Boss46

My heads gonna explode - I have read and re-read the posts for installing a Delco 105 amp alternator into my 1980 OB to replace the Paris Rhone.
At first blush it seems simple enough and then all the variables and "in the weeds" tech tangents cloud the original purpose , wires - bolts - pullys and results.
Did I miss the basic simple data & steps ?

Jetdriver69

I installed a 180 amp alternator from Power Conversions.

Complete plug and play, no problems at all. No different wires or connections.

Just order the smallest pulley available to ensure the alternator excites at low rpms.

You do not use the alternator cooling hose as it is a front cooling type and you must mount the exterior temp sensor in the wheel well.

Plenty of power for extra cooling fans, huge stereo amp, whatever.

928NOOBIE

Hey JetDriver..can you share a link? Googling Power Conversions doesn't give me what I think you used .
Thanks!

SharkSkin

On an '80 you may be stuck with a v-belt, and the diameters on the v-belts don't go as small as they do on the flat belts. Since the 928 has a relatively small crank pulley this may be he difference between working and not working. I couldn't get a CS130D GM alt to work on m '78, and it wasn't for lack of trying. With an '86 you might be OK.

waynestrutt

http://www.qualitypowerauto.com/item...orsche-928.htm

docmirror

Two things I'd like to mention on this subject.

First, for those going to a higher ampacity alternator be advise that it's a sure bet none of your primary wiring was increased to handle the type of amps that can be provided by a modern alternator. The wire sizes, lugs, terminals and contacts all support the original ampacity of the alternator from the factory. Given that this wiring and all terminals are now more than 30 years old, the ability to carry even the factory rating of power is suspect. I would strongly advise that for those increasing the amps rating of the alternator to change out your primary wiring from the alt to the jump post(s), and all the way back to the battery. This is no small feat as those wires run throughout the car in places that are hard to reach and service. There's no question that in some cases of a battery getting weak, you are badly over straining the cables provided. At a very minimum, the cable from the alt to the jump post should be increased in size, and with new terminals.

Second, many modern alternator solutions fail on install because the sense wire "S" is not connected properly. The original alternator was internally regulated, and the regulation took into account the length and resistive value of the long cabling in the 928 with the jump post way up front on the opposite side of the car from the alt installation, as well as the battery being way in the back. There are many, many feet of cabling, and that cabling has now aged such that our batteries are often not getting a full charge to the correct value for flooded lead acid batteries. This is another reason why 928s tend to eat batteries. The alternator varies it's voltage, and amperage by sensing the load internal to the alternator, this is not the most robust circuit design, but it is what it is.

Enter the GM '3 wire' or externally regulated alternator. Many installations defeat the purpose of the sense wire in new installations, and quite often they get away with it. If one is upgrading the alternator in a GM type car, with the battery in front, and a large primary cable running direct to the batt from the alt, the sense wire can be connected to the B+ (big power lug), and it becomes basically a 2 wire install, with a fake internal regulation. The voltage regulator pays attention to the sense wire, which is now at battery potential but the voltage drop of the large charging cable to the battery isn't taken into account. Usually, this isn't a problem because the cable is large, short, and newer.

The 928 suffers the exact opposite problem. The charge cable back to the battery takes a rather meandering path with at least one terminal in between at the jump post. Later models have another power post on the right front of the engine which splits off some of the power, and without going into the details, this results in even more voltage drop by the time the little electrons reach the flooded lead acid battery post.

This is a long winded way of saying two things. 1. When you install a new GM alternator, it's much better to upgrade the wire to the jump post at the same time. This is a minimum I would do to insure the alternator wiring isn't going to fry something in there, and operates at the right temp. 2. If you want it to work right, save your battery, and your voltage gauge to be semi-accurate, you are going to need to run a long sense wire back to the red post of the battery. This wire will properly regulate the alternator output to match the needs of the flooded lead acid battery voltage, which is rather critical. the wire connects to the "S" terminal on the alternator. It should be ONE continuous 16 or 14Ga wire, without splices, or terminals through the chassis all the way back to the battery where it will connect right to the positive terminal distribution screw post. Use a new, clean spade lug, properly crimped or soldered or both, and clean the terminal post before putting it on.

Now, all those failed alternator installation will be a thing of the past because the GM 3 wire, externally regulated, higher ampacity alternator is installed properly. Use the correct V belt for the rotation speed of the design, and it's all gonna be good.

Boss46

Thank you very much for your time and expertise .
An upgraded alternator will go in with my 5 ltr, untill then ...a mexican Rhone rebuild from 928 Intl will do.👍🇺🇸🎯

dr bob

Expanding on Doc's great treatise, replacing the cable between the battery and the starter terminals is pretty involved due to the circuitous routing. The cabling between the alternator and the starter end of that cable is barely adequate for the original alternator capacity. Same for the section between alternator and jump post. The wiring between the jump post and the CE panel is marginal at best, with cable and connections in that section often the cause of the low-voltmeter syndrome.

Alternator upgrades should include upgrading the primary cabling between the starter terminal, the alternator and the jump post --at minimum--. These conductors are included in the front of engine harness, so short of building a new harness these replacement conductors will be external to that harness. The other section that needs serious attention if you are powering new accessories from the CE panel will be those two conductors from jump post to CE 30 bus.

Many times we upgrade the alternator in an attempt to mask the voltage drop symptoms of tired/corroded primary cables and connections. Consider primary wiring replacement as a first step in chasing voltage drop and undercharging problems, before you go after the alternator itself as a cause.

Don't forget that the battery ground strap is a critical but often overlooked part of the primary wiring circuit. The plastic sleeve hides internal corrosion that keeps the battery from charging completely, even with the best alternator. A new heavy-duty ground strap is inexpensive, very easy to change, and should be considered a mandatory PM exercise for any car that still has the original in place.

Landseer

On the mechanical install the body of the 105 A unit is about an eighth inch short from filling the space. Add three washers as shims. Also the tensioning arrangement is removed and replaced with a thru bolt. Pry to tighten like old gm. They work great, but hen again so does th original....the wiring mentioned above is the real key.

docmirror

Primary cable wiring is not for the faint of heart. I made a nasty mistake on my 968 and should have known better. Working with hundreds of amps is bad news, and routing and securing primary cables is something that's best left to -- well, someone like Dr Bob, not me. hehe,,,

Seriously for a sec, for the OP who may be electricity challenged, this isn't an area where you want to learn. Take it somewhere with a plan in mind, have them look it over, and get the work done right with a warranty to fall back on. I would recommend a 928 expert if you can find one. Not just the wiring but the crimping, and clamping with Adel clamps is pretty important. There is another factor that folks don't often think of that can be affected and that's induced currents in neighboring wires. The primary wire shielding is not as robust as it should be on modern cables(outside of mil-spec or aviation). If it's routed near low voltage signal wires there's a chance for some induced current, although the gauge wires run in the cross engine harness, and Porsche seemed to think it was ok. I've had that harness apart, and it's suffered the effects of heat to the point the gauges were sporadic at best.

James Bailey

Then you get someone like me who installs a 60amp alternator that weighs only 7 lbs and costs all of $110. 00 and is a single wire self exciter sure the gauge is low at idle but so what I just do not spend hours at idle. Nor do I run A/C anymore. Having your car draw down on the battery when at idle speed is NOT a problem.

docmirror

Sorry chief, but this is about the worst case for the 928. It falls right into the trap of not fully charging the FLA type battery. So, the chemistry of the battery is always a bit low, even if you drive it with no AC, and run the freeway most of the time. The regulation setting is just too low to fully charge the battery to it's potential. This leads to early sulfation. Strangely, a FLA battery should be partially discharged often to help clean off the plates of the battery, so the starting cycle is good for the battery, but leaving it below it's saturation level is always bad.

If you have a newer GM car, and it has a voltmeter, like a truck, or suburban, you can watch the voltmeter during a longer trip. It will actually go through a short discharge cycle, shown by the voltmeter where it goes down to around 12V for a short time, then goes back up over 13V, not related to loads. Oxygen recombination in FLA cells starts as soon as the cell voltage falls below 85% of it's saturation voltage and stays there for more than an hour or so.

In conclusion, follow the directions in my first post. Use a 3 wire GM alternator. Connect the exciter wire to the correct terminal off the gen light, with the resister in the circuit. Connect the B+ terminal with new, or very clean primary heavy cable, and use a single piece of sense wire direct to the post of the batt.

dr bob

Jim's case is unique, in that there are no accessory loads involved. The alternator needs to restore charge after starting, and run the fuel pump, injection and ignition. Car doesn't get driven in rain, very seldom with lights on, no cabin vent fan to worry about. The very-brown car sees track days for the most part, so it's not at all typical of what one might need for a street-driven car with all the accessories.

Kibort is in a somewhat similar situation, but using a lightweight battery for starting and maintaining the original alternator. His car is pretty much a track-only car at this point. I think hementioned he'd need a day-use permit from DMV if he wanted to take it to SITP at this point, so it isn't currently registered for street use.

Point is that race car duty is way different from street-driving duty.

Speedtoys

If I'm reading Doc right..

His Battery never reaches it's full charge, always a bit low, and that's the issue...chemically.

docmirror

I've said my piece, y'all do what you want now.