Alternator
 

So, I have been reading the archives and from what I have read I can swap a 2nd gens alt into my 1st gen with little to no modification. My question is, is 80 amps going to be enough because right now my amp is making my light and stuff dim but I don't want to do the upgrade only to find out I still need more power.

It's not a straight swap for starters...

I have attached 2 diagrams from my primary rotary forum: (ausrotary)

1)Diagram Series 1,2,3 (generation 1) to series 4 alternator
2)Diagram Series 1,2,3 (generation 1) to series 5,6 and falcon alternator (pulley shaft size changes from 15mm to 17mm so MACHINING of the pulley of the early rx7 pulley and spacer is needed) the falcon is from a ford falcon, no idea what you US guys call it.

I still have the orginal alternator in my car and it has no problems. It is running 3 fuel pumps and all electrics fine. I run no stereo though, all stereo stuff I have removed. Consider removing your stereo? :lol:

Cheers,
vr4_killah

I don't really agree with those diagrams. They may work okay, but they are making things much harder than they need to be.

1. S4 ('86-'88) are 60-70A (depending if NA or TII). They are a straight up swap. The only thing you may want to do is replace the output wire with something a little larger.

2. S5 ('89-'91) are 80A and are close to a straight swap. You just have to change the connector and replace the wire that is switched 12v to a constant (battery) 12v.

3. 3rd gen ('93+) (100A+) are wired like the S5, but you need to swap the pulley.

You don't need the relay as shown in the S5 diagram above. You also don't need the FC fusebox, but may want to consider it depending on how many additional circuits you are running (for amps and such).

For how big of an alt you need, we need to know what the rating of your audio setup is. What is the RMS power or what size of fuse(s) is/are on the amp(s)?

The stock alt is only about 55A. There are a few other options too if the 3rd gen alt is not big enough.

On a S5 alternator, 2 things you have to do:
1. white/green or blue stripe: to the B terminal for constant 12V.
2. the other pigtail connects to the stock FB 2-wire pigtail

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Watts = Volts times Amps (W=V*A, classic DC power formula). By algebra, that gives you:

Volts = Watts/Amps
Amps=Watts/Volts

Working at 13.8volts (nominal charge voltage), divide your required Watts by 13.8 to get your amperage draw.

Keep in mind though that a "100-watt" amp is talking about it's maximum AC output power, fully cranked up and on a pink-noise test signal, and that it will waste around 25-40% more power (depending on design) lost to internal heat. Normal listening volume with a normal audio signal is much lower. It's not talking about supply draw power, which is DC Watts.

In other words, a 100-watt amp doesn't draw anything near 100 watts, normally.

Best bet is to either look at the amplifier spec sheet for a specific input power requirement, or do an actual current measurement while running it from battery at your loudest intended setting.

And don't forget that the car needs power, too.

S4 is a direct bolt in swap for bling.

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