B35 pistons in M30B34 US

[totheredline]

I scored a freshly rebuilt M30b34 for really cheap and I will be doing a swap here shortly. The only concern I have with this motor is its low compression pistons and the mild US spec camshaft. I plan on buying an IE regrind to deal with my cam woes and I would like to use B35 pistons to raise compression to 10:1 ish. Will this work? if not, What pistons can I use to raise compression in this engine? Keep in mind I'm on a budget.

OR should I just ditch the N/A idea and boost the stock 8:1 motor?
Any advice on a budget non-intercooled M30 turbo build? Im really only looking for 300hp.

[wildstoats]

B35 pistons won't increase compression. You also won't hit 300hp NA on any kind of budget unless your idea of a budget differs greatly from mine haha.

Sounds like you're after turbo. Search around, there are lots of turbo build threads.

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[totheredline]

From what Ive read, the B35 head has a larger combustion chamber than the B34. If you want to lower compression in a B34 (in a turbo application) you put a B35 head on it. So what Im thinking is that you could increase compression on a B35 by putting a B34 head (which has a smaller combustion chamber) on the stock B35 bottom end. OR in my case swapping B35 pistons into a B34 bottom end.

I would be more than happy with 200hp (or at least euro M90 numbers) to the wheels with an N/A M30. When I said 300hp I was referring to a turbo application.

I mean, is it possible to do a mild turbo M30 for $1,200. Running MS1 and a junkyard HX40?

[NoM54me]

B34 and B35 heads are different...B35 has coolant passages that won't match the B34 block. Different cams, also. B35 bottom+ B34 head is alleged to give a 10:1 CR. Use the 265 cam out of a B35 head in the B34, just make sure lobes aren't worn. Regrinds never seem to last as long, and you'll also have to buy a set of oversize eccentrics, raising your cost more. Or look for an '83 B32 head with the 272 cam to put in your B34 head...go to mye28 and search for compression ratio calculator. It's an excel spreadsheet that shows various combinations with heads.

[totheredline]

What I really want is "dirty" b34 piano top piston. I think I'm gonna go with an IE 300 cam in a ported and polished b34 head, with B35 pistons

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[canyoncarver]

b35 used a different piston dome configuration than the b34....it was shaped to match the new "open" chamber of the b35 head.
b35 had larger valves, and noticeably larger intake ports as well as mildly more aggressive cam profile.
freer flowing exhaust manifolds were also added.
b34 for US versions used a lo compression piston configuration. 8.5-1, as opposed to the euro spec "dirty motor which had a 10.25 to1 cr...piano top . aside from compression ratios,..the US spec and "dirty" motors are identical in terms of head, cam, valves, etc.
a b35 head on a b34 will lower compression to 8-1 or or less...ideal for boost,..worthless for anything else.........
a b34 head on a b35 block, is inviting valve to piston contact...........or at the very least.....per-detonation issues..........

[totheredline]

its been a while since I posted in this thread, butttt.

I dry assembled my B34 with B35 pistons, stock HG and B34 cam. No valve to piston contact. no head to piston contact. ect. heres my thread over on mye28.

http://www.mye28.com/viewtopic.php?f=2&t=130633

[CorvallisBMW]

Sweet, I like seeing how various OEM pieces can be put together for more hp.

[LJ851]

I dry assembled my B34 with B35 pistons, stock HG and B34 cam. No valve to piston contact. no head to piston contact. ect.

No piston to valve or head contact is not good enough, what are the clearances for each valve and the head with the cam timed in ?

[totheredline]

No piston to valve or head contact is not good enough, what are the clearances for each valve and the head with the cam timed in ?

To be totally honest I don't know how youd actually go about measuring valve piston clearance precisely. (Please let me know if you do.) I just clayed everything. With the 260 duration cam stock timing. the valves didn't even make a dent in the clay. With my radical cam, both valves were obviously hitting the piston. No good. Luckily its only $90 to get reliefs cut.

[Ether-D]

To be totally honest I don't know how youd actually go about measuring valve piston clearance precisely. (Please let me know if you do.) I just clayed everything. With the 260 duration cam stock timing. the valves didn't even make a dent in the clay. With my radical cam, both valves were obviously hitting the piston. No good. Luckily its only $90 to get reliefs cut.

Well that just seems weird. It seems to me there should have been a pretty clear valve-print. Is it possible that the timing was off when you clayed it?

[totheredline]

I'm pretty sure I timed it right. I think the b34 can doesn't have enough lift or duration to come close to touching the piston

[LJ851]

To be totally honest I don't know how youd actually go about measuring valve piston clearance precisely. (Please let me know if you do.) I just clayed everything. With the 260 duration cam stock timing. the valves didn't even make a dent in the clay. With my radical cam, both valves were obviously hitting the piston. No good. Luckily its only $90 to get reliefs cut.

Clay will get you in the ballpark. If you want to be sure, replace the valve springs with some much lighter springs (like from a hardware store) and set up a micrometer on top of the valve. Turn the engine over and every 5-10 degrees or so push the valve down til it hits the piston. The micrometer will tell you how far the valve is from the piston. It's usually tightest just after TDC, during overlap of course.

[totheredline]

Got the motor together. Ended up cutting valve reliefs for intake and exhaust which gives me plenty of valve clearance. After decking the head I should be around 10.4:1. Also decided to ditch MS1 and go with a 4bbl carb intake.

Im sure Ill be getting a lot of "what the fukk?" and "you did it wrong"s

[Ether-D]

Nope. Just an enthusiastic "Hell yes!' from me.