| Author | Message | ||
     Bob uk Unregistered guest Posted From: 94.197.122.74 |
The sole job of a spark plug is to light the fire A more powerful spark does not light the fire more and does not give the engine more power So all that is needed is enough spark at the right time One of my neighbors fitted a £100 worth of new ignition bits to his 1969 Morris Oxford which ran fine thinking that the new parts would give a better spark and therefore more power According to the oscilloscope the spark from the "sports" coil the spark is 10% stronger The car runs the same and he is disappointed The coil looks very flash but does nothing better than standard It has a starting handle and I can still start it at my age Good car (Message approved by david_gore) | ||
| Jan Forrest Grand Master Username: got_one Post Number: 555 Registered: 1-2008 |
Since you're talking about older cars with older parts - especially carbs with most probably worn jets and butterfly bearings - the fuel mixture entering the combustion chambers might not be properly atomised to 'light up' efficiently. A fatter spark could overcome this and improve fuel efficiency. However the long stroke Oxford engine is so low revving that there's more than enough time for a slow combustion wave front to 'catch up' with the fuel before the piston reaches TDC and the exhaust valves start to open. After all, they were designed to run on the poor quality jungle juice that was available at the time. In the early 70's I ran my Moggy Thou Traveller on neat paraffin! It pinked like buggery while accelerating, but it ran. By all means compare apples with apples, but not apples with courgettes. | ||
| Bob uk Unregistered guest Posted From: 94.197.122.71 |
A fatter spark does not make the charge burn faster Pinking is the charge burning totoo fast so timing is set to suit But as you say wear can cause the std coil not hot enough to overcome the fault such as oiled up plugs This engine is a very smooth free revving unit with no faults Also it has about the same specific output as my shadow 40bmp per litre If the Oxford had been tuned was being used at high revs 6000rpm then a fatter spark may necessary I made the posting because I find so many talk as though a spark plug adds power to the engine Average coil uses 4 amps at 12v 48 watts which is not a lot of horse power The spark is part light and heat (Message approved by david_gore) | ||
| Jan Forrest Grand Master Username: got_one Post Number: 557 Registered: 1-2008 |
As implied; a more efficient spark plug can help to cover up a multitude of minor ignition/fueling issues - for a while. You can do much the same by replacing any one of several components in either system. However nothing beats having them put back into original (or as close as possible) condition. All it takes is time, money, patience and access to the correct parts. Not everyone has all of them to hand at a moment's notice, so the temptation will always be to buy whatever new 'miracle' item has popped up on the car spares shop shelves. For the relative minimal cost I usually fit iridium plugs as they have an alleged 100K miles lifespan. I suppose it helps that I run my Shadow mostly on LPG, so it needs all the spark it can get. But ... I have to disagree with your primary assertion. A fatter spark will serve to give a faster and more efficient combustion! Conditions inside the combustion chambers are more conducive to detonation than they are in free air at a mere 15psi rather than the 120+psi inside the cylinders. This why 'we' used to add tetra ethyl lead to petrol: To reduce the incidence of detonation rather than the clean burn we require. A damn good flame front can prevent this without resorting to such toxic metals by burning up the fuel just that bit too fast for it to be able to detonate. With the 'correct' spark plugs and waiting for the engine to warm up first, the 'Little Grey Fergie' was designed to run on paraffin! We had one at the breaker's yard I used to work at back in the late 70's. As so many cars came into the yard with petrol in the tanks we never had cause to try it on paraffin - neither did any of us have to buy much petrol for our cars! |
