Amperage Requirement for Terminator Operation

[Big Block Dave]

I've been reading "EFI Conversions" by Tony Candela, and I see that he is very big on having an alternator/charging system which is adequate for fuel injection systems installed on older cars (like my 1972 Camaro). So, I was wondering what the amperage requirements are for the Holley Terminator system (including the ECU and throttle body sensors/injectors), not including the fuel pump/fuel system? Also, if I need to change the battery, should I disconnect the three ECU plugs before pulling the old battery?

[81 TransAm]

Look at upgrading your SI10 alternator to a CS144. They put out 140 amps. More than enough to power your EFI system.
http://www.novaresource.org/alternator.htm

[Big Block Dave]

I was considering the SI12 at 94 amps. This car does not have air conditioning, an audio system or electric cooling fans. The 94 amps might be sufficient for the ignition system (large cap HEI) and the Terminator ECU/Throttle Body/fuel pump requirements. That's why it would be nice to get the total amperage figures for the above equipment. The HEI module requires 4-8 amps (depending on who makes the module - standard GM or high performance aftermarket), and the Walbro GSS-340 (255L/hr) fuel pump requires 8 to 9 amps (at 12 volts or 13.5 volts) to run 40 PSI So, I need to know what the Terminator system (excluding the fuel pump) requires.

Other than that, I think I will take a look at the CS144. I do think it's possible to run too much charging power in these old cars which would probably require a pretty complete wiring overhaul, which I don't want to do unless absolutely necessary.

[Danny Cabral]

I was considering the SI12 at 94 amps.

I ran an aftermarket SI alternator for a while and didn't like it. It had enough amperage to support all my electrical draw, but not at idle! The modern alternators have much better idle output, and are much better for EFI use. For example, my previous GM SI alternator, and my current Ford 3G were about the same amperage capability, but the Ford 3G has so much more idle output. Below is a quote from my EFI Idle Tuning Notes post:

Another aspect of proper voltage is the alternator. Ensure the alternator can maintain the battery charge at idle. This is a big problem with older alternator designs, even if it's a high amp alternator (and they output a lot of electrical noise). However, modern design alternators are capable of producing most of their power (amps) at idle speeds. These modern designs simply have larger stators, more windings, better rectifiers, etc for greater idle speed output. Ford owners can retrofit a Ford 3G alternator. GM owners can retrofit a CS-144 alternator (CS-130 for high RPM racing use). I believe Mopar owners can retrofit a certain model Denso alternator.

[Lurbie]

I do think it's possible to run too much charging power in these old cars which would probably require a pretty complete wiring overhaul, which I don't want to do unless absolutely necessary.

This is not entirely accurate. While you may need a larger gauge cable from the alternator to the battery, it will not require anything else. The amperage output of the alternator is always in response to the amperage requirement of the system connected to it. In other words, you could have a 140 amp alternator, but it is not always outputting 140 amps, it will only output the amperage necessary to meet the system's needs at that time. You really can't go too big, although there is always consideration of need vs. cost.

[another69]

Get a hold of a DC clamp-on amp meter, hook it to your alternator output wire, and see what your car actually draws with all the accessories & lights on. I had similar concerns with my car, and went with a MAD electrical upgrade and a 95 amp GM 12SI alternator. I found that the Terminator EFI with fuel pump added about 20 amps total at idle. The MAD upgrade was well worth it, does not require a total overhaul, and uses a better 3-wire alternator instead of the 1-wire, which typically have more problems at idle.