The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: alexznam357 on May 05, 2009, 06:17:41 PM

Title: Benefits of increasing compression?
Post by: alexznam357 on May 05, 2009, 06:17:41 PM

Hey Guys...Motobins in the UK has R65 pistons in the 8.7:1 compression ratio for about $90 per set. I know the R65s had 3 possible CRs; 9.2, 8.7, and 8.2.  Has anyone increased their 8.2 engine with either of the higher CR pistons and if so, was there a noticeable performance increase?  I may buy a set anyway just because they're so cheap.
http://www.motobins.co.uk/displayfinal.php?function=show&subs=500a&title=2+VALVE+TWINS

Title: Re: Benefits of increasing compression?
Post by: montmil on May 05, 2009, 06:44:37 PM

All I've ever heard and/or read is that hopping up an R65 engine is an easy way to shorten its life while deflating one's wallet. Seems that don't take well to the nitrous bottle.

An old post along this topic advised the hop-ee to buy an R100!  [smiley=thumbup.gif]

Let the flaming begin  [smiley=flamethrowingsmiley.gif]

Monte

Title: Re: Benefits of increasing compression?
Post by: Bob_Roller on May 05, 2009, 06:53:48 PM

Unfortunately the R65 is not a good candidate for upgrading the engine, all I've ever heard, is you can pour a lot of money into it, and have a meager increase in power output, and engine longevity suffers because of it.

Personally I would not try to tinker with the engine, now if you have a destroyed engine, I would consider installing an R100 engine .

The transmission, shaft , and final drive are the same as the 1 liter bikes, so you won't cause any problems there.

Title: Re: Benefits of increasing compression?
Post by: nhmaf on May 05, 2009, 08:29:50 PM

The R65LS has the 9.2 CR pistons in it - I am not certain but I think that there maybe  some dimensional differences that may cause an  issue if you try putting them into a cast iron bore cylinder (78-80) instead of the Nikasil ones (81 ->). This might be the thickness of the rings. The higher CR might not really buy you anything except more pinging under load unless you also have the newer heads with larger valves that came along with the Nikasil bores and  higher CR pistons.  I don't know if the older heads from the iron bore cylinders have the same clearance for the squish band as the later heads - perhaps someone else can chime in on that.

Title: Re: Benefits of increasing compression?
Post by: alexznam357 on May 06, 2009, 01:51:40 AM

Thanks for the info...I wouldn't know unless I asked!