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Rb25 Standard Valve Spring Capability

turbo87

By turbo87,
in Engines & Forced Induction

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BezerkR32 Veteran

BezerkR32

Posted
Posted

Yes last two r33 ive setup experienced valve float at around 20psi out of gt 35/40, which were making 285kw or 390hp at tyres.

I have been told that the rb25 standard valve springs will begin allowing the valves to leak at around 20psi or 400rwhp. Wondering if anyone has any experience with this?

Thanks

Luke 34GTT Explorer

Luke 34GTT

Posted
Posted (edited)

I might be confused with what you mean, but if your talking about the valve springs in your cylinder head, valve springs dont have anything to do with hp ratings etc. There issue is RPM. It Shouldnt matter if you run 40psi, as long as you dont go to far over the standard rev limit and the valves and seats in the head are in good condition the valve springs should be fine.

Edited by Luke 34GTT
sky30 Mentor

sky30

Posted
Posted
I might be confused with what you mean, but if your talking about the valve springs in your cylinder head, valve springs dont have anything to do with hp ratings etc. There issue is RPM. It Shouldnt matter if you run 40psi, as long as you dont go to far over the standard rev limit and the valves and seats in the head are in good condition the valve springs should be fine.

The more boost you run the more pressure there is in the cylinder to push the valves open.

Sydneykid Grand Master

Sydneykid

Posted
Posted

Boost in the inlet system slows down the closing of the inlet valves, as the valve spring is trying to close them against the boost pressure. The closing valve no longer follows the camshaft profile (ie; valve float). Around 19 psi is a reasonable rule of thumb limit we work to.

You can increase this slightly by shimming the standard valve springs, but there is not a lot of room before coil bind becomes an issue if you are using higher than standard lift cams. So it should be done very carefully.

Hope that was of some help

:( cheers :dry:

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