Good deal on V8 camshafts but help me choose one

So assuming I have high compression then I would not want the early low comp cam as this would induce pinking due to the valves shutting early and increasing compression further. So now what cam to use. I am thinking maybe Rover car cams? These coped well with high compression and still manage to run on todays fuel. Or the high comp cam, but its a bit gutless.

But if I am wrong and end up putting a fast road type cam in a low comp motor. will that matter too much?

Me thinks I need to check compressions.

Can I check compression with no front cover on motor. Will it be ok to just put oil down bores before I turn it over? cheers

I dont see why not, but you'd be better off pulling the heads and doing some proper measurements. It could also be another problem, something stupid that you'll kick yourself for missing. I'd start by checking for evenish lift at the rockers - could be a worn cam, even with a freshly built looking motor. also check the pushrods aren't heavily loaded when the valve is home, double check static timing as per philips sugestion etc

compressions 170-175, 1@190 and 1@185psi in a 3.5, cold engine.

Plugs were dry and that includes heaps of turns of the engine with no spark, two plugs had hard creamy deposits on them. Was the mixture too lean?

It has K&Ns on it and the inside of the carbs was pretty dirty, I'm guessing in no small part to the oil of the airfilters. Blocked or dirty jets?

before I stripped the gear the idle was very smooth. and ran alright (even under load) if a bit lackluster until the engine got warm when it would pink badly under load.

Is the cam in conjuction with the higher than standard compression most likely to likely cause be the pinking. Or is it just a lean mixture due badly maintained and set up carbs.

If I can get way with it I would rather not pull the cam and heads as I would rather spend the time and money building up a 3.9 (some day). But if the cam and compression will never let this happen then I will have to do the cam now.

Really I just want this thing to go well enough to drive about until such time as I do it properly.

Any thoughts

Cheers

The comp figures are on the high side.

K&N's dont filter as well but are less restrictive which means the carbs may need to be adjusted a bit richer to compensate. A lean mixture can cause/ contribute to detonation. Before you get too carried away, I'd try a richer main jet setting setting in conjunction with premium fuel. Also keep backing off the timing until it stops pinging, without regard to the timing marks in the first instance and see how it runs. Have you tried it with another distribuor (could have broken advance springs) Do you have a vacuum gauge? - they can be used to set timing. I'd also be interested know what your idle vacuum is. Is lpg an option? It likes higher compression as the octane rating is > 100.

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compressions 170-175, 1@190 and 1@185psi in a 3.5, cold engine.

Plugs were dry and that includes heaps of turns of the engine with no spark, two plugs had hard creamy deposits on them. Was the mixture too lean?

It has K&Ns on it and the inside of the carbs was pretty dirty, I'm guessing in no small part to the oil of the airfilters. Blocked or dirty jets?

before I stripped the gear the idle was very smooth. and ran alright (even under load) if a bit lackluster until the engine got warm when it would pink badly under load.

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Well the compression figures indicate a high compression engine but it should run on 98RON without pinging.

The 180 and 195 cylinders suggest badly carboned up combustion chambers and these may be what is pinging. I am a bit baffled by the creamy deposits . They suggest use of leaded fuel such as AVGAS. PO ran AVGAS?

If I were you I would still check the springs in the dizzy. A quick check would be to get a timing light and slowly rev the engine with the vacuum advance disconnected and plugged, and see what advance you get . It should not fully advance until 4KRPM.

The carbs do not have any jets to clog! LOL. There is just the main jet and needle . Maybe add some engine oil to the dashpots and make sure the diaphragms are OK.. I wouldn't worry too much about richer jets as they richen up over time as the needle and jet wear.


If you are sure the advance is correct and the timing is correct, an "Italian Tune Up" may be in order. Load up a trailer on the back and run her up some steep hills at WOT. Maybe after adding some octane booster to 98 . Of course don't let it ping its head off but if you have some revs on board it should not ping too much.
Regard sPhilip A

I have changed the distributor for new electronic one as per the efi engines. It was this process that led me to destroy the oil pump and distributor gear. That is sorted now. From what I cam make out the compressions are around the same as a high comp 3.5, having just done a mates one. I tracked down the previous owner who said that the guy he got it off had told him that it had a mild cam done and Im quessing he did the head etc at the same time.

I am going to check the valve timing then just put it back together as is, then concentrate on sorting the mixture and ditch the K&Ns.

cheers

Not back together yet but when I looked up the spark plugs I found that is had long reach plugs fitted when my engine should have short reach. Could this have cause the **** running?

Yes possibly. The thread edges may have got hot.
Anyway put in the correct plugs and see.

Regards Philip A

finally got in to it yesterday. So as far a I know, the only change I have made is the spark plugs. It had long reach in it and I have changed then for the correct short reach which a 1975 engine should have.

Its a rocket!!! No pinking at all!!!!

Well for a 3.5 is goes better than any other I have ever driven. A rocket might be over doing it, but I have recently driven a couple of tweaked 3,5 injected Rangies and mine would wipe the floor with them. I am still trying to work out the pedigree of the engine but as yet no luck. Past owners not forthcoming so I have no idea of the spec of my engine. The power does not come on really untill about 2000 or more but still manages to be tractable at low revs and idles well. Its a nice engine to live with. It is booked in to be fitted with the twin down branch system off an injected motor so that should make it even better still. Yes header are even better bu tI got the manifold and down pipes for free.

So all this stress for the sake of some numpty, a well know mechanic in town, fitting the wrong spark plugs in. His loss.... me very happy!!