Fuel Pressure Regulator on Ebay

[Burnszilla]

Auction Description:
NEW Fuel pressure regulator or BMW K75, K100 2/valve machines only, does not fit K1100 or K1200. This is a 3.0 bar high pressure unit compared to 2.2 to 2.5 for a stock unit. Increased preformace with higher pressure.

http://i16.ebayimg.com/02/i/02/36/74/ef_1_b.JPG

Would this really increase performance?
Would the engine run richer?

[davel]

Yes it will. That combined with a K&N will give you a nice performance boost! You will feel it in the seat-of-your-pants. I did the same on my 88k75s. Only draw back is you will also notice a drop in your MPGs...:clap

[YB in IN]

Originally posted by davel
Yes it will. That combined with a K&N will give you a nice performance boost! You will feel it in the seat-of-your-pants. I did the same on my 88k75s. Only draw back is you will also notice a drop in your MPGs...:clap

I've heard that the K&N filter was run on a dyno and actually decreased the power on a K75S. Do you have any DATA?

[davel]

Under stock conditions, it may very well. And even if it did you probably would not notice the difference, but it would show on a dyno. Most people put in K&Ns to save money and labor on future filter replacements. Remember if you are adding the high output fuel regulator you are increasing the amount of fuel, so additional air is necessary to. The K&N isn't really giving you more air, its just allowing it to flow faster...:bliss

ps your bike will run a tad richer since its not a closed loop system it can't make the adjustment...

[deilenberger]

Originally posted by davel
Under stock conditions, it may very well. And even if it did you probably would not notice the difference, but it would show on a dyno. Most people put in K&Ns to save money and labor on future filter replacements. Remember if you are adding the high output fuel regulator you are increasing the amount of fuel, so additional air is necessary to. The K&N isn't really giving you more air, its just allowing it to flow faster...:bliss

ps your bike will run a tad richer since its not a closed loop system it can't make the adjustment...

Ummm.. I believe you can't have the same amount of air if it is flowing faster.. or to put it in another, how can the air increase in speed through the same opening without more air going through the opening?

Without dyno runs.. all this is just speculation. IMHO, The limiting factor in the 2 valve K engine is the size of the valves (which is why they went to a 4 valve engine in '89).

I actually have a LOT of data on K&N, high-pressure fuel regulators, different exhaust systems on the 2 valve K engines.

None of the above, singly or in combination will improve the overall power from a 2 valve K engine. Some of these actually cause a loss of power, and in the case of a K&N allow more dirt and grit into your engine (which is NOT a good thing).

I'll refer you to:

Here is into on the high-pressure FPR and the K&N filter:

http://www.eilenberger.net/k75exhaust/index.html

It also includes the go-fast (not) Staintune exhaust system.

Here is some more info, this time on my K75S, which has a ported/polished head and oversize intake valves vs a stock K75:

http://www.eilenberger.net/K75S/dyno.htm

And for the info on the K&N - in more depth:

http://www.ibmwr.org/ktech/dyno/index.shtml

and

http://www.ibmwr.org/ktech/dyno-update/index.shtml

There is one way that you can improve K 2 valve engine power - and that's by advancing the timing a bit. The caviat here is I'd only recommend doing this if you're willing to run premium fuel:

http://skylands.ibmwr.org/tom/tech/k75_timing.html

And

http://skylands.ibmwr.org/tom/tech/k100_timing.html

And

http://www.ibmwr.org/ktech/k-bike-ignition-timing.shtml

Almost ALL K75's tend to run rich. They use the same air-flow-meter as the K100 engine, which isn't an ideal match to the smaller displacement engine.

The richness can be confirmed with an exhaust analyzer (which I've done, but didn't write up), and by the propensity for the K75 to after-fire (in the muffler, often called "backfire" which it really isn't) due to unburned fuel being ignited in the header pipes. The tell-tale black around the exhaust outlet is another clue.

My particular K75S appears to be running lean (the dyno runs confirm this, not by the power produced but by the small fluctuations at higher RPMS). I believe this was due to it sitting for several years with very little to no use (which can cause the injectors to plug up).

I haven't measured the FPR output, but the former owner DID pay for a high-outout one. This might make sense with larger intake valves, as these are a restricting point in the engine air-flow.

I've run a few bottles of Techron through it and it appears to be getting better (I can now make it go BANG on decel, and there is a bit of soot gathering on the exhaust pipe outlet). I intend to do some new dyno runs on it when the peak motorcycle season falls off. I also may have a chance to dyno the new version of the Staintune K75 exhaust, it will be interesting to see if they improved the system (yes - they do know about my plots, and we've discussed it.. )

Simple answer - if you put that FPR on your K75 or K100, you're likely to loose power, and loose MPG. Net loss.

If you look at any plot of mixture vs power - optimal power is made when the mixture is slightly richer than is optimal for emissions purposed (1-lambda) - which is about where a stock K75 in good condition runs.

Oh - my bike did come with the K&N filter installed by the former-owner. First thing I did on the bike is put a stock filter back in. I gave the K&N away since I'd feel guilty selling it to anyone. The stock filter is good for WAY longer than the spec's in the service manual. I know of one person running one with over 100k miles on it - and he can still reach the same top-speed as he could when it was new. The design of the filter is rather clever - it is designed to drop the dirt out and into the bottom of the air-filter-housing (a rather common design by BMW - they use it on a lot of their cars). I might replace mine again when I get to 100k miles. And I might not depending on what the dyno tells me.

Best,