The BMW M20 engine

[zums]

nice work knight- tom

[Erland Cox]

We have over 205cfm at the lift achieved at peak piston demand.

& we have a chamber that with some work produces very nice pressure recovery, have a look at the pic of the chambers I linked too.

I am just trying to understand how this was done.
So you have nearly full lift at 73 degrees ATDC 33 degrees before ILC since max flow with the carbs was 209 CFM?
A Hemi head has very nice pressure recovery, no doubt about that.

Erland

[Hairyscreech]

I did notice both the enlarged seats (are they siamese?) and the amount the port has been raised, I assume welding has been done above the standard port in order to get that height?
From what I can see of the chamber it is fairly stock apart from the divider welded into the squishband side. I assume that is part of assisting the pressure recovery.

Welding the head is an area I am pretty limited in at the moment although I intend to get access to another TIG welder soon.
When doing this head what did you do to prevent the head warping?
I was considering booting the head upside down to a spare block i have
As for your comment about them just not being popular in the past you may be right, up until about 7 years ago these were very expensive engines to mess about with, its only through the availability of dead m52b28 engines and the popularity of the stroker conversions that the ball has really got rolling.

[digger]

maybe because these are not considered a performance engine & no-one has bothered to spend the time & $$ to develop one to it's full potential.

..........and most people want to swap in the 24V versions (if 12 is good 24V must be better...lol) so not much development goes on.

[KnightEngines]

No welding on the head other than a little on the end runners where core shrinkage left them a little thin, no welding in the chambers, but there was a lot of grinding done.
Runners are simply raised to the limit of the casting.

Erland - no, not near full lift, head flow flattens off after .400" lift, it gains right through to .750"+, but not in great leaps. It is very, very strong in mid lift flow. So no, near full lift is not possible at peak piston demand, but near full flow is.

[KnightEngines]

PS - a larger valve with the seat sunk a significant amount enables a much nicer chamber & also allows a stable short turn.

[canada1]

Very interesting engine development.
Inlet tract design - size, taper, length etc.. are all very important for peak efficiency and tuned harmonic gains as you know
I suspect reasonably high flow even at 0.300" lift. (190+ cfm?)

Big power - it will be interesting to see how it responds on the track.

[canada1]

2 valve L series Datsun (Rebello) engines are at 375 hp levels (3.1 liter L6)
The BMW cylinder head certainly looks like a better starting point than the old L series Datsuns.
I don't think it is "impossible" to build a 380 to 400hp BMW six - jmo of course.
The modified 45 Webers with 40 chokes should not be a restriction at the 220 cfm levels.

[Leftcoaster]

PS - a larger valve with the seat sunk a significant amount enables a much nicer chamber & also allows a stable short turn.

Intriguing work, Ing. Apfelbeck would be proud

Did you carry out the above mod, and if so can you share the results - - which version of the 4 different M20 series heads were you using - - if unrestricted by regulations would chamber & port welding assist further - - are the M10 and M40 series of 2v 4cyl engines as well suited to your modifications?

[Hairyscreech]

PS - a larger valve with the seat sunk a significant amount enables a much nicer chamber & also allows a stable short turn.

Intriguing work, Ing. Apfelbeck would be proud

Did you carry out the above mod, and if so can you share the results - - which version of the 4 different M20 series heads were you using - - if unrestricted by regulations would chamber & port welding assist further - - are the M10 and M40 series of 2v 4cyl engines as well suited to your modifications?

From the pictures it would seem to be an 885 casting, certainly i think you would have trouble finding enough material at the top of the port on the rounder port castings.

It does appear that the intake seat is sunk back in this head. I would expect it to be very difficult to get a 45.5mm valve in otherwise.

[KnightEngines]

Yep, I did all the work on the head.

Casting is an AMC stock replacement aftermarket (885 equivalent), they are a little thicker where it counts & don't tend to crack through the cam tunnels, but a factory casting could be used.

Pretty sure I did just share the results, what more would you like to know?

I don't weld chambers unless given no other choice, it softens the casting & the chance of head gasket failure increases a lot.
Welding wouldn't be of much benefit anyway, 120% VE @ 8000rpm says she's about as good as she'll get without welding.

I have to admit that I have no idea whether M10 & others are a similar head layout & would respond similarly, this is the only M20 head I've got serious with, done a few other milder heads for restricted class racing & street engines, but no other max effort heads.
I knew this one would be good, but didn't know just how good!

canada1 - 170cfm at .300"

[Erland Cox]

I would like to see you build a P/S engine.
With the way you use the available air flow you should be able to make 1600 hp.

Did you do any tests with and without plenum? There should be some power gains by using a plenum asides from colder air.

Erland

[KnightEngines]

LOL, I've never even seen a PS engine let alone consider myself able to build one!
Don't mistake me for an R&D guru, I've got a little 1 man shop in the backstreets of a small unknown city (Adelaide) in South Australia, all my gear is pretty basic. I've been porting heads for close on 20 years now tho & a lot of them have not been V8's.
If you asked me to replicate these results with another type of engine I may or may not get close, I was shooting for pretty dang good, didn't expect what we got - 360hp would have been awesome, closer to 400 is verging on dumb luck.

Car has an air box which would function a bit like a plenum, I don't know it's dimensions.

Theory says a plenum should have advantages, but in real life 110%+VE engines I haven't seen it, IR seems to come out in front - at least for inline engines.
Methink the neccesity of having the air coming in at 1 point for a plenum type intake messes with distribution enough to negate any benefit, if you make the plenum large enough to get good distribution you damp out the pulses you're trying to harness.
In a V8 application a central plenum can achieve decent distribution whilst remaining compact enough to work, inline engines not so much.

[morerevsm3]

we did runs with and without the side on the plenum, was no difference

[Erland Cox]

A plenum does not work well with more than 4 cylinders for Helmholtz tuning.
That is why most sixes have them divided 3 and 3 at lower rpm and united at high rpm.
I have an old Volvo with a B20 also with maxed out 45:s and 205 CFM head flow at 12mm but only 212 hp.
185 CFM with the carburetors at max piston demand.
When I tested it it was with the hood open so the engine gets cold air but the air filter alone lowered the hp 10 units to 202.
The clutch gave up on me so I could never check how much extra I will loose from hot air with the hood closed.
I am going to build a plenum and use a remote air filter and cold air and I am hoping for some additional hp.
If you want to go to Sweden for free TK I have a friend who will gladly pay for your and the cars trip if you can duplicate the power on his dyno.
That is where the Mercedes made 350 hp. A nice chance to see the other side of the world.

Erland