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

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HairyScreech
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Tue Aug 24, 2010 2:17 pm

flow was done as industry standard 25 inch water. which is considered to be the average pressure difference across a port during engine operation.

the manifold situation will be solved by yet another custom manifold. probably a tunnel ram manifold with a tuned plenum and single throttle on the end.

something like this but with longer runners. (this is for the zetec turbo)

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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.

your correct to a certain extent on that, although the average should remain at 25" water. and i expect things to get turbulent in the rough casting at higher air speeds. (note to self should have done a high pressure pull through it.)
not sure what you mean by the gains are unlinear?
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HairyScreech
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Tue Aug 24, 2010 2:20 pm

oh and i think i put a full explanation of my method in the early part of the thread, if iv left bits out let me know and ill update it. :wink:
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e301988325i
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Tue Aug 24, 2010 5:42 pm

If I might pick your brain again, would or could the manifold actually flow more if all 6 ports were drawing air. As the extra volume of air would activate the plenum (opposite to vaccum) chamber so to speak, a bit like coming on cam (when the valve overlap starts working) but the manifold coming on err manifold?

Anyway, top thread and much respect for all the M20 research. . . :D
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HairyScreech
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Wed Aug 25, 2010 2:07 am

no, the plenum works as a helmholtz resonator, the flow is restricted by the geometry, diameter and surface finish of the runner.
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Wed Aug 25, 2010 9:16 am

Hairy, if you are keen to design, build and flow-test your own intake manifold (and from what you have posted thus far it looks like you are up for it) then have a read up on on the Toyota Variable Intake System (T-VIS). It's a resonant system (just as you have described above) but uses dual runners to each cylinder between the head and plenum. Directly ajacent to the head there is a set of butterfly valves that close off every alternate runer at low RPM in order to raise the velocity (and hence momentum) of the air drawn through the runners. Due to the length and diameter of the first set of runners, and the volume of the plenum, the first resonant peak is at failrly low rpm. On the drop-off after the first peak the butterlys are progressively opened (opening up both runners per cylinder) introducing a second resonance at higher rpm.

A system that is no doubt used on other cars under a different name, but I know it as T-VIS from the Toyota's I have worked on.

Image

On another note, if you are going to tune tune your intake to "breath easy" around a certain band of rpm, then be sure to do the same with your exhaust system! It stands to reason that an engine that inhales best at say 3500rpm, but exhales best at 5000rpm, is going to be mediochre in general. I apologise if I am teaching you to suck eggs.
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Wed Aug 25, 2010 9:29 am

Geoffbob Taught me something..

Another motor that uses something similar is the Yamaha R1 engines.... However the intake stacks grow longer and shrink at certain RPMs..

Now wouldnt that be cool
HairyScreech
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Thu Aug 26, 2010 6:00 pm

certainly no need to apologise for "teaching me to suck eggs" a certain element of stating the obvious is always useful when discussing anything technical or in development, you never know what may kick off a good idea.

same as i wasnt trying to be pedantic about the drive line mass in the flywheels thread. :)


i have been considering some form of variable length intake for the e30, i think something designed to work at 5500 rpm and a longer runner aimed at 3000 rpm could be a good combination.

iv been thinking log style plenum, with 6 direct straight as possible down draught long runners that curve down by the turret to the log, with some method of short circuiting between the plenum and the port.

obviously this will require some sort of trick, and may stuff up the porting, its all things ill have to make up as i go along, cause right now i just dont know how the intake will behave on the m20 6pot, its uncharted territory.

i think the first thing ill do is build a couple of wave models to determine the best lengths for cylinder filling at 2500-3000 and at 5000-6000, which are your normal road cruze and GLF revs,
those lengths and sizes should give me an idea as to what will be needed for the manifold, and thus if its feasible to build or not.

making the intake stacks longer or constricting the length of the runners is another way of doing it, but may be much more difficult to implement.

one of the troubles of this is i intend to put it on lpg at some point so what ever i make has to be backfire proof in some way shape or form, failing that it has to have the provision for near port gas injection.
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Thu Aug 26, 2010 10:56 pm

Remember that your still limited by the cam,

Thing is that the cam is still one of the major factors. So whatever the cam is, so must the intake follow, and basically vice versa

It´s possible to design a intake manifold to gain some low end but totally destroy the cams ability in the high end, and then same again for the high end,

My concern would be that the M20 cam setup and ports do not really allow for a very strong low end torque build no matter how you make the manifold
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Thu Aug 26, 2010 10:59 pm

Still waiting on the executive summary - bullet points on a single a4 sheet
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HairyScreech
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Fri Aug 27, 2010 12:34 am

everything atm is working around the 272 shrick cam. with a possibility for a 300 shrick.

yes the cam will have an effect but as its really the motion of the air mass, which is largely dictated by the port and manifold, the port, valve and manifold can have a larger say in the peak torque and bhp than the cam.

after all the cam just says when the valve opens, the laws of physics dictate how much air gets past it in that time.

obviously severe overlap or reversion issue can cause problems dependent on engine speed, but thats again down to the port and valve. if the air had enough inertia to keep flooding in then the cylinder would keep filling even at lower speeds.

there is a way to cheat though, and thats increasing the inlet pressure differential.
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GeoffBob
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Fri Aug 27, 2010 8:39 am

HairyScreech wrote:i have been considering some form of variable length intake for the e30, i think something designed to work at 5500 rpm and a longer runner aimed at 3000 rpm could be a good combination.
:thumb:
HairyScreech wrote:i think the first thing ill do is build a couple of wave models to determine the best lengths for cylinder filling at 2500-3000 and at 5000-6000, which are your normal road cruze and GLF revs, those lengths and sizes should give me an idea as to what will be needed for the manifold, and thus if its feasible to build or not.
Hairy, I'm just guessing, but one of the first pracs you ever did at Uni was "Kundt's tube" wasn't it :D
Good idea BTW. 'Way more advanced that what I ever did.
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HairyScreech
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Fri Aug 27, 2010 2:58 pm

just screech will do, after all it is my nickname in RL.


believe it or not i havent actually come across that before, seems a simple enough method of figuring out a tubes resonant frequency.

when i said wave model i meant ricardo wave.
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Fri Aug 27, 2010 3:33 pm

Now seriously trying to read this as Ive got the parts to build a 2.8, however only have a 731 head and figuring that this wont work if bolted straight on? Need to get head ported, bigger valves and a 272 cam?

Or for a mortal like me will it do?
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HairyScreech
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Fri Aug 27, 2010 5:38 pm

731 head has the wrong combustion chamber shape for a b25 piston.

id stick with a 885 head for now.

infact i cant see much of a merit to using the 731 head at all.
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HairyScreech
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Fri Aug 27, 2010 8:53 pm

oh and if it wasnt for the squish band of the b25 head and piston then a 731 head would be ok, but nothing more than ok, it would work, but its just wrong.
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Fri Aug 27, 2010 9:54 pm

Screech - id be interested in buying an 885 head when your done with it. Don't mind validating your theory with my 2.8 build. Pm me :D
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HairyScreech
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Fri Aug 27, 2010 10:48 pm

i have a spare 885 head here that has been skimmed recently, im sure i could whip something up on an exchange basis, purely for the sake of seeing the gain on a basic build.

pm on its way.
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Tue Sep 07, 2010 11:16 pm

does shaving and filing the pistons and rods create an imbalance. i thought the crank was wieghted to the pistons?
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Mon Oct 04, 2010 11:22 pm

hey screech any updates on this??
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HairyScreech
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Tue Oct 05, 2010 2:36 am

yes and no, iv just moved back up to uni last week, so havent had any time to get some of the info typed up, there is more done than is shown here, but i need some time to get it posted.
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Tue Oct 05, 2010 8:52 am

HairyScreech wrote:yes and no, iv just moved back up to uni last week, so havent had any time to get some of the info typed up, there is more done than is shown here, but i need some time to get it posted.
no worries dude :cool:

i'll be waiting in anticipation :D
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Tue Oct 05, 2010 5:14 pm

steve_k wrote:
HairyScreech wrote:yes and no, iv just moved back up to uni last week, so havent had any time to get some of the info typed up, there is more done than is shown here, but i need some time to get it posted.
no worries dude :cool:

i'll be waiting in anticipation :D
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HairyScreech
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Tue Oct 05, 2010 8:01 pm

all right all right, ill get some more done tonight. bloody slave drivers. :roll:
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Tue Oct 05, 2010 9:34 pm

HairyScreech wrote:all right all right, ill get some more done tonight. bloody slave drivers. :roll:
good boy crack on :D
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Thu Oct 07, 2010 12:36 am

ok time to reliese some more of my research,

bit more discovered on the piston front.

i cant find any off the shelf pistons in 84mm that have a crown that is sutable or could be worked to suit the m20 head. its chamber shape and bore size is nearly unique, so all we are left with is either stock bmw pistons, modified bmw pistons or custom after markets.

having done a bit of combustion chamber research i can say that a flat top will be wank compared to a similar compression b25 shaped piston with correct squish clearance. as has already been hinted at in this thread and mentioned by ant previously.

in terms of aftermarket pistons it would appear that most are either a concentric bowl in piston type, a flat top or a gentle concentric dome.
all of which will fucking suck in an m20.

the chamber design of the m20 requires a eccentric bowl positioned over the spark plug, this keeps the combustion chamber as small as possible and centred around the point of ignition.
this design also keeps the fuel air mix as far as possible from the hot exhaust valve.
now basically bmw have done a brilliant job of designing the combustion chamber, its a really nice design with only two flaws, the compression sucks donkey balls and the squish band is a little slack.

now how good the combustion chamber is can be seen from the actually fairly low emissions for the age (remember if the engine came out in the 1977 it was designed in the early 70s or late 60s.) its tolerance of ignition advance, its tolerance of misfueling and there ability to take near 1.5bar boost on stock pistons etc.

as standard these things seem to run a large squish clearance, im not 100% why but i assume its a combination of running on the safe side (tight squish not really needed at 8.8:1), leaving a lot of room for the gasket to be compressed, leaving room for the head to be skimmed, and playing it safe on the stacked up production tolerances.
the result seems to be the stock squish band is bearly ok at 0.045" (1.71mm) and when the piston is 0.5mm further down the bore were well into the realms of harbouring end gas of the combustion chamber producing hot spots, and preventing combustion of areas, which just throws fuel down the exhaust increasing emissions and back fires.
the clearance between the piston and the head over the squish band becomes ~2.2mm
"chamber cavities ranging from 60 to 120 thou are most likely to cause detonation..." (1.524mm to 3.048mm)

what all of this has led me to conclude so far is a skimmed m20b25 piston will be by far the best solution, its allowed me to tighten the squish band up below the generally suggested 60 thou.
currently the new piston is running 1.07mm to 1.14mm from the head, which allowing for measuring error is probably a more even 1.1mm, which so far im told is enough clearance on a rod of this type and length and a piston of this type. (over the next few months we will be doing calculations and fea on rods that will allow me to say this for sure.) these were done by compressing clay and comparing the sections to gauges. so its not accurate as far as precision measurements go but its close enough for giggles.
the americans have found the small block chevy will clip its heads at 7000rpm when running only 0.024" (0.609mm) clearance to the head. considering they are dealing with a longer rod and a heavier piston then i think we should be fine at 1mm and arguably stronger rods.
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HairyScreech
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Thu Oct 07, 2010 1:12 am

the next thing is by skimming the pistons will reduce the depth of the bowl, this will bump up the compression, atm with just a piston cut down and no pockets the compression is 12:1. to me this seems high, but ant has hinted in another thread that this has been run on an m20 just fine before.

his further input here would be appreciated, as although i have a lot of technical info and analysis hes the one with the real world empirical testing to draw on.


as said before the crowns are real thick and the top ring is a way down the piston, part of the reason they work fine under boost, plenty of meat and good thermal resistance.

iv measured the two angles of the piston dome and the head bowl, and the squish bands are a 23 degree angle for the piston and a 21 degree angle for the head, im not sure on why the variation, but i intend to find out,
for now i have just cut the pistons to 21 degrees to match the head, this has resulted in a squish band that almost exactly matches the head squish band. it almost feels like im taking it back to its original spec.

i still need to work out a good way to hold the pistons in order to cut the valve cut outs, which i have measured to be 4mm deep stock intake and 3mm deep stock exhaust. im thinking a jig of some form involving a tube and a hole for the piston pin, welded to a mount that puts it at the correct angle.

next thing i have been considering is the structural integrity of the piston. the centre of the piston is no thinner at its thinnest point, which is under the bowl near the centre, which will mean the middle will be no problem in use.
the ring lands are now 3.8mm from the top of the piston. from what i can gather this is more than what quite a few after market pistons have, and there are a hand full of stock pistons from other cars that are similar to this, namely the 70s aston martin engines and once again the small block chevy at 0.150" (3.81mm)

even still i have been considering using a thermal barrier coating on the piston to keep heat in the chamber and reduce the heat transferred to the piston.

i have so far been either considering a bake on coat or a hard anodize.
im swaying towards the hard anodizing for tow reasons, it hardens the surface of the material and holds lubricant, two thinks that the bake on coatings dont.
only trouble is the anodize layer is 0.0254mm to 0.1524mm and the piston to bore clearance on these motors is 0.02mm.

so just banging anno on is going to result in binding pistons.

next trouble is just boring the block a touch will open up the ring gaps, and to stay in spec only .50mm gap is allowable, which means a 0.095mm max bore increase before the rings get a bit gappy.

not sure on the solution to this yet but ill get there.
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HairyScreech
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Thu Oct 07, 2010 1:13 am

with all that said iv got some more weights and measures of components.

Component weights
42mm valve = 82g variation 2g
36mm valve = 70g
40mm valve = 73g
34mm valve = 60g

main spring = 45g variation 1g
helper spring = 15g variation 1g

retainer = 15g variation 1g
4x collets = 4g so 1 collet = 1g

rocker = 89g variation 2g
clip = 12g

rings
top = 8g
middle = 9g
oil = 10g

rods
m20b25
rod = 363g
cap = 203g
bolts = 58g
m52b28
complete = 576g
rod = 377g
cap = 146g
bolts = 53g
m50b25
complete = 547g
rod = 376g
cap = 122g
bolts = 50g

Piston weights

Stock 325 piston = 513g with pin = 407 no pin
Modified piston 1 full skirt 12:1 = 389g
Mod 12:1 short skirt = 380g
M52b28tu piston = 342g no pin (with rings) pin weighs 112g
Pin = 54mm long, m20 pin = 52mm long, hence weight change.

Skirt length from bottom of oil ring. = 35mm
M20b25 LC = 48.6mm
Shorty piston = 43.19mm

Slipper modifed m20b25 piston = 37+39mm skirt = 376g (no valve pockets)
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Thu Oct 07, 2010 1:17 am

and a few piston pictures for your delectation.

Image
Image

Key to piston pics
1 2 3 4
1 = alpina 10.2:1 for 135mm rod 81mm crank.
2 = us SETA piston (mahle)
3 = us wieght reduced skirt cropped 325I (mahle)
4 = us long skirt 325I piston (KS)

Image
Image

m20b25 euro bottom and my cut down piston top

Image
Image

m20b25 euro bottom and m52b28 top

now from this i can see that iv got the thinnest top ring land, with the alpina coming a very close second.

it would seem the b28 piston has a lower top ring than other pistons.

it would also seem the piston i have made from the m20b25 piston is not far off an alpina piston but with higher compression and shorter skirt.

guess we cant be far off something that works.

now just to be totally clear (or as clear as mud) the modified piston was shortened even more from that pic, to this
Image

all thats changed is the skirt though.
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HairyScreech
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Thu Oct 07, 2010 1:37 am

a few things iv noticed about the rods.

bmw rods seem to be very close in weight, approximately 2g variation.
but they seem to be done as a whole assembly, and not big end little end.

in terms of polishing the beams the rods will be stronger for the removal of the stress risers around the flashing left by the forging. if this it done it must always be done up and down the beam never across the beam so as not to leave machining marks across the beam which are just as bad.

once this has been done the rods will need to be rebalanced.

internet rumor has it that the m52b28 rods are slightly heavier than the b25 rods but are significantly stronger.
this would hold true from the measured weight of the rods.

they also appear to be very similar to s50 rods.

compare:
Image
Image
Image

not the middle rod in the top pic is a b28 one and the others are s50 rods.
seem very similar to me, mainly the beam shape, cap shape etc.

considering hom much m3 tech the rest of the e36 328 used is it possible they are just slightly longer prodictionised versions of the m3 rods?
or perhaps it means m3 rods are nothing special?
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Thu Oct 07, 2010 8:23 pm

HairyScreech wrote:i still need to work out a good way to hold the pistons in order to cut the valve cut outs, which i have measured to be 4mm deep stock intake and 3mm deep stock exhaust. im thinking a jig of some form involving a tube and a hole for the piston pin, welded to a mount that puts it at the correct angle.
Hi Screech, I'm a machinist by trade, the quick method is to clamp the piston between the V's of two V blocks, of course they need to be a decent size to spread the load and match the piston, but milling valve recesses you'll only need a small pinch on a machine vice. This option also aligns the piston in the vertical axis nicely.

Best option using a vice would be to make or use soft metal mild steel or ally vice jaws, and profile them out to the diameter of the piston +.05/+0.1mm.
I said:

Can anyone suggest how to test if the boot lights are staying on with the boot shut?

e30topless said:

lock the wife in there
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kimbo
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Thu Oct 07, 2010 9:23 pm

HairyScreech wrote:ok time to reliese some more of my research,

bit more discovered on the piston front.

i cant find any off the shelf pistons in 84mm that have a crown that is sutable or could be worked to suit the m20 head. its chamber shape and bore size is nearly unique, so all we are left with is either stock bmw pistons, modified bmw pistons or custom after markets.

Dont know if its any help, but the pistons in our motor (picture on P5 of this thread) are made using a Peugeot casting.
I managed to track this down through the Mahle website, but couldn;t get any further as they were just shown as 'no longer available'.
When I remember, I'll look and get the casting number, in case its any use.

Kim
HairyScreech
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Thu Oct 07, 2010 11:00 pm

it would be interesting to know what peugeot piston griffin used for theres, i have tried to track it down but got nowhere.
even if it just comes down to tracking them down for future reference.


e301988325i = the trouble is holding the piston at the right angle reliably, im going to have to fab some sort of jig up as the included angle of the valves is something like 42 degrees.

might make a rig out of an old head like mattias on e30tech has.
2.8 development thread http://www.e30zone.net/modules.php?name ... c&t=170822

m3.3.1 m20 thread - now running, chip needed - any volunteers?
http://www.e30zone.net/modules.php?name ... =viewtopic&
e301988325i
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Fri Oct 08, 2010 7:59 pm

I see, most people I've seen do valve recesses tilt the head of a vertical mill and hold the piston upright.
I said:

Can anyone suggest how to test if the boot lights are staying on with the boot shut?

e30topless said:

lock the wife in there
HairyScreech
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Sat Oct 09, 2010 8:47 am

if i had a tilt head vertical mill that what id do too.
2.8 development thread http://www.e30zone.net/modules.php?name ... c&t=170822

m3.3.1 m20 thread - now running, chip needed - any volunteers?
http://www.e30zone.net/modules.php?name ... =viewtopic&
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