Thread: Good deal on V8 camshafts but help me choose one

I dont think it's going to matter what version of standard cam is fitted. They are all going to be around the same - probably not enough difference to notice. Just changing the cam and nothing else will not transform a standard engine into a fully sick tractor pulling schwarzinegger roid rageing beast. Its only a little rover V8 FFS. Some may be a little bit better on fuel, some may have a slight edge with the torque, but it will be a here or there sort of thing.

OK.There are loads of custom grinds but thats not the issue. To ask a simple question if I may.

of all the stock rover cams only, efi, low comp, SD1 etc..

-What works best if most driving is on road?

and to get back also to MARK2s question,
-whats the best stock cam for off road...?

cheers

The difference between most carb cams and injection cams is that the overlap is less ie the lobe centres are further apart to give a better vacuum signal to the injection.
The 3.9 injection cam follows this rule and is why you cannot/should not use a carb cam with injection..

However the best performance /economy is usually gained at non pollution carburettor cam settings.

As another general rule the lower the compression the less overlap the cam should have to minimise gas "pass through" from inlet to exhaust and the low comp and high comp cams seem to reflect this.

So once again I recommend a 3.5 low comp cam.

I cannot believe the "left field " comments here although most I am sure are TIC.

BTW maybe an idea to increase low down torque would also be to make up some extensions to place bewteen the carbs and manifold. the longer the inlet distance to Throttle the better the low down torque (and worse top end power). It could be worth 100Ft lbs if you believe the blurbs for Jeep carby isolators.

Regards Philip A

Very helpful answer.

Except now I have just removed the front cover to find that the cam chain is nice and tight and the chain sprockets are not the plastic ones that I have seen before. they are more like bike chains. Is this normal for an old engine 1976. So has somebody been in there and has the cam been done?

I have just bought this thing and it pings like mad. Virtually undrivable. Its ok when its cold but as it warms up it pings and has NO power coughing and spluttering. I checked the timing and set it at 6 btdc then backed off to 1. still bad. new diaphragms in the carbs did little to help it either. was starting to play with mixture when I buggered oil pump-dizzie drive on the cam. (Oil pump bound on cover. fixed now.) I run it on the highest octane at the pump.

I thought that maybe a worn cam could have been making it ping badly and figured I would fix it while I was in there. But in light of recent findings I may reconsider.

Another finding is the oil pump gears are non standard high pressure gears as the are bigger than even 3.9 gears, when they should be smaller. These gears were sometimes used in race engines. So have they done the cam at the same time and given me a wild one that pings.

Have they done the heads and raised the compression too much!!F___ed if I know!

Would a compression test reveal whether the comp ratio is too high.

if I squirt a few drops down each cylinder before I test it will it be ok with no oil pump on. Engine blows or burns no oil so I am guessing that the dribble of oil should not give false readings or mask other issues too much.

If I have to do the cam at least I know which I will be using.
Low comp standard.

Help needed please.

Originally Posted by PhilipA

The difference between most carb cams and injection cams is that the overlap is less ie the lobe centres are further apart to give a better vacuum signal to the injection.
The 3.9 injection cam follows this rule and is why you cannot/should not use a carb cam with injection..

However the best performance /economy is usually gained at non pollution carburettor cam settings.

As another general rule the lower the compression the less overlap the cam should have to minimise gas "pass through" from inlet to exhaust and the low comp and high comp cams seem to reflect this.

So once again I recommend a 3.5 low comp cam.

I cannot believe the "left field " comments here although most I am sure are TIC.

BTW maybe an idea to increase low down torque would also be to make up some extensions to place bewteen the carbs and manifold. the longer the inlet distance to Throttle the better the low down torque (and worse top end power). It could be worth 100Ft lbs if you believe the blurbs for Jeep carby isolators.

Regards Philip A

The 3.5 low comp cam has less overlap (62 deg versus 67 deg); less duration and more built in advance than the other cams. From my research so far, all of these parameters, support your view that it will produce the most torque at low revs and make the engine more responsive in the low-mid range, but wont necessarily result in the most power.

BUT,

while an advanced camshaft normally results in more low end torque, it would seem that the risk of pinging increases due to increased cylinder pressure. (the intake valve closes sooner on the compression stroke, leading to more mixture being compressed)

Shouldnt be an issue with lpg but could be with petrol if the comp ratio is already on the high side (as alluded to by hardchina)

I have just bought this thing and it pings like mad. Virtually undrivable. Its ok when its cold but as it warms up it pings and has NO power coughing and spluttering. I checked the timing and set it at 6 btdc then backed off to 1. still bad. new diaphragms in the carbs did little to help it either. was starting to play with mixture when I buggered oil pump-dizzie drive on the cam. (Oil pump bound on cover. fixed now.) I run it on the highest octane at the pump.

OK Nzlandies. It seems you have a problem.
From what you say, it would seem that you have a very high compression as this would be the main cause of pinging. Maybe someone has put Old Rover pistons in with a 10.5:1 CR from the days of 100RON. Some people ( including me) shave the heads also to increase the CR .

.

There is a rough guide for roughly indicating CR. A 8.15 or whatever V8 will have a compression pressure of about 150PSI . If you have say 180-200 then the engine will have a high compression. This also assumes a standard cam.

If the cam is wild , then it should be easily seen as the engine will be cammy and come "on song" in a step at 3000RPM or whatever. A standard cam should pull away in 4th gear from less than 1000RPM and idle smoothly at 550 RPM. ALso EVERY cam spec I have ever seen for an aftermarket cam has a high lift of .43 or more while every standard cam has a low lift of less than .4 inches measured at the lifter. So that can be an indication.

You should also check that the timing marks are correct and have not slipped from the outer ring of the balancer shifting. You should take no1 to TDC with a gauge in the plughole, likewise backwards , then average the 2 and check how close it is to TDC on the scale.

Another thing to check is whether the springs have fallen off the counterweights in the dizzy.

BUT the main cause of pinging is too high CR for the fuel.
Regards Philip A

Originally Posted by PhilipA

BTW maybe an idea to increase low down torque would also be to make up some extensions to place bewteen the carbs and manifold. the longer the inlet distance to Throttle the better the low down torque (and worse top end power). It could be worth 100Ft lbs if you believe the blurbs for Jeep carby isolators.

Regards Philip A

He could always fit his twin su's to a thor manifold .

Does any one know what cam the 89ish disco 3.5 carbed engine uses?