The ultimate M20 cylinder head

[Onz]

hey guys,

What would happen if you put the m50 head onto an ETA?

O

[Gunni]

nothing.

That´s what

[e21Jason]

Hi

A m50 head bolts up with a m20 block but it over hangs at the edges and none of the water/oil ways line up. Plus there is chain v belt drive.

If you had a race series were you had to retian the block you cold do it with a dry deck arangement, a lot of dosh and skill.

Jason

[E30BeemerLad]

So the upshot of this thread is ditch the M20 boat anchor, fit an M50 and then stick on the rotrex supercharger


Ya feckin dancer!

[keri-WMS]

Right, a few comments about airflow, which is what this is all about!

How good a head is depends on a lot of things, and a LOT of compromises.

"flow" vs charge velocity. Smaller ports have higher velocity for the same volume of air. This gives better "swirl" (12v) or "tumble" (24v) in the chamber, keeping the fuel mix atomised a bit better = better burn = more torque/power. This is why "high flow" big port heads loose out in torque, but you get to chase higher revs to get and more bangs-per-second which gives more power (read "expensive bottom end").

"valve area" isn't really relevant, it's "valve curtain area" that you need to take note of. This is the "tube shape" that is created in the gap between the seat on the valve and the seat on the head, and of course it varies with TIME (as the valve opens and closes) and cam specifications - lift and duration. Two points here, first off is that this is the reason four small valves are better than two big ones (two valves get to total their circumference x lift vs the single bigger valve), and secondly the exact point that this "curtain" acts is on the INSIDE diameter of the seat!

So, take a 30mm valve with a 2mm stock seat and it will behave as a "26mm virtual valve curtain". Put a 30deg back-cut on that same valve to remove 1mm of the inside of the seat and you get a "28mm virtual valve curtain", in fact the same gain as fitting 2mm bigger standard type valves!!!

Also on normal / low lift, low valve-acceleration cams (where the valve spends loads of time hovering just off the seat) and heads with big single-cut seats a really good 3-angle cut throat and back-cut valve can in some cases gain about 10% flow throughout the range on an otherwise "standard engine", about the same as a bloody good exhaust and filter etc vs a nasty setup (and BMW never really DID nasty ones anyway!)

I would get a 24V head/engine, then get a "seat and valve job" (NOT BIG PORTS!!!), and maybe look at a bit more lift in the cam but not much more duration. This then leaves an engine that will have more power everywhere but especially at the tp end, and is also open to a bit of boost at a later date! Keep standard compression and limit the boost to a few PSI and you won't have nasty turbo-lag or supercharger drive loads to worry about.

Oh, and watch for gaskets sticking 1-2mm into the airflow and robbing your power! The inlet should be "port matched" if it's easy, the exhaust should have a deliberate mis-match as the port in the head MUST be 2mm or more smaller than the manifold "port", this step is what the pressure waves that are essential to a "tuned exhaust" bounce off. Open your exhaust ports up to match the manifold, stop the exhaust working properly, lose loads of torque and power....

[oakey]

^ thanks dude. Exactly the type of info I am after

[keri-WMS]

No problem, there are two things to remember about engines due to them being SO complex:

1 - Every engine tuner does things "the best way". And 99% of engine tuners each do things differently!!! Even books disagree a lot (and as I based my post on books and speaking to race engine builders that must include my info as "opinion"!)...

2 - Due to that same complexity it's FAR easier to mess things up than it is to improve them unless you are lucky or stick to some tested combinations. You can do things one step at a time though (add boost or hotter cam, or up the compression etc) and see what effect it has.

A good example is people going on about impractical high-compression race engines and high duration cams etc. The point that's missed is that there is more overlap with all valves open on a long duration cam. This allows more fresh un-burned fuel/air charge to disappear down the exhaust than with a normal cam. Also in some cases the compression stroke has started but the intake valve is still open, so flow reverses into the inlet manifold!

So in the race engine's case the "high STATIC compression" in fact lowers right back down when running to more normal levels of actual cylinder pressure!

In the road car's case, with a normal compression engine but "it's got a race cam innit mate" the guy will have less torque "as I expected innit", but won't realise that it's because he's turned his engine into a low compression (low cylinder pressure) one once it's running!

I would suggest anyone even INTERESTED in engines (let alone messing about with them) should buy and read this:


There is a "boosted version" as well:

[maxfield]

^^^ You know your shit

[Gunni]

Very good info indeed.
Sounds like you Keri are apart of a engineer course or a graduate?

[keri-WMS]

Very good info indeed.
Sounds like you Keri are apart of a engineer course or a graduate?

Nope not me, brakes are my thing normally! I do mess about with my own engines a bit but plan to do a lot more "when I get time"! I know a few people who do serious engine stuff though.

Off topic for a sec, one bloke I know was asked to develop a "multi valve 500bhp n/asp V12" for a race car, so he built a prototype with two 24v heads on the BMW V12, one backwards (I think BMW now do one ironically?)!

It had $12,000 worth of custom CNC machined cams that had been made in the USA, external water and oil delivery etc. The customer cancelled the project, and he was sick of looking at it and the £ black hole it represented so he SCRAPPED it (ie to be melted down)!

[Gunni]

Ouch,
guess he didn´t have a good contract signed with the customer then, or a serious down payment.

but a 100hp/l from the hemi heads is well reasonable. should be reached at about 7100-7400rpm
depending on fuel regulations in the racing series, wich also leads to the compression ratio used
based on the fuel.

[keri-WMS]

Ouch,
guess he didn´t have a good contract signed with the customer then, or a serious down payment.

but a 100hp/l from the hemi heads is well reasonable. should be reached at about 7100-7400rpm
depending on fuel regulations in the racing series, wich also leads to the compression ratio used
based on the fuel.

I think it was supposed to be in a demo car of some sort, so anything went really...

The plan was "over 500bhp at 8,500RPM", it had two plenums and was coverted to run dry belts.

[StuBeeDoo]

Ideal M20 'head?????
One that doesn't crack!

[e30bmlover]

Ideal M20 'head?????
One that doesn't crack!

too true! although i have no experience of this head cracking lark! no doubt i will one day.

[he30]

This looked interesting in this months bmw car mag!

3.2 ltr M3 crank, ross pistons,crower rods, ireland engineering cam,ported and polished m20 head,custom cold air intake, custom manifold & exhausts, setrab oil coler, ali flywheel and motorsport clutch on a 3.90:1 diff . Pushing out 300 bhp. No indication on cost, but dosen't sound cheap!!

[reggid]

This looked interesting in this months bmw car mag!

3.2 ltr M3 crank, ross pistons,crower rods, ireland engineering cam,ported and polished m20 head,custom cold air intake, custom manifold & exhausts, setrab oil coler, ali flywheel and motorsport clutch on a 3.90:1 diff . Pushing out 300 bhp. No indication on cost, but dosen't sound cheap!!

any more info on the custom manifold? Is it a custom intake manifold or exhaust?

[he30]

Not really,

just said custom long tube six to two to one manifold and a 3'' diameter mandral bent exhaust, o think he fabricated it himself by the look of things

[march109]

I would suggest anyone even INTERESTED in engines (let alone messing about with them) should buy and read this:


There is a "boosted version" as well:

Got these, read them, studied them and then had to break open my A-level physics and maths books to understand 100% of them, but they are absofookinlutly excelent, theres a few more books on my shelves about tuning and engine work but these are the only two I made an effort to read and then understand 100%.

As Keri said though opinions vary, but very few skilled engine builders I know would sit down and write a book. And since I don't know anyone who would sit me down infront of an engine and show me what to do with it I go on what I've read here, and my maths and physics back up the science behind the theory presented, BUT then again I didn't get A's

[march109]

This looked interesting in this months bmw car mag!

3.2 ltr M3 crank, ross pistons,crower rods, ireland engineering cam,ported and polished m20 head,custom cold air intake, custom manifold & exhausts, setrab oil coler, ali flywheel and motorsport clutch on a 3.90:1 diff . Pushing out 300 bhp. No indication on cost, but dosen't sound cheap!!

any more info on the custom manifold? Is it a custom intake manifold or exhaust?

I'm not saying it can't be done but I know a 'good' 2.8 that makes just over 200BHP (with e36 steering rack so no room for 6branch manifold), and 2.7's with lots and lots of money thrown at them make 270BHP (zone info I've read), how can an extra 500/400cc make an extra 30BHP withought alot of £Â£Ã‚£Ã‚£?? Must be a very good ported head, at this cc the cylinders need to be fed well.

Its out of my price range. But I'd love to own it (then turbo it ).