for running in a new motor and or testing components like exhaust systems or carb set up and ignitions instead of riding off down the road seat of the pants style only to find its not right.

Just saying?
Regards Mike

That is why a lot of race teams now use onboard data telemetry recording as well, no point having loads of Hp if you only use it for 5% of the lap. The dyno is just an indication tool, and should be used in conjunction with other data. Then the bike can be set up for each track. A little hard for the Nortons though.

There is the other option which seems more fun, race down a strip against others and the clock for comparison.

MexicoMike said:

Inertial dynos are for bragging rights at motorcycle social events.

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That is the exact reason I bought a 100hp brake dyno. It is a piece of test equipment that more closely simulates real world use of a bike. An air cooled motorcycle needs to achieve thermal stability under use and then measured... As if doing a lap on the banking of daytona or taladaga or doing 75-80 mph nonstop on I 90, Boston to Seattle Washington. That can not happen in a few seconds on a inertia dyno. Inertia dyno might be OK for liquid cooled machinery that provide their own internal thermal stability...

Bragging rights?
Dyno shoot out, piece of paper with a read out...
win a road race=get a " piece of wood"(trophy)
Win a drag race, same as above.

street bike bragging rights-starts easy, runs with civilized manners in city driving, blast up the highway for a short or long haul...good fuel economy as expected. Plugs stay clean then repeats the next day, and again and again...

MexicoMike said:

Inertial dynos are for bragging rights at motorcycle social events.

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dynodave said:

That is the exact reason I bought a 100hp brake dyno. It is a piece of test equipment that more closely simulates real world use of a bike. An air cooled motorcycle needs to achieve thermal stability under use and then measured... As if doing a lap on the banking of daytona or taladaga or doing 75-80 mph nonstop on I 90, Boston to Seattle Washington. That can not happen in a few seconds on a inertia dyno. Inertia dyno might be OK for liquid cooled machinery that provide their own internal thermal stability...

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Let’s not put all inertia dynos in a box and say they are inferior to brake dynos, because in fact, many of them are fit with eddy current brakes that allow the technician the ability to precisely control vehicle RPM or speed at any throttle opening for any period of time. Thus steady state testing is routinely performed on inertia dynos.

WZ507 said:

Thus steady state testing is routinely performed on inertia dynos.

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Then by your own declared definition, it is NOT being used as an inertia dyno. apples and oranges

You are the only one that brought up inferior, They are different and obviously the physics of performin in different ways. I know both and what an inertia/brake hybrid is...

dynodave said:

Then by your own declared definition, it is NOT being used as an inertia dyno. apples and oranges

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Thank you Dave for the additional clarification of the modes in which an inertia dyno with braking may be used.

My comments were intended to clarify for the reader that some inertia dynos, specifically those fit with an eddy current brake, are useful for considerably more than performing a few rips to generate torque/HP curves, and regrettably that evidently did not come through clearly.

WZ507 said:

My comments were intended to clarify for the reader that some inertia dynos, specifically those fit with an eddy current brake, are useful for considerably more than performing a few rips to generate torque/HP curves, and regrettably that evidently did not come through clearly.

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The only thing I disagree with is your last point... your comments were perfectly clear to me the first time around !

Madnorton said:

There is the other option which seems more fun, race down a strip against others and the clock for comparison.

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Did that years ago on my first bike, my flat mate had a Yamaha TT and i had the XT. Drag race at the lights, even then we weren't completely stupid so swapped bikes a the next lights and had another go. Conclusive result, whichever bike my flatmate rode was the fastest.

I can see real value in dynos, if they give you a measure by which you can evaluate improvement, but torque and horsepower are two different things. With a commando engine, you have a fairly well defined rev limit, so going up in revs to get more horsepower is really not an option. That means improving torque at lower revs and raising gearing is the way to go. When you fit a race cam to a standard motor, two things usually happen. You get more torque right across the whole rev range, but a power band develops which has both a top and a bottom. The bottom of the power band of most race cams used in high revving bikes, is probably too high for a Commando engine. If it moves up, it reduces the usable rev range, because of the virtually fixed rev limit. So you end up with a bike which is difficult to improve by changing the gearing. If you raise the overall gearing to still have legs at the ends of the straights, you move the bottom of the rev range up, so the bike is more difficult to get around and out of corners fast. The more speed you have when coming out of corners, the faster you will be at the ends of the straights. The trick is to not get passed anywhere on the circuit, then you don't have to fight to regain your position in the field, you only work at moving forward..

acotrel said:

I can see real value in dynos, if they give you a measure by which you can evaluate improvement, but torque and horsepower are two different things. With a commando engine, you have a fairly well defined rev limit, so going up in revs to get more horsepower is really not an option. That means improving torque at lower revs and raising gearing is the way to go. When you fit a race cam to a standard motor, two things usually happen. You get more torque right across the whole rev range, .

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Not from my reading.
There is some torque lost down low and some gained up high with a race cam vs standard cam

worntorn said:

Not from my reading.
There is some torque lost down low and some gained up high with a race cam vs standard cam

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That’s probably the case most of the time Glen I agree.

But, the concept that tuning, per se, reduces low end torque for an increase in high rpm ho isn’t always the case.

Look at the 1200 Thruxton vs the 1200 T120 fo example.

Al's comment was that switching from a stock cam to a race cam adds torque across the rev range.
I don't think that's the case.
The Increased overlap found with a race cam throws away some compression. Boosting overall compression can make up for this, but the cam on its own does not " add power across the rev range" It actually robs some power from one area and adds to the other.

The Thruxton has more internal differences from the T120 than cam only. It has higher compression as well and there are fueling differences.

A great example of the effects of the two cam types is with the MK1 standard cam and MK2 or Lightning racing cam fitted to a Vincent Rapide or Shadow.
Irving designed the MK1 profile with touring in mind. It doesn't have a lot of overlap or lift and gives great pulling power to 4 k rpm while it is easy on the valve train.
Later on he designed the MK2 cam for use in the Black Lightning speed record bikes. He wasnt as concerned with valve train longevity or torque below 4 K with that one.
It has higher lift and more overlap.
Vincent owners love to fit the MK 2 into their roadbikes as a performance upgrade.
As Irving pointed out, this change effectively detunes the bikes for roaduse as they now make less power below 4 k and that is where the engines will run 99% of the time.

Glen

Well yes, a race cam should go hand in hand with raised CR. I think anyone putting a race cam into an otherwise stock engine, with no other mods, is gonna make it slower everywhere!

If you fit E3134 cams into a 1955 Triumph Thunderbird, you get a radically better performing bike. But if you do it to a 1958 model which has the ramp cams, the difference is not so great. The compression ratio makes no difference. A Thunderbird on 7 to 1 comp. will still go faster with the race cams. What you lose with the race cams is bottom end, but overall there is more torque from bottom to top. When you have race cams fitted, the way you ride the bike is usually different because you tend to ride the bike with the revs above the cam spot (the point at which it comes on song ). So if you do it to a road bike, you fall foul of the law. You need to try it, then you won't speculate about what happens.
A Commando engine is a completely different kettle of fish. You need pull from go to whoa, and whoa is at lower revs. A Triumph 650 engine will cop 8,000 revs - for a while. The race cams usually give a power band from 4 to 8, if you use the specified pipes.
With unit construction Triumphs the E3134 exhaust cam has a different number. I fitted one to a 1963 Bonneville which already has the E3134 inlet cam. The bike became much faster. Nothing else was changed.

If you fitted a similar cam into a Commando road bike, you would turn it into a piece of shit. Peak revs for most guys is 4000 rpm - you wound never be above the cam spot.

"You will need to try it, then you won't speculate about what happens"

We have tried it with the example given. Phil Irving also wrote about this.
I suppose if the standard cam was of an exceptionally poor design then some other cam could improve the entire rpm band.
That's not the case for the stock Commando cam though. Races were won with it, so maybe it is a racing cam?

Another interesting cam is the BSA Spitfire 357 as fitted to the later Super Rockets.
One of the members of the A7-A10 group did dyno tuning of 3 A10s, all with fully rebuilt but run in engines.
The hot 357 Spitfire cam combined with higher compression surpassed the lower compression engine with more sedate 356 ( Road Rocket & early Super Rocket) only above 5000 rpm. It did so quite convincingly.
Below 5000rpm, even with a bit lower compression, the 356 outpulled the 357.
5000 rpm is about where the vibration of the A10 gets so bad that you want to shift or slow down if in top Gear.
So really, the 357 Spitfire, that is considered by many as the most desirable profile, is a lower performance cam on the road in this instance.

That's one very good thing about the Commando-
When its tuned higher this generally raises the power band up the rev range. The rider can make use of the new found higher rpm power as the ISOs do their work.