Guy's

Running 260z with MSD 6AL. Notice that when I turn the main headlights on idle rpm drops noticeably(300~ 400rpm). Running a stock alternator. Any one had a similar experience ?

Eitherway was looking to upgrade Alternator anyway - what are the popular choices ?

Thanks for your help.

That is not uncommon. Cleaning all of your electrical connections will probably help. Fusible links, fuses, etc.

The problem isn't the max capability of the alternator but the output at idle. They are somewhat related but not directly and not consistently from what I've found. I had a parts store alternator that had poor output at idle, while an old factory unit barely noticed the loads at idle. Might be worthwhile to just get a new alternator and/or clean all of your electrical connections first.

Check to see if you have a 50 amp or 60 amp alternator first. That might be the easiest upgrade for you. Apparently the 260Z used either a 50 or a 60 amp alternator from the factory. LT150-10 or LT160-23 (numbers from the FSM). There aren't many easy upgrades, if you're already at the 60 amp standard that was used through 1983, unless you spend some money.

Check out Hybridz.org for alternator upgrade options. I "pioneered" a GM CS144 swap based on an earlier write-up for a CS12 swap. This helps tremendously with power output at idle, but I was also running an L28ET with GM LS1 coil on plugs, electric fuel pump and fan in my 240z. Your issue is most likely due to corrosion in the connections and 40 year old wiring. Upgrading the alternator is just a ban-aid fix.

I got one of these 125 Amp High Output Alternator: Engine Z - Electrical & Tune Up - 15009-EPEE - Z Specialties Online Store - If we don't have it in stock, we can get it!. I like this one because I didn't have to splice in a diod and I could get rid of the external voltage regulator. Though I did have to bypass my amp meter.

Hodgimus, that looks like a good unit but listen to these guys when they say the connections are more important.

Power connections as well as grounds.

Lust did the upgrade this week end. got the 145 high output fom Z specialties. could not be happier. hooked right up lots of power nice unit.

If you are still running a voltage regulator, that is probably your issue (in addition to the dirty connectors as mentioned above). Below is a link to my alternator replacement: Dave's 1972 Datsun 240z: Alternator Upgrade

thanks for your inputs guy's. I do have the rear light & headlight harness upgrades which bypasses some of the car's potentially 'resistive' wiring.

The more I think about this the more i wonder about the way the external voltage regulator & MSD are working with each other. May be even worth swopping the Alternator for a 280zx unit just for the internal VR - the cost would not be great (~ $80 ?).