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

[HairyScreech]

140 M50B20TU =547 grams
135 m52 = 576g
135 m20 = 624g





comparison of the b28 piston to a low comp m20 slug



how the b28 piston sits with a 135 rod






1st generation modified m20 piston, skirt reduced by 5mm all over.





where the 5mm cut down piston clashes is where the marker pen is on the skirt.






2nd generation modified m20 piston, clears by 2mm.


polished and 0.5g balanced m52 rods.

[HairyScreech]

pistons currently weigh in at:

408 grams for the stock m20
342 grams for the m52b28
376 grams with more to come off for the 2nd gen m20.

skirt lengths

m52b28 = 35mm
m20 low comp = 48.5mm
1st gen = 43mm
2nd gen = 37mm and 39mm at step.

[e301988325i]

So the M52 con rod weighs 50g less, and 30g removed from the piston. That in itself would gain power in an M20 b25, is it possible to work out how much, perhaps for b25and b28?

Ps) The m20 rods look unbendable

[HairyScreech]

it wont gain power but it will reduce bearing load from piston inertia, the piston on its own reduces it from a mean of 155.9kn to a mean of 144kn for a b28, havent worked out peaks yet as i havent had the calcs to hand, regardless theres more to come off the piston.
(assuming mean piston speeds of 18.43m/s for a b25 and 19.6m/s for a b28 @ 7000 rpm)

iv had it back in the lathe today and got it to clear the head by a good 1.15mm but it again leaves me at 12.1:1 so i need to reclaim that volume, valve cut outs going in later on tomorrow though as well as some other little tricks.

concerned about piston slap atm,

[kimbo]

Hi,
Watching this topic with great interest, anyone ever seen an M20B25 pistin which looks like this?


Reckon the static CR is around 11.5:1, at least this is what we'll be aiming for.
The head has been opened out to more or less hemispherical chambers and has had considerable porting. Unfortunately now scrap due to crack into the cam area, and a previous cr@p repair carried out (I think) when the motor sucked something big into no.2 and the piston / valve / foreign body interfaced and the resulting clang broke the 1st and 2nd cam journals, which were subsequently welded up but not line bored, causing massive scoring of the bearing surfaces.
We've got a replacement head which we'll use to copy from the old one, but we are watching your results with interest to see if we can optimise the porting.
Looks like we'll definately go with M52 rods, cleaned up and balanced, the difference looks well worthwhile compared to the M20 rods.
Looking to get 250+ Brake out of 2.5 litres with this motor, running ITB's, Hartge 6 branch exhaust manifold and either Schrick or Cat Cams suitably lumpy camshaft (yet to be decided).
Keep it up, really useful thread and when we ever get our motor going I'll be sure to post up the details.
Kim.

[Dezzy]

This thread is epic!
I just wish i had a fooking clue what you were going on about.

Looks like good work though

[HairyScreech]

the porting isnt really too much of an issue, the seat needs to be a multi angle, and the valve needs a little up size. do that first.

its the next thing to test.

oh and that looks/sounds like it might be an alpina engine.

[DanThe]

Looking good

So the TU crank is not as unusable as people think, that top rod is a late M50B20 BTW, the earlier/more common M50 rod is shaped more like the M20

[HairyScreech]

ahh, so the early m50s really are a bad ass 24v m20 then.

if thats an m50b20 rod then that explains why its so light, to be fair i dont think there is any way to use a 140mm rod, a 138 rod would work, as the b28 pistons could be used with a squish band worked into them, stock on a 135/140 rod though there to short/too tall. so would just suck.

just made me a valve pocket hog, so im going to go rough out some 4mm deep pockets.

iv got a load more info to post, this being a single man again thing means i can really get on with stuff!

[HairyScreech]

kimbo, i question the use of the hemi chamber in the m20 at all now, with the plug offset as it is and the increase in combustion volume causing the need for a highly domed piston such as yours, the shape of the combustion chamber is totally ruined, its turned into a curved disc shape, which is a prime way to cause det and require retarded ignition.

the ideal is a small spherical chamber with the plug placed at the dead centre (not practical.) hence why the standard chamber is offset and has a bowl in the piston to place 70% of the important area as close to the plug and as far away from the exhaust valve as possible.

a hemi has real advantages where the piston can be flatter with the plug in the centre (like a 24v head) and do like a good bit of boost.

for these reasons iv stayed away from the hemi chamber and m52b28 piston.

i think there is certainly more to come simply from optimising what is already designed in, as atm its a nice design in theory but seems to need tweeks to get it going. things like the squish band being too slack on a low comp piston and 6mm of the squish band going unused.

if you really want to know what has been done to the head, pass it down this way and ill measure the lot and then flow it. then you will know for sure.

[kimbo]

kimbo, i question the use of the hemi chamber in the m20 at all now, .

I hear what you're saying and of course, you're right.
The head is down at the workshop, so I can't take any pictures of it to illustrate what I mean, but the combustion chambers, whilst being of basically hemispherical form, have a vestigial 'land' where the standard head has that sticky out bit.
In my mind, I figured that this was there to give either a bit of added sqish or to promote some turbulence in the chamber, to promote a good flame path from the plug. Problem is, I cant remember the relative positions of the plug hole and the land.
What I do know for sure is that this motor was dyno'd at 203 bhp at the wheels running on dizzy ignition and carbs, so theres plenty of potential there!

Kim

ps where are you based?

[HairyScreech]

well im a wiltshire local for my sins, but when im at uni im in swansea, and they own the flow bench....


do your chambers perhaps look like this?

[kimbo]

well im a wiltshire local for my sins, but when im at uni im in swansea, and they own the flow bench....


do your chambers perhaps look like this?

Close, but (from memory) not identical - a more pronounced 'lump, rather than the uniform shape shown in your pic - is this an Alpina head?
I'll get a picture of ours when I'm next at the workshop - it'll be moving back home soon anyway, to live in the garage, so perhaps we'll get more work done on it then!

I get down to Gurston Down (near Wilton) once a month in the summer - marshal at the hillclimb - anywhere close?

Kim

[HairyScreech]

yep, thats an alpina c2.7 head from simon13s touring.

wilton is about 25 mins east from my house.

have you got any part numbers on any bits?

[hennie]

do you know what the difference is of flow on a stock 885 head vs a stock 731 head

[reggid]

do you know what the difference is of flow on a stock 885 head vs a stock 731 head

http://www.e30zone.net/modules.php?name ... 64&start=0

[HairyScreech]

yes i do, iv also done one with a 42mm valve in it, i just havent had time to write all the data yet.

iv got the manifold flow and a few other things as well.

in the next few days i may get a chance to write it up.

[hennie]

Thanks Screech ill keep looking for those stats from you

[HairyScreech]

i have time now, they will be up in half an hour

[HairyScreech]

firstly no ports have multi angle valve seats yet, which are worth 15% to 25% of the remaining loss, so thats the next task before going for big valves.

also important to remember this is flow per mm lift, and a stock 325 cam only goes to 10.3mm and a valve really shouldnt flow much better after its lifted 35% of its diameter. (port area to curtain area relation ship thing.)

stock intake (885)
stock exhaust (885)
best porting so far (885)
alpina intake (885)
alpina exhaust (885)
stock 320 intake (731)
320 intake with 42mm valve and throat from a 885 and opened up to work with valve (731)
duratec ka 1.3 intake for comparison
theoretical potential maximum for a 42mm valve.


conclusion, the 731 head port is shaped to work with lower lift, as expected increasing the valve size on the 731 increases the flow proportionally through out the range as is the expected convention. flow curve remains the same as that is largely dictated by the geometry of the port, valve seats and the chamber.

a 731 with 42mm valves and a bit of porting to work with them is better than a stock 885 head for an engine with a stock cam, but the 885 with work shows it the way home.

why havent i beat the alpina head yet? multi angle seats.

[m_jermyn]

Can you do the flow tests with the inlet manifold on?

And what is the difference between the 885 and 731 inlet ports?

When I matched the 325i inlet manifold to the 731 head I notice the ports are virtually identical, since we are always told the 885 has bigger ports I am thinking with the inlet manifold mated to the 885 head there will be a pressure drop as the air exits the inlet manifold into the head.

However with the 731 head im thinking there will be no pressure drop as the ports are very very similar except a tiny bit at the bottom.

I cant see the point in getting the most out of a head then bolting it to a manifold that will strangle it and not deliver enough air.

Mike

[HairyScreech]

what like this?

[HairyScreech]

[HairyScreech]

thats with it bolted to an 885 head.

its shite and only flows 250hp.

[m_jermyn]

So it does choke it?

Sorry not real good on all these data graphs

[HairyScreech]

the graphs show the valve lift along the bottom and the CFM (cubic feet per minute) of air on the vertical, the higher that peak the more air gets into the engine, the larger the area under the curve the greater the bulk flow.

the higher the peak and the greater the bulk the more air that goes in, the more air that goes in the bigger the bang.

the orange potential line is the theoretical maximum flow for a 42mm valve if it flowed perfectly according to aerodynamic principals.

[e301988325i]

Is that with the 60mm throttle body attached, if so Could you test to see the manifolds' potential with the TB removed or perhaps a 64mm TB?

[HairyScreech]

throttle body wont be any restriction on that as im only sucking through one of the cylinders, id need to suck through all 6 to choke the body.

its the runner thats being tested really.

[e301988325i]

Ok, so what BHP in theory would a 60mm and 64mm TB be capable of flowing?

[djk]

Cripes, I've got roomspin!

Note to self, the English degree was a mistake.

Awesomeness all round though, following this thread with bewildered interest.

[HairyScreech]

Ok, so what BHP in theory would a 60mm and 64mm TB be capable of flowing?

ummm, more than 4?


i honestly have not considered it.

[clarko74]

I've been watching this thread closely as I'm going to be building a 2.8 m20 at some point. Very interesteing stuff, especially the graphs, makes it all very clear.

Looking at the second graph, doesn't this confirm what m_jermyn is saying:

I cant see the point in getting the most out of a head then bolting it to a manifold that will strangle it and not deliver enough air.

Mike

You say yourself that the flow is shite with the manifold on so is there any point improving the flow of the head if this extra capacity can't be utilised due to the restriction of the manifold? If this is the case do you have any plans to open up the intake at all (if this is possible)?

Hopefully I'm reading this correctly, A-level physics was a long time ago...

[Gunni]

A better flowing head will be able to create a stronger vacuum behind the manifold resulting in more airflow (higher pressure ratio across two points). The gains are minor as they will be unlinear.

[bilun777]

For those with larger capacity motors there's the extrude honed manifolds.Ireland tuning in usa sell them and claim worthwhile gains.Check-em out.

[GeoffBob]

the graphs show the valve lift along the bottom and the CFM (cubic feet per minute) of air on the vertical, the higher that peak the more air gets into the engine

So its air flow as a function of valve lift. At what pressure purely out of interest?

Interesting thread this.