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Old 09-26-2009, 07:04 AM   #1
walkingbear OP
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Get More Punch out of your boxer

Just found my Motorcycle Consumer News: January 1994
on how to "Get More Punch out of your boxer"

I will scan and put on this thread this evening.

EMAIL ME AND I WILL SEND YOU THE PDF OR IF SOMEONE CAN POST THE
PDF ON THIS THREAD IT WOULD BE BETTER

How To

Get More
PUNCH Out Of Your
Boxer














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walkingbear screwed with this post 09-27-2009 at 08:03 AM
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Old 09-26-2009, 08:31 AM   #2
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Old 09-26-2009, 11:08 AM   #3
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1994? they will probably tell us to upgrade to an oilhead next year

I wonder if motorcycle consumer news would advocate fixing old ones rather than consuming new ones.


Nevertheless, I'm curious, too!
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Old 09-26-2009, 11:37 AM   #4
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Upgrades

When I was looking for a gs .. I followed almost everything
and it was the finest riding airhead I ever owned.

I was stupid to sell it.. that is why I went looking for the
mag. I had in storage.

So I will share.......................
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Old 09-27-2009, 12:33 PM   #5
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Walkingbear, folks,
I worked a bit on the text coming out of the OCR. Here's the result. Images missing.

{edit} oops - took same time to edit the content, meanwhile Walkingbear added the original scans. Too late...!
Thank you - this is a brilliant article.

---------------------------------------


BMW twins. are wonderful bikes. In their various guises they have covered millions of miles of pavement, dirt and sand. It seems that the only thing they can't pass is a gas station. The newest boxers are lucky to get 40 miles per gallon, and many average less than that. This was not always the ca~ In the mid-'70s, the R90/6 was one of the best mileage bikes on the market, averag*ing 55 mpg. Although mileage declined gradually over the years, it seems to have gotten worse in the mid 80s.
My first dealings with gas mileage were innocent enough. At about age 13, I rolled my mini-bike down the hill to the nearest gas station and filled its half-gallon tank to the rim. I would then run circles around the parking lot. After a while I got to know about how man:y laps I could do around the lot before the tank would run dry.
Later on I bought a real motorcycle, and all of a sudden tank size took on a new meaning. The R65 I owned had a large, 5.7 gallon tank. That bike only managed to squeeze out about 3S miles to the gallon. On top of. that, the bike had a lousy idle, not much power, and less than perfect carburetion. These were the dark days of EPA*mandated pollution controls, well before the manufacturers figured out how to make bikes run well and clean at the same time.
With the R100GS test bike featured in this article, it took almost two years of changes before it was fairly well sorted out. The changes included: a K&N air ftlter, a hotter igni*tion with two spark plugs per cylinder, much revised jet*ting, a three-angle valve job and a few other tweaks. But, when all was done, the bike got 57 miles per gallon and was noticeably faster than stock.
A friend of mine, Chris Hodgson, the founder c.c. Products in San Jose, Califor*.nia, dabbled in various odd*ballprojects before settling on becoming a premier WestCoast BMW hotrod shop. He supplied the machining, the dyno and some of the aftermarket parts for this ongoing experiment.
C.C. Products has been around for $out 10 years, but in the early, demented days the shop performed some bizarre experiments upon some innocent Gold Wings. At one extreme, the bikes were braced up, stripped down and fitted with a Weber carb and a Roots-type supercharger. Another time the boys entered a Wing in a high mileage contest. They managed to squeeze 10S mpg out of the beast.
In true mileage contest tradition, the bike was none too normal. It wore a full fairing that Chris designed md made (his degree is in aeronautical engineering), and rode on 2.75 by IS tires.
To optimize mileage, the engine was shut off as often as possible and the bike coasted. Such is how bikes win contests.
The real challenge with modifying any motorcycle for better performance is two tiered. First, we wanted to make a normal, practical bike more efficient while still retaining its road manners. Second, we wanted to do it without spending a lot of money. That was the goal of this new project.
Of the boxers, the R100GS is by far the most popular and in Germany it is the most popular motorcycle sold-period. Also, if one actually believes that some of the Paris-Dakar replicas are being ridden around the world (which quite a few are) then it would be important to the owners of those machines to be able to travel a bit further before having to push their steel camels.
Much of what we did would work on other motor*cycles, especially big two*valve twins such as Guzzis, Harleys and Ducatis. In its stock form the R100GS made 61.33 horsepower and 49.32 foot -pounds of torque as measured at the rear wheel on the C.C. Products dyno. All dynamometer measurements made in top gear. It got 38 mpg in mixed (highway and local) riding. Although no two dynos agree on how big a horse is, what is important is the relative change.
It does seem odd that with today's higher gas prices and tighter emission standards that a machine should pro*duce worse mileage, and there are certain explanations. It doesn't take an engineering degree from M.LT. to figure out that a 1000cc motorcycle engine that can barely pump out 60 hp and only gets about 38 mpg is not the peak of thermodynamic efficiency. In short, the cylinder heads are barbaric pieces of junk. No real surprise here, as the basic combustion chamber shape hasn't changed since they were invented.

DYNAMOMETER RESULTS

Stage One
Carburetion was the first thing we attacked. The as uses a pair of conventional 32mm Bing (40mm in Eng*land) round-slide constant velocity carbs. Although decidedly untrendy, these are high quality units that can be made to work quite well. We were in no hurry to swap them for some other type or brand of carbo
A rather curious thing happens when one tries to make an engine run at the stoichiometrically correct (14 :1 air-to-fuel ratio by weight) mixture - gas mileage decreases! Of course you probably don't believe me, so get hold of the brilliant Bosch technical manual on Motronic injection systems and check out the nifty graphs they have which say the same thing. Chris installed a K&N air filter, substituted a larger pilot, needle and main jet, twiddled the mixture screws and, voila, a few miles per gallon were picked up. What's more important, the rideability of the machine improved.
Problem is, BMWs just don't want to run on lean jetting. Removing the stock intake horns from the airbox and replacing them with larger ones was tried, but that gave a bad flat spot in the low end. Leaving the horns off in con*junction with a less restrictive exhaust gave the best results.
One might try leaving on the air horns and drilling a few holes in the top of the airbox.

AWstock dynamometer results. Notice "that maximum horsepower is 61.33 at 105.32 mph in top gear.

The heart of the twin-plug Boxer is modifying the head to accept another sparkplug and doing a three-angle valve grind. Moving into the Stage Two modifications, the head was milled to provide a slightly higher com*pression ratio.

Sometime during the early part of the testing the new type Bing float bowls were installed. These use separate plastic floats rather than the dense foam unit on the stocker. The new float bowl assembly is said to allow the carb to meter better because the float level remains more consistent. What's more, the new floats are impervious to alcohol whereas the old foam ones would soak up alcohol, raising the fuel level in the float bowls and causing the bike to run rich. Unfortunately, the claims about less fuel sloshing and better mileage could not be verified on the dyno. The floats only act differently when a bike is moving. Although the higher mileage claims could not be verified, it was decided to leave the new float assemblies on because alcohol in gas is definitely a problem for BMWs.
Here is a practical side of the jetting/leanness/ richness/ better mileage formula. Years ago I rejetted the carbs on a 425 Suzuki, which was about as cold blooded as a bike could be. By richening the idle circuit and picking up the needles a bit, the bike warmed up faster and ran better at small throttle openings. It also got much better mileage when used to commute. The reality of the situation was that with overly lean idle jetting the bike had to be left on full choke for minutes, wasting a huge amount of gas (and no doubt carboning up the top*end).
The theory also holds that if one has a terrific combustion chamber and ignition system, then the jetting can be leaned.

Exhaust, Ignition and Combustion

The as uses a two-into-one exhaust system exiting high on the left side. There is a collector where the two header pipes join. It was felt that the stock system was too restrictive, especially after the intake track was freed up. So the stock system was canned and a stainless steel Super*Trapp system was substituted. This is a complete system, from the headpipes to the muffler. Although the number of discs used was varied from 4 to 8 (more discs allow more air to pass, and more noise), the mileage did not seem to suffer with more airflow. .
There was an immediate difference in the power characteristics, though. With fewer discs there was better low-end power, but a flat top*end. More discs meant more top-end with a weaker bottom-end. This noise/sound issue is very important. The exhaust can be run with as few as four discs, but power will fall off. Using six discs results in slightly more noise and power. Eight discs gave the best power but also the most noise.
Chris tells me that the next batch of SuperTrapp systems will feature a different inter*nal baffle diameter and will be quieter. The pipe was used throughout the testing as it was lighter, sounded nice and flowed more air than stock. With eight discs installed, the carbs rejetted and a K&N filter, the bike made 64.421 horsepower and got 44 mpg. This was the best that was seen with single plugs. Thus, this became known as Stage One. A 5-percent gain in horsepower and a 15-percent gain in mileage with only a few bolt-on goodies.

Stage Two

The as uses a Bosch cm ignition coupled to a single, dual-lead coil to fire a single plug in each head. The triggering is magnetic, but the advance mechanism is the old-fashioned mechanical advance with springs and bob weights.


Jetting upped on idle and low end. Note the bad flat spot.

Timing is always critical. In the last 20 years BMW has retarded the timing on the boxers from 9 degrees BIDC at idle to 40 degrees full advance on the slash 5 models, to 3 degrees BIDC at idle and 32 degrees full advance.
Contrary to what many shadetree wrenches believe, more power cannot be had by advancing the timing. Actually, less total ignition advance is a sign of a better combustion chamber. The better the gas and air mix together, the faster the incoming charge, the better the swirl, and the more efficient the combustion chamber shape, the less time the bike needs to get its flame across the combustion chamber and make a complete burn.
As C.C. Products refined several other vintage BMW s, they found that the bikes needed less and less ignition advance.
In the end, most made maximum power with only 27 degrees of ignition advance. Having said that, one must understand that a lean mixture does not ignite as easily nor burn as quickly as a rich mixture. Advancing the timing three degrees from stock improved the mileage with the stock single plug setup. It was decided to not use the advanced timing position as it made the bike harder to start and would probably make the bike run hotter in the summer.
Part of the problem comes from the fact that the BMW uses a single plug located on the side of a cylinder head that lives atop a 94 mm (3.7 inch) piston. This means that the flame has a long distance to travel. The less efficient the shape of the combustion chamber, the longer the flame takes to travel across the vast expanse.

DYNAMOMETER RESULTS

In his landmark book, The Internal Combustion Engine in Theory and Practice, C.F. Taylor of M.LT. experimented with the Larger main jets, high-lift rocker arms installed. Note a net gain of 9.58 horsepower location and quantity of sparkplugs using up to 17 plugs in a single cylinder head. What he found was that the location of the plug was much more important than the quantity of plugs. A small combustion chamber with a centrally located plug is fine. A huge combustion chamber with one plug located off on the side is the pits. More plugs is more better on a BMW head. More on this later.
The timing is critical. It is of the utmost importance that the Z (full advance mark) be lined up at high revs K&N Filter, SuperTrapp Exhaust added. Note that the horsepower produced is lower than stock, regardless of where the idle mark lines up. One must be very careful when setting the timing on a BMW as the possibility for parallax error is great.
Aim the timing light squarely into the timing hole, not down in at an angle.

Compression

The squish band is the narrow area on the perimeter of the piston/cylinder head where both come very close together. As the piston reaches top-dead-center the charge at the perimeter is squirted in toward the center of the combustion chamber. This added turbulence makes for better mixing of the fuel and air and makes for more complete and more rapid combustion. Racers will reduce this area by skimming the cylinder or underside of the head (or having different pistons made up) until the piston comes within .040 of an inch of the head or less:
The problem with such close tolerances on the street is that the edge of the combustion chamber is where carbon often forms first, and before too long the carbon will be thick enough to bridge the squish band and cause an actual physical contact between the piston and head. BMW sets their squish band at a stratospheric 0.80-0.90 inch.
In a four-stroke engine, usually the tighter the squeeze, the bigger the bang.
A gas/air charge that is compressed more will heat up more and be closer to combustion than would the same mixture at atmospheric pres*sure. Or, so goes the theory.
In reality a second factor comes in - detonation. With the lamp oil currently being marketed as high test and an ante-deluvian combustion chamber, one must live in fear of detonation. It is not just the loud clattery type of detonation but also the almost inaudible detonation that drops the efficiency of an engine.
BMW used 9.0 :1 compression on most of their bikes in the '70s, with 9.5: 1 reserved for the S models and the R60 (smaller piston area and more valve overlap). In 1980 BMW dropped the compression ratio to 8.2: 1 on all models, making them easier to start and run on lower octane fuels.

DYNAMOMETER RESULTS

The twin-plug set up. Though a little hard to see, the second plug resides directly below the stock one and adds considerably to mileage and engine effiiciency.

In 1987, BMW raised the compression ratio back up to 8.7:1 with no apparent ill effects. The seemingly obvious thing to do was to skim the head, thus tightening the squish band and upping the compression ratio. This was done, raising the compression ratio almost a full point. The result was a drop of 4 mpg and 4 horsepower.
It seems that 8.7:1 is about the most compression this engine can deal with on today's high test fuel. Obviously, detonation was starting to become a problem.

Twin Plugs to the Rescue

It was obviously time to improve combustion efficiency. Considering that every serious BMW racer has been twin-plugged, there must be some reason. In my own testing, once I twinplugged my R65, I was able to make serious changes in jetting. The twin plugging in and of itself will not make a serious change in mileage, but it allows one to rejet much leaner, thus increasing the mileage.

DYNAMOMETER RESULTS
On out test as, the heads were pulled, a second 14 mm spark plug hole poked in the bottom, and the heads rein*stalled with no other mechanical changes. A pair of Dyna twin-lead 6-volt coils wired in series were installed. Conventional solid core wires with 5K-ohm resistor caps were used because the Bosch ignition cannot tolerate the radio interference given off by a non-resistor cap.
Because the Bosch ignition is fragile, a Dyna ignition booster was installed between the stock ignition and the new coils. The booster isolates the expensive stock black box from heavy electrical draw. Now the stock system only controls the timing of the spark, the actual switching occurs within the Dyna box. A nice system when one is concerned about the life expectancy of a black box.
Did it work? You bet. With no other changes the mileage picked up. We began a series of jetting changes coming down on the main, pilot and needle jets as well as playing with the needle position. All proceeded well until we ran out of gas from one container and switched to another can. All of a sudden mileage plummeted. After much head scratching it was determined that we had been using 92 octane and had just grabbed a can of 87 octane swill. That was enough to push us over the line into detonation land. A switch to high test and the mileage jumped back up.
This is an important consideration for someone who will have to run the bike on low test. Don't raise the compression ratio if you cannot find good gas. A twin-plug stock compression bike can be run relatively lean and will still get better mileage than stock.
During the course of twiddling with the bike and repeated yanking the heads on and off, a few curious things were .'noted. At one point we noticed that the valve keepers on the right side intake valve were being sucked into the top spring retainer. When I pulled the head to replace the keeper, an even more bizarre problem was noted. The valve-to*guide clearance had grown to exceed shoe-to-foot clear*ance. Where normally tl).ere should be 0.0015-0.002 inch clearance, there was 0.004*0.006 inch of clearance. I can honestly say that I have never seen such a worn-out valve guide in a motorcycle, let alone one with only 10,000 miles on it. The valves were still in good shape, though.
For the past 10 years BMWs have had problems with premature valve, guide and seat wear. This is due more to an incompatibility of materials used than it is to lack of lead in the gas.
Because we wanted to maintain consistency in the test, the only parts replaced were the guides. The seats were given a proper three angle cut and the valves refaced.

GS Gains One Horsepower on Synthetic oil

Late in the dyno runs it was decided to test the effects of better oil. I have long been a fan of synthetic oil and have seen a marked drop in oil temperature as well as an increase in gas mileage when switching to synthetic. With no other changes, the bike's petroleum based oil was dumped and synthetic oil used. The bike picked up over one horsepower and the mileage improved also. Both Redline and Mobil One oils were used.
One of the big secrets to the Gold Wing mileage bike we spoke of earlier was its aerodynamics. The GS does not have aerodynamics, nor would most GS owners want it. We decided to do some riding tests and, after puttering around, rode through the mountains to San Jose and checked the mileage. Sixty-one miles per gallon was what we calculated. That was up from the original 38 mpg. What's more, the bike had an honest 10 more horsepower than stock and ran much bet*ter. The work was all straightforward stuff with simple, high quality parts used. If anything, the bike should be more reliable than stock.

The SuperTrapp exhaust system initially caused the Boxer horsepower to drop. It was not until other modifications were made that the system could shine.

The next step would be to work on the porting and piston shape. As it stands, the GS makes maximum power and gets best mileage at stock timing. Considering that the racer does its best with less timing, that means that the GS heads have a way to go before they are at their peak efficiency. The mechanical advance mechanism can be disassembled and modified to give less total advance while retaining the same amount of advance at idle. This is important, because retarding the timing over the whole range makes for sluggish bottom end.
Early on, we tried a boost air system. By running an air scoop and pressurizing the airbox, the heads can be fed with a slightly denser mixture delivered at a higher velocity. A higher velocity incoming charge means better mixing which could mean more power and/or better mileage. The pressure in the float bowls and gas tank must also be equalized for the system to work. This has promise, and will be worked on more in the future.
Stage I:
K&N air filter.......... $49.95
- Jetting Kit............... $30.00
SuperTrapp exhaust ..$325.00
Alcohol-proof floats $69.95
Package price.......... $474.50


This package raises the bike from 38 mpg and 61 horsepower to 44 mpg and 64 horsepower.


Stage II:
Twin plug package: ...$249.95 (includes machine work, Dyna coils, booster,
brackets, plug wires, etc.)
Stage I:.................... $474.50
Cylinder Head
Machining................ $50.00
Total (including Stage I)
.............................. .$770.00

This package raised the overall mileage to 61 mpg and 73.60 horsepower.

Contact:
c. C. Products
1886 W. San Car/os St.,
San Jose, CA 95182
(415) 559-6602

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Old 09-27-2009, 03:49 PM   #6
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interesting article.

Those prices seem more than 15 years old. My biggest question is: WOULD it be more reliable than stock? I guess some people will balk at the K+N bit. I'm on the fence on that one.
So essentially dual plugging allows leaner mixtures, thereby increasing fuel mileage. Did the three angle valve job really do anything? I thought it was a just a higher quality seal and face, but to actual performance? maybe...

one horsepower on synthetic? oh, man the oil threads will never shut up, now :lol
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Old 09-27-2009, 04:10 PM   #7
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It is an old article

It's old news.. believe it or not.

I have pro's and con's on dual plugging and
had my valves cut at 3 angles ..

Use syn oil in it.......
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Old 09-27-2009, 05:57 PM   #8
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thanks for posting that up. It was a good read.

It pretty much says the same thing that I've gathered from reading stuff on the internet. bump compression, lean the mix, retard the timing, dual plug and run higher octane gas.

Gotta say that 61 mpg is way more than what I expected.
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Old 09-27-2009, 06:35 PM   #9
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walkingbear, what are the cons to dual plugging the heads?

This is probably common knowledge but I did a search on C.C. Products and it turns out he bought San Jose BMW. I think I remember reading that on here somewhere, then promptly forgot it. I checked their site for any of this airhead info and I couldn't find anything. I'd like to check into a set of those heads and the exhaust for my project.
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Old 09-27-2009, 10:33 PM   #10
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another thread from 2001

http://www.advrider.com/forums/showthread.php?t=90
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Old 10-11-2009, 10:11 AM   #11
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weekly bump

for all to read
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Old 10-11-2009, 04:02 PM   #12
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I have it all saved. Thanks for sharing. Bill.
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Old 10-11-2009, 05:49 PM   #13
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Quote:
Originally Posted by AKjeff
walkingbear, what are the cons to dual plugging the heads?

This is probably common knowledge but I did a search on C.C. Products and it turns out he bought San Jose BMW. I think I remember reading that on here somewhere, then promptly forgot it. I checked their site for any of this airhead info and I couldn't find anything. I'd like to check into a set of those heads and the exhaust for my project.
Go the old's cool forum .. there are several articles of dual plugging.

Unless you have it done correctly .. you can send lots $$ for little gain if any.

A well tuned bike would do just as well.
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Old 10-14-2009, 01:12 PM   #14
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Quote:
Originally Posted by AKjeff
walkingbear, what are the cons to dual plugging the heads?
imho, the only con for street use is the Dyna coils: They're not as reliable as the old 6v Bosche coils that came stock on BMW's in the '70's and early '80's.

Having said that, they're probably no more failure prone than the twin tower 12v Bosche coils fitted to BMW's in the late '80's and early '90's.

This is good and useful information.

I'm still really enjoying my modified GSPD.

: Modded '77 RS heads (running 12:1 with Venolias)

: Venolia 1050cc forged pistons

: Andrews high-lift cam


It's faster than an 1150GS in any straight up contest.

This winter I might convert it to dual plug coils. The heads are already machined for dual plugs I've just shied away because of past experience with Dyna coils.

The only concern with my motor is oil consumption that's inherant with the 1050cc Venolia pistons and bored iron barrels. I add a liter to a liter and a half every 1.5k kms. I plan around it and carry oil when travelling. Not a big deal if I'm prepared, but not ideal.

Solution, I believe, might be the Sidenbrock 1070cc nikasil piston/cylinder kits available in Europe. Pics I've seen of those pistons offer hope that they'd work with these heads. ie: flat periphery for effective squish band.

But they're expensive.

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Old 10-14-2009, 01:24 PM   #15
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I dream of seibenrocks with the big fat pistons. :swoon

1900 euro's is still big bucks even without the VAT.

Arent the Seiben's only 9.5's?
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