When is it recommended to upgrade valve springs.

I am writing to source some advice on my current engine build project I am working on, I am building a single vanos M50B25 to swap into my 91 E30 and I am planning on adding boost to it through the means of an M122H supercharger unit complemented by a kit from Hyde motorworks. The boost level I wish to run will be mild (in the range of 10-12 PSI) and am wondering if you think it is worthwhile upgrading to dual valve springs since I am adding boost. Gleaning the net, there is conflicting opinions on whether boosting an engine has any inherent effect on spring integrity/float etc and many state cam profile and desired rpm limit effect springs to a greater degree which makes sense. In your opinion for my application and desire to add boost, albeit mild, would you recommend to upgrading springs?

Any advice or help will be greatly appreciated :)

Kind regards,

Caleb

Look at this way, the spring is holding the valve on the seat, and increase in intake, or exhaust, manifold is going to increase the force trying to push the valves off the seats. Pressure times seat area - which may be a difference of 10-15lbs (guessing) in your case, but a large 2 valve V8 may have 2" diameter intakes and if running 50PSI boost that's around 150lbs force trying to lift the valve, same principle for the exhausts which can have significantly more pressure. That would mean a lot more seat pressure may required to close them properly and hold them closed, but "over the nose" there may be a much lower pressure difference between each side of the valves, and so one may need double, or triple, springs to get the right spring rates, seat force, and nose force from the springs.

But, more specifically, it depends - some applications it wil be fine, in others it may need the springs to be shimmed a little (assuming there is plenty of crush clearance), in others it will definitely require a change of springs, and possible some machine work.

If you're running otherwise stock camshafts, with the same max' rpm, you may be fine with a simple 1.0/40 thou' shim under each spring to give a little more seat force - that should be well within the springcrush clearances required.

Thank you for your extensive and informative reply, I appreciate the feedback, and I appreciate that increasing boost increases force applied to the valves. I've been gleaning the net trying to find just a mild single valve spring upgrade for my engine and application (M50B25 Single Vanos), however seems there are only dual valve spring options which I know add increased resistance and force required to activate the valves and act on the springs, increasing wear. And commonly these are used in conjunction with a more aggressive cam profile due to increased lift etc which ideally im not necessarily planning on wanting to upgrade for now unless absolutely necessary.

Ill have to look into shimming the stock springs, at very least ill want to buy new springs and refresh the head with new bronze guides etc but yeah my main qualm I guess was surmising if going straight to dual valve springs is unnecessary overkill or conversely, "cheap" insurance.

Engine maximum RPM are also to be considered when choosing valve springs. As we know mass times acceleration equals force so the heavier valves are and the higher RPMs are the greater force is acting upon valve seat making the valve to bounce off and move away from seat and you need stiffer valve springs (or lighter valves) to minimize that movement.

Thank you georg for your input, I think its safest bet to upgrade my valve springs given the added boost pressures. I will be tuning the engine for a slightly raised max RPM so think it would be wise to upgrade the springs to ensure somewhat of a failsafe against valve spring pressure issues.