Ok,,, simulate the workings of a cyl head --->
Close your mouth & try to blow air out.... it won`t come out will it???,,, all that happens is your cheeks puff up under the pressure & no air comes out your mouth because it`s closed right???
now,,, open your mouth really really wide,,, then try to blow air out again... yeah?,,, heaps of air came out you think? yeah?,,, but with really no air speed tho right?,,, it just came out as slow/fast as your lungs could expell it right? so,,, the harder you pump your lungs the better the air came out right?
But you only have little lungs right??? Last year i had a discovered a problem with the right side of my chest,,, thought it was just another broken rib as i`d broken plenty of them in my time & it felt much the same as all the others,,, but after a few weeks the pain 7 the lack of strength in my whole right arm, inc wrist & fingers got worse & worse,,, so of course i went to the hospital,,, cut the long story short,,, it ended up being a blood clot in my right lung.
so with all the x-rays & Ct scans all the people involved were astounded by how big my lungs were "largest they`ve seen" my lungs fill my rib cage & apparently not many peoples do
so,,, to get to the point,,, my pump is bigger than most,,, same goes with my road mini`s engine,,, i have a 1510cc road engine with quite a big race (type) head on it
Now,,, open your mouth just a little bit & now blow air out again---> heaps came out with heaps of air speed right??? Have a play with the amount of pump action & the amount of mouth opening you use & find the best amount of air passing out at the fastest rate & you have a dam good cyl head but make it in the opposit direction "IN-WARDS"
Now with the exhaust side of a cyl head, it`s (sort of) much the same but we can`t have the same sized hole for air to come out as we do going in, as we have obviously lost some energy to the motion of pushing the piston downwards to produce the power right? ,,, so in a sense we would be making for a very poor balance or "matching" of sizes if we made the same size exhaust as we have inlet, & we wouldn`t make much power
all you have to think of here is how much you eat & how much you poo,,, if you poo twice as much as you eat then you have some thing seriously wrong with your insides
same goes with cyl heads
Now,,, we really don`t want to have much of a restriction in any of these pathways do we?,,, common sense yeah??? The baby fell in the pool & has drownd,,, so you tilt it`s head back to help clear the pathways right??? same with a cyl head (where you can)But the A series head is stuck wih a few minor restrictions which can`t really be "Cured" ,,, we can only try to work with them or maybe at lest try to cover up the poor symptoms,,, in other words--> we work with what we have,,, an athsmatic 5 port A series cyl head,,, make it breath as best we can to suit the size of pump we have mounted under it
2 main parts of the problem (With any poppet valve type cyl head) is the short radius section from the lower section of port into the chamber,,, & the entire valve seat area
both these areas need some work,,, lengthen the short radius as best we can & make it "less-sharp" a curve... & make the valve seat area as smooth flowing & as large as we can to creat a large valve curtain area
Valve curatin area is an imaginary shower curtain draped from the valve circumfrence down to the valve seat area at full lift,,, this can be measured but isn`t the "be-all-&-end-all" to the equation.... as air speed & flow at "ALL" valve lifts is what i like to attain,,, but we can`t have our cake & eat it,,, but we do the best we can with what we have, an ancient old 1950s designed 5 port A series cyl head
But "WE" (as in "US" who choose to drive minis) don`t have a very big pump do we???
No,,, you all have little ones ..... (& i have a big one... or rather a few)
you would need much bigger cam profiles & a far better cyl head with higher compression & far better rocker angle & ratio, accurate valve timing, quality flowing, tuned length inlet & exhaust systems (as a complete lumpy race engine
PACKAGE) to come anywhere near keeping up with my 1500cc
ROAD mini,,, simply because my pump is bigger & my head flows really well to suit it,,,
it`s a package, mine is matched very well indeed,,, i spent quite a few years refining it to be one of the very best road engines around,,, "Every-one" that drives this thing comes back with a huge grin from ear to ear & says the magic words--> "I Want One" & i`m not kidding,,, it`s actually uncanny & i can`t express this enough, & it has "approx" 90hp at the wheels on Bob Romanos dyno dynamics rolling road here in Brisbane,,,, & i`ve done a lot of testing (a few years ago) running the same car in the same conditions on quite a number of dynos in Brisbane with all of the others showing much higher numbers than that,,, the maximum came out with 116hp (more of an engine hp figure than an "at the wheels figure") so i have a very very good knowlege on what dyno reads the LEAST up here in Brisbane, But more to the point, i have major experience testing the "seat-of-the-pants" dyno on the black stuff out front, with stop watch times from bus stop to bus stop which is where the numbers mean
"REAL" life.
so, simply because i can drive my car around at 1000rpms & wide open the throttle at 1200rpms in top gear & it pulls smooth & strong all the way through to 7800rpms without pinging, no head gasket problems, running pump full, & also ran it hard for well over 8 years , including a targa Tasmania rally & then another year of club level racing aftert that & it just in need of a general re-ring & bearing job, well,,,, i must have matched up a dam good pump with a dam good cyl head right? Anyone would think i`ve been doing this stuff for over 40 years hey???
I don`t actually know anyone else who has created such an engine.
Aaron,,, you asked me---> "
But please if you don't mind i would dearly like to have your opinion on what makes a good head and how you decide upon it.
If you can`t get a decent enough picture of what is needed from the above text, then i`m affraid i can`t help you.
it comes from a lot of years of work on mini engines,,, GR will tell you all you need to know if you want figures & numbers & measurements & what works with what,,, you`re obviously down around his way & certainly not here in Brisbane for me to show you a whole series of cyl heads lined up here in my shelves allowing you to see the differences for different
"Packages".
The Bimmer cyl head was created by some very smart people, they ran their test engines at approx 200hp (N/A) for the simulated equivilent of quite a few years running testing them very hard indeed,,, they then tamed these engines down to 100hp & sold them off "KNowing" they wouldn`t blow up,,, & if you ask any BMW motorbike shop how many bimmers they`ve seen blow up,,, well it won`t be many & any that have would have surely been through poor maintenance or some such
They have a tiny little pump (much like the mini) & they have matched the valve holes & the ports very well indeed,,, they have also created a nice
package where it`s neat & tidy & fits in confined spaces,,, they have also created a nice long "short radius" & a very good port angle to effect as best flow & air speed to suit their
"Package"
sooooo,,,, the hort answer to your question is--->
Its all in the [b
]"Package"[/b]
I can guarantee you that my big fat 1500cc roady cyl head would be a right pig down low in the rev range on a std 850 or 998 engine,,,, It`s mouth is wide open when you`re blowing your air out... altho i expect it would work far better than the average cyl head (with the same valve sizes) as i`ve tried (& i`d like to think i have succeeded) in making a very fast air speed cyl head flow at low valve lifts,,, this part is very important & comes back to angles & shapes more than size.
There are many many other restrictions involved with making a decent cyl head work well to suit your intended
package,,, one of which is mechanical losses,,, like friction (Hence the use of bronze valve guides & roller rockers & such) all in an "attempt" at making this loose less power while doing their job.
Too big a Valve size can create too much weight/mass to move so recipricating mass is also an issue,,, hence the use of expensive lightweight valves & lightened push rods & lightened rockers & titanium vavle caps etc etc etc,,, all in an "attempt" to make for ease of component accelleration.
Valve springs also have their day to show off,,, but ,,, too much tension here & all your hard earned cash & efforts can easilly go to waste by "overloading" the system with way too much spring tension just slowing the whole process down,,, go add some full race valve spring package & fit it straight onto a std 850 or 998 & all it will do is make the engine slower & wear it out in no time,,, the idea of sronger double & tripple valve springs is to help hold the cam follower on the cam & to help prevent valve bounce at high revs,,, this is definately one part of the average persons engine builds that sh!t me right off where they all tend to say they have super you-beauty double valve springs from isky or such-n-such,,,, all they have done is slow their road engine down & make it wear faster,,, "Race" engine need to have their springs to match their revs,,, not just for the sake of saying you have something "Hot" of sounds fast when saying it stuff in their road donk,,, it`s just stupidity in some cases.,,, it`s got to be a
"Matched Package"
The list goes on & on & on & i can keep typing if you want,,, but all it`s doing is boring the hell out of a whole heap of people & making me spend heaps more time on this computer than i really need to
There is (however) a theme to all this--->
You asked for figures & facts & numbers & stuff for the Bimmer cyl head,,, well one day you might acually get what you want,,, & maybe those facts will come from various sources world wide
you also asked --->"""But please if you don't mind i would dearly like to have your opinion on what makes a good head and how you decide upon it."""
Mate,,,, your answer,,, & the theme to this whole post is simply it`s a
"PACKAGE"
It`s my dads most favourit saying when building "ANY" engine/car --->
""""""Horses for courses""""""
The Bimmer cyl head is basically a dam good little horse for just about any course,,, it`s a dam good all round
"Package"
Over 250hp just been produced in the EFiminis dyno day in England
& there is penty more to come from these "Little" things
edit for spelling mistakes
They make sense if you read them a few times 
