Well boys & girls, this weeks lesson has come about for a number of reasons, one of which being an attempt to help you all understand the age old saying --> """Bigger isn`t always Better"""

Now some people are going to agree with "some" of what i say here... & some are not

big deal, whoop doop, whatever,,, Talk to the hand

if you know what i know , & if you`ve done what i`ve done , if you`ve experienced what i`ve experienced, if you`ve seen what i`ve seen, if you`ve heard what i`ve heard, & if you were as outspoken as me,,, then you`d be typing this exact same stuff right here , right now too

remember there are a "FEW" reasons for me posting this stuff...

How big do "YOU" need your head???

if you have a little donk,,, you only need a little head

if you`ve got a big donk,,, then you can certainly use a bigger head than that little donk... GET IT????

Now that statement could very well be the end of the lesson right there

but remember,,, there are a "FEW" reasons for this topic being here

sooo,,, lets get on with it shall we?

IF,,, for example, we are building a mild road motor, with some poke for some club race stuff,,, like a "To-work-&-back" mini that you want to have some fun at the race track on the weekend with too... yeah?

ok, lets start with a fairly fresh, un-mucked-with cyl head & start porting out bigger right?

well,,, not really,,, if it were me, i`d leave the main sections of the ports quite standard,,, That is to say that if you looked into the mouth of the ports they would look pretty stock std & "Most" people would "assume" (or could easilly be lead to believe) that it is a totally stock std head with no porting done

""""BECAUSE""" i have only worked on the area around the valve seats , the area around the guide bosses , & the combustion chamber would be de-shrouded, shaped & polished

I would have fitted 1st oversize valves, & made the holes that they fit into a little bigger & shaped the entry into the chamber & removed & shaped the guide bosses & trimmed & bullet-nosed the new valve guides

Now this particular head wouldn`t look like it had anything done to it if it were looked at by the average Joe/Jane Doe... such little work could quite easilly be seen to be "NONE"

But, the fact is that this particular head would be VERY WELL SUITED to the engine i described above,,, say a nice little 1330 or 1360 road engine with occasional track use,,, the cam shaft selected for this "Particular" engine would be a fairly smooth road mild cam like a Wade 240 or an Ivan Tighe 104 or a GR Re13 or such similar grind,,, mild & smooth with very little lumpyness,,, just a roady with some poke right?,,, why would anyone in their right mind fit a "RACE" cam to a road motor right??? A RACE cam would need a Big race head & big high compression to allow it to work, it would also need a crose ratio gear-box to help keep the engine within the power curve through the gear changes , & obviously hi-octane race fuel would be needed etc etc etc

In "THAT" case a bigger head would be warranted yeah?

Getting the picture???

Horses for courses right???

BUT,,,, if you were not very experienced with mini cyl heads,,, if you really hadn`t looked at a whole heap of them,,, if you weren`t "FULLY ON THE PROGRAM" with all this stuff then that mild roady head we just described above could quite easilly be seen to be stock standard with absolutely nothing done to it right? someone could tell you that & you`d Believe them yeah?

funny that hey---> cause hours & hours of hard work, die-grinding,,,shaping, de-shrouding, shaping & pollishing & cc-ing chambers, modifying the whole thing as a package to suit this little road engine etc etc etc has gone into it

Lets now look at the sizes shall we (seeing as it`s "How-BIG" is the point to the topic)

ok,,, the stock 1275 inlet valve is about 33m right,,, take away 7mm for stem thickness,,, now take away a few mm (say 3mm for arguments sake as that would be a pretty narrow seat at 1.5mm per side) ,,, ok now we have only 23mm of avaliable hole left

Now i know this should all be done using the "AREA" of the """Avaliable-Hole""" but i`m doing it this way for ease of understanding without having to baffell anyone with complicated maths,,, & it`s pretty damn obvious this way isn`t it???

ok so we have approx 23mm of avaliable """USAB:LE""" Inlet hole right

well the inlet port "mouth" has 26mm sideways (horizontally) & it`s got even more than that up & down (Vertically) so our stock std inlet mouth """"avaliable hole size""" is WAY WAY bigger than the std 23mm """Avaliable inlet valve hole size"""" at the inlet valve seat

It`s pretty damn obvious that the inlet port mouth is simply """NOT""" the restriction here

Got it???

The main restriction is quite obviously the valve & the valve seat area

ok,,, so lets work the head,,, lets""""Port it out"""""

well,,,, "THIS" is the point where you have to ask yourself a serious question---> are you going to race it full on?,,, is it a road motor or a race motor???

because i`m sure you will find very little gain (if not even loose performance) doing anything major to the mouth of the port for a road engine

lets now show you why--->

if we now carve out the valve seat area, (the hole that the inlet valve shuts on) lets whack a bigger valve in there yeah?,,, lets make it 35mm-ish like a big MK1 "S" valve,,, no,,, i`ll tell you what,,, lets make it even bigger --> a 36mm ok? (that`s pretty big inlet valve for a road motor)

so,,, now we have 36mm inlet, take away our 7mm valve stem,,, then take away our (thin) valve seat at 3mm (total) & we are now left with 26mm

funny that,,, we now have a 26mm """avaliable"" hole size at the valve seat (where it`s the most restricted,,, & yet we still have bigger than 26mm at the port mouth because remember that the inlet port mouth is bigger (taller) than 26mm isn`t it

so even with a big 36mm inlet valve we "STLL" don`t really need to open the port mouth do we??? the port mouth """""STILL ISN`T a RESTRICTION"""",,, is it?
Opening up the port mouth isn`t going to do diddly squat,,, is it?

In fact,,, if (for example) we opened this part of the port up, then we`d get a "LOwer" air speed through there & that`s not what we want to do,,, we want as much air speed as possible & we actually want that air speed as evenly distributed across the entire port area as possible,,, we don`t want a slow area & a fast area & an even faster area somewhere else (sort of) ,,, we want it the as much the same right across the whole port (particularly hard to achieve i might add)

so,,, If &/or whenever someone shows you a head,,, & they try to tell you &/or you may "THINK" it`s untouched & still totally stock std,,, just ask yourself a question---> has this head been worked on """"""""inside""""""" you know---> where it actually matters!!!!!!!!!!!---> ,,, at the valve seat , the guide bosses,,, Have the chambers been de-shrouded ???? etc etc etc

It`s not that hard to see if the head is off the car,,, & especially if the valves have been taken out

if you`re un-sure, then get a """known to be stock std"""" head to compare it to

without this type of knowledge & experience, you could well be taken for a ride

you could quite easilly be relieved of some hard earned money to "PORT" the head which has already been done quite well

Ok,,,,
so now lets get back to the start with the old saying about "Bigger isn`t always better"

"""IF""" you had a really big engine (like a 1380cc or 1426cc or 1510cc or bigger) then simply because the bore is bigger in diam then you can actually fit bigger inlet valves in there without too much shrouding of those valves by the bore

remember that we like to "de-shroud" the combustion chamber in an attrempt to let "some" inlet gasses out through the sides of the valves (beside the chamber walls) to get the best chamber fill we can,,,, well the same "shrouding" problem can occur from the cyl walls if the bore is too small or the valves are too big for that bore size

Lets look at a 74.7mm bore (1426cc or bigger with stroked crank added) as opposed to a 73mm bore (1360cc or bigger with stroker crank added) ---> now we have another 1.7mm to play with right?

wrong... we only have half that,,, we only have ,85mm to play with but we can actually use it by fitting bigger inlet valve, but the head must be de-shrouded to allow the gasses to escape through the side of the cyl/valve,,, so we "Match" the head to the block & shape the chamber to suit

we can`t go much bigger really can we??? we`re not going to gain much more are we???

so,,, there`s not much point fitting a super dooper huge valve in there if it doesn`t actually allow any air/gas through the side,,, we`d in fact be "Loosing" some because that super dooper huge valve is actually shrouded by the chamber walls &/or the cyl walls (if you had big enough cam/valve-lift such as a full race cam/head combo

You`ve probably read what GR has typed previously about ports being tooo big & how bad that is by it creating less torque,,, less air speed etc,,, now i`m not going to quote GR cause i`m not going to bother going back through the relevent threads to find them to quote them,,, but he`s right,,, he knows his heads & i agree

i don`t bother opening up the mouth of the port much,,, more of a clean-up & more importantly an """angle them up better""" job than an "opening then up" type thing.

However,,, if you looked through my own personal full race Head you`d probably ask why i opened them right up motha F#$%n huge??? if what i`m saying here is right

well,,, ok then,,, this is where i go back to saying """"Horses-For-Course"""

we`re talking about "road" engines with occasional club race use here,,, with race heads (& i know GR will diss-agree with me here but still) RACE heads need to be as big as possible,,, we`re using huge cyls , huge cams, huge valve lift & huge revs to keep our air speed high

road (& weekend club race) engines need as much "LOW_VALVE_LIFT" inlet air speed as we can possibly achieve,,, """"THAT`S""" what makes a good road/club engine work well,,, combined with all the other necessary "MATCHED" components & clearances to suit... """"BECAUSE"""" they only have "LOW_VALVE LIFT""" compared to a race engine

Soooo..... if anyone trys to tell you that a particular cyl head is standard,,,, make sure you have the head off the car,,, take the valves out,,, clean it up getting all the soot off it & then compare it to a "known" standard cyl head,,, then & only then you can see "really" what has been done to it

looking at the mouth of the inlet port doesn`t tell you diddly if you`re unsure of what you`re looking at in the first place

end of rant

edit for spelling mistakes

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

oh & just so you all know,,, these days i use a VERY late model computerised air flow bench with air speed sensor probe ,,, damn good things they are

common now,,, have a chat about heads & mods to heads here yeah?

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

interesting read, thanks for clearing up a few thing there

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one van, one mini s, one knitted cardigan

Wow Matt, someone really must have been pushing your buttons to trigger a rant like that

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Simon

The adventures of an owner builder in the Tallarook Ranges

Wow Matt that's one heck of a rant!

The 2010 rRnt of the year award Goes to... TheMiniMan!

Good read too

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Lillee - 1969 Morris Mini K

Its been Winter and he needs a Surf of a Down Hill Run
I think thats pretty much what GR did to My head

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Stop Licking the Dog...I Don't Care Who Started It

can i say that vizard states some what to the affect that one of the A series
problem was the lack of breathing capacity

People are getting way more HP from a 5 port Mini head now, than Vizard ever did.
Mostly due to cam design and better understanding the physics of gas flow through the head. Bigger ain't necessarily better when it comes to ports.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

yeah well,,, sorry about it being so long,,, but it is "to the point" right? & that`s actually quite difficult to achieve with less words

however,,, there are more reasons for this post than first meets the eye

if only a few people read this,,, & if those few actually understand what i`ve said,,, then maybe i have saved those few from being taken for a ride & having lots of money taken out of their hands for work that doesn`t really need to be done.

There is always the other side of the fence too tho,,,, if anyone reads this & then looks at a head that "seems" to have been worked on,,, as in--> it`s obviously not standard,,,, then please don`t take that as being a "Hot-head" or even being a good flowing head because it may not actually work that well at all

For example--> some common mods performed on other makes quite often don`t work on the A-series head,,,

& also just running an emery wheel through the ports does not necessarily mean that it`s done anything towards performance or efficiency,,, it just makes it "look" like it`s been ported.

one trick from days gone by was that all horny looking polished port cyl head sitting on top of the front counter,,, all the inlet ports & exhaust ports all polished up shinny & gleaming like a mirror,,,, well mostly doesn`t work & will certainly "detract" from performance & efficiency in a big way... THE MAIN REASON--->>>> fuel falls out of the air stream & tends to run like wet paint along the walls,roof & floor of those polished ports,,, now that`s not too much of a problem (altho it is still a problem) ,,, the "Real" problem with all that lot is the after effects being all that fuel running along the port walls, roof & floor falls back into the air stream as rather LARGE droplets,,, here-in lays the Big problem,,,, those rather LARGE droplets don`t burn,,, Fuel doesn`t actually burn well at all,,,, it`s actually all the """GAS""" given off & surrounding those droplets that burns,,, I`d much rather a cyl chamber full of nice burnable "GAS" than un-burnable fuel droplets---> so we don`t want shinny inlet ports at all,,, unless it was simply for a coffee table ornament

It`s all good & well having "Some" knowledge, & it would "SOUND" really good if your head porting guru had a flow bench,,,, & it`s all well & good making "Some" extra HP from your engine,,,, & it`s all well & good if most of that Hp gain actually came from just the head work,

But sadly,,, there`s a heap more usually gained from a simple decent tune than from a poorly ported cyl head,,, even if it does "LOOK" good

flow benches are great tools """IF""" used correctly, but there are way more factors involved within the "package" that "Combined" will make more """TORQUE"""

the only people concerned with HP figures are the ones who like to brag at the pub, or Behind the computer screen, (or at the drag strip) HP isn`t the "Be-all & end-all" of a performance engine,,, TORQUE is tho,,,,

the amount of time that the valve spends at full lift (tip of the cam lobe) is minisquel (tiny) compared to the "just off the seat" & "rising & falling" time (along the rising & closing ramps of the cam lobe) what we really wan tis the "low lift" air speed to be instant & massive & we want it to increase as it opens further,,, but the time at the top of the lobe is a millisecond,,,, so """full valve lift flow measurements"""""" mean diddly squat in comparison to low valve lift figures

& i know GR agree with me,,, as does a whole pile of other very well respected performance engine builders & cam grinders

we have tested quite a number of A-series cyl heads over the years & some super huge heads just don`t work as well (on a particular engine) than a smaller head,,, however, in saying that,,, on a much bigger engine those super huge heads show more promise & do work quite well,,, just not as good as a smaller valved/ported head

altho i do swear about the qualtiy performance combination of a certain particular HUGE A-series cyl head & a certain A-series engine package Sometimes bigger is better

However---> we`ve recently tested quite a few BMW heads (both 8v & 16v) & also some Yamaha R1 20v heads... & the results are quite amazing

no wonder the 16v Bimmer head is only producing a few more hp than an 8v,,,

read on if you dare--->

the 8v came on 1000cc engine & runs 90-odd hp at 7000rpms,,,

ok now the 16v head runs 100hp(almost) on an 1100cc engine @ 8000rpms

ok,,, so if it`s got an extra 100ccs & an extra 1000rpms,,, So how come it only gains (Barely) 10hp >>>> ?????????

well,,, from our testing i believe we`ve found out why (more on this later)

also,,, sooo many people who port R1 heads do actually find a gain in performance,,, BUT!!!!!!!! they usually combine all that work with other tuning gains, like removal of the std muffler, re-jetting carbs, new set of extractors & getting rid of the EX-UP valve in the exhaust system, they mod the cam timings or replace the cams with hotter ones etc etc etc,,, all at the same time (Usually)

However,,, our testing has showed that those porting out big gives "VERY LITTLE" improvement at all,,, & in some cases "Detracted" from the performance

the very same can be said about people working on the A-series heads

becareful what you ask for & becarefull of who you get to do the head work,,, maybe they`re just taking money off you & not really giving you anything in return except what may "Look-Like" some head porting (& an empty wallet) ,,, & essentially, when humans """SEE""" some work done & looks all shiney & pretty & WOW that loooks cool (sort of thing),,,, well sadly it may not actually be that cool at all

maybe a decent tune up has given you more than all that head work has

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

Reduced air speeds due to more and larger port area? Meaning that higher engine speeds are required to pump sufficient air to achieve the same filing as an 8v @ lower rpm... meaning that it requires much higher rpm to create enough velocity to achieve the filing required to make some decent mumbo ? Just guessing.....

Don't keep us hanging

I think this thread gave me some new "points of view"

Are you saying 'pure' CFM ratings are overrated? I always had a feeling this might be the case...

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No speakers, no bodykits, no six-inch spacers, no spak filler, no bullshit

ha ha, Phatty,,, good guess, but sorry,,, no cigar,,, the 16v heads have relatively small ports with (obviously) smaller valves than the 8v head , just more of them,,, the big problem is the "angle of the dangle" of the port(s) entry,,, (or rather the poor shape causing in-balanced amounts & air-speeds between the 2 ports) but more on that later (after i`ve wrecked a few more heads chasing my tail making things actually work better)

they (the Bimmer factory) tried real hard to squeeze all that crap into that tiny little area & ,,,well,,, they did a damn good job,,, they`re obviously pretty good hey?,,, just not as good as some people would "Think" ..... they actually could be better (& can be, with some awsome time consuming work)

& Jan,,, yep,,, simple as that,,, Peak flow is basically a very very tiny part of the equation, compared to flow at the lower valve lift heights

GR banged on about it ages ago & i don`t think many people got the gist of what he was saying, & he`s got more important things to do than sit on the computer trying to teach people the tricks of the trade, but still... yep,,, peak flow is not all it`s made out to be

Think (for a minute) about this----->

"""""sheep through a gate"""""

if you get the first sheep moving quickly through the gate as it opens,,, real early,,, (Just as the valve cracks off the seat),,,, then funny enough, the rest of the sheep will follow suit immediately & quite rapidly

It`s "sort of" more important than the amount of sheep you get through with the gate wide open for "Barely" a split second... effectively we will generally get more through "during" the opening & closing stages all-together, than the amount through with the gate wide open for that split milli-second

yeah?

& funny enough they run even quicker as the gate`s starting to shut, wild hey?




ok,,, it may not be the best analogy but still,,, hope people get the drift

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

oh & just to add some (obvious) physics to the equation

it`s the bore size that is the main limiting factor to valve (hole) sizes

we generally see an exh valve at about 80% the size of the Inlet,,, so when you do the math,,,, (((& we do want some room between the side of the valve & the side of the chamber to let at least "Some" gas in (& out) of the sides to give us as a complete & usable "Valve Curtain area" as possible))) Soo,,,, you can only get certain sized valves in there yeah??? any bigger & we`re going backwards cause of all the shrouding effect , got it?

EG: the early yamaha R1 has 77mm bore,,, later on they went to 79mm ,,, now why do you think they would have done that???

who wants more of this?,,,,, i can stop if it gives you a head ache

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

Keep Going Matt

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Stop Licking the Dog...I Don't Care Who Started It

Yes please, more, this is awesome!!