JRW'S 91 318is turbo build

[jrw21]

I did somewhat of a long search trying to find out the volume of a stock s52 dish. Couldn't find the answer I was looking for so I cc'd the piston. My result was ~15.5cc. Close enough to tell me that I will not be able to use the m44, s52, and 135mm rods. Compression will be around 6.87:1.

So, back to build option 1 for me. Ran the numbers in excel real quick. I am leaning on shaving 2mm (highlighted in red) with a .098 gasket ~8.6:1 compression

Block height   Stroke/2   KH   Rod Length   Deck Height   piston shave   
212                   41.75   31   140                   -0.75           0   
212                   41.75   30   140                    0.25           1   
212                   41.75   29   140                    1.25           2   
212                   41.75   28   140                    2.25           3   
212                   41.75   27   140                    3.25           4   
                  
Pie   radius         r^2            Height   Volume cc        KH   Deck Height
3.14   35.1825   1237.8083   4           15.546          31   -0.75
3.14   35.1825   1237.8083   3           11.660          30   0.25
3.14   35.1825   1237.8083   2             7.773          29   1.25
3.14   35.1825   1237.8083   1             3.886          28   2.25
3.14   35.1825   1237.8083   0             0                  27   3.25

[jrw21]

Bottom end:

Bored block 86.4mm
m44 cranshaft 83.5mm
s52 pistons 86.365
m42 rods 140mm

Going to order coated rod and main bearings and arp 2000 fasteners tonight.

[benz-tech]

just a gut feeling here so it may be nothing. You look to be using the heavy early M42 rods. I had one shop refuse to balance anything that isn't stock since it may require adding weight to the crank - expensive but doable I suppose. Again I am no expert. Since the M44 crank is not fully counter balanced it might be more succecptable (sp) to significantly heavier rods. Is there any reason you are not using the lighter M44 rod that was on the left in your picture?

[jrw21]

You are correct those are the stock early model rods I just got done pulling from my 91 m42 engine. I decided to use them as they are beefy and should hold up well for forced induction. I weighed each rod I was anticipating on using: (the weights are with bearings)


I was shocked to find that the m50TUB25 and the early model m42 rods are almost identical. The only difference I could find was there was an N marking next to the 473 on the m50tub25. Also, I found that the m50tub25 rod takes 53mm bolts and the m42 rod 47mm. So, afaik those are the only differences.

[benz-tech]

So cool to have couple of engines being built right now. Keep the pics coming. Lookin' good so far.

[jrw21]

So cool to have couple of engines being built right now. Keep the pics coming. Lookin' good so far.

Yes it is, one NA and one Turbo. Pretty cool

Just got off the phone with Mike from VAC motorsports a little bit ago. They are custom making me a .098 MLS gasket for 86.5mm bore! Awesome! Got a bunch of other good items from them as well.

[jrw21]

Ok, so waiting for parts to come in at this point.

But sitting here thinking about the m44 crankshaft and the attached impulse sending wheel. It appears that the sending wheel weighs ~345g. If I remove it I am assuming it will throw the crank out of balance. So, I would need to have material removed somewhere else on the crank to get it back in balance..potentially saving 690g.

What do you all think? Good, bad, not worth the time?

[wazzu70]

If you remove the impulse wheel, you definitely need to have the crank rebalanced. I think its best to talk to your local machine shop and see how much such a job would cost. Thats probably going to highlight quickly if its worthwhile or not

[bmwman91]

Good build thread so far, thanks for posting so many pictures of M42 guts!

Like wazzu said, talk to a shop before modding the crank at all. Maybe you could work in some knife-edging with the rebalancing job?

Are you using the M42 timing case? If so, I highly recommend swapping in a late-model M42 timing case (09/1993+) since that replaced the stupid idler sprocket with a guide rail, eliminating some major reliability issues.

[jrw21]

Thanks for the tips guys. Will converse with the machine ship on the crank.

I just happen to have a torn down 95 m42 as well.. Ok so the the deflection guide is better than the deflection wheel? Any other parts I should rob from the 95 m42?

[bmwman91]

It sounds like you already went with the 6mm valve stems, so you are good there. The idler sprocket really is an insidious time bomb at this point. Get rid of it!

Also, one thing to think about is using an M44 timing case. It has larger (thicker) oil pump rotors and flows more oil, which could be a big plus on a turbo setup. You would need to make or buy a crank position sensor holder though since the M44 case doesn't have it cast in. Metric Mechanic can probably sell you one. Anyway, this is probably totally unnecessary so don't worry too much about it.

[jrw21]

Yeah, 6mm valves are on the way. Actually, I decided not to use the high mileage bmw valves. I broke down and purchased supertech nitride coated intake and inconel exhaust valves to match the supertech valve springs. The valvetrain is looking good, I just need to find out how high I can rev the VW 48 gram hydraulic buckets. I used to know, thought I had it written down somewhere.

Ok, I will make sure I get the deflection guide on there! Thanks for the tip on this.

[jrw21]

Ok, guys. Trying to find out the specs on stock cams.

This is what I found from some hours on google, not sure on validity of this data maybe someone can chime in here.

1991 m42: Duration 252/252 lift 10.2/10.2
1995 m42: Duration 242/242 lift 9.2/9.2

Anyway, I know about zero about camshaft duration and lift. I do know that I would prefer low end power and quicker turbo spool up. So, I am thinking a lower duration would work better for my goals? So, if the 1995 cam is truly 242/242 this would put more of the power I am looking for in the lower rpm? Please someone help me out here.

[romkasponka]

there is information about m42 camshaft http://www.catcams.com/products/camshafts/datasheet.aspx?ENGINE_id=105&CAMSETUP_id=230

I have never heard that early m42 and late m42 camshaft are different. In any case stock camshafts are good for goal.

[wazzu70]

I have never seen any real evidence the later M42 cams are a smaller duration. I suppose its possible though as the DSIA manifold wouldnt command as much from the cams.

Still, stock cams are really mild and they will work fine if you want to use them. To get a little more low end grunt at expense of top end you can always advance the intake cam a few degrees. Make sure to measure valve clearance if you do this though!!!

Another option is a set of VAC/Catcams turbo cams. These will be the most optimal.