Help!! My Intake Valves Keep Wearing Out! - Page 7 - Miata Turbo Forum -Boost cars, acquire cats.

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Old 12-19-2015, 08:56 PM   #121
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Yes ^ I am going to start checking into that scenario monday with manley, ferrea and some others and see what they have to say. They have several different alloys in stainless alone.
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Old 12-19-2015, 09:05 PM   #122
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Quote:
Originally Posted by patsmx5 View Post
This part, more valve spring.

quick math for you guys:

33mm stock diameter intake valve, 6mm stem diameter, 20lbs boost.

valve area - stem area =

855.3 mm^2 - 28.27 mm^2 = 827.03 mm^2 = 1.2819 in^2

Loss of seat pressure = area * pressure = 1.2819 in^2 * 20 lb/in = 25.63 lb of spring pressure LOST due to boost.

That's a lot, and that's only 20 PSI boost. This is why I run heavy double valve springs, because I run high boost.
NO No no.....

If you have this pressure differential when the valve is closing you have serious problems. Stop this nonsense please.
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Old 12-19-2015, 10:07 PM   #123
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Ferrea no longer makes nor has anything in stock for the Mazda BP, Manley valves (according to the new shop working on my head HVH in Knoxville, TN) are a weaker product than the ST.

I spoke with Del West and they wanted $155 EACH for valves.

I spent some time with the team from Callico when I was at PRI last week. I shared details of the failure. They said that Miata engines arent alone with this issue with high revving boosted engines. They told me about their DLC coatig and between PRI and now I have chatted with several folks who have used this coating on Ti valves and actually got Ti valves to live as long as a SS valve.

I will know more in a few months, but everything I am reading and seeing is pointing toward this being a solution that will work even in the face of seat pressure that is slightly too low or valve seats that are slightly too thin.

Last edited by TNTUBA; 12-20-2015 at 12:49 PM.
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Old 12-19-2015, 10:16 PM   #124
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Quote:
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NO No no.....

If you have this pressure differential when the valve is closing you have serious problems. Stop this nonsense please.
Your thought process is flawed in this area. It is not about pressure differential across the valve face. It is about the proper amount of net spring pressure to effectively control valve movement.

In the absence of boost (no positive pressure in the intake port) if it takes 60psi of seat pressure and 180psi open pressure to control valve moment, when you apply constant pressure to the back of the intake valve you don't "reduce the effective seat pressure" BUT you INCREASE the amount of spring pressure required to properly control valve moments.

This is independent of combustion chamber pressure.

Again, the issue at hand is not about controlling the valve in a static state, it is about controlling the "flutter" of the valve on the seat which is the root cause of the valve wear we are experiencing which is compounded by bad machine work, weak valves and heat.
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Old 12-19-2015, 10:23 PM   #125
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And MANY major camshaft manufactures agree with the fact that you need to consider boost pressure when you are setting up your intake valve spring pressure.

And I'll take their position over yours.
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Old 12-19-2015, 10:42 PM   #126
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Quote:
Originally Posted by TNTUBA View Post
And MANY major camshaft manufactures agree with the fact that you need to consider boost pressure when you are setting up your intake valve spring pressure.

And I'll take their position over yours.
One thought on this, intake manifolds are typically designed to cause a high pressure wave to hit the valves right as they are closing to improve cylinder filling. If you are running boost, the density of the air goes up, thus that wave will have more energy acting on the valve.

I'll say it's complicated, and I won't claim to understand everything. But yes, it's very common to run stiffer springs when running boost or higher RPMs.

And as Eric says, valve control is key.
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Old 12-19-2015, 10:49 PM   #127
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You are exactly right Pat, those pressure waves are a significant component when selecting seat pressures for a "max effort" motor. And those pressure wave are magnified in a boosted application.
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Old 12-20-2015, 08:19 AM   #128
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Quote:
Originally Posted by TNTUBA View Post
And MANY major camshaft manufactures agree with the fact that you need to consider boost pressure when you are setting up your intake valve spring pressure.

And I'll take their position over yours.
Oh I agree that you see this theory everywhere, but I still stand behind the fact that if you have a substantial pressure behind a closing valve (not a closed valve) your closing your valve too early and have significant gains being lost. A stuffer valve spring may look like it is fixing the problem but it is just covering up the real issue.
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Old 12-20-2015, 08:28 AM   #129
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.

Last edited by Alternative; 12-20-2015 at 08:53 AM. Reason: .
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Old 12-20-2015, 12:11 PM   #130
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High duration intake cams are closing a fair bit into the upward stroke, making the gas flow momentum low during the closing event. A narrower duration (for fear of blow-through etc) cam the gas flow have a little momentum during closing, and the boost should not lower it.

Unsure if retarding the intake cam would reduce the issue, but that would be fixing things in the wrong end.

Anyone compared OEM vs ST valves on VVT heads (for the bounce-resistance on 33mm valves)?
The VVT is the most bounce-prone setup on the BP.
Some have refereed that issue as resonance.

Valve timing is a mix of a number of dynamic processes, and empirical testing always trump the theories.
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Old 12-21-2015, 08:18 PM   #131
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Quote:
Originally Posted by TNTUBA View Post
Ferrea no longer makes nor has anything in stock for the Mazda BP, Manley valves (according to the new shop working on my head HVH in Knoxville, TN) are a weaker product than the ST.
Manley claim to be made from a higher quality grade of metal that ST, no? Wait, the manley races are made from NK-842 which is the same as the EV8 as the ST. Now the Manley severe duty valves on the other hand...
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Old 12-21-2015, 09:07 PM   #132
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I never laid a hand on anything supertech except for shims, but I run stainless SI valves, and they have been awesome. Can't remember the cost.
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Old 12-21-2015, 09:15 PM   #133
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Who is SI valves
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Old 12-21-2015, 11:28 PM   #134
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Quote:
Originally Posted by jmann View Post
Who is SI valves
SI VALVES- ANTIQUE/VINTAGE ONLINE CATALOG

Call them up and a real person who knows valvetrain actually answers the phone. If they can't answer your question on the spot they really do get back with you on it. They sell direct, too.
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Old 12-21-2015, 11:36 PM   #135
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^^^Met those guys at PRI too^^^ I spent two days talking to people about Miata intake valves it seems like
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Old 12-21-2015, 11:46 PM   #136
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Where's TurboTim? Isn't he a valvetrain engineer?
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Old 12-22-2015, 08:40 AM   #137
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Yep, what's the question again? If I don't know the answer, someone I work with probably* does.

*Collectively, we have zero experience with OHC/Direct bucket valvetrains.
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Old 12-22-2015, 09:09 AM   #138
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I think that what Alternative is getting at is this: If I have +20psi on the backside of the valve pushing it open, then shouldn't I have nearly +20psi (for argument's sake, lets say +15 psi) on the inside of the valve helping to push it closed? When you add pressure to the intake manifold, you're also significantly increasing pressure inside of the cylinder. I think that the argument that you need significantly more spring to help close the valve is a very poor argument indeed.

Alternative, I think the point that they are failing to explain is this: while intake valve spring pressure doesn't make much of a difference when the valve is closing or has just closed; the intake spring pressure DOES matter when the exhaust valve is open. At the end of the exhaust stroke, when the cylinder pressure is low and the manifold pressure is still +20 psi, you don't want one of your valves fluttering and letting in "bonus" oxygen while the rest are getting their expected amounts.

When my builder told me that he wanted to put stronger springs into my engine to help close the valve against the turbo pressure, I struggled to understand his point, but trusted his knowledge, and I let him do it anyways. I still don't buy that vastly stronger springs are necessary to close the valves in a turbo car, but I do believe that they help to keep those valves closed. I think his desire to put stronger springs in was correct, but his reasoning was flawed.

Unrelated: I hate it when people argue valid points with me using flawed reasoning in real life. At the end of the argument, when I finally figure out that someone else is right, and I have to *explain* to them whey they're right and I'm wrong, they act all uppity like they just won something. I don't mind being wrong, but I want to punch them in the back of the face because they couldn't explain that their fact was correct while I'm still arguing with their argument. If they would have been able to provide the correct argument in the first place, I could have simply went on about my day a little bit smarter.

Last edited by fooger03; 12-22-2015 at 09:20 AM.
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Old 12-22-2015, 10:00 AM   #139
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Quote:
Originally Posted by fooger03 View Post
I think that what Alternative is getting at is this: If I have +20psi on the backside of the valve pushing it open, then shouldn't I have nearly +20psi (for argument's sake, lets say +15 psi) on the inside of the valve helping to push it closed? When you add pressure to the intake manifold, you're also significantly increasing pressure inside of the cylinder. I think that the argument that you need significantly more spring to help close the valve is a very poor argument indeed.
No, the argument is still valid, but you are correct too. When filling the cylinder, the port and open valve remain the restrictions. Fluid flow with a restriction means there will be a pressure differential. With boost, we are filling the cylinder with more air (that's the point, right?), but it won't be a 1:1 relationship simply because of the physics and time involved (you've acknowledged that with your +15 which still leaves a 5psi differential -- although I'd be surprised if one could actually achieve the +15 at high RPM).

So, using the full value of boost on one side of the valve is overkill. But doing nothing at all is underkill. I'd love to see data on this.
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Old 12-22-2015, 08:07 PM   #140
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now your picking up what im putting down! I dont always have enough time for a full explanation sorry if I caused any grief. Besides if you figure it out on your own its twice as valuable. You could get some egr effects if your pre turbine backpressure gets excessive, but again thats a sign that you have another problem.

Keep in mind the newer Subaru STi EJ engines use a valve spring with a 52lb seat pressure, run reasonably high boost level from the factory and utilize a similar valvetrain configuration .
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