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Originally Posted by JasonC SBB
(Post 1295045)
Rate of change in RPM is very very slow compared to the motion of the valves. If there is some kind of "harmonic" issue related to RPM, it means you need to avoid certain RPMs because some resonant frequency is being hit. Big rotating machinery such as 500 kW steam turbine generators have "forbidden RPMs". In order to avoid those destructive RPMs, on startup/ power-down, you accelerate/decelerate as fast as possible through those RPMs. If you dwell at those RPMs, then things break.
What is more likely happening is that at some RPM the lifter loses contact with the cam as it is closing, so the cam isn't decelerating the valve for a soft landing on the seat. So the valve crashes down. Rapid wear. The fix is stiffer springs, or a lighter reciprocating mass. This thread is tl;dr - is this problem less pronounced with a lightweight lifter? Sorry about my sloppy terminology, I'm trying to remember cam design which I haven't done in like 4 years. |
Harmonics != Time Derivatives
C'mon dude. |
Is there even a problem here other than mediocre head work and forgetting parts?
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It isn't rate of change of rpms for the valves.
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Originally Posted by Leafy
(Post 1294631)
Hmmm another valvetrain problem that seems to be the bane of auto-x racers (even csp) and high powered road racers that less fast road racers and street people have never run into, and its happening to cars at a variety of revlimits. Starting to sound like its a 3rd order harmonic issue related to the rate of change of rpm more than the rpm itself.
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Originally Posted by fooger03
(Post 1294028)
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 |
Originally Posted by JasonC SBB
(Post 1295045)
What is more likely happening is that at some RPM the lifter loses contact with the cam as it is closing, so the cam isn't decelerating the valve for a soft landing on the seat. So the valve crashes down. Rapid wear. The fix is stiffer springs, or a lighter reciprocating mass.
Originally Posted by Leafy
(Post 1295050)
If that's the case road racers world have more of a problem with it.
I put lots of hours on an NB2 head at ~17psi and ~7400rpm on stock valves/valve springs and never had an issue. |
So Sav, your saying the issue is NOT insufficient seat pressure but insufficient spring rate?
Its suprisingly cheap to have custom springs wound if you know where to look. Autocrossers tend to ride the limiter more than what I have seen, I do not have a theory that applies but it is a difference. |
As I posted several times above I too have put several hours on a stock head with stock springs at 18-19 psi with a limiter of 7500 which it hardly ever saw, only when trying to make a corner without shifting. Most of the time shifted around 68 to 7000 rpm. I can't do the same with dbl lite springs on ST valves, most likely being 1mil oversize has something to do with it but dbl lites ought to make up for it verses stock single springs.
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I had custom springs made by PAC. They are Pacalloy....you know the valve spring technology that revolutionized NASCAR "plate" racing. I still had a valve erosion issue.
I do think Sav is right in our desire to run 8,000+ RPM redlines and "ALLOFIT" levels of boost and in my case "ALLOFIT" levels of compression. I am still searching for the answer...and the answer for me just might be that there is no answer. If that's the case, I'll just keep rebuilding the head once a season because that's what it takes to be fast in SSM. |
I now know part of the reason. I was on the phone for about 15min with SuperTech this afternoon.
Miatas aren't alone with this issue with their parts. They used to "blacknitride harden" the entire valve. Several yesrs ago due to issues they were having with "run out" they changed their manufacturing process and no longer sell valves with a Nitrited seat. So now we know why Bundy's valves have lived and ours haven't. The end. |
Thanks Eric that explains a lot, what ticks me off is I've talked to them 3 or 4 times about this and no one ever told me that. All any of them ever said was I needed more spring psi. I used to live in Anacortes and have helped Bob work on his car and later on when I went to ST valves we could never figure out why I was eating valves and he still had the same intake valves that came with his FM head and hasn't even had to have them reground yet after talking to him a few days ago. I am going to look into having some inconel intakes made.
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Originally Posted by TNTUBA
(Post 1297210)
I now know part of the reason. I was on the phone for about 15min with SuperTech this afternoon.
Miatas aren't alone with this issue with their parts. They used to "blacknitride harden" the entire valve. Several yesrs ago due to issues they were having with "run out" they changed their manufacturing process and no longer sell valves with a Nitrited seat. So now we know why Bundy's valves have lived and ours haven't. The end. |
Here is a informative article that should help when relating to your favorite machine shop
Valve Angles - Tech Article - Chevy High Performance Magazine |
Iv been thinking about how much the ST intake vavles are sucking and if im going to be using a better valve i figure i can get something OTS and make the setup better over all.
I am thinking about getting some ferrea blank Honda valves (these should be pretty standard issue i think) and converting the intake side to 5.5mm stems with new guides. Ill have to work some magic with the keepers but im sure i can figure it out. The pros out weigh the cons being that i have to machine in new grooves on the valves but lighter, stronger, more flow all sound good to me. Thoughts? |
Why not black nitrate the seating surface of a Supertech? Based on Bob's feedback the maybe the answer. I'll know more once I get hours on mine setup. I hope to get more than 10 hours out of these valves with the new spring setup. If not I am gonna pursue have the faces treated.
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i think the ST are nitrided but once ST grinds the face, any additional lapping or grinding of the valve will remove the thin layer of nitride that is left over and then face hardness is lost and accelerated valve wear goes up. This is just a theory though.
5.5mm stems should get me valves are are closer to stock weight if not lighter. so that would take springs out of the question and leave it to valve material. Anyone here have access to a hardness tester it would be interesting to see a stock valve hardness vs a ST valve. |
May have some good news. Just got off the phone with Willie at Super tech and he said he was going to have a run of inconel intake valves done. It has taken alot of talking but it is going to happen, he said somewhere around 2 months to being available. Don't know if this well be the answer but it is worth a try.
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i spoke to Ferrea today and they were typical dicks and basically kept saying spring control is the issue and that if i used ferrea valves i wouldn't have this problem.
So i then called up Willie at Supertech and he and i talked for a bit also and it sounds to me like there will be a few different options and we will find a solution that works. we touched on inconel valves, fully nitrided non ground valves, valves that were ground down then coated with something similar to titanium valves, and valves that were from what i understood to be induction hardened. |
can anyone translate this better than google?
BP??????? I take it that they make Both intake and exhaust valves from inconel. |
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