I have a 1200 ute which runs an a15, 60thou oversize pistons, shaved head, ported+polished and running twin 40 dellorto's. I also have transister ignition. I don't have double valve springs. Could someone please explain how they work and give me some feedback as to whether they would be suited to general hooning. I have also considered larger valves, i am interested in which valves to use, the cost vs performance increase etc and if my reliability will be compromised.

For a start the double valve springs should help eliminate valve bounce at high revs.

This is a must for anything above 6500rpm

quite often double valve springs aka higher seat presure can be help full right throught the rev range as cam choise affects how soon valve float occures partiularly as the reves increass

even if you dont suffer from valve bouse you can be suffering from valve float which will reduce power

how ever the more spring you run the quicker the wear rates

well thats my 2c

Quote:
Hmmmm, time for me to go back to school. Perhaps you can tell me the diference between valve bouse & valve float, & how does this valve float reduce power, when, it would seem, that valve bouse does not.

I'm also curious to know how double valve springs are help full at lower speeds in the reve range. Seems that i still have much to learn.

sorry probably just my bad use of term's but Ive always refered to to float as when the valve dosnt close as quick as the cam allows, where as bounce as such is the effect where the engine hits the brick wall and wont rev any harder while under load

what I meant was that the engine can be floating the valves at say 4500 and losing some power well before the 6500 point where the engine wont rev out any further due to valve bounce

I didnt think that I said that valve bounce wouldnt reduce power as it obviously does

sorry for the miss understanding

Valve bounce it exactly what it says. The valve actually bounces. The spring is not strong enough to hold shut the valve in one hit at high revs/ high inertia. The valve flys back up, hits the seat and bounces. Only marginaly but enough for a terrible noise and power loss. It is also damaging to the head/seat and the valve.

Basically if you dont have valve bounce or arent on the verge of it at your motors peak rpm dont worry. Save your time and money for something else.

cheers fella's, i don't have an rpm counter so not really sure what sort of figure's i'm doing. However i'm reasonably cautious and don't recall hearing vavle bounce, would i know?. Watching my speedo i've reached just over 160k's in third(5spd) but i'm somehwat dubious as to whether or not this is accurate. I have 14X55X185's as my choice of wheel.

Tom, Talk to Keford camtech in Christchurch. 0800 338000, or www.kelford.co.nz.
Ask them for some performance springs, part # CB4A02. You may also need some shims to shim them up to installed heights.
There may be someone in Wellies who sells them too, but I wouldn't know who.

cheers bartman, exactly what i needed to know without making it clear!
Any ideas on increased valve size?