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Mount Fitzroy, Argentinian Patagonia



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  #1  
Old 19 Oct 2010
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BMW high compression ratio pistons (11.2:1)

Hello

I’m planning an expedition with a R100GS. The bike has high compression ratio pistons (11.2:1)

Will I have problems with sahara fuel? The normal pertol is 95 octant or lower?

I normally travel with diesel LRs so this problem never cross my mind

tks
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Old 20 Oct 2010
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...are you really sure about that?

Do you have 4-valve technique on the airhead?

Above 10.5:1 on an airhead is pushing it... and above 11:1 is adviced against by all sources I have have found...

It is -not- possible to run on poor petrol with that high compression ratio... you should seriously consider changing to stock 9.5:1 or even the 8.2:1 version to minimise overheating risks and allow for usage of low and poor octane petrol... there is a reason for why the Egypt Police ordered a special version of the R80 engines... 44/40 valves with Bing 40... equates about 7:1 allowing for EU 87 octane petrol to be used...

Let us know -exactly- how your engine have been modified. It is possible that my comments above may not apply - it depends on exactly how the conversion to 11.2:1 have been made.
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Old 20 Oct 2010
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Are you sure 11.2:1 is correct? I would have made a compression-test to check it.

Personally I would never used anything higher then 9.5:1 on bike intended for traveling in areas with poor fuel. It's probably a bit on the safe side but on the other hand you can get a very powerful engine with 9.5:1.



Quote:
Originally Posted by dc lindberg View Post
Let us know -exactly- how your engine have been modified. It is possible that my comments above may not apply - it depends on exactly how the conversion to 11.2:1 have been made.
Yes, please tell us!
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Old 20 Oct 2010
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hello

I have a normal 2 valve airhead and I need barrels (they have some scratches) and pistons + pistons rings

“It is -not- possible to run on poor petrol with that high compression ratio” I full agree with you if you keep the same combustion chamber shape.

http://www.moorespeed.co.uk/bmw-engine

High compression ratio pistons
Designed by Richard Moore in collaboration with Omega pistons, these high compression pistons offer the most cost-effective (and easiest) way to boost power. The dyno charts show the solid increase in both bhp and torque achieved simply by slipping in these new pistons (use your existing piston rings if in good condition) – an extra 8bhp for a couple of hours work! Combine them with a free-flowing Moorespeed air filter conversion, and gain an extra 2bhp (see also Moorespeed Tuning Kit section).”


I still don’t have the pistons installed but I have the same doubts that you have (that why I have I posted where)

Yesterday I called Richard Moore from moorespeed and I had a long talk with whim. He has a looong experience in motorsport and in BMWs air heads. He seems a very well formed fellow and not just a curious.

We said that his pistons here used in several African races with out problems. He also has some bikes that were used in Africa tours also without problems.

He says that eventually if the fuel is very low in octane level you should delay a bit the timing to avoid some knocking.


Personally I would never used anything higher then 9.5:1 on bike intended for traveling in areas with poor fuel. It's probably a bit on the safe side but on the other hand you can get a very powerful engine with 9.5:1.”


What solution do you use? Siebenrock replacement Kit?

thanks
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Old 20 Oct 2010
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I can't see that Richard Moore claims hat the pistons will give you 11.2:1 and I would have expected much better dyno-runs if they did.

There are some discussion about his pistons (and my old setup) here: Power piston kit - ::. UKGSer.com .::

Quote:
Originally Posted by bernardo feio lightweight View Post
What solution do you use? Siebenrock replacement Kit?
I used a Siebenrock upgrade kit (800cc -> 1000cc) and a few other modifications for 60kkm. The kit worked nice and will probably be re-used on my second R80.
Right now I use a setup based on narrow 1043cc cylinders (from Mahle/HPN). I spend quite some time thinking about what compression-ratio to choose before I ended up at 9.5:1.
The bigger bore increases the risk for pinging so I also installed dual-plugging.
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Old 20 Oct 2010
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Hello

The compression ratio of Richard M. pistons is not written in his web page but he told me that by email and confirmed that yesterday by phone.

“1043cc cylinders (from Mahle/HPN).”

Can you give me more information about that? Part numbers, piston rings, prices…

If you prefer please send me a PM to:

bernardofeio @ yahoo.com.br

thanks
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