OK, so a case in point. I built a 18 GV-block engine with a '67
head. I used a cam that was ground on the '66 or '67 profile. This
was, according to all the info I had available at the time, the best
"stock" cam that came in the USA Bs. I used the the dual valve springs
shimmed accordingly, and hardened valve seats, both intake and exhaust.
Also used the long lifters and short pushrods. Also using dual-row cam
gear and chain. I'm using the SU's that came on it, rebuilt, and it
pulls like a train to 6,000. Never rev it over that.
My feeling is that you have to tailor the springs to the cam and
valve gear. Barney sez as much.
]Barney Gaylord wrote:
> At 07:39 AM 5/3/2007 -0400, Paul Osborne wrote:
>> .... Looking for input on the advantages/better choice of single or
>> double valve springs on a 18v head. ....
>
> Lighter valve springs cause less wear on the entire valve train,
> especially cam and tappets. For purpose of longevity, it is desireable
> to use the lightest springs that will get the job done. The change from
> double springs to single springs with the 18V engine was accompanied by
> a change from tall heavy tappets to short light tappets and longer
> pushrods. The lighter tappets can be returned with less spring force at
> high speed, and you have a longer wearing engine. They changed from
> double row to single row timing chain and sprockets at the same time (as
> a cost reduction), as less power is required to run the camshaft with
> single valve springs and lighter tappets.
>
> A high lift camshaft imparts more motion to the valve train, therefore
> inducing more inertia to the moving parts and requiring more spring
> force to return the patrts at high speed. A high performance engine
> expected to run at higher than normal speed would need stronger valve
> springs. Inertia can be reduced by using lighter parts in the valve
> train, such as the short tappets or alloy spring caps. It is a
> functional trade-off. Heavier parts and higher speed needs srtonger
> springs and causes faster wear. Lighter parts and lower speed allow use
> of lighter springs and reduce wear.
>
> The 18V engine already has the right combination of parts from the
> factory for successful use of single valve sptrings. Since installing
> double springs can increase the wear rate, the only reason to do so is
> if you are upgrading performance specs of the engine for higher valve
> lift or higher engine speed. If you do install double valve springs in
> your 18V engine you should also install the double row timing chain and
> sprockets,
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