The V8 Owners Forum -

i have an early set of heads with the double valve springs
are these any good or are they fit only for paper weights?
i had heard that the drag racing boys like them for some reason
thanks mark

P6 heads maybe? Their the worst of them all if memory serves!

You can pick up some efi heads for peanuts off egay these days so you may aswell go for that. I think p6 heads aren't unleaded compatible so that could be another reason to change.

http://cgi.ebay.co.uk/Range-land-rover- ... dZViewItem

Or if you contact a seller on ebay called rangeroverheaven he usually has something available for a good price. You'll get a minor performance boost using efi heads too.

The double valve springs are preferred for racing. I have doubles on my heads that I have shimmed and set to suit the wilder cam. The are much stronger than the singles and ensure faster closing and a tight seal at higher rpm.
I'm using old pre SD1 heads with this setup and they seem very good for use with Nitrous. I have been using unleaded fuel and gas on these 31 year old heads for 4 years now with no problems.

Various aftermarket double springs have been used in racing but if your gonna use old rover springs from a P6 for racing i'd seriously advise you check em over first. Many will have done umpteen miles and be knackered. They also dont leave much room for the extra lift of a big cam. The P6 heads themselves dont have hardened seats so must have them fitted before using unleaded. The ports are slightly smaller than later heads but can be modded easily enough to flow plenty. The quality of the castings is not as good as the later heads though, in fact rv8 head castings have consistently improved in quality over the years.

Don't forget the valves are smaller too.

and dont they use a different size thread for the spark plugs?

Not sure about the thread size but they are definitely a different length. Not that it makes any difference to the performance I guess.

They have same plug thread, only shorter reach.

As for the springs, they limit the valve lift so if you intend to use a non std cam beware of coil bind. Another thing, the OD of the springs is different so if you use old heads and wish to update your springs it may be difficult to find an uprated option. SD1 type will not be a straight swap. There are two otions for uprated single spring that can manage higher lift, Opel CIH engine range and Ford V6 springs. They just fit the pre SD1 head and hardware.

I had old Range Rover heads that I ported with SD1 valves, mainly because I had them and to buy a later heads would have cost money. I now have modified 4,6 heads and they require a lot less porting for same end results. So, unless you really enjoy porting it is better to use later heads.