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Sleeper R75/5

Copyright, 2013, R. Fleischer

This was a posed photo, we DO NOT normally ride in jeans, nor those shoes, nor without helmets nor without leather jackets!!  This photo was taken at the Prineville, Oregon BMWMOA National Rally in 1980.

What is a 'sleeper'? 
A sleeper is a modified-for-performance motorcycle that purposely looks UNmodified.  Most 'sleepers' have highly modified engines; and may have many other modified items; including suspensions, brakes, etc.

This motorcycle started life as a R75/5 SWB.   I purchased it brand new, from the dealership where I worked as a wrench. The bike was shipped to the dealership with that AVON fairing, by the BMW distributor.  The white round item in the windshield area is a radio speaker I installed.   There is a completely hidden experimental HAM radio on this bike.  The antenna is there, but you will have to guess where it is! The hard-to-see items at the ends of the bars are a variation on a type of cold-weather 'Hippo-hands'.    The bike was quite well torn down right after delivery ...more later herein ...>>>

Fun short anecdote: The luggage-style push-latch on the left side classic Bates leather saddlebag had a raccoon push on it and the coon opened the saddlebag and ate my favorite peanut butter cookies in October 1973 when I camped overnight near the top of Ebbett's Pass, Highway 4, in California, on my way to Lake Tahoe, to check the area out, as I was thinking about moving to the area (I did).

In the photo Jean and I are wearing the windbreaker jackets of the Flying AAA Ranch, where we sometimes went in our 1957 Cessna 182 or my later 1967 Cessna 182, for a week or weekend retreats & vacations.  Over many years I had also been many times to Baja with my motorcycles or airplanes (as a member of the Baja Bush Pilots).

Backtracking in time, to the early seventies:

What is unusual about this bike is what it became; and, how stock it looked, ALWAYS ON PURPOSE.  I made lots of modifications to it over the years.  Finally, with OVER 110,000 hard miles on this bike in mostly stock condition, I decided it was time for a TOTAL overhaul.  It became very much more than a farkled bike that had been overhauled.  I had originally intended to just restore it to showroom fresh, keeping very few previously early-done modifications.    However, I had purchased another R75/5, and thought "why not go all the way with my old one".

This article is not a listing of step by step, year by year modifications, but covers the highlights.   When I sold the bike it still had those bags, that fairing, that horn speaker, etc.  It became very heavily modified, yet it looked exactly like the above photo.

I never did change the bike to the Monolever that BMW came out with in 1983. I'd thought about it, WAS going to do it, even knowing that, to the knowledgeable, it would have been a giveaway to big modifications.  I never did, as the bike was sold in early 1985.

If you looked carefully, you would see what appeared to be a stock but somehow slightly taller (and very slightly wider) cover over the starter motor. You would have to be VERY familiar with BMW's to notice that; and I spent a LOT of time trying to make that modified cover appear stock. 

You would see some beefing-up at the steering head, a somewhat weak point on the /5 models.   You would be UNlikely to see anything much that gave away what was REALLY done to that bike.

The engine had been originally thoroughly blueprinted, by ME and the other two shop techs, immediately after I purchased it. After all, my shop had not been 100% through an Airhead engine before, just a few modest shop jobs, no one had been to the factory schools yet for these new bikes ...the Airhead was a relatively newly released model, so the R75/5, top-of-the-line, was new to our BMW world.    SO, after break-in, came a major teardown, and some minor modifications (& factory service information complied with).  All of us shop guys got an education.  

After the motorcycle became mine for awhile, I began to make changes. I firstly worked-over the transmission and flywheel for fast shifting ...and on and on it went ...but it remained looking very stock.   Nothing outrageous at that point, at least nothing that showed (I had already removed the heads and cleaned up the intake tract, etc.)    But.....

I was given a very unique supercharger, but had no immediate use for it.  On purpose I am not mentioning the type of supercharger, nor its brand.     I am certainly not going to mention who gave it and spare parts to me.  From the moment I got the supercharger I went crazy with ideas (amazing what a lot of coffee ...and sometimes barley water ...will do).  After making an initial list, I decided that this supercharger needed to go on my R75/5, and I began some extensive modifications.

The carburetors, already modified by me to operate better, were sold, and a pair of identical carburetors, but with broken internal main jet castings (hence the carbs were obtained for nothing), were installed.  Before installation, the carburetors were completely sealed from the outside air in various ways, and then were bored slightly and sleeved, and otherwise very much modified, so that they were, mechanically, simply straight tubes with no irregular internal surfaces.  The cylinder head intake ports and spigots, etc., were also modified including the valves, seats, and heads.  The modifications to the carburetors were extreme ...but the head modifications were fairly radical too.   I did not dual-plug the engine at this time.  The exhaust valves were left stock, but the intake valve came from a Lincoln V-8.  The valve guides were shortened and reshaped.  Ports, squish, pistons, lots of things changed.  I even removed the middle ring, and installed a low friction dual-function oil control ring and wave spring.

If I was doing this sort of installation again, supercharged, I'd probably install some low pressure fuel injectors, something like Luftmeister sold. Not sure if this link is still operating, but you can get some ideas, if it is:
If I did install fuel injectors, then I'd have the supercharger provide air pressure ONLY, via heat insulated channels.  You could also look up luftmeister/haltech fuel injectors, or just haltech f.i.

A substantial increase in the effective intake flow ability was made by various changes, not the least the huge intake valve.  The throttle and choke cables were original, not functional, and were used as total dummies. These were not the later type lined cables, so the center hole was a bit bigger, and there was no bothersome lining-core to be removed. The cables led to an area under the fuel tanks, where they were simply chopped off and tied to the backbone area, doing nothing ...except that the inside of the cables had very thin insulated wire, not steel strands. There were NO butterflies, floats, diaphragms, or anything else inside these carburetors.    The clamshell area, which normally contains the air filter, was heavily modified, partly to allow some of the supercharger nose drive parts to protrude into it and partly to add curved fins to the inside, that acted somewhat as air directors (so I hoped) and for a bit of cooling (added to by thin ceramic wool pads type of insulation).   I did an awful lot of work to this airbox, finally using twin aircraft type temperature sensors and an aircraft differential altimeter (as inside and outside pressure gauges).  I got some goodly improvement in flow and temperature.   Later, I installed a differential manifold pressure gauge to do additional monitoring.

The engine oiling system was modified, including modifications to the rod and main bearings, the oil distribution at the main and cam area modified, the oil pump, the oil filter area, etc.  There are problems when RPM is raised way way up. I had originally been iffy, regarding the blower, so had planned on extending the RPM higher, but it turned out, with the blower, that 7500-8000 was MORE than adequate.  But, I wanted to avoid problems with oil pressure and oil cooling, etc.   Cavitation effects being just one of the possible problems with high RPM.  The oil pump modification was done as I was worried about cavitation.  As it turned out, very high rpm was NOT needed....but I used it now and then anyway!  Well, to 8000, my personal red-line.  Mostly I used 3500-6300.  At 5500 the engine was VERY sweet.

An oil pan modification was made for windage, & the oil pickup modified. I eventually tossed the modified pan & had started to get ready to mill my own pan (laboriously, manually) when I found out that a deeper pan that would be perfect for some of my modifications was available from Germany ...and I obtained one, and proceeded to modify it for more oil, better cooling (well, a bit), adding windage vanes and deflectors.  I went a bit overboard, I guess.    I think I gained some small amount of horsepower from the less violent air in the crankcase.  I went to quite some length to do this, even making a sheet metal air deflector underneath the camshaft area. Drilling the engine block and threading those holes for screws to hold that deflector was not a fun job.

While a blower, longer cam timing and larger flow at the intake valve is helpful, and I also used offset high lift rockers.   Pushrods and lifters were modified.   Goal was always less weight but stronger, and higher performance in any way I could, reliably.   In order to reach high RPM reliably the valve gear must be lightened, and be very strong.

The original camshaft was to be replaced by a BMW factory racing camshaft that I happened to have.  It proved OK, but not good enough for my bike. That was determined from tests in a friend's R75/5 which he was hopping up, but not anything like mine was.  He liked the cam. I obtained another camshaft and it was reground for longer duration, still with a a slow ramp, and then hardened.  When you do things with camshaft lobes, you often must modify the head for various clearances ...especially with high lift rockers... forewarned!  I did it both ways on purpose, so as to keep the cam ramps fairly gentle, that is, NOT abrupt, which  tends to cause increased valve gear acceleration and attendant problems.  You don't need such abruptness anyway with a blower.

Initially the engine was kept a 750.  Later, the displacement WAS increased, but LOOKED stock.  This was a very tricky thing to do to the original R75/5 cylinders.  Special oversize cylinders were available from Germany.    It is tricky to increase the displacement, due to how the studs fit the engine, especially on the early engines.  Pistons were not available (I could not use the R90/6 ones for technical reasons), so I finally installed aftermarket pistons, suitably modified.

The heads had single plugs, and the compression ratio was NOT specifically lowered, which was slightly higher than stock due to the larger bore, etc. 

I tried using dual points, but that was a failure.  The ignition I kept was the stock points type (modified for high rpm stability). The long dwell wide advance early BMW automatic advance unit was used.  An ignition points amplifier was designed and built.  Points current ...from memory here ...was about 1/4th ampere, and the points amplifier was designed with a filter circuit such that multiple triggering's from one points opening or points bounce that is, would be unlikely.  Later, I designed and built a Capacitive Discharge Ignition, that fired surface gap racing plugs.  That ignition had a very special set of racing coils.  The final change to the ignition was to make my own pickup that was crankshaft triggered, and the CDI ignition was modified so that MULTIPLE (practically continuous for some milliseconds) sparks occurred at each cylinder's triggering. I found that projected nose plugs, as stock, but colder-rated, worked better than surface gap plugs; but I was able, due to the power of the CDI unit, to increase the spark plug gap.   I had access to a really good dyno (Axtel's) so a lot of testing was done for these things, and many others.  Much time was spent on setting up the ignition ...and the ""so-called-carburetion""  (HAH!!)

I did a LOT of work, eventually, on an electronic circuit that controlled the ignition advance.   At one time I tried adding a vacuum advance unit, acting as a retard with large sudden throttle openings, but was not happy with it.

The alternator was initially changed to the late 280 watt, 105 mm type.  The battery was a small multi-wet-cell nickel-cadmium type from a corporate jet, in a metal case, located inside a hollowed stock black German Varta battery case. 

The exhaust system was simply a modified version of the stock system, with added crossover, and modified muffler innards.  It was relatively QUIET! ...but was LONGER than stock, but hardly anyone ever noticed that.... or the faint-appearing extra seam.  This was done originally in conjunction with the modified intake system.   Later this was again modified.   In the photo, the longer exhaust is not installed, as it was, as I remember, installed in 1981 or 1982.

I made various versions of the supercharger drive. Making a good drive drove me crazy.   In the first version, I removed the starter motor, removed the alternator, and made an adjustable diameter v-belt pulley that fit in place of the alternator rotor.  I mounted the special almost un-obtainium supercharger in place of the starter motor.  It was slightly higher and a tad wider than would fit under the starter cover, so I heli-arc welded higher sides, a bit offset, to the starter cover, then machined that area, and painted the the engine looked stock to a reasonable look-see.   Due to constraints on pulley sizes that would fit, things did not work out for the boost pressure and characteristics I wanted.  If I could have obtained the specifications on the blower, that would have helped.   The blower was reversed, alternator reinstalled, and a modified flywheel and ring gear was used to drive the blower.  The gears were straight cut, since I could make that myself.    Try as I did, shimming, etc., that setup would whine a lot ...REALLY A LOT.  I even tried a bronze drive gear with little help.  I needed to make a quieter helical flywheel ring gear and drive, but never got around to that massive job; although I started some design and experimental machining work.  One problem would be that if I used quieter ring gear teeth, the forces would tend to move the ring gear off the flywheel!  I developed a method of pinning the ring gear.  In the second major revision I ended up using a mill to "drill" the interface of ring gear and flywheel and installing 4 bearing rollers in them, tapering them and mounting each at 90.   I could write a small book on what I tried, what worked, what did not, and how the final supercharger drive ended up.  It was quieter, still noisy, but much more reliable, did not need hardly much in constant lubrication.  Initially I had a lot of trouble with wear on the parts. I consulted with an old-time machinist; who had some interesting ideas.  He agreed to help me make the parts, and that is what we ended-up doing.  The resulting drive was MUCH quieter, & although still quite noticeable, it was less power-robbing.  The teeth shape was quite interesting, to say the least, and I was simply fascinated watching him make the parts talents that time ...did not include that type of machine work.  He also lightened the flywheel for me, which had been intended all along, so I did not have to do that myself.  There is a photo on this website that shows a similarly lightened flywheel:

One of the problems with the drive system that my machinist friend came up with was that we had only a very crude way of adjusting the depth of engagement.  We discussed that problem and I made an adjustable pair of thin but ridged wedges type mounts were made to adjust the engagement of the blower gear and the 'starter' gear. This was crude, but easily adjusted.  He solved the final problem for me, over a beer with him.  Lubrication for the gear drive was imperative! ....we made a partially enclosed oil mist system, using the engine BREATHER system!  We tufted it, and determined how to mostly keep the mist off the clutch.  It took hardly any oil on the ring gear and blower gear to keep it lubricated.  At one time I had actually contemplated a multiplate wet clutch, and I began experimenting with a design for one; it was a big chore.   It amazed me that the drive held up for a lot of miles before I had to overhaul it again.

The starter, being gone, meant the engine was kick-started.  Starting would have been VERY difficult (and WAS, initially!), due to the long atomized fuel path (a lot of condensation of the fuel too!) and very low amount of intake flow 'per kick' a simple fuel injector was modified and installed, hidden, into the airbox, used ONLY for starting.  It operated every time the starter button was depressed (yes, that was what the starter button did, ONLY).  That was later removed.  The injector was a 1968 VW gasoline car electric injector, the same type I ended up using (2) at the intake of the supercharger.  In a modification almost no one every noticed, I installed a later model on-bars choke lever assembly, and put a teeny switch inside it, for the 'electric' choke (that injector for starting). Later, I thought better of this, due to the occasional questions, and put a tiny push button switch on the lower area of the headlight shell, which made it rather hidden. I went back to the other type eventually.

Almost no one ever saw this bike as 'modified', except the usual bags and fairing.   That had been my intention.

Backtracking a bit again:
The blower, initially, before the injection was installed, sucked air from a modified carburetor, a rather flat carburetor from an industrial engine ....gravity fed from the stock fuel tank.  There was a pop-off backfire valve, that doubled as a over-boost release valve, crudely made but effective, in the right side clamshell area, that exited from a hole, that I told people, if they asked, that it was an extra breather outlet.   The entire intake system was fully closed, and sealed from the air normally coming from the timing chest/alternator area.   It was THIS carburetor that a SINGLE cable from the slightly modified throttle twist grip area, originally operated.    This system worked, but had a lot of problems, so I removed it and used the VW injectors.  The injectors were fed by a very common car fuel pump initially, and later I used a hidden "aircraft" electric fuel pump.  The electrical signal for the injectors was a small flat industrial type Allen Bradley potentiometer, hidden INSIDE the modified (on a mill) stock-looking throttle assembly at the handlebars. It needed three wires to go to my little control box.  I used a very tiny gauge insulated wire, one run inside of each of the two original throttle cables, which were zip tied under the fuel tank, and the electric wires then ran to the hidden tiny control box.  The amount of milling and heliarc work and re-milling to enclose it inside that throttle housing was considerable.   I was pretty proud of the throttle assembly.  Only three people ever noticed the humps on the throttle assembly, and I managed to convince two of them that I had made my own throttle gear for faster action of the throttle; the other one was told it was the Euro version!

So ...the control rheostat was INSIDE the throttle assembly, and wires from that control went into and down inside the modified original throttle cable outer sheath, inner steel cable being removed.  Turning the throttle caused the potentiometer to change its wiper position.   I did a lot of experimenting with this method, and it ended up working well.  It is very much true that due to the simple method of controlling the fuel flow, that over some of the throttle range versus RPM, the engine could be lean, or rich, or VERY rich, etc.    The average initial mileage was very low, and I really had to pay attention to where the next gasoline station was!  I figured out a way to minimize the differences, and installed a modification, which greatly improved throttle response AND fuel mileage.

There were major hassles along the way getting the fuel delivery to be low enough for idle; and, to have a butterfly air control. I actually tried the butterfly method of the Bing CV carbs, but was unhappy about how it worked on my modified monster. If I ever made another of these bikes I think I could make that work though.  I ended up using a butterfly and shaft from a much larger American car carburetor, and connected it in the intake area of the blower, and controlled it from the stock throttle cables initially.     It was VERY tricky to coordinate the injector potentiometer and that cable-to-butterfly. I fiddled for hours.  I finally found a very interesting way of doing it, with selectable pins holes and a home-made small cam.  A final modification was then made to the throttle. I left the potentiometer wires and system, but I put a spring onto the butterfly, and finessed it so that incoming air helped to open the butterfly, depending on rpm. I got the idea from a car carburetor.    This worked far better than I had hoped.

The rear brake looked stock, but had high friction linings, actuating cam modifications too.  The over-all effective leverage was increased.  It appeared stock.   The suspension looked stock, but the rear shocks were opened, played with, and the front forks rather modified internally, including brazing up a couple of the rod holes, different restriction rings, etc.  The front brake was VERY much modified. Notice, in the photo, how stock it looks! That front brake was pretty touchy when cold or damp and you were on the first use in the morning.....but, after initial use it was powerful. It was BETTER than the twin Brembo disc brakes of the early 1980's BMW least until the brake was used so much that it got quite hot.

A LOT of effort was made to try to get good boost characteristics.   There are numerous types of mechanical superchargers, commonly seen are the vane, roots, and the centrifugal, and they have differing characteristics.  All pull a fair amount of horsepower from the engine, some WAY too much.  The type I used was a rather sophisticated modified vane type.  It was one of the very first ones ever made that had semi-flexible vanes, and did not have too high a power drain, and it produced boost at a quite reasonable rpm, and had a rather nice boost pressure curve.  The vanes were exotic, and, yes, they flexed (to reduce effective blade pitch) as designed as rpm rose.  I did a lot of work to prevent backfires (which never occurred), as I was sure a backfire would destroy the vanes and maybe pistons; I was sure I could never get another vane scroll. The supercharger had not only cleverly designed vanes, but a flexible diaphragm, that changed some clearances as rpm rose, to prevent damage and control boost characteristics.   There is only one supercharger ever available, and a few were sold, that had these characteristics, before the company failed.  Have fun finding out what/which!  

Avon Green Spot race tires were my standard tires later on, as I got a mess of them free.  Previously the tires were the old Continental RB2/K112.  I wore out tires at a prodigious rate if I was showing off what the throttle could do!

I did a lot of experimenting with the clutch.  I ended up with a very strong clutch, with a light feel to the lever at the bars.  This was NOT done by adding some sort of EZ-clutch pulley arrangement at the transmission lever.  I 'borrowed' an idea from a Guzzi, and went a lot further.  I made up a DUAL friction discs clutch.   All items were modified so as to allow proper fit and operation. It was tricky only in the problem with the length of the transmission input splines. I toyed with lengthening them. The flywheel had already been lightened, so installing a dual clutch had some constraints, but it worked fine after many initial problems.   My friend the machinist had a couple of inputs into the clutch and the input shaft when I got stumped.  His advice was surely welcomed.   The twin clutch was not really needed, and I wasted a lot of time on the project.

Now, you are probably asking, how about PERFORMANCE?

Well, let us start with the handling.  With the improved brakes, modified front and rear shocks and changed springs and valving, and a sturdier top triple clamp, a frame beef-up near both the battery and steering head, and a beefy brace as part of the fender mount, ...the handling and braking was good.  The short wheelbase and the fairing, made for reasonable handling.   I refused to modify to the long wheelbase version (although, as much earlier noted, I had planned to install a Monolever eventually).  

Power:   YES!!  LOTS!!    Power came on reasonably quickly, and just kept building. Acceleration through the gears (4) was VERY brisk.  The engine idled roughly and noisily (including a loud whine from the blower drive) at about 1300 rpm.  Some of this was due to the camshaft.  It was what is called a Blower Cam; with long intake duration and had increased lift (the modified rocker arm increased lift). I had made an educated guess on what the cam grind should be, and it worked out OK.    The bike was probably a bit slower on a jackrabbit take-off unless more than normal RPM was used and since immediate torque and flywheel energy was lower, I slipped the clutch more on takeoffs.  But, it was NOT excessive.  I tried to ride the bike normally MOST of the time.  Of course, when the adrenalin and testosterone kicked-in.....

I lucked out pretty good on the throttle feel. Blower drive was a fairly high ratio, which had a goodly effect on the boost characteristics (remember, also, that the blower had a diaphragm and flex vanes).  After the rpm crossed about 2800, the boost came in, and it came in very smoothly, but very slowly, until around 3700 rpm, then it boosted much faster on a steeply improving curve; this was easily seen with my 'boost gauge', which was totally not what it looked like!  It looked like a clock!    There was no control to shut off boost; but there was one to increase boost. Remember I mentioned that diaphragm in the blower?    Approaching 5000 rpm, the boost rose rather fast. A lever control connected to the side of the blower.  Originally electric, I finally made it mechanical, and it did not move much until the throttle was moved beyond about 70%, at which time it moved increasingly very fast (my homemade teeny crude cam on it).  While I could accelerate at Gentleman's rate, I could also whack the throttle when I wanted-to.

Sitting upright, in normal touring position, with sudden full throttle at about 5000 rpm, the front wheel would rise, and continue to rise to a quite nasty height, to about 7500, when I would usually back off the throttle.  I only took it beyond 7500 a few dozen times, once to 8000.     In order to keep the front wheel on the ground I had to move my butt ...and also lean WAY FORWARD against the windshield above the audio speaker in the photo.

The bike was quick for its time, and I later incorporated a lower ratio rear drive, it had been 3.20.  The bike, with the 3.20, would reach redline rather easily, and going WAY past stock redline was also very easy.    The stock 4 speed gearbox was used; although modified a second time after I experienced some breakage problems with my too-radical quick-shifting original modifications. 

The dyno was showing 74 corrected horsepower at the rear wheel at approximately sea level, when we destroyed the rear tire. I had not even been near my personally imposed red-line rpm at the time.   This was on the best premium 102 octane pump gasoline. This type of power probably meant ~80+ at the flywheel, and I felt it could not safely be maintained ...I was sure the engine would explode/melt-down.  This was even though we monitored head temperatures.   Full throttle runs that lasted any period of time to 8000 rpm were not performed; none were done that lasted over maybe 10 seconds.  I did enough runs to make sure that the engine would run on the rich side of peak power, no matter what rpm and throttle position. This ended up being very tricky to get correct.  I felt that wasting LOTS! of fuel to keep the piston and head cooler was the safest thing to do.  It had only a small effect on power, but likely a lot of effect on not encouraging melt-downs!

There was never a serious mechanical problem, in normal (yes, even very spirited!) riding.   I did have the transmission problems mentioned, and one of my earliest modified rocker arms broke, and VERY luckily that did no serious damage.   Problems, little ones mostly, did occur, and these, such as oil leaks, were fixed, although I could NEVER fix leaks permanently at the cylinder bases ...the power was too great for the cases and cylinders. The method of a large O-ring that BMW introduced much later might have helped to solve that problem, but maybe not, because I think the leaks occurred at the stud threads area and from 'walking'.  I suspect that the /5 case and cylinder dimensions would still let the cylinders 'walk' some.

The was bike ridden a fair amount with no other major problems.  I toured with my wife Jean, see photo, numerous times.  I did have an iron-clad rule, no trips over 800 miles in one direction (thinking of towing/trailer costs...).    NOT ONE PERSON ever noticed that it was supercharged.  A few asked about the gear drive whine.  If anyone mentioned the whine, I'd give a variety of answers. One (besides other's I've mentioned) was to point to the odometer, and say it really REALLY needed a new set of timing sprockets and chain.

The use of the sort of power available, even at part throttle at reasonable (?) speeds, was VERY hard on the exhaust valves. The heads were removed at 12 to 15,000 mile intervals, and a valve job done. I had other bikes in the garage, so I did not have to ride this one all the time ...but, surely did love riding it.  The intake valve, surprisingly, also had wear problems. 

Oil:  Castrol R, 40 SAE, just because I liked the smell and had used it in my Norton Manx's ...and, truth is, it was, then, a GREAT lubricant.

Rear end:  3.20 early, then later changed to 3.00, then 2.91.
Tires:  Back to Continental RB2 and K112, later, Metzeler ME88's.
Front forks:  true progressive springs and two brazed up rod holes, a few other mods too, including the restriction rings, and I used Mil 5606A oil.
Rear shocks:  stock, but internally modified to give stiffer shock action.
Oil and system pressure:  pressure was increased over stock. I don't remember the maximum, it was considerably higher than stock as I had modified the pump and the over-pressure valve (which sits above the crankshaft sprocket at the front of the engine).
Boost, high:  ~14 pounds at ~6300 rpm. It could go higher if rpm was increased. No mechanically actuated boost relief valve was ever installed, although I had a trick reliever port set for 16 psi.
Boost, low: a bit under 3 psi at about 3200 rpm, WOT.  At various times I had as much as 5 psi or tad more, at lower rpm....depending on what I was playing with.
Boost calculations were normalized to 15 psi atmospheric, thus boost pressures noted are REAL, and above absolute atmospheric.
Air intake temperature:  Too damned high, did various things, was still high ...but not terrible.  Gasoline was cheap, so ran engine rich, which helps with cooling.
Sound level:  Exhaust louder, deeper, pleasing.  Gear drive whine was rather excessive in every version, and eventually reduced to 'acceptable' ....but still noisy.
Top speed:  unknown. It would probably hit redline in 4th with the 2.91 rear end I used for awhile.
Drag strip:  never had it on one.
Wheelies:  no problem. 

Present location:  I'd love to know!

How to identify from a stock /5 toaster if you see it: 

Look at the starter motor cover .....look a bit tall to you?  Look a bit wider with a bit of curved overhang?  The throttle cover has a funny 'dual-bump' to it?     Put #1 eyeball on the carburetor shaft/linkage, careful look-see! I will add some things I did, or tried and rejected, at various times, etc.

I no longer have the blueprints nor photos of the drives I made up.  Most went with the new owner.  The first flywheel drive was simply (well, more or less) a modified ring gear on the flywheel. The flywheel was lightened as much as possible, photos of similar lightening, but not with the special ring gear, are in an article on this website. The flywheel was lightened because the supercharger drive added so much reverse direction inertia, and without lightening, shifting would have been rather slowed, not to mention the back-torque wear possible.

There was another problem that I had not thought of originally, that darn near got me and the bike into a LOT of trouble.  The inertia and the compression in the combustion chamber works on braking too!  Thus, when backing off the throttle, it is like adding brake to the rear wheel.  This could cause fun if the throttle was suddenly backed off, particularly at some decent rpm, and BAD if in a turn.  The effect would be similar to someone using rear brake and then, in a panic, backing off the rear brake; or, hitting the rear brake in a turn.  I had done some design work on paper, to try to use a one-way clutch on the supercharger drive, but never did much with the idea.  I had, twice, modified the transmission for easier shifting (particularly in widening the slots and changing the side angle entry in the dog gears).  Some of this was mentioned earlier in the article. I had failures in the early version, I made some parts too thin.

The simplest possible gear fitment was done, by shimming the bottom of the supercharger, for both height and tilt, by thin brass stock, instead of wedges, in the very last version before I sold the bike. Due to fast wear on the drive, a quite light oil MIST spray was added to the breather method I described, made of sheet metal so the drive gears were always slightly lubricated. The actual lubrication was improved by a single small ‘flag’ on the flywheel, that dipped into the small reservoir initially, but that was WAY too much oil, so I found out that just being near the oil was enough. It was quite simple, did not leak oil from spray either.  The oil level was tricky, so I finally installed another baffle. I had NO clutch problems.

This was my last extensively hopped-up motorcycle.  All other motorcycles I owned, if modified, were only mildly changed, things like oversized alternators, dual-plugging.   I did do a big modification job on my 1968 Dodge Power Wagon, with a huge supercharged engine, but that's another story.

10/14/2012:  Add QR code, add language button, update Google Ad-Sense code.
04/11/2013:  Add addendum and do a preliminary go-through of the article, to clarify and add details.
04/16/2013:  Update details....and more in October.
03/30/2016:  Update meta codes, clarify some details, improve layout, found some old figures and edited prior guesses, etc.  A bit more, 08/2016.
11/20/1016:  Fix metas, scripts, layout, excessive html. 

Copyright, 2013, R. Fleischer

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Last check/edit: Wednesday, January 17, 2018