On 13/5/2022 12:16 pm, Noddy wrote:
> On 13/05/2022 11:26 am, jonz@ nothere.com wrote:
>> On Thursday, 12 May 2022 at 17:23:48 UTC+10, Noddy wrote:
>
>>> Probably because the cylinder head people were a bit too tight on the
>>> clearances, but you'd need to take that up with them as I never did the
>>> head. However what is *abundantly* clear is if the engine was assembled
>>> had a piston to valve clearance issue it would never have survived the
>>> first dyno session, and anyone who had a modicum of experience with
>>> engines would be well aware of that.
>
>> ~~~~~~~~~~~~~~~~~~~~~~~~
>>   Yes!.
>
> It's absolutely ridiculous actually. The more he tries to invent
> ridiculous theories to push the blame onto me, the more completely
> ignorant and clueless he makes *himself* look at a result.
>
> The engine in question was a Toyota 4AGE 20 valve, which used inlet
> valves with a stem diameter of just under 5mm (4.98mm to be exact). They
> are *remarkably* fine, and you can just about bend the valves with your
> fingers. Anyone with anything remotely like relevant experience would
> know that *any* piston to valve contact would bend such a valve
> immediately, and such a bent valve would cause an *instant* loss of
> compression and result in a dead cylinder.

The above bullshit requires a little more extrapolation. Firstly, the
4A-GE and 4A-GZE engine were known for their reliability. After all,
they are made by *Toyota*! Even Wikipedia agrees with me.

Due to its durability, performance and relatively low cost,
4A-GE and 4A-GZE engines and their derivatives have been
popular for both professional and amateur racing since their
introduction

Durability, performance and low cost, an unusual combination. Just for
you Darren, *durability* means the engines are reliable and not known to
blow up for no reason.

Now here's a point to note Darren. The stock 4A-GE20, at least the last
iteration of it (black top), put out 165-167 HP (according to Toyota).
Even if you weren't quite getting there in the real world, you can
achieve impressive numbers with the 20V engines. Oh, BTW, that was with
the *stock* valves and a lightly ported head. You only needed to upgrade
the valves when you go above 190 HP. That, in anybody's language,
Darren, is bloody impressive. Damn good little breathers, those 4A-GE20
engines. Did I mention that you would need to be a serious racer to get
to 190 HP. Just think of the *volumetric efficiency*. It'd be
interesting to see the numbers on that.

Anyway, back to valves. Darren, you say the valve stems are too small
and "and you can just about bend the valves with your fingers". Well,
that's a load of bullshit right there given you can bump the engines up
to 190 HP *before* you need to fit stronger valves. I don't know, it
seems that you, Darren, just pluck this shit out of your arse! It would
be nice if you backed up your *opinions* with *facts*. Facts are like
rocking horse turds in the Gibbens household.

Why do Toyota, and other marques, fit small valves on 16 and 20 valve
engines? They do it because that is their aim, their goal. To look into
this, we need to look at what went before. Take this two valve head, a
Ford 4V head in fact;

https://cougarpartscatalog.mo.cloudinary.net/dc/13665/1502927441_y.jpg

Only two valves, one inlet, one exhaust. They are just about at their
largest practical dimensions and if you look at the *total valve area*
compared to the total cylinder area, it seems there is a lot of waste
space. What that means is that the air flow area is limited by having
just one inlet valve per cylinder and that will *limit* the volumetric
efficiency of the engine.

The three valve engine with a pentroof combustion chamber as used in
Honda and Rover allows for more valve flow area as it has two inlet
valves and one exhaust. Though the overall diameter of the inlet valves
is *smaller* than a single, the basic gain here is that the arrangement
allows a 50% port flow increase because the two valves total a larger
area than one single valve with a better fit within the cylider bore
size limitation. Big gain on VE which leads to a gain in torque and
consequently, a gain in horsepower.
There are other benefits. One benefit is that, by reducing the overall
size of the valves, you have reduced the valve *mass* so that
reciprocating inertia effects are proportionately minimised. So, Darren,
the valves have become *smaller* and that is a definite plus. If the
mass of each individual valve is less, the engine will be able to rev
higher before it encounters valve bounce, float and, critically, overshoot.
Another benefit, one which is less intuitive, is that, with the overall
benefits to the head's breathing ability with 2 inlet valves, it is no
longer necessary to have early inlet valve opening and late exhaust
valve closing, hence a much reduced valve overlap can be utilised which,
in turn, leads to reduced exhaust emissions under idling and light load
conditions and that can only be a good thing.
How about a four valve pentroof head, like the 4A-GE16? Here's the
working side of a 4 valve pentroof head;

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSpVR_UXYm-UQ1gMvbgJPOWzvv-D-rDtdHOTg&usqp=CAU
Two features become evident; there's a lot less dead space in there
*not* occupied by a valve. What's better, that dead space in the middle
of all 4 valves now is occupied by the *spark plug*. The flame initiated
by the spark plug now has the shortest possible distance to go the reach
the cylinder walls. That provides a short flame path with a wide frontal
area so a high but controlled rate of burn can be achieved. That helps
prevent any end gas from pre-igniting or detonating. That, in turns
means that the *effective compression ratio* can be higher - and it will
be because *volumetric efficiency* is further enhanced through the
additional exhaust valve. What's more, with two inlet valves per
cylinder, you can achieve a nice *tumble* air flow - that's good. Even
better, if you control one of the inlet port flows, you can turn that
tumble into a nice useful helical swirl flow. Both these flows lead to
increased turbulence which, in turn, leads to a *faster burn time*. The
4 valve pentroof cylinder head improves the intake and discharge flow
through the cylinder head by something in the order of 50% when compared
to a two valve hemi combustion chamber but a massive 100% when compared
to a two valve bathtub chamber. Where is this an advantage? Well, the
higher overall volumetric efficiency means the usual peak torque
developed at around mid-engine speed can now be maintained throughout
the upper speed range without and marked decline. This is in direct
contrast to the large torque drop off that occurs in that upper speed
range with conventional 2 valve cylinder heads. Just a reminder Darren,
VE leads to torque, HP increases require that torque to be available in
the upper rev range because HP gains require revs. As I stated once
before, there is a bit of a linkage between the two which you don't seem
to understand.
Moving on now to the 5 valve head as used by Yamaha.

https://external-preview.redd.it/L9BrZFiEsYPxslbDgxsJb4odEfdKOXT5vLKSgcRze_s.jpg?width=960&crop=smart&auto=webp&s=0269c86d52b615b2354f6602a8ea5d7cbc0890bc

This head uses 3 inlet and two exhaust valves in a pentagonal
arrangement and they form a shallow pentroof combustion chamber. The 2
outer inlet valves are inclined at about 18 degrees from the vertical
whilst the central inlet valve is inclined at a smaller 11 degrees. The
2 exhaust valves will be
inclined around 14 degrees. That gives a shallow semi-hemi combustion
chamber, again with a central spark plug. That in turn gives the
shortest flame travel with the widest flame front in all directions. The
near horizontal centre inlet valve head provides an excellent squish
zone which excites the tumble motion of the mixture into a highly
turbulent motion just before the spark plug fires. This causes high
speed propagation of the flame front with the result that a relatively
high compression ratio can be used even with 98 RON fuel. Fast flame
propagation diminishes the risk of detonation. If I recall correctly,
the valve arrangement of the 4A-GE20 was similar to the Yamaha head.
Now, back to inlet flow area, the triple inlet valve arrangement
increases the *effective intake area* by about 15% compared to a 4 valve
head arrangement. A modest gain there. As can be expected with the 5
valve arrangement, the mass of each of the valves is considerably less
compared with a two valve head - yes Darren, you observed that! This
means that *lighter* valve springs can be utilised or *higher* engine
speeds can be had without valve bounce occurring. Choose one, you can't
have both. Bottom line, the intent of the 4A-GE20 engine designer was to
use valves of reduced mass - and that included narrower stems because,
as is patently obvious, the valve head is commensurately smaller as
well. Hey, there's reduced mass there in the head too.

It gets very interesting when you look at the 6 valve per cylinder
Maserati engine. They claim a 34% gas flow improvement with triple inlet
and triple exhaust ports when compared to a 4 valve per cylinder engine.

>
> Had that scenario ever existed in the real world, it would have
> presented itself on the very first dyno session with the engine being
> obviously down on power due to the compression loss, but that never

> happened. In fact after both dyno sessions and a full track day the
> engine's performance was reported as "excellent" and there was no hint
> of a problem.
>
> Because there *wasn't* one.

Oh yes there was - the *pretender* who worked on that engine - that was
the problem! You can sit there and say you checked the clearance until
the cows come home but you are such a liar and, at the end of the day,
what happened to that engine, and the circumstances under which it
occurred, are a *classic* valve overshoot with attendant piston impact.
Everything after that initial impact followed the script perfectly and
that impact occurred exactly when I would have expected it to occur.
That WOT fast downhill run - that was just asking for shit to happen.
All that needs to be said here is that you fitted a shim head gasket
(your own words) so you *immediately compromised* the *standard*
clearance. Do you know what that clearance is supposed to be? Did you
make sufficient allowance for overshoot? Did you even *know* what valve
overshoot* was prior to my mention of it? I would put money on *NO* to
all of the above and more.
You know, when you first posted on the topic of Les' engine, I was
*overthinking* the cause. As time passed, little bits of info dribbled
out and, all of a sudden, I realised I hadn't made allowance for the
*numb nuts* holding the spanners. What happened to Les' engine was a
classic case of a little knowledge being a dangerous thing. I hope Les
has learnt his lesson - for his sake.
>
> What there was was this utterly nonsensical attempt by Clasener to blame
> me for something that he has absolutely no understanding of due to his

Oh, I understand Darren. You have shown, many a time and oft, that you
are the one lacking in *understanding*.

And I'll say it again, you don't know what you don't know.
>
<snipped>

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)