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FJ Dragbike Project

Started by fj1289, March 22, 2010, 12:39:45 AM

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Not to be a dick, but I'm gonna be a dick.  At least I'm honest (don't you hate when people start with a disclaimer like that anyhow?!)

Why Q16 fuel?  Why 113?

Are you really running that much compression?  I realize that the silly elevation isn't doing you any favors, but I think you're shooting squirrels with an elephant gun.

If you can't run a replacement-lead fuel, such as U4.4 or MR12 due to stupid laws, and still want a reasonably high octane... Have you looked at VP's Streetblaze 100?  Yes, it's a motor octane of 96 instead of 116, but if you're under 14:1 I'd feel safe to wager that you're pissing money and power down the drain.  There's some more unusual VP fuels that also fit the bill, like SV-05 (98 MON and oxygenated).  There's no reason to run a nitrous/turbo fuel if you're running on motor.

In my own racing, I found that with a DA of 2500-3000, going from pump 87 (also known as "partially water") to proper 100 octane fuel cost me a solid 4mph and 0.15s.  With a 735lb combination, that equated to nearly 10% all on its own, or 12-13hp worth!  U4.4, even with a weak oxygenation package and far too much octane gave me back half of my losses (better than 87 pump, but not as good as the DA correction would imply).

You can't swap fuel around without getting it  dead on.  It's arguably the cheapest power you can make, and a consistent and important part of your tuning package.  Dont' skimp!  It's as important as setting your squish, but easier to fix when you jack it up.  Get some spare plugs and a pail of appropriate fuel, and make some tuning decisions.

You KNOW the suspension, gearing, and clutch make a difference.  Getting the motor to output as much as you can, consistently, makes tuning the rest of the combination that much easier.  The whole trick is removing as many variables as you can and getting things as close as possible quickly.  Once you've got the fuel done, the motor gets jetted and timed appropriately, and is done.  Then the focus shifts to the suspension and tire (which I must say... you're looking to me like someone racing on a tire that's had two lifetimes worth of heatcycling... Just sayin!  I know it's not cheap, but as you start getting closer, it's going to become non-optional to have a tire that's sticky every single pass, and you know that as well as I do).  Once you can eliminate all these things as being variable, then you can begin choosing between 0.010 and 0.015 shims in the clutch, with some security that it's a trustworthy and repeatable change.  Look at it like a bracket racer, step one is consnstency.  Once you've achieved that, the tuning changes don't get lost in the noise of the variabiltiy of the runs.

And you better get a move on.  The shim kit is in my dining room right now, and within a week I expect to have my FJ doing breakin miles.  I'm hoping for very low 10.70's on motor, and once the compression checks say I've seated the rings I'll be doing my damnedest to beat your ass into the 9's, on a stock wheelbase and displacement no less.  Get to work!!! :)


Sad night last night for the dragbike -- started tearing it down for the parts I'm going to borrow for Bonneville. 

Pulled the head for the cams and whole shim under bucket setup.   Really wish I could use the whole head, but the welded on spigots for the Lectron carbs make adapting the throttle bodies a difficult task.   

Tonight I'm pulling the swingarm and in a few days I'll swap the forks out too. 

Looks like it'll be September sometime before the dragbike sees the strip again... :cray:


Have you ever seen such a mess?!

I was concerned when I first looked at this engine due to the orange "stripe" around the case seams.  


Spluge everywhere, yuck....
The glass is not half full, it was engineered with a 2X safety factor.

'86 Ambulance - Bent frame, cracked case, due for an overhaul
'89 Stormy Blue - Suits my Dark Side


1991 fj1200


Quote from: fj1289 on November 21, 2020, 05:31:44 PM
Have you ever seen such a mess?!

Haha, I feel like I've met that guy many times in my life. He's the same guy that over fills everything, over tightens nuts and bolts, uses a torque wrench on everything then adds a quarter turn to be sure, puts Loctite on every thread on the bike, over greases everything, tells everyone what a rip-off mechanics are and that he can do a better job himself and save $1000's while he's at it.

Omg, the thought of all that floating around inside the engine!!!! :dash2:

"Tell a wise man something he doesn't know and he'll thank you, tell a fool something he doesn't know and he'll abuse you"


Gotta seal those main bearing journals, lest there be a massive internal oil leak!

At least most of the overflow is on the inside of the motor where you can't see it.  (YIKES!!!)

Some people shouldn't be allowed to buy wrenches..... or RTV!


Quote from: fj1289 on November 21, 2020, 05:31:44 PM
Have you ever seen such a mess?!

I was concerned when I first looked at this engine due to the orange "stripe" around the case seams.  

That's over the top ridiculous.......

Well, at least you know you'll have some time cleaning all the passages - and checking them thrice! ;)
Columbia, Missouri


Very true!  Going to be chasing and flushing EVERYTHING!

I'm not sure the engine was run in this condition.   Although there seems to be quite a bit of oil on everything, the bearings and journals look great!  When is saw that much crap everywhere I assumed there would be oil starvation issues.   

Haven't determined why the cases were split - I assume transmission.   I need to look at the shift forks and see if they are new.  Transmission has not been undercut - maybe was R&R'd with a "good" used trans?  Does look to be some dings around the second gear windows, but the dogs look OK to my eye.   Will get an undercut trans  as insurance.   

Hopefully can get this cleaned up this weekend.   


Little projects continue.

I've been stuck on some details on the nitrous system for a couple months now.  Overall plan is two stages - 1st will be smaller used on the hit - right when the clutch is released on launch.  Then the 2nd stage will be progressed through second, third, and maybe fourth gears.  

2nd stage system is set up a lot like my original nitrous system.  The problem has been trying to optimize the system a bit.   Nitrous works best when you manage to get the nitrous into the motor still as a liquid.  Then as it phase changes to a gas state you get the most benefit from the cooling.  Also, as a liquid it displaces less of the air going into the engine - both preserving as much NA (naturally aspirated) power as well as slightly decreasing the change in the composition of the mixture for combustion.  

Anywhere there is a transition or turn in the system, there is a chance for expansion or turbulence - both which can cause some of the dense liquid to start to phase change to gas.  Transitions can't be avoided - but you want to minimize them and make them as smooth as possible.  I was having trouble in my mind with the transition to the nozzles.  As it was, it went from the steel braided lines (3AN sized) through a 3AN to 1/8 NPT fitting, through a 1/8 NPT junction to the 1/8 NPT nozzle.   The nozzle seems to be set up to seal against a male flare - but short of fabricating a fitting I couldn't find one.  As it was, it created a fairly large expansion chamber right at the "business end" of the whole setup.  

I bought a set of nozzles - but turned out they were a lot shorter than I realized and would end up well short of the mouths of the throttle bodies.  That would defeat the efforts of eliminating the expansion area before the nozzle by replacing it with a huge one just after!  So back to the old nozzles.

Here is what I finally came up with.  Re-thread the nozzle to accept the 3AN line directly.  Since the 1/8 NPT thread was a bit bigger than the 3AN thread, I was able to turn down most of the old threads on the lathe, the run a 3/8-24 die over it.  The die wouldn't cut all the way to the base, so I had the flip it over and very carefully thread it over the newly cut threads backwards - then finish cutting the threads to the base.

Next it needed to be counterbored to accept a flare jet.  The flare jet is the sealing surface for the 3AN line.  

Finished job.  Eliminated two transitions and the expansion space.  As a side note - the flare jets are quite large - slightly larger than the inside of the 3AN and slightly smaller than the inside of the nozzle.  The nitrous system is jetted at the solenoid to achieve the best response while progressing the system.  

Also - does anyone recognize these nozzles?  I'm sure they are available from an industrial or agricultural supply, but have not found them on McMaster-Carr or Grainger so far.  


Recently found what at first appeared to be a very unusual clutch among some parts that came with the billet transmissions that came from Rod Mumford's estate. 

At first glance it appeared to be a Hayabusa basket with some kind of a slipper clutch and a shaft adapter for the clutch hub.   I assumed it was something that Rod had adapted to an FJ back plate. 

Further investigation revealed the backing plate was not from an FJ - wrong number of teeth on the basket.  WTF?  Then I remember that Rod also had a Kawasaki drag bike.  Started looking through Kawasaki transmission parts.  Found a clutch hub that matched - 83/84 GPz1100.   But, wrong number of teeth on the basket.  Finally got everything to match - Kawasaki ZX-11. 

Unfortunately the shaft adapter doesn't fit the FJ transmission output shaft.   But, all is not lost.  While trying to figure things out I discovered the Kawasaki clutch steels actually fit the FJ clutch hub AND are slightly smaller diameter than the FJ clutch steels......just exactly what I was getting ready to try to address again for the drag bike clutch:

This was a hybrid clutch - a basket normally used in a Hayabusa drag clutch married to an FJ clutch hub.  It was designed to use Hayabusa frictions and MODIFIED FJ steels.  The FJ steels had to be ground to fit inside the clutch basket without fouling on the sides of the basket.  Looks like the Kawasaki steels will fit without modification.  Kawasaki also makes these steels for various models and are available in different thicknesses - perfect for adjusting the clutch pack thickness to suit the drag clutch requirements!

You never know where you are going to find the next step ahead.   :good2:


Love the ingenuity here!

I can't wait for the tracks to open up!!! :wacko2:
The Juggernaut: Dual-Engine FJ2400
Watch the build on The Freakhouse Customs Channel


Finally did a little bit of work on this one last night!  Very little - but at least it is something.  Checked main bearing clearances with plasti-gage. 

Decided to set aside the "orange sealant" cases after I found a cracked thru boss on one of the front case bolts.  I'd imagine it could still provide good service since that fastener shouldn't be heavily stressed, but I took it as being another sign that it might be better to use a different set of cases.  Now it's a set of FJ1100 cases getting prepped to go together. 

The intent of this engine is to be somewhat of a "test mule" - try out a couple ideas and see how far I can push some things - like how much nitrous it will take - but without going "all-in" on the build.  That said, I've been collecting parts for a year and a half or better - some will go to use in this initial build, some are on the shelf for "future growth". 

The biggest parts of the build will center around resolving issues we've already had (mainly shifting under larger nitrous loads and reliable crankshaft signal at high rpms) and trying to maximize the amount of nitrous the engine can effectively use (XJR cylinder with THICK sleeves, cylinder head with larger exhaust valves and exhaust cam with longer duration).

When (not if) we find the limits, then we will address those.  Hopefully without breaking the bank too many times in the process!

And all this is being updated under the drag bike build thread (instead of the land speed thread) because I'm going back to more of a drag bike setup this time around.  Focus will be more development at the drag strip and then looking to try some of the 1/2 mile land speed events.  I think the FJ setup as it is has some advantages in the 1/2 mile compared to other motorcycle competitors so we might be able to pursue some pretty high goals. 

Now, if work will ever leave me at home for more than a 10 day stretch I might be able to start making some progress ....


Took the crankshaft to the machine shop that resized the XJR rods.  He laughed and gave me the same hard time as he did with my "cute little" rods  :sarcastic:  Simple balance on the crank and polish the journals. 

I got to thinking - i should probably balance the rods too.  Broke out the scale my wife bought to weigh the kitten she rescued on my last work trip ...

Took a few tries (and a couple evenings) to come up with a way to measure the big end weight that gave consistent, repeatable results. 

3 of 4 rods weighed 371 grams, with big end weight 259g.  4th rod was 373 grams with 261 gram big end.  Removed 2 grams from the large end of the rod (took 8 or 9 attempts) to get the total weight and big end weight to match the other rods.  And yes, do I know my big end weight will be a bit skewed since the rod isn't totally horizontal - but this setup gave usable, repeatable, consistent results.   :drinks:


Pictures for the above post - didn't notice they had gotten scrambled ...  :flag_of_truce: