Hypothetical Cam Question! - BMW F800 Riders Forum & Registry



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  1. #1
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    There is a 20hp difference between the F650/ F700 GS twins and the F800GT. I know the cams are the primary difference and that the 700GS, 800GS and 800GT all three use different cams (at least different part numbers) Just musing on a rainy, cold day (not a good day for riding) but if a person were to put GT cams in an F650 or F700GS I'm curious if the BCMS would allow the additional power to be gained.

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  3. #2
    Daboo's Avatar
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    Not sure, but here's a way to let your fingers do the walking on a rainy, cold day. Look up the horsepower curves for each bike. Check to see where the differences are along the rpm scale. My guess is you'll find they are very close to each other till you reach about 5-6000 rpms where the GT will increase more.

    Chris
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  4. #3
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    I would be amazed if the fueling and ignition maps were not significantly different. You can't just throw a different cam in and expect it to work.

    Sent from my SM-T813 using Tapatalk

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  6. #4
    Richard230's Avatar
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    My guess is that the timing on the F650GS is retarded compared with the other 700 and 800 models since it uses 87 octane for fuel. No doubt it also has smog cams with little or no overlap and likely other differences, too. However, I don't know much about the F700GS. I think it has slightly more HP and needs 91 (motor) octane fuel. So its ignition timing might be advanced compared with the 650. I seem to recall that they both have the same compression ratios, though.
    Richard - Current bikes: 2016 BMW R1200RS, 2018 16.6 kWh Zero S, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2020 KTM 390 Duke, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior. 

  7. #5
    308bever's Avatar
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    put a 15 tooth sprocket on it and try that, changed my 700gs, living in the nanny state top-end speed is to expensive to use anyway (((-; cheers mate

  8. #6
    Lag's Avatar
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    Yes, I did the same with the front sprocket,,. A totally worth while change for badly needed off road bottom end torque,,. Could even go down one more tooth but it will peter out on the top end sooner,,. I think I was getting 195 Kph prior to the change which is plenty for the 700GS,,.

    Is there anything in the way of a flash available for the 700GS,,. It really goes flat on torque after 7000RPM,,. Haven't really tried an 800 at those rpms however thats likely where they stuck the 10 or 15 ponies,?

    Quote Originally Posted by 308bever View Post
    put a 15 tooth sprocket on it and try that, changed my 700gs, living in the nanny state top-end speed is to expensive to use anyway (((-; cheers mate

  9. #7
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    Quote Originally Posted by 308bever View Post
    put a 15 tooth sprocket on it and try that, changed my 700gs, living in the nanny state top-end speed is to expensive to use anyway (((-; cheers mate
    I changed to a 16 tooth front (same as 800GS). The original 17 is way too high for off pavement but the 16 still gives me good road speed and mileage. I was just thinking that since you have to remove the cams to shim the valves, (if they ever need it) it might be fun to just swap them out with a used set of F800R or GT cams. Sure would be nice if the GS 911 could reflash... Just kind of bugs me that the engine has another 20 hp just sitting there not being used.

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  11. #8
    Lag's Avatar
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    Watched a vid where they re-flashed a 1000 HR SX,,. They had to literally remove half the bike in order to get at it but it seemed to be worth as they found that the power just died after peak torque as set up by Kawasaki,,. I think they found 30 HP by the time they were done,,, these guys obviously knew what they were doing,,.

    If someone were able to crack that nut on the BMW 798 they would have a highly coveted service, same with the current crop of 750/850's,,. Probable a well hidden secret,,!!

  12. #9
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    Click image for larger version. 

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    Here's a very old graph I saved shortly after the F658/F800GS bikes were announced.

    FWIW:
    Note the F658 actually is a little better on the low end, and that the F800GS only has an advantage starting at about 6500 rpm

    They do have same compression ratio, there is (was?) a modification available at dealerships to reprogram the ignition timing of the F800GS
    so that it could run regular (87) octane gas like the F658GS.
    Blue 2009 F650GS - H-B crash bars, TT luggage rack, Pelican top case, BMW Vario Panniers & bash plate, 20mm handlebar risers, LED voltmeter, Sargent seat, MudSling, a few other trinkets ... I may be just about at the end of the farkle train  

  13. #10
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    Quote Originally Posted by jrwooden View Post
    Click image for larger version. 

Name:	powercurve.jpg 
Views:	12 
Size:	229.3 KB 
ID:	369553

    Here's a very old graph I saved shortly after the F658/F800GS bikes were announced.

    FWIW:
    Note the F658 actually is a little better on the low end, and that the F800GS only has an advantage starting at about 6500 rpm

    They do have same compression ratio, there is (was?) a modification available at dealerships to reprogram the ignition timing of the F800GS
    so that it could run regular (87) octane gas like the F658GS.
    Did a search and it seems Max BMW does performance tuning, including F bikes. That might be a nice ride up there to get it done if I ever change cams.

  14. #11
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    Quote Originally Posted by rreynold6 View Post
    Did a search and it seems Max BMW does performance tuning, including F bikes. That might be a nice ride up there to get it done if I ever change cams.
    If you go, I'd be real curious to know what they can actually do on our bikes without spending buckets of cash!
    Blue 2009 F650GS - H-B crash bars, TT luggage rack, Pelican top case, BMW Vario Panniers & bash plate, 20mm handlebar risers, LED voltmeter, Sargent seat, MudSling, a few other trinkets ... I may be just about at the end of the farkle train  

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