Some of the more recent Duratec versions uses a larger front pulley trigger wheel than before. The trigger wheel diameter must match the style of the engine front cover, at least if you plan to use the standard crank sensor and mount.
Also, if the pulley size is large on high rpm engines it may cause the alternator to over-rev, and the water pump could experience cavitation that causes cooling problems. It is also said that unnecessary power is lost. For these reasons aftermarket under-drive pulleys are available in various models.
On the picture above there is to the left a 164mm under-drive pulley, in the middle a stock 146mm old style pulley, and to the right a stock 164mm pulley.
Aftermarket underdrive from TTV Racing.
Weight: 776g
Trigger wheel: 164mm
Pulley: 100mm
Alternator rpm @7800: 13000 rpm.
Waterpump rpm @7800: 7428 rpm.
Stock old pulley
Weight: 1529g
Trigger wheel: 146mm
Pulley: 137mm
Alternator rpm @7800: 17810 rpm
Waterpump rpm @7800: 10177 rpm
Stock large pulley
Weight: 1949g
Trigger wheel: 164mm
Pulley: 155mm
Alternator rpm @7800: 20150 rpm
Waterpump rpm @7800: 11514 rpm
The alternator pulley above is 60mm, water pump pulley 105mm.
According to the book Four-Stroke Performance Tuning by A. Graham Bell, a water pump's maximum efficiency zone is usually between 4000-6000 rpm.
A good article/calculator addressing how the pulley weight affects power output can be found here: http://hpwizard.com/rotational-inertia.html#flywheel
Weight: 1949g
Trigger wheel: 164mm
Pulley: 155mm
Alternator rpm @7800: 20150 rpm
Waterpump rpm @7800: 11514 rpm
The alternator pulley above is 60mm, water pump pulley 105mm.
According to the book Four-Stroke Performance Tuning by A. Graham Bell, a water pump's maximum efficiency zone is usually between 4000-6000 rpm.
A good article/calculator addressing how the pulley weight affects power output can be found here: http://hpwizard.com/rotational-inertia.html#flywheel
