Is 2 inches of vacuum better than .5? I was thinking that a good ball park would be just off of full throttle in case there is a map over ride of the O2 sensor at full throttle, with rpms either side of the first torque peak of 6,000 rpm which is way too high for cruising but should be the best volumetric efficiency for high power pulsing. In the gear that gives pulses from 40mph to 60 at those rpms which will be 4th with the longer, 15 / 36 gearing that I will be running daily by then. Ideal ballast would be to add mass until I can just barely still accelerate up the big hill. But, I would need to get a few practice laps which it doesn't sound like would happen. I will have to find a local practice hill to check it out ahead of time. The other variable is the traffic. I would hate to carry ballast while touching the brakes regularly.
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Originally Posted by Old Mechanic
Adding weight is basically the same as making a bullet longer and heavier. It's called sectional density, more weight behind the same frontal area increases retained energy.
The bullet will retain a greater velocity at long ranges when it's sectional density is greater, even though it's initial velocity will be lower.
Either way you can rationally debate both scenarios. In the end it may actually be the configuration of the track and the elevations changes that determine your final decision. Longer glide periods that match the downhill portions of the track, while maintaining the required average speed may be your best bet.
Make the glide fit the track essentially, but I would still use some instrumentation to get the best data before you get on the track. Even a vacuum gauge so your acceleration is at the highest BSFC for the engine will help you P&G with consistency. Also you can mitigate the higher than desired engine power by simply using a higher gear for your pulse. 4th gear at 2 inches of vacuum will be better than 3rd at 5 inches, but you have to avoid too high a gear which will not be as efficient as the gear that gives best acceleration at the desired 90% load, with lowest RPM, on the engine.
regards
Mech
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