Pulse and Glide for competition. Added mass?

[sendler]

Originally Posted by FXSTi

Not to be a naysayer, but are you sure want to add the ballast to the back end? I thought the idea was to put the weight up front like an arrow.

Kirk

Full sit up motorcycle tail section add ons get so high that they get blown around in cross winds quite badly so these guys talk about adding ballast to the nose to make the system into a dart but I have never read any reports as to whether this really helps anything or not. I would think not. Unless they could get the weight up behind the headlight. The Honda CBR250R has a really excellent self correcting mechanism whereby the side winds force the trail in the front geometry to countersteer and set up an opposing lean. Right back into the wind! (Thanks for the excellent explanation Ken Fry!) It is really an amazing feeling. As if the bike had some sort of active crosswind compensation. The feeling is intensified while riding in a tuck with my chest on the tank as I always do at highway speed because the body weight and stiffness is removed from the handlebars so the steering is free to respond as it can. And, the mass of the bike and rider is centered with a lower polar distribution right on the cg of the longitudinal roll axis. This makes it feel as if side winds blow only on the bottom of the bike. The wheels go back and forth as if by magic to correct for the wind while the nose of the bike, anchored by the concentrated mass, stays straight on line. Adding 100 pounds on the seat, right behind my hips will only lock that roll axis in even tighter while taming little instantaneous gusts with it's increased soak.

[user removed]

Originally Posted by sendler

I guess if I want to get really serious I should hook up an MPGuino for practice.

I 100% agree, plus I think you are serious and dedicated to the objective. Hope you win big time.

regards
Mech

[sendler]

Originally Posted by Diesel_Dave

I guess I don't see how the extra weight is going to help. It's definitely going to increase the rolling resistance, and I don't see how it'll improve the P&G efficiency. Sure you can glide longer, but it'll take more energy to accelerate the additional mass. More energy out only because of more energy in.

You can still P&G going down a hill, just accelerate faster so the %load stays roughly the same.

The concept of adding mass to a competition vehicle is hard wrap your head around as a car driver but motorcycles have such a high power to weight ratio (even my 250) that to get even close to 80% throttle where peak ICE efficiency lies, the bike will be trying to rocket right out from under you up to a speed that is much higher than any average that you really want. Adding ballast would tame the violent swings of speed. This is why I would rather have a CBR125R for hypermiling to work on and for competition. It's peak efficiency power of 6-8 hp is closer to the demand that is needed for 50-65mph cruising. Less pulse and glide needed. The CBR250R is good at hypermiling but is also powerful enough to have passing power for out of town/ cross country trips.

[Diesel_Dave]

Originally Posted by sendler

The concept of adding mass to a competition vehicle is hard wrap your head around as a car driver but motorcycles have such a high power to weight ratio (even my 250) that to get even close to 80% throttle where peak ICE efficiency lies, the bike will be trying to rocket right out from under you up to a speed that is much higher than any average that you really want. Adding ballast would tame the violent swings of speed. This is why I would rather have a CBR125R for hypermiling to work on and for competition. It's peak efficiency power of 6-8 hp is closer to the demand that is needed for 50-65mph cruising. Less pulse and glide needed. The CBR250R is good at hypermiling but is also powerful enough to have passing power for out of town/ cross country trips.

Okay, gotcha. That makes sense.

[user removed]

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

[sendler]

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.
.

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

[user removed]

Difficult to determine on your 250 but it seems like 90% load is best. Here is a thread by Sentra with a lot of good data that may be relevant, but I would do my own testing to determine which is the best. 90% load should work out to 10% of atmospheric vacuum reading or about 2-3 inches.

http://ecomodder.com/forum/showthrea...oad-19594.html

Of course they are completely different vehicles-engines but I think you may find the best acceleration is more a function of load that anything else, as long as you are in the right gear, neither too low or high.

regards
Mech

[sendler]

I did happen to read through that thread. I believe he tested three loads of around 70, 80, and 90% and found 90% to be the best. But I still wonder if 95% would have beaten 90%. Basically, manifold vacuum is wasted power. I wouldn't be surprised if 100% load had the best volumetric efficiency as long as the O2 sensor was allowed to stay in closed loop. Which they are sometimes not due to fear that the lean end of the sweeps will take the mixture lean enough to burn something at such high load. I might be able to borrow the Honda scan tool to find out what throttle angle if any takes the the O2 sensor out of closed loop. The service manager at Honda is a long time gear head and enjoys talking about my edgy ideas. He builds brand new Gold Wings into trikes several a year.
.

Originally Posted by Old Mechanic

Difficult to determine on your 250 but it seems like 90% load is best. Here is a thread by Sentra with a lot of good data that may be relevant, but I would do my own testing to determine which is the best. 90% load should work out to 10% of atmospheric vacuum reading or about 2-3 inches.

http://ecomodder.com/forum/showthrea...oad-19594.html

Of course they are completely different vehicles-engines but I think you may find the best acceleration is more a function of load that anything else, as long as you are in the right gear, neither too low or high.

regards
Mech

[sendler]

So he did try 95% and 90 was better as is also shown on this BSFC map of a Saturn 1.9. I will try to pulse at 90%, either side of 6,000.

[euromodder]

check the competition rules.
they might include max. speeds at certain points of the track - IIRC they did last year.
that might well negate the extra speed over distance while coasting due to more weight.

while you can coast longer, it'll also take more fuel to get up to speed de to higher weight.