Hey i'm new. M20b24 81x80 stroker

[Steven320]

Hey guys,

I'm new on this forum, my name is Steven i life in the netherlands.
i drive a 320i 1988 and a 316i 1988 ,both cars i love to drive and to repair them. i'm now busy with a engine rebuild and i have some qeustions about that maby you can help me out.

The engine where i am talking about is a M20b20 motronic from 1988. i have a m20b23 compleet engine kit(pistons,crankshaft etc.) but i was reading some engine specs of the e30 and i find out that de M21b24 a.k.a Diesel engine has the same Bore. so my idea was to use the diesel crank(81mm) and use 130mm rods and shave a few mm of the piston out of the 2.3l. actually 2.45mm of the top.
Is this possible or did some one try it before.

plz let me know

Special greetz Steven

[HairyScreech]

i don't think anyone has done that before, should give an interesting combo, would become a very undersquare 2.44 litres.
The effect should be something like an eta motor with a bit less capacity.

The crowns of all the e30 pistons are pretty thick, most are around 8-8.5mm and with the minimum recommended for an 84mm bore being 5.5mm there is some room to play if you dont mind being close to the margin.

Have you figured out the compression? if not i will have a play later, remember you will have to cut the valve recesses deeper.

I expect the compression to be high, mixture motion to be very high and the thermal efficiency to be real good, it should build a real nice efficiency motor.

[Steven320]

i was thinking the same whay, the piston is deck is around 6.3 mm, if i measurt correct. so i was more thinking of creating a little dome on top of de piston, maby 1 mm height and small enough to afoid most parts, make higher comp. and also the strength of the piston will maby almost untouchd.
the holl idea to remove material is of a engine rebuild company and they say is that the old pistons like myn, are over kill what im saying is there is to much material for its function off use.
And im only put the ref limit. on 6800 or 7000 so there isnt much work on the head.

so my compleet idea of custum piston is like:

Remove skirt : less weight
remove 1.5mm of top pistons (less weight)
1mm dome design dont know the dia. i have to find out. (higer comp)
and off course deeper valve recesses.

i still have to make the exact caluclations.

thanks for your repley

Steven

[HairyScreech]

Have you considered an M5x 2 liter piston, as you will be using the 731 head and a flat piston is not an issue.

There are also two versions of that piston, one for a 135mm rod and one for a 140mm rod, without looking I bed one of them could be used with the diesel crank, for what its worth they are already a lot lighter, have slipper skirts and moly coating and are ~2mm taller due to the increased deck height of the m5x series.
As you are 7.5mm longer on the stroke maybe a 140mm rod M50 piston combined with a 130mm M20 rod?
I make that + 7.5mm on the crank, - 10mm on the rod, +~2mm on the piston.
That should put you bang on for what you need.

[Steven320]

so what your meaning is so if i'm gonna use your combo. i dont have to remove any material, lighter componts and a relible engine.
and wich head gasket will be the best, 1.88 mm or 2.08mm


81mm crank (eta)
130mm rods
pistons (m50b20 or m52b20) 140mm rod version.

btw my 731 head will be back next saterday:

325 valves
30 angle valve seat
polisch poorts
poort algiment

greetz

Steven

[Steven320]

i was searching on the internet, and nobody is selling there pistons. and i was looking on the desgin of the piston and there not flat add all. so if i wanne use them is still have to remove the standard valve recesses. i know that the pistons are better in desgin and strenght but i can better order some custom pistons. but thats not what i want for now.

greetz

Steven

[HairyScreech]

The m20 block is 206.7mm deck height and going by this:
http://www.euro-detal.ru/en/engine/bmw- ... u4v-33071/
The compression height of the m50b20 KS piston is 31.64mm

Thus,
diesel crank = 81mm stroke / 2 = 40.5mm
Piston = 31.64mm
Total = 206.7mm

206.7 - 40.5 - 31.64 = 134.56mm

Thus, a 135mm rod should give you and ideal length for the piston to sit 0.46mm above the deck height.

Diesel crank, 135mm m52 rods (100g lighter than m20) and m50b20 pistons and off you go.
With a stock gasket in there you should have a nice tight piston to head clearance and lots of meat on the top of the pistons to cut valve pockets.

Compression should be somewhere around 11:1 as the m50b20 piston is dead flat.

[Steven320]

oke now i see, jup no doupt thats gonna work.
but the problem is where do i find those pistons and i whant them second hand or i can just order custom one's of IE if you know what i mean. for that money on brand new ones they can probly be even lighter with custom ones. 100gram lighter rods is alot didnt know that. thanks btw for you resurch.
With those rods i aslo get less side load on the pistons right?
so only what i can here from you is that this holl idea is not that bad ad all, but why doesnt try somebody that before

greetz

Steven

[HairyScreech]

I don't know, I guess no one has thought of it yet.
Perhaps no one has bothered to look as its a hard way to get 2.5.

Pistons should be easy to source from here, they are not really a desired engine on these shores and a set of pistons should be at your door for no more than £80.

[reggid]

so what your meaning is so if i'm gonna use your combo. i dont have to remove any material, lighter componts and a relible engine.
and wich head gasket will be the best, 1.88 mm or 2.08mm


81mm crank (eta)
130mm rods
pistons (m50b20 or m52b20) 140mm rod version.

btw my 731 head will be back next saterday:

325 valves
30 angle valve seat
polisch poorts
poort algiment

greetz

Steven

interested on what you find with the 30* seat. does the head place have a flow bench?

[Steven320]

i find out that i can also use the m52b20 pistons if you compare them. The comp. will be even higher, dome is higher and the Valve recess are less deep but the m52b20 is longer.


http://www.euro-detal.ru/en/product/0830400-piston/ (m52b20)
http://www.euro-detal.ru/en/product/0826700-piston/
(m50b20)

M52b20
Cylinder Bore [mm]: 80;
KH, Compression height: 31.7;
VT1, Valve recess depth 1: 2.87;
BU, Dome height: 2.1;
GL, Total lenght: 51.3;
Outer diameter of pin: 22;
Total lenght of pin: 51;
Height of ring 1: 1.5;
Height of ring 2: 1.5;
Height of ring 3: 2;
Ring type 1: R;
Ring type 2: NM;
Ring type 3: SSF;
Coating 1: Cr;

M50b20
Cylinder Bore [mm]: 80;
KH, Compression height: 31.64;
VT1, Valve recess depth 1: 2.94;
BU, Dome height: 1.66;
GL, Total lenght: 50.8;
Outer diameter of pin: 22;
Total lenght of pin: 51;
Height of ring 1: 1.5;
Height of ring 2: 1.5;
Height of ring 3: 2;
Ring type 1: R;
Ring type 2: NM;
Ring type 3: SSF;
Coating 1: Cr;



i dont know reggir didnt ask that i'm on a small buget you know.
exctuly i ask the guy if he can upgrade this head and he came with the list i wrote down so, I can't wait.

We now know wich parts we can use for this combo.
But what about the Ecu, i know you can use the 1.3 on th eta only this is not an eta and i dont wanna have detonation. so what's he best way i already was thinking of a W.A.R miller performance chip.

greetz

Steven

[HairyScreech]

Sticking with the smaller overall 731 ports and going for a 30* seat may be of an advantage here, 2.5l is a lot for 731 ports and valves to feed without fitting bigger seats and heavy port work so maximising low lift flow may be the best bet.

Its no good specing a seat for high flow when the port and valve curtain area have no hope of feeding the cylinder, so getting as much area under the flow curve and maximising the air than can be inducted at low lifts either side of the max lift choke point sounds like a good idea to me.
(^^Total speculation at this point based on what I hope is sound logic)

It will be interesting how this turns out, if it works (and I have no doubt that it will) then I am thinking it may be a good candidate for a '78 e21 320/6 I have just acquired, hopefully around 160+hp can be achieved with decent consumption and greater torque spread and general drivability than the short stroke/low compression motors.

[Steven320]

I have the 731 head back for 2 weeks already it looks brand new!!. those valves look BIG!! if you compare them with old 40/34 mm valves. actually the seat job was 30/45/70.

the holl idea of the stroker is great but. im extually not sure about that. nobody try it and what if it turns out bad... it is my daily driven car and i am on a budget. but i will think about it more and try to search more about this combo.

but what your saying about the consumption and the torque curve. if it will be better than the rest why didnt bmw do this combo.

i still have a few questions about the head.
i started yesterday with removing the material whats left after the bigger valves. but i have to make the bowl a little bigger and i dont know whats it gonna down with my cfm. or maby great more turblence.
on a diff forum there talking about it and i dont really understand the mods i have to make.

http://www.e30tech.com/forum/showthread ... 38&page=25

maby you can help me out with this.

greetz

Steven

[HairyScreech]

The simple answer to why didn't bmw go for a small bore long stroke motor for efficiency in the 320 is simple, that's what the 318is or 325e was for. The normal m20 was a performance motor.
(The 325e 2.7 is actually an example of them going for a small bore, longer stroke, low rpm for efficiency).
Also in this case there really wasnt much need, the consumption of a 320 is still better than a lot of its carborated contemperies.

The answer to the head is an easy one, Between a few of us on here most issues of the m20 head have been discussed here:
http://www.e30zone.net/modules.php?name ... sc&start=0
(begins more general then we get a bit more head specific)
The flow tests are in there but the actual pictures of the port seem to be missing, if you need i can solve that one.

What i did with the port is not perfect by any measure, but it did pick up flow (graphs are in the thread), At least if you follow that you know you can do little harm.

p.s. has there been anything new on that thread recently? I know the guy that started it has been too busy to make any progress due to a new job etc.

Re the stroker, in mechanical terms I see no reason why it wont work fine, the m50 rods are a proven match to the m20 crank and the pistons have been used in steel bores before, the 731 head has been used at those kind of compression ratios before with a flat piston and no issues, and 80mm pistons have been used with 6.5mm thick crowns many times.
The only unknown is everything all put together at once but I doubt there will be any issues.

I quite like the proposed combination and I am considering putting it in the e21 so I will knock together some dyno sim results for the combinations later, I have most of the m20 stuff already on file so building a sim of the b20 should take no time.

[HairyScreech]

Ok, modified a b25 file to suit the b20, kept the tried and tested parts and ported over the data for the valve size, head flow, cam spec, throttle body, inlet manifold, bore/stroke and compression.
Result was this:




Factory spec says peak torque at 4000 (so i am a bit high but it has the b25 exhaust spec and a tuned inlet length in the absence of that data) and peak power at 5800 so all the trends add up.
I have flow data for the 731 casting with the 42mm valves in and all the rest should be simple to estimate.
Will come back with some simulated data shortly.

[HairyScreech]

This is a sim with just the bottom end in place (81mm crank, 135mm rod, 80mm piston), corrections have been applied for the smaller skirt of the m50 piston and the lower tension rings (part of the program) everything else is exactly the same.
Compression has been left the same (as it's in the head specs and i forgot to tweek it.)

The torque boost is noticeable, as is the way the 731 head quickly chokes at high flow demand.

BSFC brake specific fuel consumption, is improved as expected up to the point the head chokes off and it falls off a cliff (less is more in this case)

BMEP Brake mean effective pressure, is improved as expected this is simple a measure of the force on the piston.

Conclusions to draw from that:
1. the 731 is good for the b20 but choked for a b24.
2. b24 bottom end would be potent at low revs but poor higher up without other mods
3. if kept to low revs would give better fuel consumption than the b20 (in this case)

Will play further.

[HairyScreech]

This is the simplest best combination of the parts i have on file.

Combination uses the proposed b24 bottom end,
a 731 head with the 885 inlet valve and 34mm exhaust (to keep inlet/exhaust ratio right) and uses the flow from my test on the 731 with the 885 valves and +1mm csa to account for port work
a b25 cam
a b25 inlet manifold with throttle

Results look nice and the bsfc is lower throughout the range, with the head/manifold and cam the power dosen't fall off the cliff either.

Take all results with a pinch of salt but thus far i have found the sim to be pretty accurate provided the inputs are sound.

I think this will be going in an e21 in the near future, will start keeping an eye out for a spare 731 and a set of b20 pistons.

[HairyScreech]

and finally a b24 vs b25, you can draw your own conclusions from that but i know which looks better to me.

Edit - current is the b25 the last is the b24

[Steven320]

Oke i will read your topic multiple times thill i understand. and if you can send me some pic's i will be very happy.

Sometimes they post something but mostly its about the 885.

didnt know there was a software program for this. but your right it does look like a good combo. sorry i doubt on your info a bit but this is something i never saw before. i know its just a program but still you can see the diff between those engines pretty clearly.

so in thery this combo is pretty good so what if we mod this engine with some tuning parts.
so what if you can make a 731 head that have same flow as a 885 or better, with 288 cam or 285, stiffer springs, HD rockers, retainers, standalone ecu, long headers and around 10:1 comp or even higher.

is that possible to sim?

[HairyScreech]

Tip: Styles can be applied quickly to selected text. hold together, that's up to you and is why things like hd rockers, ecu etc are all left out.
The outputs of x are what you can expect if you get all of the things required to hold it together and run it correct.

The best combination assumed the 11:1 that can be expected from using flat pistons and 81mm stroke. It was my mistake leaving the CR boost out of the first sim.

I think in this case it is not an engine to go plowing money into and buying expensive cams and rockers etc, if that was the intention then far better results could be found by building a 2.8 or larger.
In this case it is a nice cheep motor that could be put together and still keep the standard 320 block and head, which may be desirable in some cases. (certainly in countries where the stock block has to be retained or racing classes that restrict block and bore but crank etc are free)

[Steven320]

my intention was more to tune the m20b23 above the 170hp exactully what hartge and alpina did with this engine.
without going over the 7000 rpm.

Hartge H23/AlpinaC1 2.3 73.91 hp/L

2.5@170hp - 68hp/l
2.5@180hp - 72hp/l (btb chip all the bits you would stick on a 2.8 you gave a toss about)
2.7@190hp - 70.37hp/l (weak head flow as 730 casting)
2.8@206hp - 73.57hp/l
3.1@226hp - 72.9hp/l

(your info)

You can see that this engine is better tuned
but i wish to get a little bit more thats why i was thinking about the b24, it has a longer stroke but still a good rod/crank ratio and light weight components. and with some mods i think it will rev clean till the 7k. or maby little less or more.
all the parts that we gonna use like you said are tested many times even over the 7k execpt for those pistons cause nobody is useing them.

m20b24 piston speed:
6000 rpm 53 fps 16.20 m/s
6500 rpm 57 fps 17.55 m/s
7000 rpm 62 fps 18.90 m/s (redline around here?)
7500 rpm 66 fps 20.25 m/s

m20b23 piston speed:

6000 rpm 50 fps 15.36 m/s
6500 rpm 54 fps 16.64 m/s (redline 6400rpm)
7000 rpm 58 fps 17.92 m/s
7500 rpm 62 fps 19.20 m/s

M50b20tu piston speed:

6000 rpm 43 fps 13.20 m/s
6500 rpm 46 fps 14.30 m/s (redline 6750rpm)
7000 rpm 50 fps 15.39 m/s
7500 rpm 54 fps 16.49 m/s

but i cant see a reason why a 1982 old piston can hold more gforce than a piston out of a m50
i think the most simple idea is thinking of a m50b20tu thats reving 9k with standard pistons (19.8 m/s)
but 7500 rpm is a little high for a custom stroker and not useful in daily drive car, so 7k would be good and also your sim is saying that it can deliver power thill around 7k before it drops big time. so im thinking why not.

Rod/crank: 135/81=1.666666
looks good to me a little lower than a b23 130/76.8=1.69

greets Steven

[HairyScreech]

the derv crank is ok at 7k and the m50b25 piston are the same design but bigger and heavier and will cope with 7.5k.
certainly 7k for that combination should be ok.

[Steven320]

oke so everything is able to work ad those speeds. you ask why im not building a 2.8, now the reason is pretty simple cause everybody is making a 2.7/2.8/2.9/3.0 and 3.1 and the b25 block are getting pretty expensive here so i dicide tho take the path of the unknown. with your sim im pretty confince that this engine run good with some mods and make a track/daily engine.

and the torq. is starting from 235nm over a little wider and better range than the b25 (sim) with a 2.44l i mean thats sounds great to me. if i understand that correct.

[Steven320]

i found thiss! a m20b24
[youtube][/youtube]
and i think this is the same car if you look on the int. and sound but im not sure.
[youtube][/youtube]

[HairyScreech]

I think that might be a 323 with an 82mm bore.

[Steven320]

maby it is. is it possible that you send me your saved file of b24 of engine anulizer?

[HairyScreech]

Yeah no sweat, pm me your email address and I will fire it over, there is a trial of EAP available.