Vulcan Engineering

[iain.hamlton]

Did anyone else notice the ignition timing in Sadlotus's PDF file? 18 deg BTDC static and 33 BTDC at high revs. The difference between static and maximum is not much different than standard at 15 deg as opposed to 14 deg. But the static is loads more. 18 as opposed to the normal 12 for a big valve.

I am surprised how little advance a standard weber-carbbed twincam uses

My questions to those who have used a dyno or rolling road:
Does more advance give more power for a standard bigvalve?
How do twincams run at idle and low revs with lots of static advance?

best regards, iain

[msd1107]

The question has come up about dyno (in)accuracy. It used to be that you could get accuracy?s of 2% full scale. On a 1000 hp dyno, that is 20 hp full scale, and more proportionally at lower readings. So putting a TC on an old 1000 hp dyno would not be very accurate.

However, new dynos offer considerably greater accuracy. I have seen claims of 0.01%, which translates to .1 hp on a 1000 hp dyno. It would be suitable even for a TC.

On an older dyno, you would take a torque reading, note the rpm and hopefully the temperature, barometric pressure and relative humidity to be able to produce a corrected reading chart.

Now, the process is automated. The only thing that is suspect is the calibration of the thermometer and barometric pressure. Even if the calibration is not spot on, the absolute reading would only be off a degree or so, not producing a great amount of error.

The comment by some dyno operators that disparage competitors seems to be sour grapes. Someone like QED could not exist by producing inaccurate runs.

As to the engine setup for testing. Was the stock intake system used? On a TC, that includes the air cleaner, intake tube, and air box. Rohan has found that you can get more hp by giving increased clearance to the back cylinders. Was the stock exhaust system used? Some dyno test cells exhaust into a partial vacuum, which could give an increase in hp. And the water temperature has an effect. If you use an 80 degC thermometer on the road, the engine will develop less hp than 40 degC water temperature in the test cell.

Also the test methodology has an effect. The Vulcan run had a sweep up the rpm curve, producing what is known as a ?flash? reading. This can be quite a bit higher than a stable reading achieved after 1 or 5 minutes continuous running at a rpm figure.

Finally, as to the specifics of Sean?s engine. The torque curve is indicative of a rather standard rate cam, not a high rate cam used in more modified engines. The peak torque rpm is a little higher than I would expect. But Sean?s engineer could have timed the cams to emphasize peak hp without having to use a modified cam. And Rohan?s comment about the importance of porting is important. It is not widely recognized what gas velocities are achieved at times in various areas of the inlet and exhaust track. So Sean?s engineer with good visualization skills and knowledge of gas flow dynamics could have made some hard to detect changes that produce more torque across the rpm range.

In conclusion, I would say Sean found a capable engineer who built him an entirely satisfactory engine. He is happy with it. And there are suitable explanations for the results achieved and documented. And I would say that any dyno operator that publishes their results on the web is probably quite confident about their accuracy and reproducability.

David
1968 36/7988