the m20 developement thread. Some progress and a new lump.

[mikep]

screech would it ne possable with 130 mm rods and 325 ks pistons to obtaine piston to crank clerance machine the counter weights down on a cnc and rebalance the crank

[eta]

I have had a thought that has no doubt has been done before.

86mm s50 crank with 130mm conrods and 325i pistons. So the stack height will be 86/2 + 130 +34.2 = 207.2mm

For a normal 325i the stack height is 75/2 +135 +34.2 = 206.7mm.

So will that extra 0.5mm mean valve - piston mating rituals or will they just get remain forever seperated?

If no piston maching needs to be done then a CR of 11:1 will result using a stock headgasket and 885 head. This also looks viable. I am geting the itch to rebuild my engine.

[bss325i]

the alpina pistons were mahle pistons
the hc ones had a short skirt similar to the way Screech has cut his
in South Africa we got the 325 IS that was from bmw with the alpina 2.7 motors and the m 3 suspension there were 2 versions one had a 145kw motor the other made 155kw
when i inquired from bmw Sa the alpina pistons was about 600 pounds each
one could buy a full set of 325 Ks pistons for less than half then this is agents price aftermarket was less than a 3rd for the ks ones about 120 pounds then

I recently priced 6 Alpina pistons and it came to £1200 including VAT.

[eta]

Who are are asking for these alpina pistons. Also what is a 325Ks piston?

[bss325i]

Any BMW main dealer.

Would you like a part number?

[phelix]

Would you like a part number?

Yes please!

And I presume KS = KolbenSchmidt, the piston manufactuer, as opposed to Mahle?

[eta]

Yes please as well as I have yet to find the p/n. I presume these pistons work with 81mm crankshaft and 135mm conrods.

[bss325i]

Yes the C2 2.7/B3 2.7 Alpina M20 engine uses 81mm M21 forged steel crank and 135mm M20 rods.

Not catalyst engine

83.96mm 91471125149 standard size
84.21mm 91471125150 +.25mm oversize
84.46mm 91471125151 +.50mm oversize

Catalyst engine

83.96mm 91471125152 standard size
84.04mm 91471125154 +.08mm oversize
84.21mm 91471125153 +.25mm oversize
84.46mm 91471125155 +.50mm oversize

As far as i know they are Mahle pistons.

Piston rings are standard M20B25 ones in the corresponding sizes.

[Simon13]

they are mahle and the skirts are much shorter and lighter overall than any 2.5 piston regardless of CR.

[e21Jason]

m20 rods will not fit an s50 crank and an s50 crank will not fit an m20 unless you mean the fake usa s50

Jason

[bss325i]

the fake usa s50

Jason

The S52 then?

[eta]

Why will the s50 crank not fit an M20 when the M54/s52 89.6mm crank will?

I just thought as M20 rods fit on the M52 crank they would work on an s50 crank as well. It might explain why no one use an s50 crank in the M20 as well.

I had not realised that the s50 usa crank and euro s50 crank where different. I was aware of the difference in intake manifold, cylinder head cams e.tc but I thought the crank would have been the same.

[e21Jason]

euro s50/52 cranks have a different crank nose that means the m20 crank damper will not bolt up and the rod bearings are larger on a s50/52 than the m20

In the uk you want the m54 cranks

[hennie]

i did some ccing on my stock and alpina head
my stock head cc at 37.8
the alpina head cc at 41.8 the motor this one came of was a 2.7 that made 170kw @6500rpm about 228 horse
these are both cracked
i did a spare stock head to alpina combustion chamber and got it to 41.8 cc

2 was spot on one was 41.2 the rest 41.6 will start the flowing next weekend will post some picks after im done

[HairyScreech]

let us know what you get, it would be interesting if someone else has the same dropoff in flow,

are you cutting multi angle seats? as i think this is the cause of the flow drop off, i think the flow was separating and going turbulent at the exit of the seat, so preventing it flowing any more. (turbulent flow chokes faster)

what lifts are you planning on flowing at and what test pressure?

[hennie]

im just going to copy the flow on the alpina head the only difference this head don't have multi angle seats but the hole in the valve seats are bigger than the stock one ill get the exact dimensions when i work on the head again it had a bit of extra flowing done to it after it came from alpina
i dont have access to a flow bench i only did some test with water will post some picks of how the water comes out of the port compared to a stock head
the cam im using has a 11.5mm lift
the long side is not flowed the same amount the one side is higher than the other will post some picks with dimensions

[HairyScreech]

where in the country are you? if your willing to allow it i could test both heads on the superflow 600 i have been using at the uni.

[gooner1]

hennie,s in South Africa Simon.

[HairyScreech]

ahh, bit pricey on the postage then.

[phelix]

A bit of speculation on my part as I haven't done the maths - did Alpina increase the CC size for performance reasons or to reduce the CR as they were using a longer stroke crank with the same rods?

[hennie]

the alpina pistons had a shallower dish to raise the compression the combustion chamber mods improves combustion the sa alpinas had a 10.4-1 cr for the 155kw version and a 9.8-1cr for the 145kw version those figures were in the 97 leaded petrol days
Simon postage will bankrupt us but it would have been nice to see what the flow on this alpina head is
my head on the car is 125.1mm the one im fixing up will be 124.8 this is the head high measurement from the tappet cover seat to the bottom of the head
that will give me a estimated cr of 10.02 compared to 10.5 with the head on the car
if one uses this Compression Ratio HP Change Calculator i will have a 1% loss in power but with the better combustion i might gain a bit more as the squish will be tighter
link to the calculator http://www.bgsoflex.com/crchange.html
i will post all the measurements and picks this weekend as im not home and the stuff is there

[hennie]

here is some measurements
the first one is the stock size the second one is the alpina head
intake port 37.2 vs 38.1
intake port 45.2 vs 46.3
intake valve seat hole 36.9 vs 38.1
exhaust valve seat hole 30.5 vs 31.9
exhaust port 31.2 vs 34
the step in the bowl of intake by the valve guide has a .5mm difference the one to the front of the engine is the higher one
alpina copy combustion chamber

original alpina

stock head

water test stock head



alpina flowed head

[hennie]

on the alpina head the water is coming out on the whole of the valve seat hole on the stock head there is always a part that gets no water

[HairyScreech]

you have picked up on quite a key thing in head porting, the short bottom radius of the port, this is generally too sharp and causes the fluid flow to come flying off the floor instead of turning the corner.

[hennie]

when i do a similar test with a paraffin gun and soap water it is more noticeable than with just the water on the other cracked heads ive tried a few different approaches on changing the short port will experiment more this weekend to see which one works the best hopefully my new cutting tips that ive ordered will arrive to make it easier to do
the head in the first pick is going in for new guides and opening up of the hole before ill work on it again

[HairyScreech]

http://www.flowdata.net/tech-articles/b ... bench.html

http://www.jalopyjournal.com/forum/show ... p?t=309410

[hennie]

will look and see what i can source locally to build my own but i dont have high hopes as i stay in a 4th world town

[HairyScreech]

its mostly hovers, pipe and some clear pipe to pin next to a ruler.

[hennie]

im looking into one of these blowers they use to inflate air castles or even a leave blower to do the sucking

[Simon13]

Don't know if these help the cause but i took these the other night when sorting out my alpina engine rebuild. The silver slug is from my 88 built C2. The other is a facelift 2.5 slug of some CR of which i don't know

[Simon13]

On my alpina touring engine which is post 91/2 built i think, the pistons had 2.7 and 9.7 written in the crown. Hennies heads look exactly the same as my engines!

[hennie]

had the 2.7 alpina build where the 2nd head in pics came from on a dyno for a tune up and remapping it now pushes
183kw or 245hp at 6300 rpm with 302nm of torque at 5200 rpm

[HairyScreech]

so which head was on it at the time?
whats the spec of the engine?

thats some quite healthy hp for a 2.7, what was it making before hand and do you have graphs form this time and the last time it was on the dyno?

would be interesting to see the curves.

[eta]

Am I right in saying those alpina pistons look almost flat top. They seem to lack the significant protrusion and resulting bowl that can be seen on the 2.5i slug. In fact the alpina piston does look like it has a raised area but its not as pronounced.

[HairyScreech]

the alpina piston is not flat topped, it has a similar shaping to the normal piston, with a lesser bowl the same diameter but not as deep.

its almost like they have machined the crown of an m20b25 piston back 2.5mm

which to me seems totally backwards considering they have eliminated the squishband from the head.

a right banana move if you ask me, it goes back to the post several pages back about open and closed chambers, a chamber with squish will always produce more power. (ford+cosworth did extensive testing, this was the result).

i would almost say that a ported 885 head with the squishband intact would produce better results when stuck on an alpina bottom end than the original did.
if the pistons were flat then i could understand the hemi open chamber.

i wish i could question the guy then did the alpina m20, as it seems a step backwards in many ways.
i get the feeling dave built the bottom end and bob worked the head over and they never spoke during the build.
resulting in a bottom end that would appear to want a stock combustion chamber and a combustion chamber that would on the face of it need a flatter piston or one with a larger protrusion at the squish band.