v00d00child Posted October 29, 2005 Share Posted October 29, 2005 So, here I am, bored to death, and reading online cycle reviews instead of riding (it's raining). Every time I see the rave reviews of the BMW K1200S, my chest puffs out with pride--the thing looks just like an XX (although not quite as good IMO). Anyway, I took my 97 to a dyno event in Sept., and even the 40K, much neglected XX still cranked out 133 hp/80 ft-lb. on an eddy current dyno. Less than I hoped for, more than I expected. After reading some of the K1200S reviews that claim 164 HP, I noticed that the XX is only squeezing at 11:1 compression ratio. I can't seem to track down the K12's CR, but remember that it was more on the order of 13:1, IIRC. Has anyone kicked up their XX to 12:1 or greater? If so, what dyno numbers did you see? Were there any issues--leaking head gaskets, knocking, etc? Quote Link to comment Share on other sites More sharing options...
Northman Posted October 29, 2005 Share Posted October 29, 2005 My big bore is running 13.2:1 compression, and I do get some pinging unless I'm using very good fuel. It will run on 91 octane, but prefers 93 or better. FWIW, you can raise the stock compression by shaving the head, careful to check V/P clearance, as well as your squish height. This will give you a small gain in compression ratio, without costing you a fortune, but may only give you a few hp in return, and cause you to have to run better fuel. BMW gets away with the CR ratio because of a very efficient combustion chamber (almost flat), and dual knock sensors. Quote Link to comment Share on other sites More sharing options...
v00d00child Posted October 29, 2005 Author Share Posted October 29, 2005 North-thanks for the info. Like I said, I'm just amazed that people are all gaga over the K12S, when it costs sooo much more & uses black magic, just to barely equal (so I'm told) the uber-reliable XX. Quote Link to comment Share on other sites More sharing options...
Northman Posted October 30, 2005 Share Posted October 30, 2005 Well, it's still new. IIRC, it's down about 15hp or more to the Busa & ZX-12, and heavier than the XX. Top speed won't break 170, either, and magazines have reported it to be slow handling & heavy, but incredibly comfortable & smooth. Quote Link to comment Share on other sites More sharing options...
tomek Posted October 30, 2005 Share Posted October 30, 2005 Comparing compresson ratios from different bikes does not really tells us much.Just becouse bimmer has 13.0 and XX 11.0 does not mean much.There is couple factors,like filling efficiency,cam duration and combustion chamber design. Longer duration cams allow higher CR becouse intake valve closes later on compression stroke basically ,,,,,,,,,,,uh compressing mixture less. Or you could retard stock intake cam,but that is kinda counterproductive. Northman bike has,I think,nonstock cams,that is how he can get away with 13.2 CR. Stock XX has mild,short duration cams and doubt that number would work well.I would try something in 12-12.5 range. There is no pont in going to really high CR and then being forced to retard ignition due to detonation. Shaving cylinder head does nothing to squish number.Squish areas on cylinder head side are flesh with cylinder head surface.Only thinner cylider head gasket or shaving cylinder block improves squish.Due to one piece upper crankcase/cylinder block design that means taking whole engine a part. Quote Link to comment Share on other sites More sharing options...
Northman Posted October 30, 2005 Share Posted October 30, 2005 You're right on the cam timing issue, but the tolerance to CR is more in CC design, and the amount of turbulence in the cylinders during firing, as well as the CC's efficiency to transfer (or not transfer) heat. I also run a very cold plug. I suggested shaving the head, as he won't gain 2 points in CR there, but maybe .2-.3, depending on squish (and you're right, block surface needs to be machined - I had two strokes on the mind :oops:). If there's room, running a thinner head gasket (or removing one of the wafers) will give you the rest of your gain, without spending a pile of $$$. Still unlikely to get you over 12:1, however. Also, FWIW, my stock compression measured 10.7:1, which my engine builder said is much closer than usual. He's measured many that were at least 1 point lower than advertised. Meaning, it's possible the BMW is only around 12-12.5:1 Quote Link to comment Share on other sites More sharing options...
Red J Posted October 30, 2005 Share Posted October 30, 2005 I would wager that headwork and cams would open more HP with the bird motor, rather than simply dicking with CR. If you are building a motor to the nines, and you want to target a CR to get something special out of it, that's one thing, but simply changing the CR without altering anything else in the system is going to cost plenty for the benefit it provides. Just one guy's opinion. J. PS - The smallest nitrous system will offer more cylinder pressure than an aggressively skimmed head or block, without even unbolting the head... Quote Link to comment Share on other sites More sharing options...
v00d00child Posted October 31, 2005 Author Share Posted October 31, 2005 Just for the record, me likes me XX fine just as she sits--I have no desire or $$ to mod the heck outta her for a few vain HP numbers that I couldn't put to use anyway. Just curious. Interesting discussion though. Continue... Quote Link to comment Share on other sites More sharing options...
HamrTym Posted November 1, 2005 Share Posted November 1, 2005 PS - The smallest nitrous system will offer more cylinder pressure than an aggressively skimmed head or block, without even unbolting the head... Or forced induction. Sorry, back on topic.. Quote Link to comment Share on other sites More sharing options...
XX4me Posted November 2, 2005 Share Posted November 2, 2005 Yea what he said Quote Link to comment Share on other sites More sharing options...
Ranchw Posted November 10, 2005 Share Posted November 10, 2005 Gentleman, All works good until you try to get it exited through some crappy exhaust system. I've got a BB that made 148 hp on a Dynojet dyno with stock degreed cams, a little head work and much exhaust system building and testing. Don't throw money in the wrong places. Quote Link to comment Share on other sites More sharing options...
pug Posted November 11, 2005 Share Posted November 11, 2005 Gentleman,All works good until you try to get it exited through some crappy exhaust system. I've got a BB that made 148 hp on a Dynojet dyno with stock degreed cams, a little head work and much exhaust system building and testing. Don't throw money in the wrong places. Can we have more details please? Quote Link to comment Share on other sites More sharing options...
DSRbikes Posted November 11, 2005 Share Posted November 11, 2005 Gentleman,All works good until you try to get it exited through some crappy exhaust system. I've got a BB that made 148 hp on a Dynojet dyno with stock degreed cams, a little head work and much exhaust system building and testing. Don't throw money in the wrong places. Can we have more details please? +1 let's see, Mine dyno'd at about 145hp. Mods: K&N Air filter D&D full exhaust 4-2-1 44t sprocket &... that's it, oh I'm at see level +20ft maybe. From what I've heard people always dog D&D for being only noise makers (and mine looks like piss) but I seem to get better HP with that than with the D&D drag can on. Ranchw, care to elaborate? What do I need to do to get more HP out of my exhaust? I'm planning some more mild mods but I'd like to get some more info first. Dameon Quote Link to comment Share on other sites More sharing options...
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