Launch RPM

Had a chance to run the KZ on an 1/8th mile track last night.Stock tire ,no bars , 15/42.Launched at 4000 rpm and the bike seemed to do well (6.8 in the 1/8th) with very little wheelspin at launch but more about 100 yards out.Any advantage to launching at higher rpm or is this an issue of traction only.I am not a professional dragracer nor do I intend to be.Would like to break 6.5 in the 1/8th and I would be satisfied.Thanks.bj

Running a stock motor? 6.8 in the 1/8th is damn fast for a KZ. That's mid-10's in the quarter and a 6.5 is about 10.15 sec. e.t.!!! You should run better with a higher rpm launch but only if the tire can handle it. I have a stock motor except for a 1075 kit and run a 130 tire and can't launch as high as you are now. I break tire loose about 3000 rpm on launch. Your gearing is low also. I'm only running 15/39 and have trouble hooking up most times. Higher rpm launch will put you closer to shift point once moving but it all depends on your combination of right hand and left hand co-ordination. The higher you can launch at, generally the quicker you will run but ultimately it is the tire that will determine the rpm to launch at. The first 60' will make the biggest difference in your e.t.'s. so anything you can do to be quicker there will translate into a faster overall e.t. Sliding the clutch out is a tricky "touch" but that will decide how fast you go. Faster you can get clutch out and to full throttle...faster you will go. Higher rpm's will change how you use clutch and higher rpm's you will be making more HP that your tire has to deal with. It's a combination deal. Try a higher rpm while doing everything the same til tire breaks loose and that will be as hard as you can leave. You can change gearing to a higher (15/39) which will help traction some by not have as much torque multiplication and you can use more rpm without tire breaking loose.

Damn bj,you da man! :laugh:
i watched my 1327 heading down hwy 66 this morning with the frontend about 6" in the air running through the gears with the new owners wife trying to follow in a ford pickup and trailer loaded full of spare parts looking like she wanted to shoot me! :woohoo: :woohoo: :woohoo: :woohoo: :woohoo:
i told him you dont need to trailer it,ride the damn thing and proceeded to pack his trailer full of more stuff i sold him! :woohoo:
anyway that bike has run a best of 6.18 at 114 on our little 1/8 mile track with no bar on back,i was bumbed out to see it go but now ive got some money/room to build an even better replacement.
anybody living in the abilene kansas area beware of the new missile in town!

Thanks all who responded. I normally run the "stock" 15/39 but changed it for the strip. Bike is "sorta" stock with the J cams,Dyna ignition,Zuki swing arm,Barnett clutch (damn that thing is stiff),V and H pipe,Satrab cooler and a few other goodies.If I hear everybody correctly, first 60 feet is critical and with what Ive got engine and tire wise, a 6.8 is pretty good.That is 1 second quicker than when I first ran it last year. So I think I will stay there and be happy.Thanks all.bj

wireman wrote: Damn bj,you da man! :laugh:
i watched my 1327 heading down hwy 66 this morning with the frontend about 6" in the air running through the gears with the new owners wife trying to follow in a ford pickup and trailer loaded full of spare parts looking like she wanted to shoot me! :woohoo: :woohoo: :woohoo: :woohoo: :woohoo:
i told him you dont need to trailer it,ride the damn thing and proceeded to pack his trailer full of more stuff i sold him! :woohoo:
anyway that bike has run a best of 6.18 at 114 on our little 1/8 mile track with no bar on back,i was bumbed out to see it go but now ive got some money/room to build an even better replacement.
anybody living in the abilene kansas area beware of the new missile in town!

U sold the 1327? I wish u had let me know u were going to sell it . I would have loved to have had that bike.Damn.bj

sold it to a guy i worked with over the winter down in kansas with,his wife did not look happy at all with me when i convinced him to ride it home! :sick: :woohoo:
that bike was too well known around here.so now im going to start working on a new line of street sleepers to sell around here locally,im gonna call em 'saturday night specials".
kind of like the restored stuff redline cycle sells,but the base line motor will be mild mannered looking 900 or 1015 packing a 900 crank /1197 bore kit and a stage 1 head with 28 pumpers or 29 cr's. :woohoo:

I always had good luck letting the clutch snap out at low rpm's on my roadrace bikes. They were mostly low torque/high revving 600 and 750's, so I'm not sure how it would work on a lower revving big-bore. It also worked pretty well on my single cylinder supermoto bikes.

I used to be a high rev, clutch slipper until I noticed that Tommy Hayden was getting a lot of holeshots by using the low/rev clutch dump technique. The initial lurch gives you a full bike length over the slipping clutch guys, but after that you gotta catch it just right to hold the advantage. You need just enough revs to fall just between bogging and having to let off if the front wheel comes up too far. IIRC it was about 6000 rpm on a 600 SS bike and about 5000 rpm on a 750.

Just hold the throttle/rpm steady and let the lever go.....

mjg15 wrote: I always had good luck letting the clutch snap out at low rpm's on my roadrace bikes. They were mostly low torque/high revving 600 and 750's, so I'm not sure how it would work on a lower revving big-bore. It also worked pretty well on my single cylinder supermoto bikes.

I used to be a high rev, clutch slipper until I noticed that Tommy Hayden was getting a lot of holeshots by using the low/rev clutch dump technique. The initial lurch gives you a full bike length over the slipping clutch guys, but after that you gotta catch it just right to hold the advantage. You need just enough revs to fall just between bogging and having to let off if the front wheel comes up too far. IIRC it was about 6000 rpm on a 600 SS bike and about 5000 rpm on a 750.

Just hold the throttle/rpm steady and let the lever go.....

I think I will give that a try.This damn stiff Barnett clutch hooks and holds like crazy but it is a biotch to slip-plus I aint as strong as I used to be.Lol.Thanks Much for the tip.bj

Start at a low RPM if you are going to try dumping the clutch.

It will probably just spin, but it would suck to loop it.

Higher RPM should give you a faster time if it doesn't break traction or make the front end come up to far.

What's done to the engine?

tachrev wrote: Start at a low RPM if you are going to try dumping the clutch.

It will probably just spin, but it would suck to loop it.

Higher RPM should give you a faster time if it doesn't break traction or make the front end come up to far.

What's done to the engine?

hes got a really good set of spark plugs and a set of bs34s race prepped by calf-n-ah racing and bait shop! :woohoo:

wireman wrote: sold it to a guy i worked with over the winter down in kansas with,his wife did not look happy at all with me when i convinced him to ride it home! :sick: :woohoo:
that bike was too well known around here.so now im going to start working on a new line of street sleepers to sell around here locally,im gonna call em 'saturday night specials".
kind of like the restored stuff redline cycle sells,but the base line motor will be mild mannered looking 900 or 1015 packing a 900 crank /1197 bore kit and a stage 1 head with 28 pumpers or 29 cr's. :woohoo:

What are they gonna go for? :huh:

tachrev wrote: Start at a low RPM if you are going to try dumping the clutch.

It will probably just spin, but it would suck to loop it.

Higher RPM should give you a faster time if it doesn't break traction or make the front end come up to far.

What's done to the engine?

J cams (Andrews 2x),Dyna S,Dyna coils,Barnett clutch,Satrab cooler,Taylor wires,de-smogged,street ported head,Tsubaki cam chain,APE tensioner,V and H Sidewinder,Schnitz oil gate,15/42 at the strip,15/39 on the street,GS1100e arm,Hagon HD shocks,etc,etc ,the best I could afford at the time. Plus the Calf-in-Naw super tuned , gold plated,one of a kind,BS34s.LMAO.bj