Underdrive Crank Pulley - BMW Forum

M3Daemon · 04-04-2004, 08:31 PM

Has anyone underdriven the crank pulley? Do I need a shorter belt if I do it? I know there are underdrive pulley kits available for particular accessories but which option is better (crank or accessories)? Or could I do both?

Daemon

Kevin325i · 04-04-2004, 09:33 PM

Underdrive pulley kits ussually give you new pulleys and belts that will work, but i suppose it would be possible to buy your own parts.

Either way I think most underdrive pulley kits make a note that your cars idle won't be able to charge the battery properly. Which doesn't sound like much of a problem unless your constantly in traffic. Sorry i didn't have more info.

dutchbmw · 04-05-2004, 05:27 AM

What's the purpose to install an underdrive pulley??

Andrewsd1985 · 04-05-2004, 06:34 AM

Underdrive pulleys rotate less tha the stock pulleys allowing your engine to do less work in turn giving you more power. Check understeer.com for some advice on the pulleys, the say underdriving everything except the altenator is ok. You can do the altenator but it doesn't do much for engine power and charges slower.

Andrewsd1985 · 04-05-2004, 06:34 AM

Also have you heard of the fan delete mod? Its on the same lines as underdriving.

M3Daemon · 04-05-2004, 12:21 PM

UUC Motorwerks and understeer.com seem to have quite a difference in opinions there. I will get more into it in the next couple days.

I was thinking about the fan delete mod but it's extremely hot where I live and I don't want to take chances during the summer.

Daemon

dutchbmw · 04-05-2004, 02:10 PM

The required power for the alternator is max 1.5 kW....lol

Kevin325i · 04-06-2004, 01:45 AM

Quote:

Originally posted by 325i_daemon@Apr 5 2004, 11:01 AM
I was thinking about the fan delete mod but it's extremely hot where I live and I don't want to take chances during the summer.

Why not install an electric fan? Mount a switch inside to flip on when it's a hot day, or I imagine it would be possible to rig it up to a thermostat. I haven't seen any kits for BMWs though.

Anyone else with more info?

Andrewsd1985 · 04-06-2004, 06:57 AM

When doing the fan delete mod you actually change the fan switch to one that kicks on your auxillary fan at a lower temperature along with the new thermostat. You can upgrade your fan to one with a higher cfm rating, but i'm not sure what the stock cfm is. Where do you live that it is so hot. I live in florida and plan to do this mod this summer. If i do see my car getting too hot its not that big of a deal to throw the fan back on.

M3Daemon · 04-06-2004, 07:58 PM

Quote:

Originally posted by Andrewsd1985@Apr 6 2004, 07:37 AM
When doing the fan delete mod you actually change the fan switch to one that kicks on your auxillary fan at a lower temperature along with the new thermostat. You can upgrade your fan to one with a higher cfm rating, but i'm not sure what the stock cfm is. Where do you live that it is so hot. I live in florida and plan to do this mod this summer. If i do see my car getting too hot its not that big of a deal to throw the fan back on.

I live in Mobile which is about 20miles from the Florida state line. Keep me posted on how the fan delete mod works out; I might do it after all...

Daemon