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Discussion Starter · #1 · (Edited)
hi,

I have got an rb26dett with tomei cams 280 degrees and 10.8 mm lift. Now i was wondering what people set their valve (intake and exhaust) opening pressures at?

Mine was set at 90psi for intake and roughly 75psi for ehxaust, this was too high becuase after only 1100km's of running the engine in the cam lobes were showing signs of wear (really polished lobes just at the start on the up ramp on the lobe and the again at the peak of the lobe.)

Spring are tomei type c racing spring which has a inner and outer spring.

was thinking of setting opening pressure at around 65psi, also would people use double valve springs or just one spring shimmed up? Forgot to mention engine was built with the intenion to spin up to 10,000rpm

all opinions and feed back are welcome cheers.
 

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Discussion Starter · #3 ·
Opening pressures.....valves........Eh????

Don't know what you mean.
Yeah the inital pressure that is required to open the valve. Or another way to look at it is the pressure required to keep the valve closed at high rpm when valve is not being opened
 

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Surely a function of spring tension??? Doubt anyone measures that, they just install an upgraded set like your Tomei C's
 
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No ,some people measure lift load , they adjust the preload to correct the springs opening pressure.

To be honest we just make sure the installed length is correct as per manufacturers spec, never measure the opening pressure.
 

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90 psi is pretty high for bucket based valves. You'd normally go with 70 psi installed pressure, if you have roller bearings like the S2000 you can go a lot higher yes.
 

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Discussion Starter · #9 ·
90 psi is pretty high for bucket based valves. You'd normally go with 70 psi installed pressure, if you have roller bearings like the S2000 you can go a lot higher yes.
Thanks i think we are going to be aiming for around 55-60psi this should be heaps to hold the valve closed. From what you said this knid of confirm this.
 

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it depends on the boost pressure, the revs you're running and the weight of the valve train.
You must subtract the boost pressure times the area of the valve from your install pressure. Rule of the thumb is that the valve area is about one square inch so if you run say 20 PSI of boost you are already loosing 20 PSI from the spring pressure. With an installed pressure of say 50 PSI you only have 30 PSI left for closing the valve and that is not really sufficient.
Did you also check the install height and the maximum lift on the springs?
 

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Discussion Starter · #11 ·
it depends on the boost pressure, the revs you're running and the weight of the valve train.
You must subtract the boost pressure times the area of the valve from your install pressure. Rule of the thumb is that the valve area is about one square inch so if you run say 20 PSI of boost you are already loosing 20 PSI from the spring pressure. With an installed pressure of say 50 PSI you only have 30 PSI left for closing the valve and that is not really sufficient.
Did you also check the install height and the maximum lift on the springs?

yeah checked the installed height and the maximum lift on springs. The only thing i don't think we thought of was the boost level however because it is on the back side of valve less surface area and because you have forces on the front side of valve such as compression and exhaust gasses i don't think that the boost would effect alot.
 

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Boost plays a big part in spring pressures required and the pressure you have I'd say is pretty close for a 10,000rpm 2 bar+ motor.

Might pay to also check oil restrictor size and feeds etc.

Rob
 

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Discussion Starter · #13 ·
Boost plays a big part in spring pressures required and the pressure you have I'd say is pretty close for a 10,000rpm 2 bar+ motor.

Might pay to also check oil restrictor size and feeds etc.

Rob
yeah the engine would be 25-28psi for street duty but i don't know what the aim is going to be for race fuel maybe higher. Rob what would your seat pressure be? Also has a resitrictor in the head and the two feeds for the turbos
 

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When you say shows signs of wear, then say shiny and polished, that sounds fine to me. If the cams were losing their moses or the buckets were scuffed, then you have an issue. I would have just fitted the springs on the stock seats at stock fitted lengths, and left them alone. I wouldn't want to increase the seat pressure without VERY good reason. They will be made to support a stock valve and top hat combination at a designed RPM. Unless you are going well over that RPM (and then the cam profile probably won't be efficient there, anyway) or are running a *huge* amount of boost, I'd say stock seat pressures are fine.I am in the process of having some Mugen MF-308 valve springs made, it's a VERY involved science, and unless you are trained in this area I think youi could get yourself in a right pickle. The questionairre for the springs has taken myself, and Engine Developments, a week to complete satisfactorily, plus they (Performance Springs) have sample springs. Have you got detailed photos of this cam wear? Have you measured any wear? Do Tomei suggest that spring for use with those cams?
 
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