6 replies to this topic

[n00b]

Hi all i have a question about my next purchase i am looking at. . double valve springs on a stage 3 cylinder head for my 998 A+ stage 1.

Will my engine be able to provide the power needed for the stronger valves to work sufficiently and will it provide any more power or am i wasting money/time without the use of a higher output cam?

Thanks ERic

[Dave33]

You have answered your own question,more power is consumed compressing higher poundage springs.
With a standard cam and some mild aftermarket ones,double valve springs are not needed.
Hth
dave

[Ethel]

The idea of double springs is that, because they are different stiffnesses, they vibrate at different frequencies, damping each other. That should mean you can run to higher revs, without needing higher poundage springs to avoid valve bounce.

In the real world, such stuff is made for performance "race" engines to run at higher revs so you can expect higher poundages as well. Discus it with the supplier of the head, no reason why you can't specify less heavy springs.

[Cooperman]

With a mild state of tune you shouldn't need double valve springs.
The downside is that they put muh more load from the cam followers onto the cam lobes and thus consume more power.
The only benefit is that at really high revs, like, say, over 6200 rpm, they prevent the valves staying open after the cam lobes have moved round (i.e. prevent 'valve crash').
With standard springs which have covered a high mileage it's worth fitting new standard springs, but as Ethel says, use strong double springs only for race/rally engines where very high revs are used. I use them in my 1310 c 'S' rally ar, but then I use 7000+ rpm (and wear out the cam quite quickly too).

[n00b]

Just to clarify this as i have been offered a stage 3 998 head for free which has double valve springs you see.

You say it wouldnt benefit the double valve springs because i currently have a standard thou A+ cam, would the engine prefer more standard springs to be replaced on the stage 3 head? As i mentioned above i only currently have a stage 1 kit installed.

Also what type of power increase will this achieve apart from higher CR, the owner says its been port polished and gas flowed if this helps.

ERic

Thanks in advance

Edited by n00b, 06 July 2010 - 05:35 PM.

[Cooperman]

'Stage xx' doesn't actually mean anything really.
However, with the standard cam you should have single standard valve springs.
It's impossible to give any sort of figure for power gain as the compression ratio is not quoted - you should measure and calculate to make sure it's OK before fitting any new modified head. Also you don't give the valve sizes or any details of other mods.
One might guess you'll gain a few bhp, but without a better cam, better inlet & exhaust system and the other mods whih would normally go with these changes, don't expect too much. Even the most gas flowed head can't give much improvement if the cam doesn't open for long enough or lift the valves high enough for more mixture to flow in, or if the carburation or exhaust system are blocking up the flow of mixture and/or exhaust.

[n00b]

i completely understand where you are coming Cooperman from, it may not sound impressive with my current setup but i was hoping for a bit more flow throughout the clinder head with this modded head. Currently i have a HS4 K&N with richer AAA needle and a 3 branch manifold single boxed RC40 system and atm it runs sweet as a nut dont get me wrong! But then again for a free head im not going to let it gather dust, this is the head that he is given me - Clicky

The owner said he had it fitted to a standard 998 just like mine pretty close spec execpt manufacturers and he said it gave a good high reving range with sufficient pull at the lower end, even with a standard cam. Obviously i would like to also change the cam but after the 4th engine change iv done on the car im nearly tired of them for the moment!!

Although iv heard you can still change the cam with the engine retained still my knowledge of this is short lived for the time being, as I say its a constart learining curve for me and mini engines!

ERic