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Old 01-23-2016, 12:37 PM   #1
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Default Valve spring installed pressures and valve lift

I am running a super tech dual valve spring kit in my engine build. I'm basically rebuilding a new engine for an old fmii setup that made 250whp/250tq on a 2860. I am running the exact same setup but want to up the boost to make 300whp. Supertech lists specifications for lift, pressure, installed height and coil bind on the box. If I am running the stock spring seats with the supertech spring seats in the configuration recommended by supertech with the stock cams, is it really necessary to check bind, lift, pressure, and installed height at the machine shop? Thought this was something you only did when running aftermarket cams I just wanted to make sure before I put it back together.
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Old 01-27-2016, 08:23 PM   #2
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I had to check that on my 99 head when I put in the Maruha cams but I don't think I had it checked when they were put in with the OEM cams. Which kit did you get, the 56, 63 or 72 pound set pressure? I went with the 63. My clearance was CLOSE with the Maruha cams, but still passed. With OEM cams you're probably fine. I'd check at least one on either side anyway if you can with some feelers - just make sure that the valves don't touch while spinning the cams or you could bend something.
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Old 01-28-2016, 11:05 AM   #3
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Thanks for the reply! I went with the 56lb springs from flyin miata. I didn't want to kill my seats with lots of spring pressure.,
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Old 01-28-2016, 12:09 PM   #4
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Quote:
Originally Posted by gdoehl View Post
Thanks for the reply! I went with the 56lb springs from flyin miata. I didn't want to kill my seats with lots of spring pressure.,
You won't kill the seats with too much spring. You'll kill them with not enough spring.
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Old 01-28-2016, 06:23 PM   #5
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Copy. I talked with flyin Miata about it and they said I would be fine. I was mainly worried about valve float since this will be a high psi boost application.
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Old 01-28-2016, 07:53 PM   #6
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Originally Posted by gdoehl View Post
Thanks for the reply! I went with the 56lb springs from flyin miata. I didn't want to kill my seats with lots of spring pressure.,
Valve springs do not work that way.

The punishment that is inflicted on valve seats comes from the valve stem leaving contact with the cam lobe. When this happens, the valve gets a running start at the seat instead of gently riding the cam lobe back to the seat.

It's like the difference between pulling a rubber band and then gently moving your fingers back together vs pulling it and then letting it go so it smacks your fingers. In the camshaft scenario, the more spring pressure you run, the better attached the rubber band is to your fingers. Valve float is what happens when you lose your grip on the band and it smacks your fingers.

Running lots of boost puts pressure on the backs of the exhaust valves, roughly double the amount of psi you're running. The pressure on the fronts of the much larger intake valves has a similar effect. This has the exact same effect as running excess rpm- the valves stay open even though the camshaft lobe is not holding them open anymore... and then they crash back into the valve seats. Do this a whole bunch of times and you end up with the end of a valve broken off the stem and embedded into the top of a piston and your engine needs a rebuild.
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Old 01-29-2016, 08:32 AM   #7
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Thanks for the explanation. Are higher spring pressures always a good thing? What about wear on the cams and spring retainers?
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Old 01-29-2016, 01:31 PM   #8
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Dunno about the retainers, never heard of those wearing.

My hunch is that unless you run a steep lobed cam at CONSTANTLY HIGH rpm, it won't make that much difference because I suspect accumulated heat has the most contribution towards increased wear. The higher the RPM, the less time the cam face and the bucket have to dissipate the heat until another lift event comes along and adds more. If you're only spending like 1% of the time above 7000 rpm and you have plenty of oil, it isn't going to produce any wear IMO. I'm sure someone on here knows the math for how much cam profile vs rpm vs spring rate contributes to wear but I think a short period of oil starvation would produce a lot more wear than any of these things.

In any case, a little wear that can be easily corrected without even removing the head is preferable to a dropped valve that requires a complete teardown.

Last edited by AlwaysBroken; 01-29-2016 at 02:23 PM.
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