Thom

I probably don't have your experience with 4V heads, but unlike you I am probably bright enough to listen to people on this board who have had successful results with them.

Raceboy

Combustion tempretatures are a moot point because that heat actually never touches the aluminium surface, unless detonation occurs. This is because of gas boundary layer that isolates the surfaces from direct combustion heat.

Voith

Why then does diesel engine ignites when it is hot and needs warming plugs when cold?

Duke

The 16v head compared to the 8v head is less sensitive to detonation, both from a theoretical point of view as well as experience.

Regarding the 16v heads cracking this was a problem on the 2.5l 16v head but solved by an improved design on the later heads.

The cam tensioner and chain is really not a weak link. Properly maintained they work just fine. But if you really want to take the "less parts is more reliable" mindset to the extreme I would suggest putting a 2 stroke one cylinder engine in there.

Raceboy

Lol, because it is the gas itself that is compressed It is not because the alloy of the engine will heat to 800c and more to ignite diesel fuel...

You claim to have wide knowledge of 4v motors, but seems you haven't heard of boundary layer in the combustion chamber? Just a friendly observation, nothing else..

Voith

No, you are claiming it doesn't make any difference where I claim that is not true.

Diesel gas is cold as it is sucked in to an engine then compressed. That causes it to heat up.

If the combustion chamber and piston is hot, it adds the heat to compression heated gas and that leads to self ignition.

In cold chamber that doesn't happen, does it?

Voith

4V head cracking is not something that is solved as the aluminum is only as strong as it is and solid material between orifices is only as thick as it is possible.

It is improved, but heads crack and 4V crack more than 2V because it has thinner walls on highly temperature stressed areas.

I love 2 strokes.

Duke

We've come a long way from the topic talking about how diesel engines work.
FACT is that the 16v is LESS senstive to knock as well as showing no higher water or oil temps compared to an 8v. That is been stated several times. If you still don't want to accept it that is fine. I just wanted to challenge some incorrect statements you did about 16v engines blowing up all the time. You have chosen the 8v head and I'm sure it will be a good engine. What I don't understand is why you seem so desperate to undermine the 16v turbo engines that you have to make things up.

Duke

The casting around the head studs were reinforced on the later 4v heads.

Voith

Hotter combustion chamber surfaces affect combustion temperature, that is a fact. The best proof for that is diesel engine. So here diesel is in context and on topic, yes?

I am talking about area between valves and spark plug, the thin walled areas. Those can not be improved more because of design limitations.

Point I am making here is that 16V in fact is a better head in areas you mention but not in all areas as Thom is saying.

Seriously? What did I make up?

Can you stop being such a hurt feeling princess?

Duke

Sorry but I still don't understand why we're talking about diesel engines. Are you saying I'm incorrect in my statement that the 16v turbo have less issues with knock and no noticeable increase in temperatures?

Voith

It is a result of better shape of chamber not better temperature management. Temperature management is worse. If that too was better it would have even better knock threshold.

Do you understand now?

Duke

Sorry but I still don't understand how it is relevant when the fact is that we don't have issues with temperatures.

Raceboy

Yes, air is compressed and that ignites diesel fuel, not engine itself. And that's why glow plugs are needed: to heat the air, not engine itself. And when engine is hot, it means that the air is also hotter in the combustion chamber - > glow plugs not needed. It's all about the air temp, that's all.

Engine heats up, but not to 800+c or otherwise aluminium pistons would be melted long time (aluminium starts to soften already at ~300c depending on the exact alloy).

Voith

Duke: different properties of the head are better or worse on one or the other. In this case temperature management is better on 8V. 16V has other property (shape) that makes up for worse temp management short comings.

Raceboy: Valves heat up to 700-800°C in turbocharged engine, go back a page and count cracks in picture I posted.
There are 3 cracks.
In one chamber.