The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: tog123 on November 11, 2013, 08:04:51 AM
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hi guys are 1980 r65 / r45 cylinder heads interchangeable because i have recently acquired some r45 cylinder heads that have had the unleaded conversion that came with a r45 barn find. Witch i would like to fit to my r65.
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I think you will find the valve sizes are smaller.
Barry will chime in shortly and confirm.
Cheers
Rev Light
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Yes,
1980 R45 34mm inlet 32mm Ex
1980 R65 38mm inlet 34mm Ex
81 - on R65 valves are even bigger
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That will certainly be a good way to strangle any performance out of it. Put them on ebay and use the cash to help with converting your current heads and if you can get them made up to the post 81 valve sizes, even better!
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To answer the original qusetion would they fit. Yes but not sure what would happen to the compression ratio.
Not sure what you are looking for from the engine. My guess is the smaller valves would reduce peak power to something in the region of 40HP but it should run well enough lower down the range with maybe even slightly more torque due to increased velocity through the smaller ports and valves. Economy might also improve a little.
Many, many years ago I had a little 1400cc Peugeot 205 that was fitted by the factory with the cylinder head from the 1100cc version.
power was reduced from 70HP to 60HP at lower revs but it was very tractable and economical.