I'm replacing a 327 with a 454 and need to purchase all new brackets, accessories, etc. and was wondering if an alternator upgrade should be done as well. I'am running an electric fan and a MSD distributor but besides that I don't have any other major items (a/c,pw,etc.)that would require more juice, although I would like to add an MSD 6AL box in the future. My first question is how can I find out how many amps my current alternator is producing and how high should I go with the replacement? I'd rather not get into re-wiring the car just yet. Oh, and how can I tell if the regulator is internal or external? Thanks!

My suggestions:
I like the Delco 10SI or 12SI alternators over the aftermarkets. Drop in fit on all Chevy engines if they are clocked properly. Some good reading in the attached link. Wes Vann's tech reference article will help you make the conversion to internal if you have to do it. Not hard to tell the difference between an internal and external. That connector pins go different ways. An external CS alternator has pins going (II) while the internal regulated alternators have pins going (--) as shown on the 10SI (internal) in the picture. The alternators are stamped with a number like 37A. Assume that is the amperage output that you have.
http://www.madelectrical.com/electricaltech/delcoremy.shtml

I'll agree with John. The 10SI is a very good external replacement if you're not adding any heavy electrical loads (electric fans or BIG stereo). The 12SI is a good 94A unit for an electric fan.

A lot of people tote on the CS alternators but I've read/heard about more early failures with them and they're more expensive. Just enough to make me leary of them.

I think the electric fan will be too taxing for an older externally regulator alternator.

Peter

Your electric fans could possibly need up to 20 or so amps, the headlights w/brights on might be 8 to 10 amps, and the MSD 6AL consumes 8 amps at it's highest output. If you add it all up, you would probably need a minumum of 40 amps to keep from draining the battery during the worst-case periods such as at extended idle at night. If you have any type of newer stereo w/ bigger amps then add that amperage to the total.

The biggest issue is that the amp rating for all alternators is a number produced by the alternator while at it's maximum output AND while being driven at a specific rotational speed that is higher than the speed it operates at idle in the car. The idle speed amperage output is dramatically lower than it's rated maximum output.

The biggest benefit of the newer CS130 series alternators is their higher idle rpm output than any previous series used on GM vehicles.

The most common divisions of alternators among GM vehicles past and present are:

10DN - 60' to early 70's externally regulated

10SI and 12SI - early 70's to late 80's internally regulated

CS130 - early 80's to present internally regulated

Your local auto parts store would probably test your alternator for free and tell you which type you have. Do a little more research before you decide which type to install.

Good luck,

Louie

Thanks for all the info, I did a ton of reading on the M.A.D. site (great link!!) and it looks like I have an external regulator. I couldn't find the amp rating with the alt. on the car so I'll wait until I have things apart during my engine swap. I'll probably put my old alt. on the 454 (new engine) and maybe do the conversion to an internal 12SI, 94 amp. next winter because right now I have a single fan and would like upgrade to dual fans. Thanks again for all your help.

I will throw my 2 cents in (though it's probably worth a penny). I purchased an upgrade kit for a bad 12SI I had sitting in my garage and installed it on my 71 Chevy pickup which had the original externally regulated VR. If memory serves me, I purchased all the parts from here (http://www.alternatorparts.com/) to upgrade my 12SI to 140 amps. It took less than 30 minutes plus it gave me the opportunity to paint the casing.

On my Chevelle I am running a 7AL2, CSI Water Pump, twin electric fans and a Barry Grant BG400 fuel pump. It kills my 63 amp 12SI....I will be upgrading it to 140 amps. graemlins/thumbsup.gif

Oops, I forgot...I purchased a $15 conversion harness (externally regulated to internally regulated) from here. It made my life alot easier...It's seems they have them for Chevells too!

http://wiringharness.com/custommods.htm