1 Getting "European horsepower" out of a US K75? Sat Nov 28, 2020 3:54 pm
roach374
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Last edited by Laitch on Mon May 08, 2023 10:44 am; edited 2 times in total (Reason for editing : As stated above)
Not in Switzerland, but, yes 90 crank HP in other markets.brickrider2 wrote:A K100 doesn't make 75 hp?
Last edited by daveyson on Sat Nov 28, 2020 8:37 pm; edited 1 time in total
Well, if we come at the task using numerology... 7 & 5 = 12. 1 & 2 = 3. 3 is a nice triangular, roundish number. Sold!daveyson wrote:Please don't ask me if 75 is a round number.
Having 3 2v K100s, as in 83 K100RS, 84 K100RT and 92 K100LT.......the 83 and 84 Ks both have the vacuum sensor to advance ignition timing, the 92 K100LT does not have this. The 84 RT felt much more lively than the 92 LT.daveyson wrote:It's a while since I read up on it, but I thought European horsepower was a reference to the k100, with earlier models having hotter cams, and later models different cams to comply with US exhaust regs (or was it Californie..i..a)
The higher compression for the k75 results in k75=75 horseys, easy to remember. The k100 doesn't reach that.
I was asked to give a K-tech session at the RA National Rally in Greenfield MA some years ago. (Dave was Chair of that rally..)
At the time, I owned an '85 K100RT, and was somewhat defensive about the scorn heaped upon the '85s by owners of later K's.
During the tech session, several people made somewhat disparaging remarks about the '85 K.. and finally in response to one of the remarks I sarcastically said "Oh - you mean the FINEST YEAR K?"
It got rather a large laugh and I thought that would be the end of it.. but I started referring to my K as the FYK100RT in messages to the IBMWR mailing list.
The name stuck. I started seeing it used in ads for '85 K bikes, it started appearing in people's SIGs on messages, and questions like this started popping up - "Why is the '85 the Finest Year K?" I've even seen it used in articles in a certain national club magazine
As Paul Harvey would say - now you know the rest of the story..
Oh - the '85 K100's had one advantage over later K100's (until the 4V engine) - they were the "fastest" ones. They had a euro intake cam (except in California) that gave a real 90HP. Starting in '86 all K100's received the California intake cam (Edit: not true according to clear BMW ETK listings. California models were the only ones to have 256 cams both intake & exhaust) that gave about 5 less HP - but BMW never changed the specifications.
There were some features that BMW did improve with later K100's - heat management was generally better (but still awful on an RT) and buzz/vibration was reduced a bit... but the '85 bikes were a real bargain since you could usually find one for $1,000 or more cheaper than the same bike as an '86. This changed as the FYK rumour spread
Best,
Don Eilenberger http://www.eilenberger.net
Spring Lk Heights NJ NJ Shore BMW Riders"
Last edited by Two Wheels Better on Sun Nov 29, 2020 4:49 pm; edited 1 time in total
Laitch wrote:According to Anton Largiader at Virginia Motorrad, the compression ratio was changed from 11.0:1 to 10.5:1 in 1986, lowering horsepower and torque, but it looks like the reduction happened to the K100 instead.
Point-Seven-five wrote:I have heard that the K100 power output, on the other hand, was limited by European regulations so the higher output from increased compression wasn't necessary.
Point-Seven-five wrote:I believe the K75 has a domed piston with valve interference as opposed to the K100 that doesn't.
I suspect this was to increase the compression ratio slightly to get a small increase i power output. With the race for power output at the time, I suspect it was to keeep the smaller K75 engine competitive with the Japanese 750's.
I have heard that the K100 power output, on the other hand, was limited by European regulations so the higher output from increased compression wasn't necessary.
I have heard that there have been engine builders who replaced K100 pistons with K75 pistons to increase power output for racing.
I am pretty sure of the accuracy of the above, I may be mistaken, and if I am, the Duck will be here soon to make corrections.
Point-Seven-five wrote:Are there any German members here who can comment on German regulations on power output for motorcycle engines in the early/mid 80's. I seem to recall reading something about limits on engine output at the time.
Rick G wrote:
I have never en-counted a different piston in use in the K75 than the higher dome 11:1 that is stated in the factory literature here in Australia.
Max Power | 75 hp (55 KW) at 8500 rpm |
Max Torque | 68 Nm at 6750 rpm |
Compression Ratio | 11.0 : 1 |
The red text in the above quote is from Anton Largiader's useful site but is unfortunately a transposition of K100 data into a K75 reference in a section of his site. It was quoted in one post then corrected in another during earlier in this thread. Here is a screen shot of the entry at Largiader's site.flying finn & brick wrote:More I check this, more convinced I am that post 1986 K75 models have 10.5 : 1 compression.
K75s went from 11.0 : 1 to 10.5 : 1 compression. Power went from 75@8500 to 70@8200, and torque went from 50@6750 to 48@6500
Do you have any BMW publication after -86 that states 11.0 : 1 compression for K75?
Rick G wrote:
I am not trying to pick an argument but where did you get this information.
Laitch wrote:The red text in the above quote is from Anton Largiader's useful site but is unfortunately a transposition of K100 data into a K75 reference in a section of his site. It was quoted in one post then corrected in another during earlier in this thread. Here is a screen shot of the entry at Largiader's site.
Last edited by flying finn & brick on Mon May 08, 2023 5:03 pm; edited 1 time in total
Because the 1994 USA BMW Rider's Handbook published the 11:1 figure for the K75;flying finn & brick wrote:Hypothesis I would like to make is that american model K75 bikes have lower compression 1986-> as the original poster was suggesting
I am not trying to prove anything right or wrong but this confused me quite a bit and I sure hope my K75 has 11 to 1 ratio .
92KK 84WW Olaf wrote:One of the answers to this debate must surely be the spare parts catalogue.
Surely if different compression ratios prevailed then spare parts would reflect this? As in multiple types/shapes of pistons?
I am not aware of different ratios being available but maybe I am wrong.
I am only aware of the 2v pistons being in two configurations, K100 10.2:1 and K75 11:1 but maybe someone can clarify all this.
The Wikipedia article might have mentioned it thusly—flying finn & brick wrote:Wikipedia talks about US model made for EPA regulations that has slightly less power but it doesn't mention compression ratio nor it mentions source for info.
HelloRick G wrote:If you want horse power from a K75 get rid of the rev limiter they turn into little screamers
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