Tinkering with exhaust

acotrel said:

So numbers off a dyno are better than lap times off a race circuit ? Many dynamometers work off torque, and torque wins races. How reproducible are the torque readings off a dyno and how is it calibrated >?

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Dyno measures bike
Lap time measures rider

acotrel said:

So numbers off a dyno are better than lap times off a race circuit ? Many dynamometers work off torque, and torque wins races. How reproducible are the torque readings off a dyno and how is it calibrated >?

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Al, I can only assume you’ve jumped in half cocked after not actually reading this thread.

Some points that seem to have passed you by include:

1. No one mentioned race bikes, or thus lap times. The conversation, hitherto at least, was about road bikes.

2. The primary point being put forward by Glen is that he has an up hill road near him, and accurately measuring the speed attained up that hill is, he suggested, better than a dyno in terms of reliability and objectivity.

3. A second point made was that without some such objective measure, it is very easy to allow sound, feel, preconceptions, etc to make a rider think a bike is faster than it actually is.

4. I basically agree with these points. And can reflect on errors I have made myself whereby I have convinced myself of the gains to be had, before they’ve been had! And subsequently disappeared off down rabbit holes.

5. However, Glens hill not withstanding, he who argues against the benefits of using a dyno during race engine development, argues against every successful race team on this planet !! Development means making incrementally small gains. Each often unlikely to show itself in lap times. Any engine blueprinter knows that each and every thing that they do is largely unimportant on its own, but collectively they make a win or lose difference. It’s a fascinating combination of blind faith, and logical thinking, or if you prefer, between art and science ...

THe ONLY problem with a dyno, which we ran into occasionally is that a poorly designed or poorly set up air intake system can be affected by the air movement of the car on the track. I have seen noticeable HP losses due to that effect - like 30+ HP on car engines. That's why good airboxes are so important.

RE HP vs torque: the engine that makes the most power will win the race. If it has a narrower power band than the competing engine, it may need more shifting to keep it in the power band but assuming equally capable drivers, a 450 HP engine will always beat a 445HP engine in an identical vehicle regardless of how much 'torque' either engine produces.

Preparation H gives much more conclusive readings on the Butt-Dyno than any other petroleum gel, and also soothes any inflammation brought on by extensive testing with no known loss of flatulence.

jbruney said:

Preparation H gives much more conclusive readings on the Butt-Dyno than any other petroleum gel, and also soothes any inflammation brought on by extensive testing with no known loss of flatulence.

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Great, another oil additive I've gotta buy....

I guess the beauty of the dyno is that it gives results for the whole useful sweep of rpm.
The hill just gives results in a fairly narrow range, basically the midrange.
I can use a lower gear and higher rpm to add a bit of range, but have to be careful as the speed at top can be too great for safety.
And there are no bragging rights with Dyno hill!
Me- " I just race tuned my bike and it dynoed 113 kms/ hr on dyno hill!"
You - Whaaa? Who cares?

Glen

Does to me.… A bike screaming down, or up, the road is more exciting to me than a printout.

MexicoMike said:

THe ONLY problem with a dyno, which we ran into occasionally is that a poorly designed or poorly set up air intake system can be affected by the air movement of the car on the track. I have seen noticeable HP losses due to that effect - like 30+ HP on car engines. That's why good airboxes are so important.

RE HP vs torque: the engine that makes the most power will win the race. If it has a narrower power band than the competing engine, it may need more shifting to keep it in the power band but assuming equally capable drivers, a 450 HP engine will always beat a 445HP engine in an identical vehicle regardless of how much 'torque' either engine produces.

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It depends on how many bends there are in the road. A torquey motor will beat a top end motor every time on a tight circuit. The only time top end is better is on long straights. On most circuits there are both corners and straights. What you lose on one, you make up on the other. With a Commando, it is wise to stay away from power circuits. My 500cc short stroke Triton was extremely fast on a big circuit, but always too slow coming out of corners. If I dropped the overall gearing, I used to lose out at the ends of long straights. With the Seeley 850, it is very fast around corners but loses a bit towards the ends of the straights, even though the gearing is very high.
My friend has a 650cc Triton which is an absolute blur. It has always been tuned for torque. It will out-accelerate 750cc two-strokes and out-run them at the ends of the straights. I know because I did it.

With a top end motor, the level of anxiety is always greater when you are racing. So you often lose out to the guy who is doing it easier.