Help!! My Intake Valves Keep Wearing Out! - Page 6 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 12-17-2015, 08:42 PM   #101
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So if I understand, you say the head is original oem intake valves, not ST ss valves? I've never heard of oem intake valves having a problem. I've ran oem under pretty extreme conditions without issues.
This whole thread was started by Rick, who had issues with OEM valves.
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Old 12-17-2015, 08:47 PM   #102
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Okay so I'm old and forgot. Also reread the thread and if I read Ricks later posts correctly he took a stock junkyard head, did a valve grind and used the OEM valves with dbl lite springs. So I guess we need to hear from Rick.

Last edited by jmann; 12-17-2015 at 09:32 PM.
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Old 12-17-2015, 11:03 PM   #103
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This is a throw in the dark that may or may not help.

I raced at national level open class Motocross so had a new bike a year for many years..... The first Honda CRF450's had titanium valves and some bikes ate valves. for ages no one could figure it out, turns out a faulty air filter seal let dirt in BUT when mechanics replaced the valves they were lapping in new ones.

These would then fail causing poor starting/no starting within 10-12 hours.

Eventually it was realized that the common practice of lapping valves was not ideal for titanium valves as it was wearing through the required surface hardness...Honda eventually released a Service Bulletin specifically not to do this.

Probably NOT an issue here but in the interests of a weird solution for a weird problem I put it out there....possibly am repeating myself as well....(im old, have a 6 month baby...so no sleep and no memory at this point )
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Old 12-17-2015, 11:14 PM   #104
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Basically, I switched machine shops when I rebuilt my latest head. It's running fine with no issues. It is all-OEM with the exception of ST light doubles.

I think my earlier problem was improper valve seat machining. It ate a set of OEM intakes and a set of ST SS intakes.
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Old 12-17-2015, 11:34 PM   #105
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Thanks Rick that is what I'm planning of doing this time but use the inconel exhaust. Atleast it sounds like you solved your setup. I wonder if on your original head valve job that grinding the valves lowered the spring pressure somewhat as the valves sat lower in the seats after gring both and the machine shop didn't check the spring pressure thinking it was just a normal valve job. I have ran a pure stock head for 4 years on a 247 whp setup with no issues so I'm hopeful that doing something similar to what you did well fix things.
Do you know what the seat width ended up being and the spring pressure? Thanks
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Old 12-17-2015, 11:53 PM   #106
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Rick I have one other question, on the OEM setup from 8-9 was there any mods done to the ports on the head, mainly the necked down area under the intake valves?
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Old 12-18-2015, 04:16 PM   #107
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I specifically told the second machine shop to make the seats fat. He did .060 which is the top of the Mazda specification. He also carefully checked the seat pressures but I can't remember what the setup was (North of 70#'s IIRC). Didn't Savington make a recommendation somewhere in here?

Also, keep in mind that my car is normally aspirated. With boost, you need to compensate for the tendency of boost to keep the intake valves open and add a bit more seat pressure (basically, shim to add (intake valve face area in in^2 x psi) to the seat pressure).

We did no other work on the head. It was a low-mileage core and was in really good shape when torn down.

The first machine shop sandblasted the head and left grit in the oil passages. That should give you an idea of their QC.
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Old 12-18-2015, 04:33 PM   #108
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Quote:
Originally Posted by hornetball View Post
I specifically told the second machine shop to make the seats fat. He did .060 which is the top of the Mazda specification. He also carefully checked the seat pressures but I can't remember what the setup was (North of 70#'s IIRC). Didn't Savington make a recommendation somewhere in here?

Also, keep in mind that my car is normally aspirated. With boost, you need to compensate for the tendency of boost to keep the intake valves open and add a bit more seat pressure (basically, shim to add (intake valve face area in in^2 x psi) to the seat pressure).

We did no other work on the head. It was a low-mileage core and was in really good shape when torn down.

The first machine shop sandblasted the head and left grit in the oil passages. That should give you an idea of their QC.
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.
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Old 12-18-2015, 06:43 PM   #109
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Quote:
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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.
"Only" 20psi. LOL.

Thanks for the math. Rule of thumb, add 1.28lbs per psi to your seat pressures. It does add up.
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Old 12-18-2015, 06:53 PM   #110
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Data point. Not supertech, but Manley valves. Take it for what it's worth.

Manley +1 intake (and exhaust)

stock-spec widths valve grind pretty sure 5-angle. Need to find my paperwork.
Stock bp4w shim over buckets
Stock bp4w seats
Supertech heavy doubles
no boost, but just under 8k miles of no ***** given revving to 8k+ (soft 8k, hard 8200)
Soon to see lots of boost, but 7200 rev limiter.

Still at same lash specs as when I installed them.
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Old 12-18-2015, 09:49 PM   #111
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I understand what everyone is saying and knew that running boost was creating pressure behind the valves as that is pretty basic. I still think it has something to do with the metallurgy of the ss valves for the conditions they are seeing. I run 16 psi on most of the track, hit the porsche button and go to 18-19 psi down the straights so I would think brand new dbl lites with the oem shim in should be enough spring pressure. I well have it checked this time. What makes me think this, I have run a stock head with stock oem springs and never had an issue.

I called a guy who used to do my work before we moved to Or. and he does lots of race motors and he said there is 3 things that well wear the valve seat face.
1. Too little spring pressure
2. Too much spring pressure
3. HEAT
As stated in a previous post I suspect nbr. 3 with the ST intake valves. The setup gets pretty hot in 20 to 30 minute track sessions. It doesn't seem to effect the oem intakes,
just burns the oem exhaust after quite awhile.
Thanks everyone for your replys. To be continued
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Old 12-19-2015, 02:16 PM   #112
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I added spring pressure to the super doubles on the intake side. I took the boost pressure and determined valve area and came up with that. I forget my math but I remember it being more than boost pressure because the surface area was greater than 1.
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Old 12-19-2015, 04:24 PM   #113
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I understand what everyone is saying and sure don't disagree, but I revert back to my original thoughts. Why is it that others in the area and I have ran a stock head even with oem single springs and had no issues on the intakes ???????
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Old 12-19-2015, 04:32 PM   #114
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Quote:
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I understand what everyone is saying and sure don't disagree, but I revert back to my original thoughts. Why is it that others in the area and I have ran a stock head even with oem single springs and had no issues on the intakes ???????
Honestly, I would guess the stock valves either had a wider seat, or the valves are a harder and more durable metal than the supertechs. Or both.
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Old 12-19-2015, 04:34 PM   #115
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I agree with the latter as the second time the seats were ground to stock specs.
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Old 12-19-2015, 04:38 PM   #116
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I'm hopeful for the Calico DLC coating going on my valves this week.
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Old 12-19-2015, 04:50 PM   #117
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How are you guys getting so much pressure differential behind a closing valve?

This always makes me chuckle...
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Old 12-19-2015, 04:56 PM   #118
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The issue isn't keeping the tappet in contact with the lobe of the cam (traditional thought of valve float), it's keeping the valve firmly on it's seat the instant it closes and not "fluttering" or "bouncing" on the seat for several degrees of crankshaft rotation. That "flutter" or "bounce" will effectively "lap" the valve seat to the point of the seat cupping.

It's pretty simple and not sure why you have a hard time understating it.
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Old 12-19-2015, 04:59 PM   #119
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that well be interesting to see how that works with your setup, unfortunately we won't know for quite awhile. I think I'll call manley monday and talk to them. I was just on their interweb site and they have quite a few options.
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Old 12-19-2015, 07:42 PM   #120
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Dunno what happened, but I wrote a reply and it's not here. Short version, there are high dollar valves out there that may be a better valve than the supertechs if you're willing to spend the $$$ on them. Most race cars I've seen run something other than supertech valves, though they are popular in the miata world.
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