Ignition Timing

[Mike Pim-Keirle]

I have a 1965 MGB Roadster with a lightly tuned engine - bored out to 1865cc, head and block lightly skimmed, standard camshaft, K&N carbs. Does anyone have any thoughts on the possible benefit of advancing the standard ignition timing from the factory setting of 13 degrees BTDC??
I am now running on Super unleaded, as this is still E5 rather than E10, so I could probably advance it a bit without risk of detonation, if there were any advantage in doing so.

[Bumpa]

Because fuel is so different now, and most engines have been altered in one way or another, the standard timing settings are probably not the optimum any more. For best results you need an expert to set it up on a dynamometer. Failing that, one thing you can try is to advance it little by little, taking it out each time to see if it pinks (pings) under hard acceleration, or hill climbing in too high a gear. When you get to that point, take it back a small amount until the pinking stops. That ought to be pretty close to optimum.

[Ian F]

X2 on what Mike has advised,

Ian F

[Vic Butler]

I timed my Land Rover by ear about 10 years ago and have never felt the need to adjust it since. I got the engine up to working temperature, slowed the tickover as low as possible, disconnected the vacuum advance, slackened the distributor clamp bolt, turned the distributor clockwise until the engine started running rough then backed off until the tickover speed just started to drop, tightened the clamp bolt and reconnected the vacuum advance. This is how I was taught to do it in my impoverished teenage motoring years. Carburettors and distributor must be in good condition and the fuel mixture correct. The Land Rover has electronic ignition, the distributor and carburettor had been rebuilt before I timed it.
I'll do the MGB GT the same way once I have cured the overheating. It's been neglected for some time due to a hip replacement last June.

[Paul Hollingworth]

Ignition timing is the single most critical setting in tuning a car for performance and economy. Most peoples cars are set too retarded. The factory setting were a good compromise for a standard car and if you set to that you wont be too far off optimum. Most of us have cars that have been modified over the years, re-bored, gas flowed, heads and blocks skimmed so are probably above the standard 8.8:1 compression ratio. The MGB was intended to run on higher octane fuel that the regular 4 star 95 RON. Having said that my car has all the above mods and doesn't pink on 95 RON. In fact I generally try to sneak on a few degrees of advance via the Vernier adjustment above the standard setting. I had been running regular E5 and found my idle was a bit unsteady so I wound off the extra advance on its better now. I've recently had to fill up with Esso premium 98 RON which is reputedly E0 even though its labelled E5. Perhaps I should try sneaking on a little more ignition again. One of the problems with the B series and an old car like mine is that its so rattley that it maybe hard to pick up pinking. Its often said that you can damage your pistons if you are too advanced even if you don't hear pinking so caution is advised. I wouldn't go more that 3 degrees away from factory settings. (11 clicks to a degree ?). I always set my 18G engine to 20 deg BTDC at 1000 rpm vacuum disconnected. This is further up the advance curve. I have checked that my distributer follows the 40897 curve and it seems to. I have replaced my points with Luminition magnatronic, although this seems to have made little difference to anything but it means I don't have to fiddle with points and timing every 6000 miles.

[Vic Butler]

With the micro adjuster on the 25D distributor the timing can be done more accurately. Both my vehicles have 45D distributors unfortunately.