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Old 04-18-2013, 04:14 PM   #1021
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Quote:
Originally Posted by soviet View Post
The only thing I'm impressed with is the low boost for 400whp.
It took me 28psi to reach the same - but that was on 93oct.
Yeah - After looking over the AEM file - There was no GPIO selected for VVT.. Inactive completely.
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Old 04-18-2013, 04:18 PM   #1022
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Is that fab9 someone you know or work with Bryan? I might end up ordering some engine internals from them. More than likely get the Supertech pistons. I like the price of those way more than the Wiesco ones.
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Old 04-19-2013, 12:56 AM   #1023
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I like the new setup your going with. I have heard some pretty good things about that spring setup. Still can't wait to see a video too. In the next couple months I'm planning on doing a built motor as well. A lot of inspiration has come from you. I just don't have the time to put one together. I've been looking at track speed engineering's motor. Heard or seen good things anyone? Or should I just do the same route you went?
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Old 04-19-2013, 08:56 AM   #1024
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Quote:
Originally Posted by rx7autoxer View Post
Heard or seen good things anyone?
You won't go wrong with it.


Dem, I didn't realize you were revving that high. I will agree with you it is likely a valve issue due to inadequate springs. I just hope you aren't going to need to replace pistons.
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Old 04-24-2013, 11:18 PM   #1025
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Bought a new head. with... 30k on it! I feel bad taking it apart. The new valve setup should be here shortly.
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Old 04-25-2013, 01:03 AM   #1026
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Quote:
Originally Posted by Dem768 View Post
Bought a new head. with... 30k on it! I feel bad taking it apart. The new valve setup should be here shortly.
It's for a good cause
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Old 04-25-2013, 11:15 AM   #1027
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did you ever get the old one apart to see what happened?
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Old 04-26-2013, 12:02 AM   #1028
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Old 04-26-2013, 12:40 AM   #1029
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This thread always turns me on.
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Old 04-26-2013, 02:04 AM   #1030
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Quote:
Originally Posted by redturbomiata View Post
did you ever get the old one apart to see what happened?
This.
I want to know what is so magical about 400whp that causes your head to fail.
I only dyno'ed once at 400whp and went back to a more streetable 3??whp
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Old 04-26-2013, 02:44 AM   #1031
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Quote:
Originally Posted by soviet View Post
This.
I want to know what is so magical about 400whp that causes your head to fail.
I only dyno'ed once at 400whp and went back to a more streetable 3??whp
It's not Magic. Think of it this way..

Lets say, just to keep it simple my valve is one square inch of surface. It has a factory seat pressure of lets say.. 45LBS return pressure. Then I boost my car to 24PSI. That means there is 24lbs per square inch fighting my valve springs. Leaving me with only 24lbs of seat pressure do do the same job it was supposed to do with 45lbs of seat pressure at 7000rpm... Valves can't close quickly enough so they start to float.

Also this dyno is seriously low. Locally known as the heartbreaker. I just watched a video of my car pulling on a Stage 3 Roush gutted and caged with a 575cal. When earlier that week my car made 310 on that dyno.


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Old 04-26-2013, 08:58 AM   #1032
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I assume the head is off and you have no piston/cylinder damage?
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Old 04-26-2013, 02:04 PM   #1033
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Quote:
Originally Posted by Dem768 View Post
It's not Magic. Think of it this way..

Lets say, just to keep it simple my valve is one square inch of surface. It has a factory seat pressure of lets say.. 45LBS return pressure. Then I boost my car to 24PSI. That means there is 24lbs per square inch fighting my valve springs. Leaving me with only 24lbs of seat pressure do do the same job it was supposed to do with 45lbs of seat pressure at 7000rpm... Valves can't close quickly enough so they start to float.
I read that before from BogusSVO but I don't agree.

24psi is not fighting your 45psi springs.

Intake stroke - valve is open, pressure inside combustion chamber is same as pressure in intake manifold. Net pressure on valve = 0

Compression stroke - your engine has compression of 150+ psi. So pressure inside combustion chamber is several times higher than 24psi of boost in intake manifold

Power stroke - Pressure inside chamber is even higher than compression stroke

Exhaust stroke - this is about the only time when the pressure in intake manifold may exceed pressure in the combustion chamber. But the intake valve is not moving at that point, so no float can happen.


In my honest opinion, higher valve spring rates are only required for more aggressive cam/higher rev limiter. I run more boost on 7200rpm limiter. You run less boost on 7500rpm limiter. Your valves float, mine don't. I call bullshit on the "I need stiff springs for high boost" theory.
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Old 04-26-2013, 07:40 PM   #1034
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I see what you're saying, but.

I think it's more a matter of the valve cant get it's *** closed fast enough.

Though, i bet what happened was just valve bounce. They were probably getting closed fast enough, but just didn't have enough pressure to keep them from bouncing on the seat.
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Old 04-26-2013, 08:24 PM   #1035
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You absolutely need stiffer springs for more boost pressure. The net pressure does not equal out because the valve is open. You can't just think of it as one pressurized system.

There is air velocity to consider and more importantly volumetric efficiency. There are very directional things happening. IT's literally 20psi blowing AT the back of the valve INTO the cylinder.

My example is not accurate above, it was just an example. You are correct that we must consider the pressure on both sides of the valve but more boost absolutely equates to an increase in seat pressure.

My example was based on the older theory that still hold some truth. Volumetric efficiency is the key to the equation..

If for example my engine is running 20psi and has a volumetric efficiency of 100% when the piston reaches the bottom of the intake stroke and the intake valve closes there will be 20psi on both sides of the valve surface. So 20 on the intake manifold side and 20 in the cylinder side. Since the air pressure is the same on both sides there is no additional force trying to keep the valve open.

But if the engine has a volumetric efficiency of only 50% there will be 20-psi pressure on the manifold side but only 10-psi on the cylinder side when the valve closes, because the cylinder did not completely fill, the pressure of 10-psi will be present across the valve head. If the intake valve has a surface area of 1 square inch a force of 10 pounds will be trying to open the valve thus reducing the valve spring pressure by 10 pounds.

Make sense? So basically what I've just realized is that I probably went a little overkill on my seat pressure.
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Old 04-27-2013, 10:05 AM   #1036
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No matter how you look at it, you have more RPMs and more pressure on the back of the intake valve than what the Mazda engineers designed it for. I agree with tighter springs as a preventative measure.
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Old 04-28-2013, 10:42 PM   #1037
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Got the head off. Look what I found...








Walls are lightly scored so I'll be dropping that piston, doing a light hone and slapping the bitch back together. Should be a couple of weeks..
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Old 04-28-2013, 10:48 PM   #1038
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Tis but a scratch.
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Old 04-28-2013, 11:02 PM   #1039
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Some crazy *** carnage is this thread. Sucks but I like your spirit!
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Old 04-29-2013, 02:56 AM   #1040
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Explains why the spark plug wouldn't come out. Hope you get it sorted soon
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