Open Road

Hello All

So what are people doing for alternators these days?

On my 91, I installed one of GB's upgraded alternators in about 2017 with the engine out service... I have not had any problems with it, but I have never really trusted the fact that it has no vent for fresh air like the stock alternator. So, I was actually thinking to just rebuild my spare OEM and someday put it back in. But I have not got around to finding a shop I trust to do that yet.

On the other hand, it has come to my attention that there is a drop in alternator option that I didn't know about:
https://928srus.com/products/928-603-01 ... 6c99&_ss=r
Also this one doesn't seem to have the air vent. At least I have upgraded harnesses on both my cars now, but the 90 GT should at some point have a rebuilt alternator.

What are other folks doing? No hurry here on my side, but just wondering.

I have roger's version and the voltage is so rock stead you'd think the needle was painted on the guage face. I sat on heat soaked concrete with an ambient temp of 105 and the temp measured on the concrete was 130 degrees. I have 5 cooling fans (two 12" spal on the radiator and 3 4" spal fans on my oil cooler) along with AC, and vent fan on full, with audio going for at least 30 minutes. Guage never dropped below 14 at idle. The alternator design negates the need for a cooling hose. notice the curved shape of the cooling fins on it. it has a fan blade on the inside.

My understanding is that GB's alternators are based on the 996/997 alternators, with a reworked face to have it be able to mount appropriately. If you look at how those alternators sit on the M96 or M97 motors you'll see that, in comparison, the 928 mounting has significantly better air cooling, not least because it lives under the engine (meaning, heat rises, which would work out worse for the M9x mounted parts).

There is also a very good guide to making a Ford alternator (basically) drop in, on TOS and I can say that the install procedure works well on a 968, from personal experience.

Cheers

I seem incapable of generating a data-supported opinion on which of the two (of three) options that I have tried is better.

I gotta try to remember to collect some data on the way to SITM.

I think there are a number of things that make alternators and the 928 a challenge. The factory cable from the starter to the batter is the lowest quality cable I've ever seen. I've routinely measured a 1.2-1.6 volt drop from the starter to the battery, so years ago that was my 1st charging upgrade and it made a huge difference in keeping the battery charged. The second challenge is that the CE panel is 6+ feet away from the battery and the guage of the wiring from the battery is too small. SO that was my 2nd upgrade. This helped dramatically with blower speed, as well as window speed and headlight brightness.

The 3rd and final problem is heat. here in Texas heat affects everything. Today is the 14th of May and we are expecting it to hit 103 today. It's going to be a long hot summer. Stock alternator was not able to cut it for me especially since I added some power hungry audio gear. I upgraded to the GB alternator and it mild temps it seemed to solve the problem but the Texas heat proved last summer that it was not up to the task, so I was able to get my hands on a beta version of Roger's alternator. It set itself apart immediately on my 1st drive as it solved the heat soak problem. No more dropping voltage at idle when the temps were over 100.

Yet another voltage challenge for the S4 and later cars is the factory cooling fans. They pull monster amperage. I upgraded to some thinner spal fans last summer just for more efficiency and as a side note they pull half the amperage of the stock fans. I'm upgraded again to some brushless fans for this summer so I can ditch the factory fan controllers and use the PWM output on my ecu to give me greater control over cooling.

maddog2020 wrote: ↑Wed May 14, 2025 10:23 am I think there are a number of things that make alternators and the 928 a challenge.
1.) The factory cable from the starter to the batter is the lowest quality cable I've ever seen. I've routinely measured a 1.2-1.6 volt drop from the starter to the battery, so years ago that was my 1st charging upgrade and it made a huge difference in keeping the battery charged.
2.) The second challenge is that the CE panel is 6+ feet away from the battery and the guage of the wiring from the battery is too small. SO that was my 2nd upgrade. This helped dramatically with blower speed, as well as window speed and headlight brightness.
....

Maddog, these are a couple very interesting points and rather change the direction of the thread in the way that I probably intended but was too lazy to actually properly title. I am not having any problems per say with voltage or charging being mostly in Central Illinois and having only 2 months of hot weather, but...

My thinking when I upgraded my harness is that the electrical connections get bad, insulation deteriorates, etc. and if I put a higher output alternator on instead of rebuilding what I have, I probably need to upgrade the harness anyway. But I was only thinking about the FMH. Probably that point 1 you made is also a real important thing to upgrade as well if you put on a higher output altnerator.

I have to re-think what I am doing (as usual).

I spent the winter working on making some new FOE harnesses for some '87+ cars (and an '82, which is more complicated) and one of the things that became clear quickly was how marginal some of the wiring was, from an ampacity perspective. When @Benno and I were talking things through it became clear that, while it was probably OK for the cars as designed it became questionable one you start introducing high amp draw components or, in the case of the alternator, a high amp output component.

Because of this we decided to go to much higher gauge wire in the design. I also came up with a way to simplify the power circuit portion of the harness that helps with overall complexity and shorter overall wire runs between the connected components.

One final thing that you might run into is that, as you move to higher gauge wiring, the lugs that are easily sourced for those wires will no longer fit easily at the junction points (the hot post and the connection by the ABS pump). I filed down the lugs to make them fit but have since then worked out a 3D printable design that fits in the stock place and accommodates the larger lugs.

It's all a bit of a rabbit hole, to be honest, once you really start digging in.

Cheers

I live in north Texas as well and concur with Maddog’s experiences. I currently have my original (89) alternator which worked as intended as well as the upgraded GB alternator. I ended up upgrading to Roger’s unit and couldn’t be happier. I think the GB unit would be a significant upgrade over the factory unit if you lived anywhere north of Kansas. It cranked out about 14 volts up to about 100 degrees of ambient temperature. Over that, performance starts to fall off. I would be willing to sell either one of them if anybody is interested. I only used the GB unit for about a month.

Wish I had seen your post before I ordered a rebuilt OEM unit from a shop in CA. If it doesn't work out, I'll reach out about buying the GB unit.

JBallard wrote: ↑Mon Jun 09, 2025 10:26 pm I live in north Texas as well and concur with Maddog’s experiences. I currently have my original (89) alternator which worked as intended as well as the upgraded GB alternator. I ended up upgrading to Roger’s unit and couldn’t be happier. I think the GB unit would be a significant upgrade over the factory unit if you lived anywhere north of Kansas. It cranked out about 14 volts up to about 100 degrees of ambient temperature. Over that, performance starts to fall off. I would be willing to sell either one of them if anybody is interested. I only used the GB unit for about a month.

Weird that i just saw this. Just bought an alternator last night. Stock replacement, 115 amp. Don't really need the extra juice I barely drive it nowadays