I keep hearing about these underdrive pulleys but don't understand what it is. Is it a smaller, lighter bottom pulley or what? I've been working on cars in the motor trade for 14 odd years, just having trouble with the lingo. I have an N/A manual import, any serious poer gains from this mod?

yep you got it slightly smaller main pulley normaly made from aluminium so quite a bit lighter as well helps with power gains.

10-15hp increase apparantly, although the biggest difference noticed is the ability for the engine to rev quicker, making it more responsive.

There is a group buy being organised for headers at the moment, these are supposed to give the biggest power gain for an NA.

just done a cambelt on the car and didn't think it was that heavy for a bottom pulley, is the underdrive drive that much lighter to make a difference?

There is a BIG difference in weight.

does it affect the power steering or A/C efficiency?

Probably does a little bit and also the cooling which is probably a more important side effect of the lighter pulley also being smaller but they are minimal and I personally have not noticed any difference in all the time mine has been fitted.

I'm only getting about 21 mpg for my N/A, i was told that the TT's do this as well, wondering if i should have bought a turbo.

I'm only getting about 21 mpg for my N/A, i was told that the TT's do this as well, wondering if i should have bought a turbo.

Thats been done to death mate and people will never agree, but there are not many Zeds TT or otherwise that I would swap my NA for.

Is the underdrive drive that much lighter to make a difference?

 

A lightened Underdrive Pulley is 9lb lighter than the stock pulley.

According to some reports, a 2.5hp increase can be gained for every pound taken off the pulley. That's approx 25hp gain.

However, I agree with Dave (Legrath). The main difference you'll notice, will be the the engine revving quicker and feeling a lot more responsive.

There are not many Zeds TT or otherwise that I would swap my NA for.

 

There are no NA's that I would swap my TT for :tongue: :tongue: