Fitting a 3.9 cam to a 3.5 engine

[mr_s]

Is there any advantage fitting a 3.9 cam to a 3.5 engine in terms of torque? I've heard that it can give an extra 10bhp or so, but what would it do to the midrange/bottom end?

Or would I be best getting hold of a stock 3.5 cam. I'm far too tight to buy a piper or a kent cam

All to be going on a flapper controlled 3.5 engine in a Rangie

Oh, and it's also on LPG if that makes any difference?

Cheers, Martin

[badger]

The flapper EFI system needs a certain vacuum level in the inlet for correct metering, any sudden change in this level can cause stalling, hence the flapper-type landrover 3.5 efi's had a totally different cam profile to a carburetted 3.5 engine, to allow them to cope with the load change on the auto versions.
People who regularly claim bhp increases for a 3.9 cam are almost always comparing a new cam to an old one and the difference would be just as noticeable with a new std cam. A 3.9 cam is the same as a 3.5 carb cam, but running 2 degrees advanced. Some landrover engines on carbs had a different carb cam to give a slightly wider torque spread, but still similar. You don't say if it's an auto or manual - if auto, fit the correct 3.5efi cam or you'll most likely be plagued with stalling on selecting "D" due to the low manifold vacuum/idle torque. If a manual, fit whatever floats your boat, I used a 3.9 cam (in a 3.9) with a modified flapper efi system and the efi setup coped ok with the cam change. SD1 used the same 3.5 carb cam with efi also. If rebuilding, get the compression ratio up by using Vitesse pistons - great for lpg, allows you to make use of the higher octane rating of the fuel, increasing torque (and hence power) virtually across the rev range with correctly optimised ignition timing.

[kokkolanpoika]

My another car has got (manual gearbox) 3,5 flapper efi, and Range Rover, sd1/vitesse 285deg cam.
And its running fine. Also heads are cleaned.. CR is 9,35:1
Emissions are ok Co 1,5 and Hc is near 150-200ppm max..
Ecu system is std, only fuel pressure is 3bar@full throttle.. (give extra 4hp at dyno vs 2.7bar fuel pressure) (it gives over 200hp with this cam)

Also my friend has got (auto"gerabox") Range Rover 3,5efi with this 285deg cam. All other parts are std 89 efi, and its also running fine at idle.. No proplem at all..

[mr_s]

Cheers for that Badger, most informative! Mine has an auto gearbox, so I'll most definitely use the 3.5 cam in it. As it's something of a budget engine rebuild, I'll most probably use the stock 9.35:1 pistons in this engine (it'll be a sight better than the low comp engine that's coming out!!).

Marti