Horsepower K1200S > K1200GT but WHY - K-Bikes.com - Excellence in Motion
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post #1 of 16 (permalink) Old Feb 13th, 2020, 3:13 pm Thread Starter
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Horsepower K1200S > K1200GT but WHY

I'm replacing an engine in my 2005 K1200S that threw a rod right through casing because I forgot to put the hose clamp back on the breather hose connected to the oil canister after working on the ABS pump not realizing the ramifications as I was unfamiliar with the dry sump external oil bucket concept. Those ramifications were that all the oil backed up into the bucket but the breather hose without a clamp wasn't able to create enough positive pressure to push it back out the bottom and into the engine. Coincidentally and just my bad luck one week earlier the ZFE had failed after all the magic smoke that makes electronics work leaked out! I replaced with one off an '06 from eBay which only partially worked in that I had low beams turn signals and brake lights but the dash display only showed the bikes mileage but nothing else no backlight no tach nothing like say... an OIL PRESSURE LIGHT!!

ANYWAY the new engine is from an 07 K1200GT and I was wondering just exactly what about the S gives it the additional performance is it simply a more aggressive tune or is there a hardware component to it? I'm retaining the original throttle body & fuel injectors and know the specs actually give the '07 GT 13.1 vs the original 13.0 / 1 compression ratio so I can check that off the list so I guess what I'm asking is if it's the valve train and if so what is different just wilder cam profile or are the valves a bigger size? Answer in as much detail as possible.
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post #2 of 16 (permalink) Old Feb 13th, 2020, 3:51 pm
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The GT only has one snorkel..... just like the R.
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post #3 of 16 (permalink) Old Feb 14th, 2020, 10:21 am
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So, you are, in effect, saying breather pressure, or air pressure taken from the engine, pressurizes the oil tank, and that is how oil from the tank provides lubrication to the engine? Does that mean that if the dipstick is missing or not tight enough, the engine will be damaged?
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post #4 of 16 (permalink) Old Feb 14th, 2020, 2:37 pm
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IIRC there's a pump in the oil sump that returns oil to the tank, and another that pressurizes the oil and feeds it to the engine. I dunno what role air pressure plays in this.

The GT engine as I understand, lacks the exhaust flap that the S has. There are other differences as well. Mix-and-match parts might work, and they might not, and there may be codes collected by the ECU. Hope you have the capability to sort that, but if you're changing the engine (yourself) you likely do.
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post #5 of 16 (permalink) Old Feb 15th, 2020, 1:01 am
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Let's start with an easy one. Torque! The GT is tuned for torque rather than Hp. The two bikes have different cams. The K12S is a bit nasty at 268 degrees and the GT is listed at 247 degrees. Different part numbers. I do not know the fueling control data or other stuff but you can check between the engines on MAX parts listings at
https://shop.maxbmw.com/fiche
I think you jumped the gun on this project. The K12 is a serious hot rod and has terrible around town manners.
But on the highway it rips. Your engine choice will move you around but you may notice lots of hp loss. And may not run will without the matching computer.

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tire guy, I'll mount your tires.
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post #6 of 16 (permalink) Old Feb 15th, 2020, 5:02 am Thread Starter
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I'm keeping all electronics unchanged besides a replacement ZFE from another 2005 S exactly the same labeling hardware C6 software 1.10.0 matching part numbers from what I've been able to ascertain this will work negating the need for an ICOM D hardware and laptop imaged with OEM exclusive CIP utility. Also throttle body injectors fuel rail and airbox all remain. Basically the only thing left is the valve train which has been confirmed as the difference I hoped it wasn't going to be but I am going to transplant the long block from the donor GT and get it running and then decide if it'd be worth the trouble of swapping the cams out in order to get the horses back in the stable. Does anybody make aftermarket / custom cams to avoid the likely possibility my originals being FUBARd from the lack of oil that threw the connecting rod through the case as below so above...
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post #7 of 16 (permalink) Old Feb 15th, 2020, 1:22 pm
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Motorcycle wrenching 101 question.

What is the purpose of the exhaust flapper valve? Can it be removed? If so, what are the ramifications?
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post #8 of 16 (permalink) Old Feb 15th, 2020, 10:39 pm
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The bike will be louder and have less low end torque. It is a good thing unless you are a track bike and ride at high rpms all the time.

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post #9 of 16 (permalink) Old Feb 16th, 2020, 8:58 am
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Thanks, Beech. I definitely donít need louder or less low end torque.
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post #10 of 16 (permalink) Old Feb 16th, 2020, 4:23 pm
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On the subject of looking for a fresh camshaft. You are going to have the blown engine out of the bike, it will only take half and hour to pull and inspect the old cams. (intake won't come out unless you remove the waterpump) I bet they are okay, hope so anyway.

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