New cam into 3.5V8

[thermidorthelobster]

I'm never sure where to post these V8 questions, but I thought you Range Rover boys would probably have some ideas.

The 101 has (just to recap) a 3.5V8 on SU carbs, but it's the High Compression version of the engine from a Rover SD1.  It was rebuilt about 3,000 miles ago so should be in good nick.

The 101 weighs 4.25 tonnes so it's no dragster.  The economy is still under investigation but I'm suspecting it's as bad as 8mpg on the IWEMA LPG conversion.  Not sure about Unleaded as I never run it on petrol for long!

Somebody suggested a 3.9 cam might give me more torque out of the same amount of fuel, or to turn that around, better economy if I drive it the same.  I've spoken to RPI Engineering and they do replacement cams, but the whole kit will cost me about £300.  I don't think I'd tackle fitting myself, so I've got to add in the cost of paying somebody to fit it as well.

Anybody got any opinions on how much difference I'll notice?  I don't mind trying it if it's going to be worthwhile, but I don't want to shell out and find it's pretty much the same as before.  RPI suggested if the existing cam was knackered, it could make a huge difference, but I've since found out it's not.

Thanks.

[v8kenny]

3.9 cam is supposed to give about another 8-10 bhp
Maybe not make that much difference in your big lump !
Try Buckley bros. - a 3.9 cam , set of followers and a new timing chain and sprockets (daft not to change them at same time) will set you back about £140 all in
Made a difference to my 110 on su's
Maybe better spending your money on a gizmo that advances/retards the timing when switching between petrol/lpg as there is always a compromise in timing to run both fuels

[thermidorthelobster]

Maybe better spending your money on a gizmo that advances/retards the timing when switching between petrol/lpg as there is always a compromise in timing to run both fuels

I've got one of those, but it actually seems to run better on LPG than Unleaded.  I think it needs optimising.  Another thing to add to the list.

[Budgie]

Rpi do a range of Piper cams for the 3.5 and I'm sure there is a high torque one in there somewhere. If you're paying that much for a cam set then have a look at these before getting one.

Also, have chat with Real Steel (01895 440505, based in Cowley) they will also do high torque cams and also the needles for the SU's to match.  

[veeeight]

I dont really think you will notice much difference unless your cam is shot, you would need to take off the inlet manifold to have a look and see if the lobes are worn, but if they are ok then I really wouldnt bother (if it aint broke dont fix it), I put a 3.9 cam in a 3.5EFI and didnt notice any difference so took it out again to keep for a 3.9 rebuild.
If your gonna do it then its really quiet an easy job, just a bit long winded.
But if you know how to use a spanner then you will be fine.
V8's are [throw it] easy to work on, I love them, you cant go wrong.
If it aint got a V8 then I aint interested.

[Range Rover Blues]

The big difference between a 3.5 EFi and a 3.9 is the cam.  Some of it is down to the exhaust (which is way better on the EFi anyway) but mostly the cam.  If you don't notice any difference I'd be surprised.  Whether it's worth the cash.....

If yours is the SD1 engine, what about fitting EFi heads at the same time? 3.9 cam and decent manifolds, even if they come from a carbon steel 3.9 system they would be better than what I suspect is there already.

As for the LPG, you are loosing a few Hp running on LPG, I find an advance of around 5 degrees makes up for about half of what is lost with my timing on 5deg to begin with (9.35:1).  Those advance modules do seem fragile though, mine is always sulking, doesn't like the damp.

If you are fitting a performance cam think about a vernier pulley at the same time, a performance cam poorly timed in will be worse than a stock cam set within tolerance.

The trick to performance/economy tuning is engine breathing.