The side effects of underdrive pulley kits?

[Ian.G]

Hi folks,

I am maybe going to order some new inner tierod ends for my hachi very soon as one of them has some play in it. I may end up ordering some of the ueo-style 'branded' ones so It may pay to get a few more bits at the same time.

One of the other things I am interested in is a lightweight underdrive pulley kit as I am hoping to get my engine overhauled soon and makes sense to do at this point. Maybe like these



I know they are often lighter and lead to less mass the the engine to drive - but I also believe they can alter the gearing of some of the ancillaries on the engine - in these cases maybe the alternator and water pump.

Does anyone have any experiences of running these on a 4AGE?

[Dogs Danglies]

I dont know about running them on 4age's, but I've underdriven a old skool Triumph TR5 race car before by fitting a smaller crank pulley, It supposedly helps engine cooling at high speed, as the water pump was 'aireating (sp?)' the water, also adds maybe 1-2BHP at most, by reducing wasted power spinning the alternator, and W/pump, too fast . It did tend to over heat at idle, due to slower water pumping speed.

IMO the reduced weight, will do sweet FA, in increasing engine responce by reduced mass, if you want throttle responce loose 5kg off the flywheel, saving 100g at the pulley wont make any difference.

Maybe an Underdriven 'harmonic damper' pulley would be cool, as it helps dampen crank vibration, and helps an engine pull higher revs, safer, and with less vibration

[Aico]

Do NOT use these unless you're always driving above +-4k RPM.

[BenR]

DO NOT use at all.

When you replace the crank pulley on the nose of the crank, you remove the only form of harmonic dampening there is.

You can run a larger waterpump pulley to stop cavetation, but do not replace the front pulley.