96-98 Vortec Alternator Upgrade AD244

Output will vary with load. The alternator will only put out enough to match the load on the system, and maintain system voltage within a certain range. The battery will place a higher load on the system initially to recover what it discharged during starting. That higher load from the battery may cause the voltage to run higher than what it will maintain during normal operation. Could also be an effect of the diode pack heating up and changing the charging characteristics. Either way, 72A seems high for a "no load" situation. I think you may have a parasitic draw somewhere that is slowly discharging your batteries beyond the alternator's ability to recover them. The dual battery setup masked the problem, since it takes a very long time to discharge both. It is as I said: one is completely dead and the other marginal.

If you have an inductive current meter you can clamp it around tbe battery cable and monitor current flow. Do it first with the key off, doors shut, etc. Give the truck a few minutes for any timed circuits (interior lights, ECM, etc) to go idle. I don't know minimum specs for current draw on our trucks, but it won't be more than 10 milliamps. If you find you have a draw, you can pull fuses individually to isolate the circuit. A common place for our trucks (and GM vehicles in general) are the vanity mirror lights. The bulb can burn out and short internally, and when the switch fails it will cause a constant draw while not putting out any light. Aftermarket radios, alarms, CB's, etc are also common sources.

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I did this swap a little while ago and wanted to comment on a few things that nobody seems to address in any of the swap threads I've seen about this.

1. The heater pipe does not fit. I don't know why people say it does but if you have a 98 Suburban like mine then the hole on the bracket that bolts between the idler and thermostat housing will not line up. I have left mine unbolted as a result. Any insight in to why this is and why people say it does fit when it clearly does not is appreciated.

2. About a month after the fact my newish Interstate battery started noticeably pushing small amounts of acid out of it. Why this is I don't know. I suspected that it was because the battery is specd for a truck with a smaller alternator and now the 145 amp one is overcharging it causing it to leak.

3. Purchasing the other belt isn't necessary in some cases. I did as the thread has suggested and bought the belt listed but it is ever so slightly too long. The hash marks on the tensioner are out of spec in the loose direction. The pulley sizes were the same on my old one and the new one.

Picture of heater pipe clearance. It's close but not enough.

You'll have to massage that tube a bit to make it clear. The case of your alternator may also be slightly thicker than some of the others, depending on who made it.

Alternators only put out enough amperage to satisfy system demand and maintain system voltage. That's the purpose of the regulator. The only way to be sure is to monitor system voltage and verify that it isn't charging at too high a voltage. That could indicate a problem with the regulator. The battery on your truck is the same spec as the 2500HD that the alternator would have been originally installed in. A top quality group 78 battery doesn't know what vehicle it's in.

http://www.powerbastards.com/categories.asp?cat=108

This might help

I have a DC engineering 320amp alt on my truck and group 31 battery under her hood. I have a pretty big stereo in the truck so I need it and it holds up well under load. With around 3400watts I don't drop voltage below 14.1v ever lol

I just have a simple question, in doing this upgrade everyone says you need to get the 140amp belt, why hasn't anyone tried clocking the tensioner? I am replacing mine today and it just has a nipple that locks into a hole, seems a new hole can be drilled to lessen the amount of tension so as to allow more slack and not overload the alternator bearings using a factory belt.

1997-Z71 said:

I just have a simple question, in doing this upgrade everyone says you need to get the 140amp belt, why hasn't anyone tried clocking the tensioner? I am replacing mine today and it just has a nipple that locks into a hole, seems a new hole can be drilled to lessen the amount of tension so as to allow more slack and not overload the alternator bearings using a factory belt.

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Mostly because changing the belt is a simple and elegant solution to the problem, and is what the factory did to accommodate different alternators.

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SAATR said:

Mostly because changing the belt is a simple and elegant solution to the problem, and is what the factory did to accommodate different alternators.

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I understand that much but it just seems like an extra trip to the parts store and then you have an old belt that doesn't do any good anymore. I just thought that while someone was already removing the bolt and installing a new alternator why not remove 1 more bolt and drill a new lock hole for the tensioner and retain old belt and save a trip to the parts store. I haven't seen it mentioned before so I was just throwing it out there. My belt is pretty new and I hate wasting money so buying a $40.00 belt and leaving my $34.00 belt useless would feel like I wasted some money and an extra trip to a parts store.

I really like my idea, and it would allow me to go back to an original alternator if I ever needed or wanted too without buying another belt. Seems like once the new hole was there it would just take a couple minutes to switch from one to another, almost seems more elegant to me.

1997-Z71 said:

I really like my idea, and it would allow me to go back to an original alternator if I ever needed or wanted too without buying another belt. Seems like once the new hole was there it would just take a couple minutes to switch from one to another, almost seems more elegant to me.

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It sounds fine. If switching alternators without changing belts is a functionality that you want, by all means do it. That need never crossed my mind, as I don't really plan to go back to the 105A alternator.

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