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

[HairyScreech]

every little helps, thanks for the offer dan.

im running some more numbers as i type this using the superflow manual as a guide, ill report when im done.

[e21Jason]

My mate Rup who done the orginal m20 flow testing post is back over for a couple of weeks, the stuff he posted is only a fraction of what he has carried out. I can pm who his email if you want

Jason

[HairyScreech]

that would very much be appreciated, as my goal here is to build a better 2.8 not spend a year becoming a head porting jedi. if he can point me in the right directions for a quick easy win then that would be fantastic. (and to the benefit of everyone on here).

[StuBeeDoo]

731 chamber shape seems to work well with eta flat pistons,gives good low down torque and there is room for at least 325 sized valves....but....bigger valves seem to loose the low down torque at the expense of more bhp above the 4000rpm mark,any scientific answer here,please?
Just thinking out loud on this one,would 731 head with eta pistons suit any of the available rods for a torque laden 2.8?

Just reading this thread for the umpteenth time, because I've been wondering along these lines too.
731 'head doesn't look to me like it would need much work to make it a pukka hemi - it's well on the way there. It will take 325i valves no problem. The ports can be taken to 325i size no problem, if it's powaaaah you're after.
So, how about this??.......
M52B28 crank and rods
M52B28 pistons, modded to suit the M20 valves
731 'head, modded to your preference
Cam of your choice.






....... Waits for the flaming to begin.

[daimlerman]

I'm with you on this Stubeedoo,I would expect that there is a rod/piston compatability issue....but I do not have the knowledge to say!
But the OP is at least sharing his thoughts and findings,so we can all learn a little more.

[HairyScreech]

we HAVE fitted a 320 head to a prefacelift high comp 2.5, the head required some bits of the chamber cut away to clear the piston but it did run and work fine. (for the few hours it ran before it was decided the rest of the car was crap and my mate blew his bottom end up. )

the 731 may also provide a better base for a high power head as well, the ports are smaller so will allow more work to be done before they become so large the flow is slowing down.

if someone has a cracked one or a scrap one let me know and we will find out for sure!

i havent had much time to do a lot on this the last couple of days as iv been trying to finnish uni work.

progress is i have some new burrs for porting, iv had a fiddle with the head again for another round of flow benching, iv had some ebay goon sell his engine and then decide to refund the payment and not to sell it for that price (prick ).

as always people thoughts are welcome as it can lead to new things to investigate.

[daimlerman]

Uni work must come first,young man,then you can play to your heart's content!
As there is a known difference in pin hieght between eta and 325 type pistons,this may be the stumbling block for Stu's/my ideas!

[Simon13]

why are we banging on about the 2.0 heads still? its the 2.5 head for the win, you can have big valves and long rods and still get low end torque with HP up top with the right camshaft. Alpina did it

That friend of jasons, i remember his post, 2.0 heads are ok but modding the 2.5 head gets the best result

I have on my desk here an alpina piston, low comp 2.5 and high comp 2.5 slugs, maybe of use?

[StuBeeDoo]

Uni work must come first,young man,then you can play to your heart's content!
As there is a known difference in pin hieght between eta and 325 type pistons,this may be the stumbling block for Stu's/my ideas!

I've never actually seen a 325i piston, but is there enough metal on the crown to allow it to be "flatted"?

There's got to be good reason(s) why this has never been done before. We can't be the only people who've pondered on it in the 25 years since tuners (Apina, Hartge) started working with the factory M20B25.

Another thought..... There must be an amount of potential in the 731, IIRC the M20B23 based Alpina 2.5 (the 84mm bore 76.8mm stroke 2554cc one) used it.

[StuBeeDoo]

why are we banging on about the 2.0 heads still?

I don't know why anyone else brought it up, but my reasoning is that it would work with M52B28 pistons.

[daimlerman]

I have on my desk here an alpina piston, low comp 2.5 and high comp 2.5 slugs, maybe of use?

How different is the top of the Alpina piston,Simon?
Just thinking that a flat top piston would suit a re-worked 731 head,afterall,all Alpina appear to have done is to make the 885 chamber a similar shape to 731,then slightly changed the shape of the exhaust port.
If we could start with the chamber more or less right,it should be almost easy to mod the ports of the 731 and ease out the exhaust side.
Bods such as Stubeedoo and myself are far more interested in the torque curve than the outright BHP,additionaly,an engine producing most of it's grunt lowdown will consume less fuel,BMW's own work with eta establish's this,and modern diesel engines work on much the same basis.
All this is pure conjecture,of course,there is probably no suitable rod available!

[HairyScreech]

im going to see if the spare pistons i have will take a 2mm skim around the outer edge. as the 2.8 crank is what? 3mm longer stroke?

1mm should be ok to accomodate somewhere,

although this last post could be balls as im on the cidre.

[StuBeeDoo]

im going to see if the spare pistons i have will take a 2mm skim around the outer edge. as the 2.8 crank is what? 3mm longer stroke?

1mm should be ok to accomodate somewhere,

although this last post could be balls as im on the cidre.

Don't forget, though, that 3mm extra stroke means that the piston travels 1.5mm further up the bore and 1.5mm further down.

[Simon13]

I have on my desk here an alpina piston, low comp 2.5 and high comp 2.5 slugs, maybe of use?

How different is the top of the Alpina piston,Simon?
Just thinking that a flat top piston would suit a re-worked 731 head,afterall,all Alpina appear to have done is to make the 885 chamber a similar shape to 731,then slightly changed the shape of the exhaust port.
If we could start with the chamber more or less right,it should be almost easy to mod the ports of the 731 and ease out the exhaust side.
Bods such as Stubeedoo and myself are far more interested in the torque curve than the outright BHP,additionaly,an engine producing most of it's grunt lowdown will consume less fuel,BMW's own work with eta establish's this,and modern diesel engines work on much the same basis.
All this is pure conjecture,of course,there is probably no suitable rod available!

its not, the top is identical to a normal 2.5 slug it just has a different wrist pin height, much shorter skirts and is alot lighter

[daimlerman]

Righto,so the differing pin height removes the need to 'deck' the block,as is the usual practice when using 325 pistons for a 2.7.
As I read the posts on 2.8 builds,the M52 crank/325 piston combo means that the block does not require decking,so the Alpina lightwieght piston would be of no use here....as it's top is the same as a stock piston,hemi-ing the head must have been done for reasons other than to suit their piston!
Seems to me that what we are looking for is a lighter piston that is compatable with a suitable rod.I would guess that a very short piston would have a tendency to 'rock' in the bore,perhaps creating wear and causing 'slap'?

[Bob_S]

m52b28.. no headache, no fuss, just 200+

[Simon13]

my touring engine doesn't slap its nearly 190,000 miles up

Alpina used to hemi all M20,M30 engines not sure on the V8's. Must be a reason for why they favour this type of chamber over BMW's swirl design

[StuBeeDoo]

Must be a reason for why they favour this type of chamber over BMW's swirl design

Aren't all the "best" yank V8s hemis??

[daimlerman]

Must be a reason for why they favour this type of chamber over BMW's swirl design

Aren't all the "best" yank V8s hemis??

As are BMW's 24 valve heads...
Just odd that the OP's flow tests showed no gain!
Does seem to me,though,that the secret to this lays in the lighter piston.Given the known high cost of Alpina pistons,is there a workable alternate?
How many 'replica' pistons do we need to have made to get a sensible cost per set?

[StuBeeDoo]

Given the known high cost of Alpina pistons,is there a workable alternate?

I'm sure Simon will correct me if I'm wrong, but aren't Alpina pistons either......
a) Only available if you can supply the full VIN of an Alpina converted car?
or
b) Totally NLA?



....And BMW pistons at over £100 a pop + rings at over £25 extra ain't exactly cheap.

[Simon13]

alpina slugs can be bought still £200 each though you need to prove what have also but there are ways around that

[m_jermyn]

Was talking to my cylinder head man the other day regarding this thread and the reason why you might hemi the head.. He said it improves gas flow... However you obviously lose compression. Apparently the gains in a hemi head out weigh the lose in compression.

[HairyScreech]

the simple solution to moving the piston up a little would be to offset bush the rod.

but alpina pistons is pointless in this situation if as simon says they are the same just slightly higher pin to crown height.

i dont think the reason for the hemi is the flow, i just wanted to know what it did in isolation. iv now ported that chamber as well, and as airflow in the port effects what comes past the valve the results may be very different.

just learnt that the m50nv engine uses a lighter 135mm rod and the m50tu engine is a 140mm rod with flat top piston.

so, im going to calculate the cr of a 135mm rod and tu piston...

[HairyScreech]

right 4 hours porting work, another 5 hour flowbench marathon today, 2 hours of calculations yesterday and the graphed results from last time to post tonight, stay tuned.

[HairyScreech]

ok heres the photos from the first flow bench session.

the bench in all its glory. its a superflow 600-e, what ever that means.
all i know is it sucks big time and it blows pretty hard.




the head is mounts on an 84mm bore tube. theres a spark plug sealing the hole, theres just the helper springs in to keep the valves closed and theres a bluetack head gasket and a bluetack bell mouth.



these two show the bore placed over the head, you can see the valves fit quite tight in there, theres not a lot of room for more without shrouding going on.

the dti on top of the bolt is what i have been using to push the valves open the required amount, you just turn the bolt and read the dti at the same time. easy.

[HairyScreech]

right heres the first set of results, shown in picture form but if anyone wants the raw excel file then let me know.

[HairyScreech]

so some gain and some interesting results.

went out and got some nice new sharp carbide burrs and set too again to get ready for round 2!

round two consists of the ported chamber taken out even more extremely. this consisted of even more work in the bowl, the valve guide totally reduced to a bullet shape, the channels either side of the guide being opened up larger and smoothed into the bowl, the port floor was also taken right out to a D shape.
the next cylinder along having a lighter and more accurate version of the ported cylinder above with the port floor short side radius totally untouched in the centre and on its curve but with the D shape still present (if not slightly more promenent) as i wanted to see if i had made an error.
the hemi cylinder having the same as the above done to it.

in addition to this i also did the same to the ported exhuast as the ported inlet and stuck an experimental porting job on the hemi chamber. those results are shown as well.

[HairyScreech]

i have the results for that right here but havent looked at them much yet.

[HairyScreech]

as always, thoughts and parts donations appreciated...

[HairyScreech]

found some oversized valves, one at 43.5 and one at 44.4 for a massive 11.2% flow area increase.

[daimlerman]

In terms that I can understand,what does it all mean,please?

[m_jermyn]

uuummmmmmmmmm whats that mean dude?

Its good right? Oh wait mmmm far out I dont understand.

[Ric_Vezza]

Must be a reason for why they favour this type of chamber over BMW's swirl design

Aren't all the "best" yank V8s hemis??

As are BMW's 24 valve heads...

BMW's 24V heads have a "pent roof" combustion chamber shape as do most 4V per cylinder heads, not hemi spherical.

[HairyScreech]

the pent roof hemi for a 4 valve motor comes about more from packaging constraints than design.
its simply not possible to get good valve area into the bore with a plug in the middle any other way.

[reggid]

In terms that I can understand,what does it all mean,please?

it means there is not much improvement to be had so it should not be a priority