Oversized valves

[apostate]

Don't go, please.

Ask a technical question, listen to the people who know, understand it, ask another question to clarify, avoid "No you're wrong" statements.

That's a very good advice, except it doesn't work when I disagree with the people "who know" and then I cannot avoid the "No, you're wrong" statement. Sorry.
Anyway, good day (night) everyone!
Life is bigger than a small argument/fight in here. And no one is bigger than life.
Cheers!

[LateFan]

Don't go, please.

Ask a technical question, listen to the people who know, understand it, ask another question to clarify, avoid "No you're wrong" statements.

[apostate]

Good night. I will bother you all no more.
Sorry for this thread, did not mean to insult anyone.
Banning myself for another 5 years.
Cheers, everyone!

[digger]

Regardless of displacement, the bigger valve will kill velocity. More on the lower displacement and less on the higher.
Let's assume that the throat size is at Max. Then what? Do you need oversized valves? What is the reasoning? What for?
Honestly, think about it. I do not want to fight over this with you guys for no reason.
This is just a topic for some thinking.
Have a great day (or night).

@zaq123: Calm down and cheers!

when you want to move more air through the air the engine to make more power there comes a point when things are too small to do it efficiently, the key is to work out the correct size for what you are trying to do and whether what you have is the best size or not (it is not easy). killing velocity means it is reduced to the point of being detrimental to your goal (whatever it is), it isnt always the case depending on the specifics. for sure if you put a 2" valve then yes it will be detrimental but when you are talking a mere mm or two the changes are much more subtle

there is no one size fits all and certainly just making things big isnt always the answer

[LateFan]

Can somebody explain the benefit of having oversized valves in a M20 head?

Don't you think that bigger valves will hurt flow?

Now, would someone tell me why should one have oversized valves in a 885 head?

Are you serous with this example? You must be joking.

My point here is that oversized valves are a total nonsense unless the head porting is driven to its extreme limits.

No, I won't do neither of those.

No.
Whilst for the engines you give as examples, they are irrelevant.

I do not want to fight over this with you guys for no reason.

Mr apostate -

You have asked a simple question. Some of the most knowledgable people on the M20 have answered it. Mr zaq explained how a 43mm valve opening at 1452 square mm is larger than a 42 at 1385, which allows more flow at max rpm. That's just physics.

It's not clear to us who you are arguing with, or for what reason. You haven't given a specific engine or any parameters to compare. If you don't want or need to use larger valves in your engine build.......then don't. Mr digger has explained examples where performance depends on it.

Good night -
Mr late

[apostate]

its a big assumption that a bigger valve is going to kill velocity.

you haven't even mentioned anything about the engine or what the engine is to be used for which is what determines if the velocity will be too low or too high. a 2L m20 vs 3.2L m20 might behave slightly differently and have different requirements. without more information the answer is yes, no or maybe

the answer is you need the right size hole. not too big nor too small

Regardless of displacement, the bigger valve will kill velocity. More on the lower displacement and less on the higher.
Let's assume that the throat size is at Max. Then what? Do you need oversized valves? What is the reasoning? What for?
Honestly, think about it. I do not want to fight over this with you guys for no reason.
This is just a topic for some thinking.
Have a great day (or night).

@zaq123: Calm down and cheers!

[zaq123]

Ignorance is always misleading.

couldn't agree more. I suggest you to revisit that post about the kitchen sink. I thought it was a great post, kind of proud of myself because of it

[digger]

No. A bigger valve that kills velocity is never a good thing.
Whilst for the engines you give as examples, they are irrelevant. Because you do not have the same engines with the same specs and only the valves different to compare with, yeah?

Edit: The throat porting has its limitations, as I mentioned above (see page 1). Whatever valves you put over 42/36 will only hurt flow. 1 mm oversize both for intake and exhaust is a good choice for reliability with extreme porting. Everything above this sizes is purely optics for forum threads. 885 head ports in general have their limitations and all else over is an overkill that can only hurt performance. Because there is no sense that you tap a "small hole" with a "big cork". You'd rather tap a hole with the smallest cork possible.

its a big assumption that a bigger valve is going to kill velocity.

you haven't even mentioned anything about the engine or what the engine is to be used for which is what determines if the velocity will be too low or too high. a 2L m20 vs 3.2L m20 might behave slightly differently and have different requirements. without more information the answer is yes, no or maybe

the answer is you need the right size hole. not too big nor too small

[apostate]

un freaking believable...

Ignorance is always misleading.

[zaq123]

un freaking believable...

No. A bigger valve that kills velocity is never a good thing.
Whilst for the engines you give as examples, they are irrelevant. Because you do not have the same engines with the same specs and only the valves different to compare with, yeah?

Edit: The throat porting has its limitations, as I mentioned above (see page 1). Whatever valves you put over 42/36 will only hurt flow. 1 mm oversize both for intake and exhaust is a good choice for reliability with extreme porting. Everything above this sizes is purely optics for forum threads. 885 head ports in general have their limitations and all else over is an overkill that can only hurt performance. Because there is no sense that you tap a "small hole" with a "big cork". You'd rather tap a hole with the smallest cork possible.

[apostate]

...

Also since there is a limit on the minimum area you can achieve before you break through the walls near the guide, so a bigger valve helps slow the air before the cylinder which is a good thing rather than dumping the flow into the big volume. it works like a venturi which is the best way to get highest mass flow through a fixed size hole (apart from a snail)
...

No. A bigger valve that kills velocity is never a good thing.
Whilst for the engines you give as examples, they are irrelevant. Because you do not have the same engines with the same specs and only the valves different to compare with, yeah?

Edit: The throat porting has its limitations, as I mentioned above (see page 1). Whatever valves you put over 42/36 will only hurt flow. 1 mm oversize both for intake and exhaust is a good choice for reliability with extreme porting. Everything above this sizes is purely optics for forum threads. 885 head ports in general have their limitations and all else over is an overkill that can only hurt performance. Because there is no sense that you tap a "small hole" with a "big cork". You'd rather tap a hole with the smallest cork possible.

[digger]

One thing that happens when you use a bigger valve and throat is that you are able to achieve a better shape on the short turn radius which is pretty bad on the stock head. i will dig out a flow sheet Rama did with a +1 ST O/S valve with about 2min work and you can see the vastly improved flow characteristics even though it was just a quick test. justing fitting the valve made no difference to flow until the port was blended properly

Also since there is a limit on the minimum area you can achieve before you break through the walls near the guide, so a bigger valve helps slow the air before the cylinder which is a good thing rather than dumping the flow into the big volume. it works like a venturi which is the best way to get highest mass flow through a fixed size hole (apart from a snail)

- Local guy did a 45.5mm valve on a 2.8L. made over 330whp with enormous cam (~320+* )

- Same guy did another head made 305whp 2.8L (dont know the valve size) (cam ~316*)

- Rama (e21JPS) did a 44mm valve engine with a 2.9L made over 290whp (smaller cam than other two ~305*)

the head waiting to go onto my new engine is 45mm valves (done by guy who did first two examples) but unlike above mine is a street engine but 3.3L but much less duration (292*) that’s why it needs a bigger port and valve, just too many cubes so even at 6000rpm its well and truly maxed out a stock head….

As for oversized valves hurting, they hurt the wallet but if the valve isn’t shrouded (not usually problem on hemi/semi hemi) provided the valve job, port shape and areas are done well then you won’t be disappointed with a small increase on even a mild stroker. At the same time if you aren’t revving the engine hard enough with everything else in the engine working in sync then you are not going to use the additional area. With stock port areas you can make ~250bhp based on the superflow equations.

On the flow bench you wont see big gains with oversized valves, more incremental gains, but the flow bench only tells you so much and the engine is not a flow bench. The engine cares about pressure differentials and geometry (cross section areas, lengths, shapes, lift) and time

[apostate]

go re-read my example with a kitchen faucet , let it slowly sink in and just let this thread die

No, I won't do neither of those. This thread is important but may be not to you, sorry.
Waiting for Digger's input instead.

[zaq123]

Hi guys,

Can somebody explain the benefit of having oversized valves in a M20 head?

Thanks. Cheers.

My point here is that oversized valves are a total nonsense unless the head porting is driven to its extreme limits. And even if this is the case, nominal valves can still be used, but for reliability's sake oversized valves are recommended, but only for this reason alone.

In any other case/reason oversized valves will hurt performance.

Looks like you answered your own question. Go re-read my example with a kitchen faucet , let it slowly sink in and just let this thread die

[apostate]

read my post i edited it

Thanks, that's also in my example on page 1, did you read it?
Do you know someone that did such an extreme porting which required oversized valves? In fact, even such an extreme porting of the throats can be closed with nominal valves but it is not considered reliable for a street engine.

My point here is that oversized valves are a total nonsense unless the head porting is driven to its extreme limits. And even if this is the case, nominal valves can still be used, but for reliability's sake oversized valves are recommended, but only for this reason alone.

In any other case/reason oversized valves will hurt performance.