Thread: 3.9 Camshaft Upgrade

Originally Posted by Richard Kaye

Basically, after more power/torque across the whole rev range

That is not how it works. You must lose something in order to gain something.

Originally Posted by Richard Kaye

I have been looking for an upgraded camshaft for my 1988 Range Rover. All I have managed to do, after reading about camshafts, is to confuse myself. Some companies are claiming a 22Hp increase, and extra torque, is this achievable?

The engine is a 3.9 litre v-belt with distributor. It has 9.5:1 compression, the heads are stage 2, and it has a 5-speed manual gearbox with standard size tyres. It runs on LPG though a BLOS mixer and has the standard EFI intake manifold. Currently have an ER5924 in the car. Spends most of the time on the road, do very little in the bush.

Basically, after more power/torque across the whole rev range

What have people used that they could recommend, or has anyone tried one which didn’t work out and I should stay clear of? I would like to fit one in the next few weeks.

basically yes,

realistically no.

moer torque= more power at given RPMS however all out across the board improvements are rare, if the cam makes it breath better down low it will suffer at the top end, if it makes it breath better at the top end it will suffer down low.

That said... if you stick to the normal driving RPMS the rover v8s were already happy running at you can have an improvement across the whole range because your taking it away from areas you dont normally run the engine in. You can take all the performance you like out of the 4k+ rpm range and not worry about it if you never spin the engine that fast. SImilarly if you never go below 1500rpm, you can pull almost everything you like out of the revs below that as you only need enough there to get it to start and idle.

the biggest issue is... Fueling it. if your injection management system isnt setup for the cam, it'll run too rich or lean in some areas.

It's been said before - to make a gain somewhere, you sacrifice something else in order to achieve the desired gain.

You have an LPG setup, which has different operating parameters for power and efficiency. This will be key in deciding your cam profile choice. Dual fuel or LPG only, will require some other sacrifices beyond the physically obvious of fuel system duplication.

It's a case of knowing every detail.
Unfortunately, "stage 2 heads" means very little to anyone other than the person who ported / modified them - unless you have the flowbench numbers matching the valve lift figures.

That is ultimately what a cam grind should use for reference and noting the head CC and swept volume, some basic calculations can be made.

From there, you have endless other parameters. hydraulic or solid or roller lifters, rocker ratio, port volumes (equal or not?), the list goes on -

Intake runner length, plenum volume.. exhaust primary length, diameter...
Then you might not have a standard bottom end either - o/s pistons? longer or shorter rods (resized?) offset ground crankshaft (stroker?) so many variables, that the cam selection process needs to take into account to make it efficient and fit for purpose.

Camshafts can be generic profiles for the most part - and those may be suitable - but they may also be inefficient, or rob you of power in a place where you currently have (and need) it.

The only way to go forward is to get all the information you can on your engine, and give that information to one of the few specialist cam grinders locally.

Try Clive cams, Waggott engineering, Tighe, Crow. All of them will want to know detail, so make sure you have the info before you seek their advice.

Here's an off-the-shelf list from Tighe in Brisbane (below). You'll still need to do some homework to work out which direction you want to go, if you want to modify lift profiles or reduce the LSA in order to get more power from the same profile, beware that you will lose low speed vacuum when reducing the LSA.
Whoever you choose to grind your cam- make sure you get them to supply a matching set of new lifters, and if you haven't already got an adjustable timing gear, I humbly suggest you invest in a quality adjustable timing gear and chain set. It WILL be necessary to get the timing spot on.

good luck. More research required and more data needed.

Screenshot 2023-10-12 at 12.28.42 pm.jpg

What is the maximum valve lift without altering the springs?

Looking at a cam with .450 lift and 296 duration, I think it's the RPi285 camshaft.

The answer to that is how long is a piece of string..

1. Installed height vs free length differences
2. Also depends on the valve stem length (tip) retainers and collets AND rocker ratio.

None of this is verifiable without physically measuring.
This is especially important for a modified head - because the valve pockets may have been machined, new guides may have required the valve spring seats to be modified, or the springs themselves may not even be stock spec, or perhaps none of them are even equal installed heights.

Only way to know is to physically check - and to be fair - this is something that should have been done (provided) when the heads were modified (ported).

Spoke with the person that ported the heads.
Valve guides were not changed, and the valve height was set back to standard after the valves were reground and seats cut, he said it is back to stock figure in terms of valve stem length and installed height.
Also spoke to a company who can supply valve springs good for 0.525 valve lift.