FJ Land speed racer

[fj1289]

Got the full auto transmissions out of the box to check them out. 





These are definitely full billet transmissions.  Cool!  Then it dawns on me - a full custom transmission may have custom gear ratios.   Get a very bad feeling these could be close-ratio transmissions - - the exact opposite of what I need!  Time to start counting teeth....

Get out the FSM and a stock FJ trans (stock gears that have been nitrous cut) and start counting teeth.  I confirmed to myself which gear set is which and my counts matched the FSM numbers.  Now on to billet transmissions.  Immediately I'm getting different tooth counts for each gear and I get a knot in my stomach.  Crap.  I really hope this wasn't a huge waste of money.   

Got lucky!  Turns out the billet transmissions ratios are pretty close to the stock FJ transmission ratios - just achieved with fewer teeth on each gear set. 

Stock Gears:
1st  40/14    2.86 ratio
2nd 36/18   2.00 ratio
3rd 33/21    1.57 ratio
4th 31/24    1.29 ratio
5th 29/26   1.12 ratio
Overall transmission "spread" (1st ratio divided by 5th ratio) =2.55

Billet Gears:
1st  36/13  2.77 ratio
2nd 30/15   2.00 ratio
3rd 26/17    1.53 ratio
4th 25/20    1.25 ratio
5th 26/24    1.08 ratio
Overall transmission "spread" (1st ratio divided by 5th ratio) =2.56

A couple things jump out at me - first the RPM drop on the 1-2 shift will be a little smaller than the stock ratios.  I think that is a good thing as this is a pretty big drop normally.  Second - the RPM drop on the 2-3 shift will be a little larger than stock.  I think that is fine too, and a more than fair trade off for raising the 1-2 shift recovery point a little while keeping the overall transmission "spread" the same.  Finally, the lower tooth counts on each gear means the individual teeth are larger since the center of the shafts the gears rotate on remain the same distance apart as stock.  I assume these larger teeth will be stronger vice smaller teeth. 

[fj1289]

An "auto" trans for a motorcycle (at least in drag racing terms) is nothing like an "automatic" transmission in a car.  It is more accurately known as an "over-riding" transmission.  

This picture was supposed to be in the last post - not sure what happened to it?



The transmission gears, shift drum, and shift forks are modified to allow the transmission to be shifted to the next higher gear while it is still in the current gear.  When the higher gear engages, the faster rotation "over takes" the previous gear and a ramp cut into the back side of the "window" forces the dogs of the engaging gear out of engagement.  What this does is allow a full throttle up shift with having to "unload" the transmission via an ignition kill, fuel kill, "fanning" the clutch, etc.  At higher levels of drag racing competition this can save two tenths of a second or more in a quarter mile run.  

A couple pictures showing the "ramp" on the back side of the "window"





Shift drums get modified allowing the shift forks to engage two gears at the same time (while then allowing one fork to move when the previous gear gets "kicked out" by the ramp



Even the shift forks get modded - especially the center fork!  (See the half round segment welded on the back side)



And other forks ground to allow more movement on the shift shift



Auto trans come in a variety of options.  Originally just the 1-2 shift was done this way.  Later 1-2-3 autos or 1-2-3-4 autos were developed.  Eventually people set up all the shifts for a "full auto" trans.  BUT, nothing comes for free - the BIG drawback of an auto trans is you CANNOT back out of the throttle until you have shifted past the auto gears.  For example, with a 1-2 auto, you can safely roll off the throttle in 2nd gear or higher.  It if you roll out in first, the back torque on the transmission will cause those over riding ramps built into the back side of the gear window to try to force first gear out of engagement - but the shift drum and shift forks are still in position for first gear.  This usually ends up bending the shift fork and ending your day.  Likewise, with a 1-2-3 auto, backing out in 1st or 2nd will likely cause damage.  So, with a full auto you have to stay in it until top gear to avoid damage.  This means you better have your power delivery and your suspension pretty well sorted before starting down this path.   Your only choice if you wheelie or spin is to attempt to shift out of it.  

OK, so shaving .2 sec is all fine and dandy - but not why I am really interested in these full auto transmissions.  My interest is in not having to kill ignition or fuel flow while spraying a large shot of nitrous.  I'm hoping to avoid large potentially damaging back fires or a miss-match of nitrous and fuel at the end of a shift when ignition and/or fuel is resumed.  Also nice to not unload the suspension during the shift.   So, for now these pretty pieces sit in a box on the shelf waiting for everything else to be sorted first and then we'll give these full auto trans a go.

[ribbert]

An "auto" trans for a motorcycle (at least in drag racing terms) is nothing like an "automatic" transmission in a car.  It is more accurately known as an "over-riding" transmission.  

Thanks Chris, that's really interesting (and great photos)

Drag racing, standing mile and all the variations are not as popular here as they are in the US. They're all here but in proportionately smaller numbers, so I don't come across drag specific mods much, and I guess they all do their own work anyway.

Noel

[freakhousecustoms]

Hello from Castle Rock!

Glad to see a fellow Land Speed Racer!  I was wondering if you'd be able to answer a few of my questions?  I've been running Bonneville with Suzuki GS1100E's but this year I'm using a pair of FJ1200's as the base for my Bonneville build.

• Are you using the stock swingarm and rear wheel?
• If so, which rear tire would you recommend?
• Are you using the stock size/width?  150/80-16?

Thanks in advance!  I'll be starting my own build thread, now that I've found - what seems to be - THE place to ask my FJ-based questions.

-Fran

[fj1289]

Hello from Castle Rock!

Glad to see a fellow Land Speed Racer!  I was wondering if you'd be able to answer a few of my questions?  I've been running Bonneville with Suzuki GS1100E's but this year I'm using a pair of FJ1200's as the base for my Bonneville build.

• Are you using the stock swingarm and rear wheel?
• If so, which rear tire would you recommend?
• Are you using the stock size/width?  150/80-16?

Thanks in advance!  I'll be starting my own build thread, now that I've found - what seems to be - THE place to ask my FJ-based questions.

-Fran

You are in Castle Rock?!  I'm in Franktown. 

The race bike has a lengthened FZ-1 swing arm.  It runs a 17x5.5 or 17x6.0 rim depending on land speed or drag racing.   

Since the FJ falls into all the "Busa" classes, you are going to have to pass tech based on the speeds for those classes.  I have no idea if there are any 16 inch tires that will pass tech?  I've been running pavement and currently have a Michelin Power RS 2CT+ based on a recommendation from Ransom Holbrook (fastest nitrous only bike - Busa- in 1/2 mile, 1 mile, and 1.5 mile) .  Previously I ran a Bridgestone Battleaxe BT-003R Race.  This was to meet the SCTA requirement  (I think) for a "race" labeled tire for speeds over 200 mph if I remember correctly.  Bottom line - get hold of tech (are you running SCTA or BMST?) and confirm they will pass you with that tire.  I'd hate for you to show up with a tire they let run.  As you already know, tire ratings is a very messy topic with all land speed organizations.  The best suited tires for all surfaces seem to be good quality ZR rated street tires vice any tire intended for racing.   The harder compound of the "street" tires are a lot more tolerant of the heat stresses of a relatively long time at speed vice the race tires  that are really designed for grip more so than high speed durability. 

What classes are you looking to run in?  What event do you run in - Speedweek?  Or BMST? 

Randy (owner of RPM Racing in the banner at the top) is a huge sources of knowledge on these engines - especially when it comes to pushing them harder than 98% of motorcyclists will ever stress these engines. 

[freakhousecustoms]

  I have no idea if there are any 16 inch tires that will pass tech? 

Darn,
That's the exact "problem" I'm running into.  Now I do have a ZX14 rear wheel, but I'd need to have to buy a complete swingarm/shock for that.  And then I have a complete Busa swingarm/shock, but no rear wheel. LOL - "Ain't that always the way".   I was hoping against hope that you were still running a 16", but no worries, I know there's a solution out there. 

Franktown?  Well that's even better.    We're practically neighbors.  Is the Stagecoach on Parker Rd doing takeout?  Maybe I can buy you a coffee? 

I went to my first BMST in 2014 & I've been chasing AMA records since 2015. 

I'll start my own build thread, so I don't step on your space here.  Super stoked to be able to talk to someone, locally, about LSR.

[andyoutandabout]

Land speeders. These juicy builds are going to get the Fjers all steamed up.
If the vaccine program works, then i'd Like to think that I'd make a pilgrimage to the salt flats.
I would imagine others may also be tempted to visit.

[freakhousecustoms]

I would imagine others may also be tempted to visit.

I like to consider myself a Salt Messiah, preaching the good word to anyone who will listen.

The Bonneville Motorcycle Speed Trials has a "Run Whatchu Brung" class, $250 gets you 2 runs down The Salt, just have to do a few things to pass Scrutineering.
I think every moto-head who's able should take a run across the Holy Ground, it's absolutely like nothing you've ever done before.  No one judges you on the speed you've run, but you'll never look at the word "fast" the same way again.

https://bonnevillespeedtrials.com/