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Discussion in 'Yamaha 250cc In-Line 4's' started by dave, Nov 27, 2005.
They're good numbers, 9.24 1/8 and 14.74 1/8. Are you planning to run 13T with 57T rear?
That muffler look's similar to mine, is there a front DB killer fitted to it still ?
I just put some rough data into a HP estimator and it come's up as making 29HP, with a 100kg rider
The 13T front sprocket will change you rev's over the line from about 14,600 rpm with the 14T front sprocket to around 15,700 rpm.
That might help your time/mph if you short shift the last couple of gear's so it keep's in the peak torque range longer and keep it nailed over the line as the HP start's to drop off.
Will be interesting to see your next time slip
I will run th 13/57. I found that changing gear around 17k in the higher gears gets me in the 14's. The flag marshal at the finish line said it sounds like an F1 car coming up the track. All the attempts to video it off the line have failed sound wise as louder bikes drown it out.
Exhaust is a straight through absorption, a rear baffle is provided but "it must have fallen off officer".
Yes, that's what I do too. As long as the revs don't drop out of the maximum power RPM range, you're fine. Where you running 15/57 or 14/57 on those runs?
The calculator would be useful if it didn't have adverts blocking all attempts to use it. The one Calc I could use shows my 998S producing 80bhp rather than the 120 at the rear wheel dyno'ed figure. In the past I used formulae to work out performance for my kitcar. Checking the formulae against publish figures for cars showed very little errors, but checking against bikes did not work.
All runs so far were using 15/57
That's a big jump in ratio. I'll be watching to see how you go. Wheelstands might be on the cards (more so).
I do a short burn out, then almost drop the clutch at about 17k. It does snake off the line but very quickly settles. Without the burnout I go sideways up the track for several yards. Not manage a wheelie yet thankfully. A methanol burning 500 Daytona engined Greeves Silverstone that I hill climbed many years ago pulled an 80mph wheelie that ended up with me have plates fitted to my ulna and radius. Hence I do not like wheelies.
You might need a different Tank like Hor Hey on his Ducati.. that way you can get more weight forward.. keep the front down
Enough kidding around.. so.. never having drag raced a bike before but I have very old experience in a heavy and powerful 55 Chev and more recently a VW Scirocco with 205kW at the front wheels. Now I guess the Scirocco is more akin to the bike in that I didnt want rear squat as that moved weight rearwards and hence lost traction at the front.
I would assume (not sure if it is correct or not) that a softer rear suspension would help the FZR hook up but would also take weight off the front.. not ideal.
Interested really as to how your bike is set up... suspension wise I guess.
For no other reason than I like all the technical stuff of going fast
You would just about want to strap the fork's down to limit the upward's suspension travel,
that way when it want's to pull the front up launching it the weight of the front wheel should help keep it down
Cant wait to give mine a run down the 1/4.
To combat wheelies my wife has developed the TOT technique.
First sign of front wheel lifting its TITS ON TANK
I should have said all runs have been on an unprepped tarmac runway. If I ran at Santa Pod with it's superglue surface I would slip the clutch and not do a burnout. Times are generally slower at the Pod as the stickyness holds the bike back.
Haven't touched the suspension. I sprint the 250 because it is a grinner(ie cannot stop smiling when you ride it) and I do not have to replace clutch plates every second event like the Ducatis.
I had a feeling it was unprepped when you said it "snakes around" on the launch. If you run at Santa Pod or any VHT prepped surface, try and line up outside of the traction window. Traction compound is sticky to the touch when it's laid down, but doesn't get "sticky" until heat has been put through it, so if you line up just outside the wheel tracks of all the cars, then you won't suffer from "track pull" friction. This (murky) run video shows what I mean.
Personally, I don't line up in between car burnout marks. I'm on a bike so any fluids anywhere can be fatal to my health.
The ideal launch, for me, is a squat and shoot i.e. the rear is nailed down because the clutch take is right on the "meat" and the front rear is wanting to get some air, but the forward momentum is negating that. I weigh 100kg (on a good day), so suspension travel is not a huge issue as it's already pretty compressed (no laughing). I do run my front end 25-50mm below normal height. Personally, trying to get a small capacity 4-stroke to run as hard as possible is much more challenging than jumping on a big bike and just using power to get good numbers.
@my67xr I might try and get over there for one of those bike meets and have some fun with the SA 2fiftycc crew.
I haven't run at the Pod since I got the big C, but when I did the Ducati was at least half a second slower. The Pod was dug up at the end of last year, new concrete laid, then rubbercoated and glued. the start area is very uniform and sticky from wall to wall.
I haven't been to Santa Pod for years. I recall it being very cold and a bit windy last time I was there. When do you run the 13T/57T combo?
The 13 only arrived yesterday, next meeting at Westonzoyland will be in October. Youtube has Westonzoyland vids if you search.