Oversized valves

[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

[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

[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!

[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

[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

[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!

[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]

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]

Then show us why you think you're right....with numbers, bench flow tests, dyno numbers, etc. We want to learn. I love engine theory threads.

Look up many many posts by digger and ForcedFirebird for just two examples - real world testing and years of experience in engine theory and building.

[digger]

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!

maybe dont ask generic questions and claim that you have all the answers already and that it is black and white scenario

[apostate]

This all is nonsense. The thread was supposed to bring a discussion for a specific issue.

I am sure that the people that understand the material content here, have benefited one way or another and this is good enough for me.

I will say no more.

[digger]

you are the one that killed it, i explained why you might want them and no matter you said that absolutely no, never....

[digger]

if you want a discussion lets have an open minded discussion, with some specifics

[e30davie]

Well this is awkward.

engines be about trade offs, thats why there is no number 1 solution. what works for someone on their home race track might not work for you on your home track.

If only i had unlimited money, I could test all the combinations.

[rturbo 930]

Since you apparently knew the answer before you even asked it, why make the thread in the first place?