Discussion
Can anyone recommend a good manfr of valve springs? I want some way of reducing valve float ('bounce') at high revs (over 7k) (Porsche 911)
Simply fitting springs with very high spring rates isn't really the answer, as these typically impose a degree of wear on the camshaft (through the rocker arm or whatever) and also on the timing chains/belts - and normally rob the engine of power. I will probably go to Ti valve caps and retainers to lessen the reciprocating mass, but would like to hear your opinions on springs. Honda race springs are a wierd 'egg' shape (i.e. elipsoidal) which apprarently menas they don't need a very high spring rate to acheive the same effect.
cheers
Simply fitting springs with very high spring rates isn't really the answer, as these typically impose a degree of wear on the camshaft (through the rocker arm or whatever) and also on the timing chains/belts - and normally rob the engine of power. I will probably go to Ti valve caps and retainers to lessen the reciprocating mass, but would like to hear your opinions on springs. Honda race springs are a wierd 'egg' shape (i.e. elipsoidal) which apprarently menas they don't need a very high spring rate to acheive the same effect.
cheers
A current trend is to go for "beehive" shaped valve springs (Merc and BMW use this)- it allows a better overall compromise and nearly everyone uses progressively wound springs to vary the spring constant so that there is less chance of resonance- hence less need for dual valve springs.
In terms of what's on offer to the after market- I'd contact Schrick in Germany. They're not cheap- but they know their stuff and they of good quality.
Have you thought of reducing your valve system mass further? I don't know what the 964 has, but the 930 shape 911 clubsport used hollow valves- this might be worth investigating. Also look into the rocker arms - does the 964 use the same hydraulically compensated rocker arms of the 993? I believe - but am not sure- I'd have to look it up- the 993 rocker arms are also lighter! Might be worth further investigation....
In terms of what's on offer to the after market- I'd contact Schrick in Germany. They're not cheap- but they know their stuff and they of good quality.
Have you thought of reducing your valve system mass further? I don't know what the 964 has, but the 930 shape 911 clubsport used hollow valves- this might be worth investigating. Also look into the rocker arms - does the 964 use the same hydraulically compensated rocker arms of the 993? I believe - but am not sure- I'd have to look it up- the 993 rocker arms are also lighter! Might be worth further investigation....
In general terms to reduce or delay the onset of valve bounce you have two options.
Reduce the reciprocating mass (Rather expensive) or fit springs of a higher on seat load. These springs may also be an improved design such as the beehive already mentioned.
It may be better to forfeit some camshaft life compared to the cost of hollow valves and titanium this & that.
Steve
Reduce the reciprocating mass (Rather expensive) or fit springs of a higher on seat load. These springs may also be an improved design such as the beehive already mentioned.
It may be better to forfeit some camshaft life compared to the cost of hollow valves and titanium this & that.
Steve
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