Valve springs with 272 cams

[super_supra]

Just brought some hks cams 264 intake 272 exhaust do i need to upgrade the valve springs to cope with the extra lift?

[JamieP]

Only if you are planning to rev it high.

[super_supra]

Not planning on rasing the rev limiter, but it will be taken to the end of the revs every now and again will this be ok?

[johnny g]

Some upgraded springs wouldn't go amiss, but if you're keeping a stock limit, you should be ok, as Jamie says.

[TLicense]

Again, HKS only recommend using the stock springs. Those camshafts are also designed for a max RPM of 6750.

[Chris Wilson]

Unless you plan on running mega amounts of boost new stock springs wil be fine. Boost acts against the valve spring when the valve is closed, how much comes off the spring rate is calculable from the area of the valve opening (seat ID) V boost pressure.

[super_supra]

only going to run 1.5bar which is what i ve been running fro the last year.

[Digsy]

See this post. Might surprise you a bit.

 

Matching the valve spring to the cam profile has little to do with just duration and lift alone. Its how aggressively the cam tries to open the valve and close it again after maximum lift that is important.

 

The spring is there for four reasons:

1) To hold the valve closed against the boost pressure (intake) or pre-turbine pressure (exhaust).

2) To hold the tappet in contact with the cam as it approaches MOP.

3) To hold the tappet in contact with the cam as it closes.

4) To keep itself under control throughout the whole opening / closing cycle.

 

The first one is a relatively simple calc if you have the right information to hand, but figure around 150N seated load for exhaust valves and

The other two are dependant purely upon the cam profile. Put simply, the slower your valve opens and closes the less spring load you need. If you keep the lift the same but increase the duration then the valve does not have to move as fast to open and close in the time allowed and you can get away with a lighter spring. If you keep the duration the same but increase the lift then the opposite is true and you need a stronger spring. However with increased lift you also compress the spring more so you get a higher spring force as you approach MOP "for free".

If you increase lift and duration together and are clever about it you could in theory get away with the same valve spring - as in my linked post.

 

Cams and springs should be designed together IMHO. If HKS recommend the stock spring then hopefully they have used this as a design constraint and made an aftermarket cam accordingly.