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[Joseph Davis]

Is there any significant problem with running intake valves in place of exhaust valves, and vice versa?  This would be for a NA application, IIRC the exhaust valves on a turbo car are a different variant of stainless and of course all exhaust valves have more guide clearance. 

I'm sitting here fapping to a catalog of OEM valve dimension and my hamster wheel is spinning.

[dvst8r]

I have run all intake valves in a cummins head with out issue. Many trips past 1800 F egt's. I would say most valves should be okay in either app.

[Joseph Davis]

Why didn't you drown in the huricane?

[Joseph Davis]

Do you have a turbo car?

[Joseph Davis]

If I wanted a $500 kit making 225 whp I would have one.   

[DmC]

If I wanted a $500 kit making 225 whp I would have one.   

Why would you not want one. Are you fucking stupid?  ;D

[Joseph Davis]

If I wanted a $500 kit making 225 whp I would have one.   

Why would you not want one. Are you fucking stupid?  ;D

225 isn't fun anymore. 

[DmC]

If I wanted a $500 kit making 225 whp I would have one.   

Why would you not want one. Are you fucking stupid?  ;D

Whatever he's scheming on is going to fail again.  Only then will he see the light.

See this is where I have everyone on the site beat. Usually don't post to much about my car making claims and bragging. And when it does fail as all turbo cars do atleast once a year I get on it and have the thing fixed so fast that even locals never knew it was down. Except for Fowwee he holds my tools for me.  while he talks about things like tensile loading and his fasination with det cans.
  He truely is the only good help in town.

[DmC]

If I wanted a $500 kit making 225 whp I would have one.   

Why would you not want one. Are you fucking stupid?  ;D

225 isn't fun anymore. 

But 140 is?

[Joseph Davis]

If I wanted a $500 kit making 225 whp I would have one.   

Why would you not want one. Are you fucking stupid?  ;D

225 isn't fun anymore. 

But 140 is?

From a stock cam D16?  Yup.

[Joseph Davis]

High compression turbo D-series is the worst possible parts combination I think I have ever heard of.

[Joseph Davis]

I have no desire to make an engine bleed oil into the combustion chamber due to poor design.

[88dx]

put a stick in that hamster wheel, when its spinning nothing good happens 

[patsmx5]

Some OEM cars the exhaust valves have s black something coating on them where as the intakes don't. Mazdas are this way.

[patsmx5]

Black Nitride coating I think, but no I really don't know. It's harder than the valve itself. A thermal barrier coating of sorts to keep the surface of the valve cooler.

[Joseph Davis]

Black nitride and chromium are the two popular OEM coatings.  There are writeups on them, and the correct guides to use.

[d112crzy]

He's building an NA K.

[Joseph Davis]

Mr Davis.. answer my goddamn question.  What are you trying to achieve?

To increase headflow??  I thought it was fucking obvious, Dullard.

[Conceptz-X]

They are on to much more advanced coatings and shit now..  Lookup Exceldyne

I think you'll be ok   Just have to keep your timing right

[Joseph Davis]

Ferrea is the only valve I've seen that withstands being revved past 8500rpms, and if you go to PRI and talk with the tech guys at each booth you understand why that is. 

[patsmx5]

Also, could a much larger exhaust valve (relative to the size of a given intake valve) hurt performance?

Yeap. If you make it too big it becomes too shrouded. And heavier.

[Joseph Davis]

1.25:1 is the typical ratio of intake:exhaust.  This may change depending on port dynamics, flow, and ideal powerband.

[Conceptz-X]

for a N/A motor,   Would the larger exhaust valves not help in a turbo application where you have higher backpressure than N/A or supercharged?

I was thinking 1:1 or close

and Ferrea valves are fucking awesome, unless you go del west or exceldyne

[Conceptz-X]

Also, could a much larger exhaust valve (relative to the size of a given intake valve) hurt performance?

Yeap. If you make it too big it becomes too shrouded. And heavier.

Pent roof chambers naturally unshroud the valves at higher lifts

[Joseph Davis]

for a N/A motor,   Would the larger exhaust valves not help in a turbo application where you have higher backpressure than N/A or supercharged?

I was thinking 1:1 or close

Everyone I've heard discuss it, who could find their ass with both hands, says make the intakes larger to get more air in and the exhaust finds it's own way out.  The 752 whp record setting D16 is supposed to have big intakes and stock sized exhausts.  There are a number of superbikes that increased power dramatically in the late 90s by making the exhaust valves smaller while keeping the geometry/CR/cams approx the same and bolting on some different induction and exhaust, Motoguy or whatever his name is who advocates the hard break in method has some writeups on it. 

Still, what an engine wants is what an engine wants.  I would not be surprised, at all, to find out that engines wanting bigger exhaust valves (especially in a non forced induction app) is commonplace.

[Conceptz-X]

I figured the scavengin effect in a turbocharged engine to be minimal therefore larger exhaust valves would help compensate flow losses.   Theory for you...   

need to take a motor, run it, swap heads to the larger Exh valves run again and see what happens.   Might pick up, might need to be sent to the chineese for melt down...

[patsmx5]

Also, could a much larger exhaust valve (relative to the size of a given intake valve) hurt performance?

Yeap. If you make it too big it becomes too shrouded. And heavier.

Pent roof chambers naturally unshroud the valves at higher lifts

Higher lift and bigger valves are two different things. So what's yoru point?

You always want the intakes bigger than the exhaust. If you make the exhaust bigger, this compromises the intake size, which is more crucial. The engine has to do work to pull the air in. But on the exhaust side the valves are opened before BDC, and most of the mass of exhaust exits on its own before the engine has to do work to push it out.

[Conceptz-X]

First off technically air is not pulled in.  its pushed from a higher pressure to a lower...  Understand that before you comment. 

A pent roof chamber provides little shrouding, therefore bigger valves should not have a problem with shrouding, regardless of lift. 

If Boosted with a Turbocharger, you have far more exhaust pressure and volume to release into a restriction, if the turbo is efficient and has low back pressure all is well, but is not always the case.  If you have a system where you have alot of backpressure, more exhaust flow will benefit.

Also, if the chamber is not entirely purged of exhaust gasses, your wasting energy re-compressing heated inert exhaust gasses from the previous cycle.

[patsmx5]

First off technically air is not pulled in.  its pushed from a higher pressure to a lower...  Understand that before you comment. 

A pent roof chamber provides little shrouding, therefore bigger valves should not have a problem with shrouding, regardless of lift. 

If Boosted with a Turbocharger, you have far more exhaust pressure and volume to release into a restriction, if the turbo is efficient and has low back pressure all is well, but is not always the case.  If you have a system where you have alot of backpressure, more exhaust flow will benefit.

Also, if the chamber is not entirely purged of exhaust gasses, your wasting energy re-compressing heated inert exhaust gasses from the previous cycle.

You're wrong. The pressure in the cylinder right when the intake valve opens is higher than the intake charge. The residual exhaust gasses push into the intake contaminating the charge untill the piston decends and expands the chage in the cylinder enough that it's of lower pressure than the intake, at which point the charge flows in.

I said bigger valves will be shrouded more. There is nothing wrong with that statement. I also said bigger valves will be heavier, which is also true. You can talk combustion chamber design all day long, but my points still stand.

Pressure and flow are two different things. If you have high backpressure from an incorrectly sized turbine, then you need to select a correctly sized turbine, not change the exhaust valve size.

The chamber is always contaminated with exhaust gasses. Welcome to <100% VE.

[Conceptz-X]

You're wrong. The pressure in the cylinder right when the intake valve opens is higher than the intake charge. The residual exhaust gasses push into the intake contaminating the charge untill the piston decends and expands the chage in the cylinder enough that it's of lower pressure than the intake, at which point the charge flows in.

I said bigger valves will be shrouded more. There is nothing wrong with that statement. I also said bigger valves will be heavier, which is also true. You can talk combustion chamber design all day long, but my points still stand.

Pressure and flow are two different things. If you have high backpressure from an incorrectly sized turbine, then you need to select a correctly sized turbine, not change the exhaust valve size.

The chamber is always contaminated with exhaust gasses. Welcome to <100% VE.

Look up Scavenging,  your off as usual, how do you think N/A motors can achieve VE's above 100%?
Scavenging and intake pulse tuning.

I said nothing about valve weight, easily overcome with spring pressure.

You really have no clue...