The principle behind the underdrive pulleys is to reduce power drain to the alternator and water pump - so effectively these items run slower. You are not so much gaining power as not losing quite so much. The makers build in a certain amount of leeway but on a cold night with the lights, heater, wipers and radio blaring you can max out so if you do it wrong your alternator will no longer deliver enough power - well maintained cars should be OK but the makers play it safe for a reason.
It worries me a little that the cooling is also operating at reduced speed so you really should get an oil temp and water temp gauge fitted at the same time so you can keep an eye on things.
IMHO it's not much of a gain for the effort although it is a very cheap mod. You may look to an electric water pump as a compromise which is intelligently controlled rather than engine RPM dictated so less power is taken from the engine. If you have ever tried turning a water pump over by hand you will realise the amount of effort taken. |