Building a drag bike | GTAMotorcycle.com

Building a drag bike

Brian P

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Last year I took my ZX10R to the dragstrip for the first time ever ... mostly because as a SOAR competitor we got a dragstrip ticket for free so why not. Well, it was entertaining, but running a stock literbike on the dragstrip has a few issues, mostly being too hard to launch hard because it does nothing but shoot the front wheel up in the air. So, this project is to do something about that.

Objectives: Build something entertaining. I am not setting out to build a "pro stock" drag bike (i'll never be good enough, I'll save the pro license for roadracing) this is just something to be entertaining at test and tune days. So, it has to remain streetable and road legal and it has to not handle like an absolute pig. Slamming the bike to the ground is not in the cards. Has to retain the full useful suspension travel front and rear; has to have proper steering geometry so that it will still turn; has to retain reasonable ground clearance and cornering clearance. Obviously some of the things that need to be done would compromise corner exits if one were to do a track day with it, but for street riding, I can live with that. I have other bikes that I can use for corner carving anyway. Has to be reversible back to stock form, too.

Anyhow, here's the starting point

zx10r1.jpg


As you can see, with the exception of a steering damper and a taller windscreen, she's bone stock.

Phase 1: A little bit of tuning.

I have a wide-band lambda (air/fuel) ratio gauge that has been making the rounds on every bike I own - really helps with carb tuning for my vintage race bike. A while back, I had a bung welded onto the exhaust ... this is a titanium header so TIG welding this in place was left to the pros. This is the lambda sensor screwed into place, tucked in behind the right footpeg

zx10rdragbike002.jpg


and this is the gauge and a little bracket that I welded and painted to hold it in a place where I can see it

zx10rdragbike001.jpg


Does no good without a Power Commander. I had this loose under the passenger seat, but by flipping the sensor located here upside down I found enough room to tuck it in here - fits under the trim panel between the rider and passenger seats with the bodywork in place.

zx10rdragbike003.jpg


Plugs into the main throttle body wiring harness - airbox has to come out to do this, I had this done previously so no photos of the process

zx10rdragbike004.jpg
 
Part two: Quick shifter. This is an easy one. The business end

zx10rdragbike005.jpg


I use reverse shift pattern, so this is a "pull" sensor. The shift rod that it comes with is exactly the right length as long as it is screwed 1/4" into the ball joint at the shift shaft before starting to screw it into the other end - this way it bottoms the threads on both ends at the exact moment where the shifter gets to my preferred height - works for me. A minor nuisance is that when mounted like this, the switch was rubbing the return spring for the sidestand. I fixed that with a washer underneath the pivot for the gearchange lever to space it outward a couple millimeters; it has come up in internet discussions about this type of installation but it was dead simple to fix.

In the photo where the Power Commander is mounted, it's already plugged in, and it comes with a little CD-ROM that you run while the Power Commander is powered up, to enable the shifter. Haven't test ridden it yet, though ...

The other electronic gizmo to address "streetability" is this.

zx10rdragbike010.jpg


and it's plugged in here.

zx10rdragbike011.jpg


Purpose is so that I can have a correct speedometer with the much shorter gearing that's to be installed at a later date.
 
Next step: Disassembly! The bike has to be supported with the weight off the suspension in order to disassemble it. I have a setup in my shop for exactly this purpose ... a couple of hooks tied into a steel beam in the structure of the house ...

zx10rdragbike006.jpg


Bodywork was already off. Front sprocket removed - air impact makes quick work of it. Chain removed - had 30,000 km on it and was likely due for replacement soon anyway - ground the heads off the master link and separated it and took out the chain. Rear wheel out, then these links need to come off.

zx10rdragbike007.jpg


Then this nut has to come out to get to the ride height adjustment for the rear shock - access is underneath the fuel tank in this case.

zx10rdragbike008.jpg


Now, for something that some people may dread ... math.

First, note the drill bit that I'm holding in the next photo. The purpose of this drill bit right now isn't to drill anything ... it's to measure the distance between the lip of the fork seal and where the fork tube goes into the casting at the bottom. That's the maximum possible amount that the suspension can compress from this point. There is a section of that inner fork tube near the bottom that has a bit of dirt on it ... that's the part of the suspension travel that I don't use in normal riding, but it's still possible for it to be used. So, this drill bit represents the maximum amount that the front suspension can compress from this point as the bike is sitting right now.

zx10rdragbikeforktravel001.jpg


Now, this same drill bit is held as parallel to the forks as I can see, up against the bottom of the upper fairing.

zx10rdragbikeforktravel002.jpg


Note the gap between the bottom of the drill bit and the top of the front fender ... it is about 8 millimeters. (The forks have already been slid up in the clamps about 3mm from stock height.) If I lower the front end any more than 8 millimeters from its current height, there is a risk of the fender hitting the upper fairing at full bump compression. For a "full drag bike" ... it's not an issue, and you'll hear people recommending to lower the front end 1.5 inches or even more. But for a "street" bike ... you betcha it's an issue. Hard braking combined with the fender getting jammed against the upper fairing means "loss of steering" which means "crash" which means "we're not going down that road". So, 8 millimeters is the maximum amount that the front could be lowered while retaining full use of the suspension.
 
OK time for the math.

The plan here is to install extension blocks for the swingarm to get the wheelbase a bit longer. Because of the down angle of the swingarm, this would add to rear ride height (not good for drag racing) unless something is done to compensate. The solution is to install lowering links, which (for this bike) are available for lowering 2 inches and 4 inches. A 4 inch drop might be okay for a "pure" drag racing bike with turbo or nitrous or whatever, but for something "streetable" ... there is no way to do that without causing major suspension geometry problems. So, 2 inch lowering links are what it is going to be. You have the lowering links bringing the bike lower, but the extra length raising the bike up because of the down angle of the swingarm (which will be reduced with the lowering links in place ...) and at the same time I want to preserve the front end rake and trail at their current values. The front end has 8mm lowering available - I'm targeting a 6mm lowering to keep myself some room for fine tuning - but in addition to that, the longer wheelbase will transfer additional weight to the front end which will lower the front slightly just due to the spring compression.

This is complicated.

I made up a spreadsheet with a whole bunch of formulas in it to take into account the new weight distribution, the expected additional amount that the fork springs will compress due to the extra weight (which is about 7 mm), the target amount of lowering the front ride height (6 mm), plus the fact that the back of the bike is already 9.5mm higher than I'd like it to be due to the use of a 190/55 rear tire instead of the stock 190/50 size, *and* took into account the shock linkage rate, and the outcome was a 0.45" thick additional ride height spacer at the shock ride height adjuster, which I did using ordinary 5/8" diameter steel washers so that I can fairly easily add or subtract from this first-guess estimate depending on "actual field experience".

zx10rdragbike009.jpg


Also I'm not going to actually slide the forks up or down in the clamps until such time as I can actually take this thing for a test ride. All this is to "get it in the ballpark" - fine tuning will have to be done based on how the bike feels in a test ride.

Anyway, at this point I'm waiting for parts to arrive ... on order from Champion Cycle, which is run by a drag-racing guy who ought to know the right things to do to the bike.

In the meantime, there is one other little problem that needs to be resolved ... clearance for the rear tire. There is no way that the stock rear fender was going to work with the rear wheel slid back.

In the interest of remaining as original-looking as possible, I modded the stock fender. I found out that the two bolts for the original license plate bracket have the same spacing as the two bolts for the original license plate light ... so up went the license plate. Minor issue was that the rounded shape of the fender didn't look right - visible behind the license plate bracket - so I solved two issues at once, by cutting and painting a little sheet metal bracket and installing a stick-on reflector on it. It covers up the odd shape and it also means the bike has a DOT-marked rear reflector (normally mounted underneath the license plate in the area that had to be removed). I'll use lighted LED license plate bolts eventually to illuminate the plate - those are on order. Original turn signals, original side reflectors, DOT marked rear reflector, license plate will be lit, and it's far enough back and up to be out of the way, it's as legal as I can make it.

zx10rdragbike012.jpg


And that's where it stands right now, until I get some parts!
 
Great write up. I'll be following this thread!

The ZX10R should be a really good drag racing platform. The last time I was at TMP, I got laned next to a guy with an 04 that looked like it had relatively minor mods (geared, exhaust, strapped, lowered, stock wheelbase) running low 9's at 155+ mph irrc.
 
Have you thought about a improved shift light? I guess you wouldn't care too much about shifting as the dyno jet module would take care of that.
 
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Yeah, the stock shift light is pretty small, but it hasn't been a bother so far, so at this point I'm not doing anything about it. The quickshifter doesn't shift for itself, I'll still have to tap the foot pedal, it just saves having to close the throttle and/or use the clutch.
 
Dragging the zx10 has obviously got ahold of ya Brian!!! I think its great that your going through so much to post it all on here...Alot of guys are gonna see that with a little time and a small amount of money spent these bikes can be set up to run 9's with relative ease!! I'm sure I will be seeing ya down there this coming year.....I'll stage beside ya with my new bag of tricks for the 14...hehe....Great work..keep us posted!!
 
any swingarm extenders planned?

also, you are leaking oil somewhere...probably a seal, cant really tell from the pictures...maybe take care of it while u got the bike partly dissassembled?
 
That oil is what I use to lubricate the chain! The engine doesn't leak or burn any oil at all ... YES this bike is dirty underneath!
 
Phase 1: A little bit of tuning.

I have a wide-band lambda (air/fuel) ratio gauge that has been making the rounds on every bike I own - really helps with carb tuning for my vintage race bike. A while back, I had a bung welded onto the exhaust ... this is a titanium header so TIG welding this in place was left to the pros. This is the lambda sensor screwed into place, tucked in behind the right footpeg

zx10rdragbike002.jpg


and this is the gauge and a little bracket that I welded and painted to hold it in a place where I can see it

zx10rdragbike001.jpg

Hey Brian, I wonder if you could talk about the a/f guage. I have similar (NGK Power Dex) for carb jetting on some older bikes. I've had the bungs welded in but the bikes are on the back burner atm so have not used the guage. I'll be taking the information right off the guage, no data logging. I assume you're doing the same? What are your experiences with that?
 
That's exactly what I did ... no data logging, just watching the gauge and paying attention to RPM and throttle position at any conditions that are too far off the mark. That gauge has made the rounds on all of my bikes.

The two FZR's are carbureted. I made changes that you would never figure out by just seat of the pants. I ended up with richer pilot jets which allowed leaner mixture screw and leaner needle settings, and the right size main jets. On the little cbr125, which has a different camshaft and a different exhaust system, I calibrated a resistor that's in the air intake temperature sensor circuit to get it right. The zx10r is fully mapped but because you can make changes every 250 rpm and at nine different throttle positions, there are a lot more variables than with carbs. The goal was the same as with the carbureted engines ... "lean cruise" 15.5:1 - 16.5:1 at light throttle and moderate revs for best fuel consumption and range, and 13:1 give or take at full throttle for best power. It took a long time to get it exactly right, but the map that I ended up with bears no resemblance at all to anything I've seen on the internet ... BUT ... starts easily, good throttle response, good fuel consumption, good power, no hiccups.

On the big bike, calibrating full throttle and higher revs had to be done at the dragstrip - and in those conditions this bike gets your attention, there's no time to watch the gauge. For that, my data logging consisted of a digital video camera temporarily rigged up so that I could have the gauge and the bike's instruments in view at the same time; I did a run in which I short-shifted to 3rd gear and then let it pull all the way through.
 
Great, that's kinda what I was expecting except I didn't think about the full throttle on the ZX10 lol.
I took a little flak for buying the Powerdex because all jetting for my bikes is well documented but I will be going to a 40mm flatslide pumper on the Buell where everybody is running the 42 f/s or stock CV.
I'm pretty much forced to stay with the stock CVs on the old BMW which would make throttle position a little harder but I can play with it. Just trying to avoid spikes and valleys.
Looks like you're running a pretty lean cruise. I should probably get a cyl.head temp. guage if I decide to go that lean on aircooled motor.
Thanks
 
Got a bunch of parts, got a bunch of stuff done. Actually I wanted to finish everything up except the license plate lighting (still waiting for fiddly bits bought on Ebay to show up in the mail) but that was not to be ...

First, a minor change of approach caused by a little booboo. When I did the calculation of how thick that shim stack at the rear shock mount needed to be, it was meant to be the additional thickness on top of the stock spacer. Well, when I put it together, I measured the total thickness, forgetting to account for the thickness of the stock one! Oops. It means the rear will be sitting a little lower than originally planned. Rather than taking it apart to change this, I opted to lower the front to the maximum that I'm comfortable will not allow a collision between front fender and upper fairing. See earlier photos for this measurement.

zx10rdragbike015.jpg


Lowering links installed and nuts torqued to factory specs. I had to clean up the holes a wee bit with a die grinder for them to fit properly over the pivot bolts - typical aftermarket fitment tolerances - but no big deal, it's done.

zx10rdragbike016.jpg


Longer rear brake line installed, all fasteners torqued and air bled out of the line (Side benefit is that since this bike has had braided front lines for years, it now gets a rear one to match!)

zx10rdragbike017.jpg


Now the business end.

zx10rdragbike018.jpg


These are nicely finished bits of billet aluminum. That connection where these attach to the original swingarm is a big area of suspicion. But having put these together, I'm not too concerned about it. There is a slight press-fit where these fit into the original adjuster slots, which means they won't be working loose because they can't move. A machined projection fits through the slot where the original axle normally goes, and there are two M10 grade 12 machine screws attaching these from the inside. Those bolts are assembled with Loctite and torqued Pretty Darn Tight. Recommendation is 85 N.m which is beyond what my torque wrench goes to, so I tightened them to the maximum for the torque wrench (50 N.m) and then a bit more. These are NOT going anywhere. Suggestion from Champion Cycle (although I haven't done it yet) is to put a contrasting paint mark between the edge of the fastener and the plate that the machine screws fit into, and then you can check whether the fastener is staying home.

There is a nicely machined piece for locating the brake caliper which is part of the clamping plate for the right side.

And that's as far as I can take it, because it looks like there was a mix-up of some sort, and I got the wrong rear sprocket. Without the correct one, I can't go any further.

I did stick the axle through with the wheel on it and set the bike back down on its wheels for the first time in weeks, though. Jeeez a few inches of extra wheelbase makes the bike feel long. If that's what it takes then so be it.

I did discover that the slid-back position of the wheel made the tire touch the chain guard; I trimmed a little bit off. Another advantage of not lowering drastically is that the side-stand is still okay without having to modify it.

And that's all, until I get the correct rear sprocket. Then I can put the rear wheel in, put the chain on, put the bodywork on, and get this out of my shop and ready for a test ride when the weather co-operates.
 
One more. On this bike, the chain and sprockets job that still needs to be done is possible with all the fairings in place, so I put them on and stuck the axle thru to see how this is going to look.

zx10rdragbike019.jpg


The Power Commander location worked out well. I can get to the USB port simply by removing the passenger seat ... and I have my trunk space back. The reflector that I made to sit above the license plate also worked out - doesn't block the tail lamp at all. There's ample clearance for suspension travel in the rear.

Things to do:
Chain and sprockets job after I get the correct rear sprocket
Wire up lighting for the taillight after I get the parts needed
Replace a couple of fairing screws that have gone missing over the years (nothing to do with this job)
Test ride to see if I need to adjust ride heights to get the steering correct.
 
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the only thing i would have suggested would have been a air shifter,intead of that powercommander one...only reason,the one -two shift is the hardest one to get your foot up..and its way easier to push a button....

just my 2 cents
 
Yeah, I hear you, but I am not setting out to make a Pro Stock bike or anything of the sort. I don't want to go too far so as to ruin it as a street bike. I sure hear you on having trouble getting my foot in place. An air shifter would have meant more gizmos and gadgets to (A) pay for and (B) find a place for, so that's not happening, at least for now. I highly doubt that I'm ever going to get anything comparable to the black numbers on my roadrace bike ... For now, this is just something to play around with ...
 
Brian, I can look for the LED plate bolts that I wanted to use, but never did. Same goes for a beefier torque wrench (it'll definitely do 85), with a 1/2" drive. I can loan'em to yu.. Pretty pimpin' setup.. For a Kawi :cool:
 
If you have a couple of extra LED plate bolts, I'll take them from you. I ordered some from Hong Kong ... they never showed up ... Paypal refunded my money ... still need 'em!
 

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