Let's Go Racing

[Wolfe_11B]

And that would explain the weight- my google digging shows that the yx600 swingarm is steel.... I think the guy sees a box section and just assumed alloy.

Maybe a DR500 will work.... Only one I see for sale is quite expensive. Would be better off with the brand new Motolana

 

[Wolfe_11B]

Got the bike weighed yesterday at an Ohio BMV certified scale, the weather has been nice the whole weekend until today so I'm glad I got it there when I did.

Total weight in street trim, wet, with full tank, full oil- 347lbs

Pretty impressive when compared to stock weight, but I'd still like to get a little lower before I get to the track. Just for reference, Yamaha gives their listed weights as 'net' weight. This is the weight of the bike as crated when shipped to the US, minus the 'tare' weight, which is the weight of the crate. So this would be with no engine oil, no fuel, and (possibly?) no fork oil. Yamaha lists the net weight of the 81 XS400 SH (what I started with) as 375lbs. Add ~22lbs of gasoline on a full stock tank, and ~3lbs for oil, that's 400lbs wet on a stock bike.

So I dropped 53lbs of weight!

I'll be interested to see what I get when I pull the headlight, starter, front disc/caliper, and kickstand.

 

[xschris]

Running only a gallon or less of gas will save a lot of weight. For you I would look into a small aluminum gas cell. Losing all the e-start stuff and putting in a 1lb small battery will be big. I think well under 300 is very doable.

 

[rshutchinson]

I'll have to go to a good scale but when I put my bike up on scales at home here I got ~330 lbs. Drum brakes and a smaller gas tank though.


Don't eat or drink for 2 weeks prior to the races. That's got to be worth about 10 pounds at least

 

[Wolfe_11B]

Running only a gallon or less of gas will save a lot of weight. For you I would look into a small aluminum gas cell. Losing all the e-start stuff and putting in a 1lb small battery will be big. I think well under 300 is very doable.

I'm really curious on running a smaller tank. We had a discussion on the land speed forums about it, and some engineers cautioned that a tiny tank will affect flow at WOT. They say that the weight of the fuel helps push through the petcock, lines, and float valve. They couldn't give specifics of course, but said the only way to get accurate numbers is to test out both a normal tank and a smaller tank with the carbs, and measure the flow rate over time passed. Seems like a whole lot of work for nothing, but they do bring up good points and I would be interested to see results.

I switched to a lithium battery a while back, weighs 1.2 lbs

 

[Wolfe_11B]

Don't eat or drink for 2 weeks prior to the races. That's got to be worth about 10 pounds at least

I'm 6ft, 150 lbs, so no more weight loss for me. Small breakfast and maybe a few minutes on the can before hand though

 

[xschris]

I'm really curious on running a smaller tank. We had a discussion on the land speed forums about it, and some engineers cautioned that a tiny tank will affect flow at WOT. They say that the weight of the fuel helps push through the petcock, lines, and float valve. They couldn't give specifics of course, but said the only way to get accurate numbers is to test out both a normal tank and a smaller tank with the carbs, and measure the flow rate over time passed. Seems like a whole lot of work for nothing, but they do bring up good points and I would be interested to see results.

I switched to a lithium battery a while back, weighs 1.2 lbs

If that was so as to need more fuel to feed the carbs at wot. A large displacement bike would need like 20 gallons of gas to keep flow rates up. Saving 20lbs of weight will out weigh any benifits of .002lbs of extra pressure more gas would cause. If you have a good flow petcock and a well vented tank you would be fine. I don't think at wot for a mile would use more than a pint or so of gas anyway with these bikes. One day I forgot to turn the petcock back on in my 80 and was able to go for more than a mile before it started to cut out.

 

[Wolfe_11B]

Some of those guys even run positive pressure into the tank to help force the fuel out!

I can have the dyno man setup a scenario for a mile course at WOT, and we see what happens when the tank is full compared to nearly empty. If the float valve can't keep up, it will be pretty evident on the AFR.

 

[16VGTIDave]

Some points to consider:

- The volume of fuel in the tank will create a "head pressure". The less fuel in the tank, the lower the pressure at the needle seats.
- Pressure is only required to get the fuel past any restrictions before the needle seats. i.e. filter, petcock, kink in fuel line.
- The Main Jets should be the limiting factor for fuel flow. As long as the fuel delivery system is able to flow more than the main jets, you will be fine.
- Pressurizing the tank is neat, but unless you have some way of maintaining the pressure as the fuel is consumed, it won't help. The end of the run is where you need the most fuel delivery as the engine is at it's hottest and under the greatest load.
- aerodynamics are the biggest challenge with anything involving speed. Spend more time, money and effort on reducing drag and less on trying to make power. Power requirements increase exponentially with speed due to drag. Decrease drag!
- Forget about weight. Once the weight has been accelerated to speed, no further power is required to keep it at that speed. You aren't running an acceleration test (1/4mi drag race), you are running a speed trial. The goal is to be the fastest, not get there the quickest.

Thats all I got for now.

 

[xschris]

With only a mile to get to full speed every little bit helps. If he had 3-4 miles to do it that would be a different story.

 

[rshutchinson]

I believe he said he'll be at top speed by half a mile.

 

[drewpy]

I'm really curious on running a smaller tank. We had a discussion on the land speed forums about it, and some engineers cautioned that a tiny tank will affect flow at WOT. They say that the weight of the fuel helps push through the petcock, lines, and float valve. They couldn't give specifics of course, but said the only way to get accurate numbers is to test out both a normal tank and a smaller tank with the carbs, and measure the flow rate over time passed. Seems like a whole lot of work for nothing, but they do bring up good points and I would be interested to see results.

I switched to a lithium battery a while back, weighs 1.2 lbs

why not pressurise the tank with air first, just putting it out there. just seen your other post damn you computer

 

[Wolfe_11B]

Yep I should add that most of the guys on the landspeed forums are racing Bonneville so they give advice based on around 4 miles at WOT most of the time.

I 'should' be at top speed by the half mile. But, there is rpm and HP to spare. It's just a matter of utilizing it. So weight and aero are the 2 variables I can control at this point. Weight is cheap'er'. Anything aerodynamic at this point is going to be expensive unless I make parts myself. I can add a landspeed style front fender, but they are not cheap and require mounting points that I would have to weld on to the fork lowers. I'm not too hip on adding those, but it may come to that point. I was contemplating adding small fairings to direct airflow over my hands on the controls, but this is still a street bike somewhat and will look utterly ridiculous with them added on and riding around town. I could get another fairing and strictly use it for landspeed and it could look as crazy as I want, but it brings me back to the $$$ equation...

At this point the bike is fine as it is, I'm just trying to get peoples brains turning here, and maybe come up with some ideas that can be put to use

 

[Wolfe_11B]

Chainguard I made out of scrap 1/8" angle aluminum I had laying around. Got a little saucy at the swingarm brace. Might have been all for nothing, since I may be going with an unbraced swingarm. In that case I'll just build another, I have more laying around.

 

[Wolfe_11B]

Took the bike out for some more testing today. Couldn't pass up the 60 deg F weather!

Need to go a few sized bigger on the mains, I'm sitting at 17.1 at WOT on the AFR, and that's with my power jet dumping fuel.

Took the bike up to its top speed. The calculators have lied to me on the sprocket sizes. As it sits now, I hit 85mph in 6th gear, at 9200k rpm! Impressive that I can get to that point at 3/4 throttle though

Obligatory Starbuck's break-

 

[Wolfe_11B]

Ok so this gearing issue is frying my brain. I've entered in the bikes values into 10 different calculators, and they all give me the same result. I've gone out and measured my tire a few times to verify the data I'm inputting for that is correct. I've tried 3 different tachs hooked up 3 different ways to ensure that the readings I'm getting are correct(they all read the same). I can confirm I am in 6th gear. My speedo is gps, and confirmed it is reading correct using a second gps unit. So at 9200rpm, I should be at ~115mph. Where the hell is the 85mph coming from?

Clutch slipping in a weird way? Am I driving through a space time vortex? I'm at a loss here. I can't blame the numbers given in the manual, they are correct for the gear ratios, I know because I've counted the teeth. I'm thoroughly stumped.

 

[xschris]

What size sprockets are you running? I know on at least three of my bikes at 85mph I am turning around 7.5-8k rpm. That's with a 16-37 sprocket and a 110/90-18 rear wheel and 17-37 sprocket and a 120/90-16 rear wheel. You should be well over 100mph at 9200 rpm's.

 

[Wolfe_11B]

17/37, 25.6 tire diameter

 

[xschris]

See next post.

 

[xschris]

Have you counted the front one again? In a pic from your build thread you posted a pic of the sprockets you will be using and the front one was a 14 tooth.