Hello all,

If you had to draw a line on the track where would it be when the clutch is FULLY let out?

My understanding is when leaving the line one hi revs the motor and slips the clutch to "slowly" apply power to make a smooth launch.

I have been holding rpms at 2000-2300 rpms and not dumping the clutch but letting it out very quickly then whacking the throttle open.

I have a "2 step" but have not used it yet because the low limit is 4000rpms. It is full adjustable from 4000 to the rev limiter.

Get wheelie bars, put about 4-5# of air in rear tire, heat tire, stage and hold the revs at around 5500 depending on track condition, dump clutch to launch as you peg the throttle. Rear tire should break loose just a bit as you ride the wheelie bar till you need to shift.
If you do that good, you should get 60 ft times around 1.6 sec. I used to do it very good and had 60 ft down into the 1.5 sec. range.
Ted

I'd say you should be at WOT within a few feet after launching and the clutch fully engage before the 60ft beam. 2K is too low, get the rpms up around 4K. If you strap the front end down you can launch at a higher rpm. Get aggressive with the throttle and you'll see a differance.

No, I will not run wheelie bars. This is a daily street bike and just want to run some ET races. I am just trying to go as fast and consistent as
the bike can with out changing the street ability. I will be lowering the forks in the trees around an inch. That should help the 60 ft times
along with possibly strapping it down more.

My quickest run at an "ET" 1/8 mile sportsman(.500) tree was
0.6688 reaction
1.8791--60 ft
5.0284--330 ft
7.2002--ET @ 594 ft
7.6891--1/8 ET
92.05---1/8 MPH.

I am using 1st to launch, shift 2 times and running 3rd thru the traps on the Rev limiter ( 3 hits at the limiter.) I will need to adjust that (gearing)

I launch at 6250 rpm with wheelie bars. Takes me 3 min to take them off and I'm on the street for a joy ride. The clutch is slipped for just a few feet to maintain traction. I will try to post a video.

http://s95.photobucket.com/albums/l125/ninjaboy311/?action=view&current=CajunShootout8-11-07010.flv

1st or 2nd gear launch?

burnout in 2nd, launch in 1st

Even with a street setup, drop your tyre pressures, makes a big difference to traction. I dropped mine to 25psi initially, still spun, so dropped to 20psi, no spinning now. Run this over a 1/4 with no rotation on the rim. Easy to pump up afterwards. Not as much grunt as you have, but I can launch on the limiter with a little clutch slip - gotta work on that myself. BTW, I run Metzeler ME 880's - not sticky at all.

Horace18, What are your 60 ft and 1/8 mile times?
What size is the Metz?

hi,
i run metz ractec ,tire p.s.i @14 and launch @4500rpm sliping the clutch,
you want the front to come up about 4" or so and carry 10/20 feet or so

60' 1.70 et 11.45 @115mph 1/4mile 5gears ,i need to change gearing up
thie is differant from tire to tire and bike combo (no bar)tire is important and the softer the better ,and must heat the tire up good
and i ride to track ,at track and back home

Mine is stock internally and geared way too tall. My best 60' times are 1.9 and 1/8 mile (660' ? - metric here) is in the 8's. I can nearly run the quarter in only 3 gears, so heaps of room to work on this.

My point is that you'll improve your 60' times by dropping your tyre pressures quite easily, without dire consequences. Unless you lift the front too far :D

I'm running a standard 150mm Metzeler

You don't want to lower it to much or it will effect your mph, i run mine about 28-30 and do a good 2nd gear burn out, my 60 ft times are in the low 1.6 .Unless you are spinning the tire you don't want to lower your tire pressure.

Here's my plan from what is stated here:

---Burn out in 2nd gear ( I was doing 1st gear, short duration )
---launch (1st gear) @ higher rpm, slipping clutch longer ( I was @ 2200-2300 rpm launching )
---lower tire pressure only enough to control spin.
---Lower forks in tree ( i have room for up to 2 inches )
---Strap front down ( amount to be determined )


What have I overlooked ?





great info here, Thanks

This is going to be a tad different as I don't race vtwins yet, but I have officially sold all my Jap bikes and parts and will be moving into vtwins but anyway... I held rpms right at 10k, when I launched I'd let the clutch out just enough to move the bike, then twist the throttle the rest of the way. Just as the clutch was all the way out it was time to grab 2nd. I always tried to make it so you could never hear an rpm change through first gear.. from launch to shift. Course the bike I was running was torqueless and relied upon rpms so theres a difference.
But no matter the bike or the engine you don't want to give it enough clutch to bog, never bog, bogging slows et's dramatically.
Not a big fan of strapped front ends either.

As far as rear tire pressure heres the trick... leave it alone and get consistant passes under your belt. Once you can do consistant passes with matching et's and trap speeds lower your rear tire pressure 2 pounds and start making passes, make a few at this pressure then drop 2 more pounds. Keep dropping 2 pounds at a time until you start to lose trap speed, then up it one pound and thats where you run your rear tire pressure at on the track. You don't need wheelie bars as you don't have enough engine yet to be on them without bogging the bike.

I ran a ZX12R with the Muzzy 1361 stroker kit and a good bit of engine mods on a bone stock bike that was lowered 3 inches in the front and had a 6 inch extended swing arm for a LONG time before I built a chassis and added more power. That original setup was good for 210 horse 116 foot lbs @ 11,200 rpm. Made consistant passes with 1.5 60 foots, 3.9 330's, 5.9 1/8's, and 8.8 1/4's @ 165ish mph.

~Terry

Okay, I tried upping my tyre pressures last Saturday night. Ran them at 28 instead of 22psi. After I did a good 2nd gear burnout (only got confident enough to do this in recent months), had no problems with traction at all. TS didn't go up much, maybe 1 or 2 mph, but times were more consistent.

My bike is mostly stock though, so more powerful bikes might respond differently.

Mikel, your times are very simlar to mine (time slip posted in this forum "1/4 mile ET ...) I'm Launching around 4800 RPM and slipping out there a ways just trying to balance wheel spin and wheelie. My 60' is barely faster, but you've already got me by the 1/8, you must be running pretty strong, what gearing are you running?

stock 06 883 gearing with 1 change... a 38 tooth engine sprocket.
38 t engine... 57t clutch (stock)... 28t trany(stock)... 68t wheel(stock)

I asked a question about gearing and got no answers... so I will ask again here:

I am toping out at the trap(1/8 mile) 6500 rpm limiter, 92mph in 3rd gear.

Should I regear to shift one more time, use 4 gears, to possibly accelerate quicker to gain more ground speed, OR just add 1 tooth trany, remove
a couple wheel teeth to give a plus 1-2 mph through the trap.

If I gear down to use 4 gears, It may be harder to control the wheelie, AND the extra shift may offset any gain in quickness

I'm also curious about gearing. 1st to 2nd is a bit if a jump, I think mine drops 1500 rpm from 6,000 in 1st to 4,500 in 2nd. The other shifts show a drop of 1,000 rpm only.

How short can you make your final drive ratio before 1st is useless? I want to put the US 883 gearing from both the primary and belt drives on mine to get a 4:1 overall ratio (currently 3.4:1). I'm still foot shifting with forward controls and plan to keep it this way as it is my daily rider, but I used to struggle to get my foot forward before I hit the rev limiter. I'm getting better now, but when I shorten the gearing this will become an issue again I suspect.

Mikel, I'm curious about why you upped the gearing in the primary from the 34 to the 38 tooth. Did you do any runs before you changed this for comparison?

No, I did not make any passes before I changed the gearing. I built the motor and during brake in, I thought that the bike jumped
SO quick that I needed to add some gear. The bike is a daily STREET bike... I only went to the track one Friday night for a test and tune...
I had so much fun that I went back the next day for their Street Bike Blitz ( I went 2 rounds and was sent home).
With the gear change, The butt Dyno "feels" tons more pull from the bars.

I am slow off the line. With that said, The gearing now is just right for 3rd gear rev limiter through the 1/8 trap at 92 mph.

I have a real problem smoking the tire when I shift it to 2nd gear. I have to come off WOT, shift to 2nd, then return to WOT. (heated Stock tire, aired down)

With a great launch, and a good 2nd shift with no spin, I think I could get 95-96 mph in the 1/8th

That awesome for a street Sporty. You're getting the same mph through the 1/8th that I'm getting in the 1/4! That's a fair lump of motor you've got. I'm jealous.