m30b25 head on m30b35 block

E28 technical advice asked and given! Troubleshooting, modifications and more.
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kiskikiski
Posts: 1
Joined: Mar 25, 2021 8:19 PM
Location: Denmark

m30b25 head on m30b35 block

Post by kiskikiski »

hi.
has anyone tried to bolt the m30b25 head on the m30b35 block ?
does the head bolt straight on and does the engine run good ?
Mike W.
Posts: 24984
Joined: Feb 12, 2006 1:00 PM
Location: Covid 19 Life during Wartime

Re: m30b25 head on m30b35 block

Post by Mike W. »

I don't think the valves would hit, but I'm not positive. From an old post it looks like the compression ratio would be 9.9:1, high, but no higher than the 10:1 on high compression B34 engines. I haven't heard of anyone doing it, but that doesn't mean it wouldn't work. I would think it would actually be very similar to the high compression B34 engine as they all used the same valves until B35 era. Do be aware that the b25 cam probably will not work, I think they were all L jet with a conventional distributor unlike the Motronic setup on B35s.
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