What is Twin Spark ?
Discussion
The old 8 valve twinspark used both plugs to fire on the power stroke of the piston. Burn time of the mixture in the combustion chamber was reduced and, because one plug fired slighly after the other, the pressure wave did not meet at the centre of the piston, and thus risk punching a hole in the piston crown. It offered the advantages of faster flame propagation and a more compact and efficient combustion chamber by using a narrow angle (46 degrees) total valve inclination. The standard 1962cc engine produced 148BHP and 137lbft in the 75TS.
The newer 16 valve engine have two sizes of spark plug. The larger fires on the power stroke, and the smaller plug, which is located to the side of the chamber nearest the exhaust valves, fires on the exhaust stroke. This is purely to clean up the exhaust gases, and burn any unburnt fuel. This is termed 'wasted spark'. This technology is used in most modern 16 valve engines such as Ford and Vauxhall (who also used this in 8 valve engines). The only benefit that the Alfa engine has is that the extra plug is better placed in the combustion chamber and that a different plug is used, which reduces electrode wear. It has no power enhancing benefits, however, and is a poor substitute for the old engine.
The 16 valve engine produces more power, 150, 155 or even 165BHP in the latest JTS engine. However, in 150BHP guise, it only produced 138lbft of torque. Maximum figures do not do the engine justice though, as the torque curve was flatter, the engine was smoother and more efficient, and thus, it is a better unit. However, I still regard the newer unit as blasphemous to the Twinspark name. It does not employ such unique and clever technology. In my opinion, it is a more mundane engine which has less character than the 8 valve.
All in all, progress, I suppose.
>> Edited by Alfa Mad on Tuesday 28th September 00:03
The newer 16 valve engine have two sizes of spark plug. The larger fires on the power stroke, and the smaller plug, which is located to the side of the chamber nearest the exhaust valves, fires on the exhaust stroke. This is purely to clean up the exhaust gases, and burn any unburnt fuel. This is termed 'wasted spark'. This technology is used in most modern 16 valve engines such as Ford and Vauxhall (who also used this in 8 valve engines). The only benefit that the Alfa engine has is that the extra plug is better placed in the combustion chamber and that a different plug is used, which reduces electrode wear. It has no power enhancing benefits, however, and is a poor substitute for the old engine.
The 16 valve engine produces more power, 150, 155 or even 165BHP in the latest JTS engine. However, in 150BHP guise, it only produced 138lbft of torque. Maximum figures do not do the engine justice though, as the torque curve was flatter, the engine was smoother and more efficient, and thus, it is a better unit. However, I still regard the newer unit as blasphemous to the Twinspark name. It does not employ such unique and clever technology. In my opinion, it is a more mundane engine which has less character than the 8 valve.
All in all, progress, I suppose.
>> Edited by Alfa Mad on Tuesday 28th September 00:03
Alfa Mad Alfa Mad said:
The newer 16 valve engine have two sizes of spark plug. The larger fires on the power stroke, and the smaller plug, which is located to the side of the chamber nearest the exhaust valves, fires on the exhaust stroke... This is termed 'wasted spark'.
'Wasted spark' means the plug fires every engine revolution, even though each cylinder only has a power stroke every two revolutions.
I'll take a look at the engines forum, but I've generally found some pretty informed people there.
Andrew, glad we agree. I use strokes as a reference as to when the wasted spark occurs, because some people seem to think that this spark occurs on the induction stroke when the reference is taken as revolutions. The Alfa engine,I believe has slightly different timing of this spark due to the better placing of the secondary spark plug.
Andrew, glad we agree. I use strokes as a reference as to when the wasted spark occurs, because some people seem to think that this spark occurs on the induction stroke when the reference is taken as revolutions. The Alfa engine,I believe has slightly different timing of this spark due to the better placing of the secondary spark plug.
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