Dear Editor and Fellow Club members:
The response to "Basic Road Rod Tuning Tips" has been very positive and I appreciate your interest. Keep the letters coming and I will do a follow up piece soon that answers all the questions you have written in and asked about. I had no letters about the new 1100 twin engine but we have decided to go ahead with the following report anyway.
What a fine motorcycle they have sent us! That front end sets a new standard for all other manufactures to deal wit h as they will now have to move thru us to go forward - its that good. Mid-speed rough pavement sweepers that shake a K four valve around some what while whitening your knuckles are as simple as "point and shoot" on the new RS twins. The Bridgestones we ar out much quicker than other tires but stick, stick, stick, right on over till the heads touchdown. Quick changes of direction however, require a little practice - especially if the new bike is loaded two up, has heavy baggage, or both. Its not the bi kes fault, its quite willing to flick till the cows come home, its that lag time between the rider sending the message and the bike receiving it.
Please BMW, rethink the rubber bar mounts before someone runs off the road. At least offer us three har dness grades of rubber insets to choose from, for as it is now a BMW with merely "vague" handlebar feedback in the colder areas and climates will be impossibly "soft" when summer rolls around down in the Del Rio area of Texas. I bought the first 1984 K10 0RS sold in Florida, wrote at once to BMW about the rubber mount bars, and was amazed at how much better that bike handled when I solid mounted the "rider to fork link". Already the C and C boys in California who are getting one of the puppies ready for Daytona have solid mounted the 1100 twin bars and Chris H. is reporting "serious, no prisoner" handling even on tight road courses.
As you know BMW puts safety first and they must feel a rubber mounted bar prevents vibration fatigue, or "bar grip lo ss" if the front wheel were to strike a "line altering" object in the road. Perhaps, but for those who want maximum feedback and immediate precise handling, the rubber mount bars have go to go.
Everyone has been struck with the quickness of the new bikes and their ease of transition from dead stop to moving - they just don't stall very easy and will pull away in first gear even with no or little throttle opening. Strike a big point for the touring and two-up group who remember so well how easy the old 1981 - on twins would bog down off idle when loaded with luggage and passenger. How many bikes fell over because of this? Their light flywheels and long rods made for a "easy bog" combination. Not so the new twin! BMW choose a fine, strong, short, connecting rod to help prevent anymore "ease off slow" problems.
How so? you ask. The shorter the Rod Length Ratio the more mechanical advantage (power transferred) in the first 90 degrees of crank movement - that is in a Short RLR engine the pis ton has moved further down the cylinder when the crank reaches 90 degrees ATDC than on its Long RLR counterpart. So nice that BMW has given us a bike with so much torque right off idle. Remember, there is only one bike engine being currently produced wi th a shorter RLR than the new 1100 twin - the most notorious non-bogger of them all, the Harley 1340cc V-2 evolution with its 1.68 RLR.
The new twin spins up quick and pulls easily thru its mid-range in top gear until right around 6700 RPMs where a slight struggle starts and by 7000 RPMs a wall of resistance is encountered. By 7400 RPMs its over for most of the 1100 twins. The most we've gotten out of a perfectly stock, well tuned, RS with 9000 miles on it, is 135 mph at 7450 RPMs and it took a wh ile to get there. Why is this and what can we do about it.
For now we must settle for pipes, chips, and hi-flow air cleaners which will only help a tiny bit on top-end but quite a bit on mid range - a place where the bike already shines. Luftmeist er seems to be the first out with the most although C and C and BMW of Fort Worth are not far behind. I'm sure Iron Horse BMW in Tucson is mulling some things over also. Matt and the "Luftcrew" have chipped in where BMW chipped out and offer a twin carb on-fiber muffler setup which is combined with a chip that keeps a ignition advance curve tied directly to engine RPMs rather than the stock chip from BMW which flattens the ignition curve momentarily in the 3000 to 5000 RPM range before letting it arch ba ck up (advance) for its remaining 2900 RPMs. BMW's decision to slow the curve down some in this middle "cruise" range was/is a effort to make sure that you can run the bike at highway speed for a long time on any gas, no matter how bad it is, without pin ging. Then if you decide to go fast on "bad gas" (low octane) they put the timing back where it should be and let a obscure SRLR factor take over from there on up to prevent a ping problem.
As a general rule the lower the RLR of a engine the less l ikely it is to detonate or ping at upper RPMs and even if it did the damage would be much less over a accumulated time than on a high RLR engine run under similar conditions. Why? The window of opportunity for detonation is open very briefly on the SRLR engine because the piston simply does not hang around long enough to get in trouble at higher RPMs.
Luftmeister's chip takes advantage of the stock flat mid-curve and fills it out offering more power in the middle. Then the trick pipes, and hi-flo w air cleaners take over to let the engine pull up top a little better. Matt told me that they are getting a much quicker bike with his power-pack set up but still it takes a while to pull up top - even though they have rechipped the Rev-limiter to 9000 RPMs. They did manage 7900 in top gear, but that is all (142 mph), even with pipes, hi-flow, and full-curve ignition chip. Why?
Just like I said before - Rods. Too short for high RPM power. We will just have to wait a little longer. The Califor nia boys are making up two sets of long rods to specifications I suggested and plan to try these in the new twin. If they work well (I know they will) then soon we can all have Long Rods and new pistons in our 1100 twins and if we chip-up, re-pipe, and e asy-suck at the same time it'll be Adios Ducati or anything else twin wise. 9000 RPMs on a R1100RS is 163.8 mph so come on "Luftcrew" lets have um.
Back in the here and now, however, there is still a small problem. What can 1993 R1100 owners do ab out their transmissions? These things up shift so poorly from 1st to 2nd and 2nd to 3rd that the owner is ashamed to drive in a quiet part of town. Forget soft clunk - think ball peen hammer. And downshift? Are you crazy? The best way to downshift a 93 R1100 is to come to a stop then downshift. These are simply the clunkest, loudest, bangingest transmissions BMW has ever put in a machine. Why?
They decided to gear up in the transmission and gear down at the rear end - the exact opposite from past practice and a embarrassing problem they have already tried to correct in the 94 bikes. Think like this - when a transmission is geared higher thru out its five speeds the opportunity for proper gear mesh in a time/RPM frame is less than in a transm ission that is geared lower throughout its five gear range. Both units can shift properly if engine speed, rear wheel, and clutch are perfectly coordinated, but the lower ratio geared unit can tolerate much more leeway of coordination than the higher rat io unit.
BMW must have come to the same conclusion (I wish they had asked me first) because the 1994 bikes clunk much less and have been geared down in the transmission (from 1.32 in 93 to 1.54 or 1.45 in 94) and up at the rear end (3.09 in 93 to 2. 81 in 94).
Is there a silver lining in these dark 93 transmission clouds. Yes! Now I feel lucky to have that high ratio transmission in my 93 RSL because I can gear up three more ratios on the rear if I so desire and the 94 bikes only have one (2. 75) option left to go. So thats exactly what I did. The first class, absolutely professional, BMW of Orlando pulled some tricks and got me a 2.81 rear end (off the 94 assembly line) and that is what my bike now has, sure I'm geared a little tall but it shifts so much better and I can put that mid-range torque to really good use. As mentioned earlier the bikes pull real good til about 6700 at which point their short (no-ping) rods start to work against them. With my new 2.81 rear on my 1.32 transmissi on I'm geared for 136 mph at 6800. the bike will pull just above 7000 RPMs (140 mph) so I'm very happy and recommend that others consider this update if they don't mind losing a little down low. The bike shifts smoother and runs 4 mph faster and gets be tter mileage - all by switching out a $900.00 factory part. More over, with a progressive ignition chip, low pressure pipe, and a hi-flow air filter I may be able to touch 150 mph, who knows? We'll see!
Some unusual things have started to show up about the bikes. Windshields are cracking around the four mount screws. Use a bigger washer here and don't overtighten. Perry B. and the boys at BMW of Fort Worth have reported several occurrences of what I'm calling "blip and flip". If you have the choke on and are blipping the throttle during warm up - don't blip the throttle and flip the choke off at the same time - a carb cable can come out of its pull slot if the two conditions coincide just right.
Nobody knows how the velcro patches are s upposed to work. I've talked to a few people who were marginally satisfied but most had given up. Seems the oily protective spray that covers the new bikes for shipping renders the velcro useless. Most dealers are replacing these on demand.
I've had at least one report of a defective transmission gear indication switch and these require a swing arm pull to replace. Nobody likes the gear shifter and some people (me included) think the transmissions have too much end play on their gears and shafts .
The bikes are very susceptible to cable stretch and I recommend taping the twist grip open when the bike is not in use to stretch the cables on a new bike so that when your dealer does set the two injector bodies one to the other they will stay in sinc longer. The rattle sound the bikes make when idling in neutral are the gears shaking in the transmission and this can be quietened by having perfect sinc between the two intakes. Would you believe it? Sinc them perfectly and the neutral chatter s tops - let one butterfly out and the chatter starts up. This lets you know how loose things are inside the transmission - bear in mind that pulling the clutch in stops neutral chatter at once.
BMW - we want a totally new transmission by 1996 to go with the new engine castings for the K bikes that will include big nobs on the front to hold a new tele-a-lever front end. I also hope that variable cam timing will be considered for the new generation K's to further complement a move toward one injector per intake port, longer rods, and "tube stem" (hollow core" valves). Just wishing.
There are a lot of things starting to gel down the line and the biggest one for me and I hope a fun one for the members, will be the August issue of the News in whi ch I hope to have a report on riding the turbo K bike of Luftmeister. All of this is in the works and I hope to pilot the bike at El Mirage this coming May 29th. The idea is to write a overview of the Luftmeister turbo projects that have culminated in t heir current 200 plus MPH bike. Wish me luck. i'm getting in shape and promise to put safety first in the hope that speed will follow. Those guys would love to help me get that puppy up near the 200 mph mark and they certainly have a willing pupil to w ork with. As always, if you have a specific performance question on which you would like a second opinion please write to me. Til then, keep the rubber side down.
Jim "Dr. Curve" Roche P.O. Box 881 Tallahassee, FL 32302
Jim(Dr.Curve) Roche jroche@mailer.fsu.edu high performance old twins