RJD2614

Hey folks, I know there are a ton of threads in the search function about alternators, upgrades, rebuild, etc. I've read through a good chunk of them. I'm looking for some updated info...

For a 1987 S4 car, what upgrade options are there? I put a brand new yellow top battery in this car and it still feels like I'm suffering from undercharging. I've had some uncomfortable rough run/stall out drives if the battery is even
marginally charged. I reached out to Precision Motorwerks, but didnt hear back, about their upgrade. I do have the option to pull the unit and have it rebuilt locally. The car is supercharged; I would assume this could only increase the current demand of the vehicle. What options are available in 2021? Thanks for any tips!

Speedtoys

When was the last end to end cleanung of power and all ground points?


Call Precision, ask for Mary.

Bulvot

Your current options are:

-Have yours rebuilt locally for in the ballpark of $100. A reputable rebuilder can do a good job and is a good option if you want stock performance.

-Order an after market one from RockAuto or a local auto parts dealer for between $120 to $200. I have no experience with this route personally, but others have reported good results (https://www.rockauto.com/en/catalog/...generator,2412)

-Order a remanufactured stock Bosch alternator from 928sRus.com for $255. No details available on this so it might truly be remanufactured, or it might just be a regular rebuild. (https://928srus.com/products/928-603...ctured-115-amp)

-Order a high output one from 928 Motorsports for in the ballpark of $1k. Their site doesn't list it anymore, but they used to resell Ford 6G alternators made by Mechman and installed in a case that fits the 928. Mechman has a very good reputation and builds true high output alternators and provides output curves (essential if you're buying a high output alternator).

-Order a new one from Precision Motorwerks for in the ballpark of $1k. Looks like it's a standard Bosch alternator that you might get for a BMW or Volvo, but installed in a case that fits the 928. No output curve available, which is understandable because it doesn't appear to actually be a true "high output" alternator. (https://rennlist.com/forums/928-foru...85-1995-a.html)

-Order a brand new one from Porsche for $842 (https://www.sunsetporscheparts.com/o...or-928603011fx)

-"Roll your own" for between $150 to $400. You can go for as low as 130 amps, or 200 or more amps. This is what will get you the most "modern" alternator if you pick one that is made from scratch by a place like QuickStart. This is the route that I went and it is easy to implement, reliable and has been working very well for me (https://rennlist.com/forums/928-foru...ter-928-a.html)


There is no reason in particular that a supercharger will put more electrical load on your car unless you are running more fans than stock or an intercooler pump. It's unlikely that you have more fans than stock, though. Most likely you had to remove your factory fans and replace them with fans that fit around the supercharger, and those probably don't draw as much current as stock. But I'm only guessing since I don't know anything about your car.

I have a turbo on my car and I am running fans with a combined greater load than stock plus an intercooler pump. My stock alternator was "ok", but when idling it couldn't keep up. Any of the above options will be fine when cruising, even with an increased load. For me, it was all about the idle performance. Which is why an output curve is critical for any alternator that is touted as "high output". It's easy to raise the maximum current when not at idle, but raising the idle current will cost substantially more to do properly.

Anyway, pick your poison, but there are lots of options.


The following may not apply to you at all. You may be way beyond any of this kind of advice, so please don't take it as me assuming that you don't know this. Just general thoughts on where I would start if it were a car new to me that I didn't know the history of...

Cleaning the CE panel, grounds, battery connections, 14-pin connector, and positive posts under the hood would be good places to start if there are rough running issues with voltages above 11v, or inconsistent voltage readings at various test points. They are easy to clean up. Even the CE panel is surprisingly easy to remove and work on. The instrument pod can be removed to calibrate the voltage gauge to be sure that it gives an accurate reading. Coil connections are also potential causes of rough running, but that starts to go down an entirely different rabbit hole.

A battery/alternator tester is cheap in case the battery might be suspect or to confirm alternator output. It's saved me money and helped to identify root causes on all of my vehicles. This is the one that I have, but there are a lot of options out there:
A good multimeter is critical as well. This is my current favorite which I use a lot: https://www.kleintools.com/catalog/c...dance-loz-auto


Let us know which route, if any, you pursue and how it works out for you.

SwayBar

If you only drive your car on weekends, disconnect the battery via the ground strap.

While disconnected, you can hook a battery charger up to it every now and then to top it off and take a load off the alternator.

RJD2614

Bulvot-that is amazing info, thank you! I ordered the Ford 200 amp option you put in your vehicle, and downloaded your instructions. This is great! With all the parts, it looks like I will be into it for just shy of 500. It all looks very doable; the shimming is the only part I think should be challenging. I too see most of my needs being the charging at idle.

Thanks Swaybar; I definitely need to address the alternator. I drove the car last night with a full charge on a brand new yellow top battery. With 15 minutes driving with the heating fan and headlights on, I measured 12.34V across the terminals when I shut the car down. It will idle strong at the outset, but will start to waiver after a while if I have any of the lights or fans on.

Bulvot

Glad to help. I assume you ordered it with the right case.

The shimming is easy in practice. Mount it and make sure everything is straight and square. Add shims as needed. Use a rule or straight edge to make sure the belt is straight.

If you feel like it's not generating enough current at idle, you can always go with the Powermaster 115 pulley, which is 49mm.

Let us know how it goes and feel free to drop me a line if I can help.

RJD2614

I hope I ordered the right case; it was this item:

https://store.alternatorparts.com/82...lternator.aspx

# 8253M-HD200 - High Output Alternator, 6G, 200 Amps, Power Stroke and Ford Diesel, Heavy Duty, Large Case

Bulvot

That's the wrong one and definitely won't fit as is. It's possible to put the 6G into a different case so it will fit, but I don't know of an off the shelf method for doing that. Mechman might be able to. The case needs to have a "10 o'clock" ear configuration with 10mm ID mounting holes that are centered 90mm from the center of the alternator shaft. The case dimensional diagram is on the first page of the PDF.

The one that I ordered was from this page (model F1-3G-HD200): https://alternatorparts.com/ford-3g.html

Here is my post on that one specifically: https://rennlist.com/forums/928-foru...l#post17565744

This is a direct link to the product: https://store.alternatorparts.com/3g...variation=2480

When you place the order, you need to specify that you want it built in a Lester 7774 case. You should also request that they install a non-LRC regulator (preferably F794HD but I provide a parts cross reference in the PDF for other options). And then, I recommend following up with a phone call to make sure that they are putting it in the right case. Everything else is cheap and easy to fix if it's wrong, but the case isn't. That needs to be right.

In case you didn't already get it, you'll also want the pigtail (WPT119) and stator connector (WPT1129) and a longer belt (Gate 340J6 or Continental 4060340). All of which, including the regulator, can be bought anywhere, including local auto parts stores.

For the pulley, I'm happy with the 54mm diameter GP712. You may want to ask them to include it with your alternator, or you can get it somewhere else. If you need more amps at idle, the 49mm Powermaster 115 will move the alternator RPM's up enough to make a big difference in idle output but still be ok for brief runs to redline.

Bulvot

I added a step-by-step guide and an alternator RPM calculator as attachments to the first post on my original 3G alternator thread. The step-by-step guide doesn't require you to be able to do more than place an order, turn a wrench, and crimp a wire. If you can do that, you can install the alternator.

https://rennlist.com/forums/928-foru...ter-928-a.html

RJD2614

Thank you sir! I called and changed the order today. I also have an order in to Summit for the ancillary parts. Your PDF was the deciding factor on going with the same unit, thanks!!!

Bulvot

You're welcome. Let me know how the alignment and spacing works out. I was very particular about getting mine perfect, so I'm hoping that it translates smoothly to other cars.

slownrusty

I bought the 928 Motorsports alternator (175-Amp) for my '88 and installed it in October 2019, I paid $654 which at the time I felt like it was a lot of money. I had no idea they were at the $1k mark (wow!).
It is a 100% plug and play unit.
The 928 Motorsports alternator is nice and compact, it is 5-lbs lighter than the OEM big Bosch and has provided fantastic service since installation. As it is smaller, doing work in this general area of the engine is now easier, like when I had to replace my oil pan gasket.
Infact the dash gauges are a bit brighter and all accessories all work a bit better with the higher output unit.

If you have a few minutes here is video I shot on the 928 MS alternator:

Hope this helps.
Yasin

Bulvot

Thanks for the report on the 6G alternator. When I bought my 3G several months ago, the 928 Motorsports alternator was around $1k. But, it's no longer listed on their site, so I don't know if that means that they no longer sell it, or if you have to call to get it. The price that you paid is a bit high for what it is, but certainly not nearly as out of sight as $1k. At $650, it would be tempting just to save on the hassle of dealing with pulleys/shimming/wiring. At least for "normal" people. I kind of like cooking up my own stuff

In general, smaller case alternators, like the 6G, should be able to spin faster than bigger alternators like the 3G or the Bosch. However, all of the information that I could find on the 6G indicates that it has a maximum shaft speed about the same as the 3G. The 3G is very popular with the custom engine community and they run their cars very hard. Sometimes 8k+ engine RPM for drag racing. I don't know if that translates into reliability in the 928, but at least it means there are a lot of 3G options out there to choose from.

Yasin, if your alternator ever dies, I bet that you could transfer your case to a new alternator. Which would let you buy a 6G from just about anywhere. Do you have any photos of the wiring in the back? I'm curious to see how Carl dealt with the factory ring terminal connection for the exciter wire since the standard 6G case doesn't have a lug for that.

Thanks again for sharing. Options are good!

slownrusty

@Bulvot - You're welcome! I'll snap some pictures showing how the alternator is wires and add them to this thread. I thought I had a few random shots on my PC, but I don't, even though I try to do a good job photo-documenting everything.

RJD2614

Hey folks, I just wanted to give a heads up to this community; i ordered a ~$350 Ford 3G alternator from qsalts.com or alternatorparts.com back in december 2021. I never received it, have been doing back and forth with emails and crap for months now, calling, etc etc. Never received my alternator, and now the phone is disconnected. i'm chalking this up to being scammed on parts.

As an aside, can anyone confirm if the 1985 and 1987 alternators are or are not the same model/swappable? whilst waiting, I dropped the rebuilt '85 alt into my '87 car. It's connected the same way and rebuilt by a reputable local company, but my DVM readings are definitely off. the battery read 12.6V at rest yesterday, and 12.1 when I started the car. My most recent shakedown drive returned me
with an 11.5V battery and a gauge reading flat down. I am wondering if my fan issue may be related to a low battery/alternator error.