Triumph Repair: TR4A - Timing Fast Road Camshaft, coolant temp, road cam

Question
I have just installed a rebuilt engine into my 1966 TR4A.  The engine has 87mm pistons and a piper fast road cam.  My problem is knowing where to start with ignition timing for the cam.  The cam was bought from a friend, it is secondhand but had been checked out by piper.  Piper also provided installation data:  Timing - 26 - 66, VL 0.417", VC0.012", FL 110", TDL 0.054".  I phoned the factory to ask about ignition timing figures but they said they couldn't help, they don't keep that information.  Could you advise where I should start?  Is it just trial and error?
Many thanks
Tim

Answer
Hi Tim,
The appropriate ignition timing for any engine that has had any modifications is dependent on many factors and that is why the cam manufacture could not quote a timing. As soon as you alter anything on an engine, you alter what is the best timing. You have also altered the best advance curve.

Even the car manufactures need to compromise and set the advance curve below best timing and they just set it to a general setting.

Detonation is the problem. The most horse power in ignition timing is just before detonation (misnamed valve rattle, valve ping). Because of small differences in each cylinder ignition timing has to be set a little retarded so that the worst cylinder will not go into detonation.
Some new cars have an ignition system that can adjust the timing of each cylinder to it's optimum.

For you to get a good advance curve and total timing you would need access to a dynamometer and a distributor machine. If you had these you would not be asking about it. All is not lost though. It is possible to get in the ball park with timing.

Keep in mind that detonation can and will destroy an engine in a very short time.
You should do all your testing with the gas you intend to use and the engine must be fully warmed up (not just coolant temp but oil temp also) To get a base for low RPM setting loosen the distributor and with the engine idling snap the throttle open a few times and note if you get the sound of "Pinging". slowly advance the distributor and open the throttle several times and keep advancing the distributor until you get the Detonation (Ping). Then check the idle ignition timing and write it down. That is you dead limit for low RPM in timing. I usually use about 5 Deg. less for my lower limit.

This is only the low RPM limit. As the RPM and load increases the chance of higher RPM detonation still is there. Now you need to locate a steep hill and climb the hill in the next higher gear than you would normally and apply full throttle and note if you get any detonation. If so you need to back the timing off another 5 deg. Don't keep doing this test as "Lugging" an engine is also a good way to destroy an engine.

If you want to keep your freshly rebuilt engine good you may need to spend some money by getting a knock sensor display system like the one MSD has. High RPM detonation is not easily heard like low RPM is.
You can have high RPM detonation that is destroying your engine and you will not even know it. A knock sensor display system allows you to see detonation real time and thus you can take steps to correct it.

Many things can cause detonation like ignition timing, engine temperature, Air temp, Altitude, grade of fuel, oil burning, engine load, fuel mixture, Incorrect spark plug heat range.

I know all of this seems overwhelming so you should be able to use the factory timing until you decide to purchase a knock sensor system then you can do all the low and high RPM tests.
Howard