M30 B34 and B35 bore/ stroke

[FredDeuel]

I was under the impression that these two engines did not have the same bore and stroke, but that the B34 had a larger bore and the B35 a larger stroke even though they had nearly identical displacement. Now I can not find that information anywhere else (except to show that they are the same) and the Wiki article has been changed to show identical bore/stroke and displacement as well. I know the B35 head flows much better and has a more aggressive cam, along with higher compression compaired to the US B34. I have also seen a few places claim that the B35 head on the B34 block increases compression, while others say it drops, which is correct?

[EuroGeorge]

I believe the bore is 92mm and the stroke 86mm for both. The difference is the B35 has larger intake valves, a more breathable intake and a different cam profile. Putting a B35 head on a B34 block will lower compression.

Someone please correct me if I am off target.

Cheers,

George

[88m53453]

sounds right George

[EuroGeorge]

sounds right George

Coming from you, that means a lot. I used to be able to rattle off tons of BMW trivia, but we are gettin older buddy. I struggled with that one.

G

[88m53453]

i know it well old friend, I remember being able to rattle off part numbers and the prices to go with them.

[rvaughnp]

Read here on the b35 head "flowing more" than the b34. It's only 14.3 cfm at 28".http://forums.bimmerforums.com/forum...manifold/page2
The b35 head has a larger cc chamber volume than the b34(65 vs 58). That's what decreases the cr when placed on a b34 block.
B35 in vlv 47mm, b34 in vlv 46. B35 head intake port is wider by 3mm.The above post explains in more detail.
The pistons are different as well. The b34 are flat top and the b35 has swirly cuppy thing. The "piano" top are the "dirty b35's on the euro b35 10:1.
Summarize: the bore, stroke and rods are the same. The pistons are different. The b35 has a slightly higher cc and swirl shape piston. The b34 are flat. The b35 47 mm in vlv. The b34 46mm in vlv. The b35 head chamber 65mm and the b34 58mm. And as stated above, the cam is slightly bigger. A slight bigger cam, more duration and lift.

[Shipper]

It is the M90 that has a larger bore and a shorter stroke. Stroke is 84mm.

[88m53453]

and if I remember correctly, the bore is 93.4 or possibly 93.37...

[FredDeuel]

Thanks guys, I was wondering if I should hold on to my B34 (and use parts from a B35 to build) or sell it and buy a B35 to build; since the bore and stroke is identical I'll go with the latter.

[pthm]

b35 piston

https://www.dropbox.com/s/8mbki7che4...2000.29.08.jpg

B35 head valve side

https://www.dropbox.com/s/wce5gawsyx...2000.30.34.jpg

[Shipper]

Thanks guys, I was wondering if I should hold on to my B34 (and use parts from a B35 to build) or sell it and buy a B35 to build; since the bore and stroke is identical I'll go with the latter.

The B34 has smaller valves than the B35 but has a higher compression. This comes from the B34 combustion chamber CC'ing at 58cc's and the B35 at 64cc's. The B35 is popular as you can get more top end hp for racing but the B34, if warmed up, will give you more torque across a better range. My B34 built as an endurance racer has 330hp and 387lb/ft of torque. Enough to put a 6.2 litre V8 corvette engine to shame. So, you can sell it and buy a B35 or, use the money you would probably lose in this transaction to freshen up the B34. No reason why you cannot get 250hp out of a good B34 build.

[FredDeuel]

I was planning on throwing it into an E30 coupe while I work on my 6 and put a different engine in that, then sell the E30 once the 6 is done. The North American spec B34 has a lower 8:1 compression than the B35's 9:1 (sadly I don't have a euro car ) I'm thinking of a bored 3.5L exactly (I think I figured it to something like +1mm bore) with a cam (aggressive while still being streetable), 10:1 comp, and the biggest valves I can fit. If I am not mistaken the B35 head already flows better so it would make a better starting point if you will .

I must say your racing M30 is VERY impressive. I followed that build from the side lines with much interest! Love the sound too!

[USMarineRetired]

Hello,

(Preface)

Reviving this thread as it is as close as I can come to finding my answer. I have a 1987 320i with a 1985 635csi M30B34 "dirty" motor. I'm experiencing an overheating issue that came out of nowhere. Oddly enough I checked coolant level before I drove it the 10 miles I went. I have changed thermostat, bypassed the heater core and insured I had/have no obstructions. It acts like it doesn't want to circulate coolant. Radiator cold, upper hose hot, hoses that would be going into the heater core stay cool also. Engine did not smoke at all. What I did when I bypassed the heater core is I placed one of those Prestone "T" fittings that has a cap so you can hook a water hose directly to the "T"fitting and fill the system. I turned on the hose to flow an adequate amount of water. The one thing my wife and I noticed RIGHT AWAY is that the idle was the smoothest it has been since I bought the car a month or so ago. After I shut off the water and recapped the system. I began to get some white smoke (damn..) and the bad idle started to slowly reappear. I'm hoping for the best but leaning toward the worst. I removed the water pump to find that it appears to be just fine. No play, no noise, tight impeller. After doing a bit of research I found that the overflow hose (1/4 hose) can get plugged and cause over heating. (Checking that when I get home today.)

My reason for explaining the above here is that if this turns out, after some more troubleshooting, to be a head gasket and subsequently a cracked head, can I use a B35 head on this B34 "dirty" engine?

Any help/insight would be appreciated.


Thank you,
Tony

[88m53453]

b35 head on a b34 block will lower compression IIRC...works if you want to turbo it I guess..otherwise not

[USMarineRetired]

Thank you for the response. A turbo will come in the future. I need to iron out all the issues first. (suspension, brakes..) I saw that the difference in the cc's of the heads is about 6 cc's. Just wanted to be sure there were no physical attributes to the B34 10:1 pistons that were going to interfere with a B35 head. May be a moot point right now. I ran compression last night with 175-180 across all 6 holes. Numbers may seem low for a 10:1 engine but from what the previous owner stated the cam in not stock.

Side note: with heater core bypassed, known operational t-stat, new water pump and car elevated in the front well beyond 1" car still overheats. I blew into the expansion tank until water streamed out of the bleeder port. Radiator is ice cold with the exception of the top 4 inches, where it's warm to the touch but not hot. Wants to boil back to the expansion tank. No circulation.

[88m53453]

drag that bad boy down here and we will figure it out...

[Dash01]

How hard is it to install pistons?

With the head off, can you remove the oil pan, put cylinders 1 and 6 at TDC, and easily remove the connecting rod bolts, and simply push the pistons out the top of the headless block?

(I have spare B35 head, pistons, intake, and wonder how hard it would be to swap them into a B34 engine to convert it to B35 for greater power.)

[USMarineRetired]

I have a new radiator coming in today. Ordered one for a 535i. I talked to the previous owner and he added some "stop leak" to it sometime before I bought the car. Where in W. Central Ga are you?

- - - Updated - - -

Dash, I would think it's doable. I've done that in both a Triumph Spitfire and an old Opel Kadett.

[88m53453]

1 hr south of griffin off US 19

[dm635]

You mention the small coolant hose that runs from the nipple on top of the radiator to the reservoir. This is a different car but I did have a problem there on a 960 Volvo. I did an engine swap and had a problem of the coolant level jumping up and down every time it cooled down. The reservoir would be empty or completely full, or any where in between. It was driving me crazy trying to figure this out. So much so I thought I got a bad engine. On the install I replaced every coolant hose except for 2. That small hose from the radiator to the reservoir. I finally pulled that hose and it indeed had a clog. With that clog it prevented the radiator from filling completely to the top. Since removing the clog the coolant level has stabilized as it should. With the engine I got for replacement I also grabbed

[dm635]

Hit wrong button and didn't finish post. I grabbed the reservoir from the same car I got the engine from because it was much cleaner than mine, nearly new. With the reservoir I also took the small hose that went to the radiator. I have no idea how much coolant was not in the radiator due to that clog. Like I said, that clog prevented the radiator from filling completely so it couldn't bleed correctly. I have never had that issue on any car, only replaced one because of a leak. Looking at the 6 setup and the Volvo they both perform the same exact function and are run the same.

[Shipper]

How hard is it to install pistons?

With the head off, can you remove the oil pan, put cylinders 1 and 6 at TDC, and easily remove the connecting rod bolts, and simply push the pistons out the top of the headless block?

(I have spare B35 head, pistons, intake, and wonder how hard it would be to swap them into a B34 engine to convert it to B35 for greater power.)

Take the engine out, do it properly. You'll need to hone the block and if you are replacing pistons check the rods and bearings. New pistons will mean new rings. Additionally, you may deck block and head to ensure they are perfectly planar.

[USMarineRetired]

Ok, I have a rough idea of where you are 88M. I head that way once in a while to see my wife's family.

Radiator took care of everything. Runs nice and cool now. Heater output temp is obnoxiously high when maxed out! Register vents were blowing 167*! I know my temp gun works pretty well. Testing the t-stat with it was within 1 degree of advertised opening temp. Crazy!

+1 on pulling the engine and doing it right. Always cost more than twice as much to do it a second time..

[Shipper]

+1 on pulling the engine and doing it right. Always cost more than twice as much to do it a second time..

It does, check my bank account. Someone on here once called their car 'the money pit'. Mine was a black hole that sucked in galaxies. All the fault of early shoddy mechanics not worth kicking squarely in the nuts and nothing to do with the car itself. Treat her well, the first time, properly, and she'll be cost effective (well as cost effective as performance builds in old cars can be) and an absolute blast to drive.