What is an Underdrive Kit?

Another great question this week on Steve’s TikTok.

The follower asked, what is an underdrive kit? He is curious to learn about the purpose of it.

Steve has graciously given us one of his wonderful explanations. He replies….

“So, an underdrive kit is basically a slightly smaller crankshaft pulley, to reduce the RPM of the alternator, air conditioning and power steering. Basically, any of those. 

I believe on a commodore they create around a 15% reduction in speed. Apparently its to give you a little bit more top end power. 

free quote

But, I would say personally, I like air conditioning and I like an alternator working at idle. So, unless you are running drag strip all the time I generally wouldn’t bother. And then you’ve got the opposite side which is if you have got a supercharged one, so LSA or whatever, you get a 10% larger pulley to make the supercharged spin faster. 

So, these are all the differences in them, I guess! 

But, primarily that is what it is. It’s to give it a little bit more power “



If you want to ask Steve a question, then make sure you firstly, follow him on Tiktok, and then throw him a question on one of his videos! He loves to give insight, debunk myths and share his opinion on all things mechanical.

If you are on the Gold Coast, then bring your car to us for its scheduled service. We are Repco Authorised, meaning we have nationwide warranty on all repairs.

You can book your car in for its service through our website, via our app (Google or Apple) or give us a ring and chat to our friendly team in the office.

Be sure to explore the rest of our blog page for other great topics and learn more about your vehicle!