So I'm working on a project to increase the capacity on the factory alternator above 100 amps, and I came across this page on the Delco Remy website which I believe says the 27SI was superseded by the 28SI.
http://www.delcoremy.com/find-a-part/product-details/27si-alternator
The dimensions of the 28SI seems roughly the same as the 27SI, and they both seem to use the same "J180" mounting style. The 28SI seems to be used a lot on heavy duty trucks, school buses, etc. and is offered in factory amperages of 130-200 which slots in nicely above the 27SI.
I have an email inquiry in to Delco Remy to see if they can confirm this information, but wanted to check here to see if anyone may already be running a 28SI.
Looking online, it appears you can find aftermarket 200amp 28SIs for a little over 100 bucks... And Genuine Delco Remys for a little over 200 bucks.
Either way, I will post back here with what I find.

TR 1 wrote on Fri, 20 November 2020 12:46

So I'm working on a project to increase the capacity on the factory alternator above 100 amps, and I came across this page on the Delco Remy website which I believe says the 27SI was superseded by the 28SI.
http://www.delcoremy.com/find-a-part/product-details/27si-alternator
The dimensions of the 28SI seems roughly the same as the 27SI, and they both seem to use the same "J180" mounting style. The 28SI seems to be used a lot on heavy duty trucks, school buses, etc. and is offered in factory amperages of 130-200 which slots in nicely above the 27SI.
I have an email inquiry in to Delco Remy to see if they can confirm this information, but wanted to check here to see if anyone may already be running a 28SI.
Looking online, it appears you can find aftermarket 200amp 28SIs for a little over 100 bucks... And Genuine Delco Remys for a little over 200 bucks.
Either way, I will post back here with what I find.

Mark,

What do you hope to get with a larger alternator? Even if the house bank has been relocated to the rear and you ran a pair of welding cables to it, It will still take about 5 or 6 hours to recover a 4D or pair of GC2s from 50%SOC to 95%. Another issue I will caution you about is that the 28SI is a much larger frame than the 27SI, so be sure to collect the real dimensions before you go too far.

Matt

There was an optional 145 amp alternator offered in 1978. Roger Black had one on his coach. I researched it one time about 15 years ago after seeing it on Roger's engine when we swapped it out of a GMC transmode people mover.

Try finding a 1978 Z87 GMC Motorhome parts book. I have it in a .pdf file and it is 32.2 meg. Billy might all so have it on his bdub web site.

It is in section 7.02H with a part number of

7.02H GENERATOR—145 AMP DELCOTRON (1978)
1117148 GENERATOR-145 AMP (w/RPO L04)

It might be a one wire alternator. Check carefully before using.

I would weed them out by remote sensing first to shorten the list before form factor. If not you will be under Voltage chronically and batteries junk in a year from sulfating.

But remember that if you can't find a remote sensing alternator like you
want, adding a combiner will eliminate the voltage drop across the isolator.On Mon, Nov 23, 2020 at 11:35 AM Mark Sawyer via Gmclist <
gmclist@list.gmcnet.org> wrote:

> JohnL455 wrote on Mon, 23 November 2020 10:16
[color

Ken H.

Yes, but it will not compensate for the rest of the losses in the system. The fusible link is an example of only one of the voltage loss culprits. IIRC the remote sense is connected to the terminal on either the horn or fan relay. Both of these are after the fusible link.

Yes a combiner will fix the isolator drop problem but not anything else like cables losses at a 150 or so amps.

I think a installing a one wire alternator is looking for low voltage problems in several places on the coach.

All true, Ken, which is why I worded the comment as I did. However, he's indicated that he intends to replace the existing wiring with new, larger, conductors. He seems knowledgeable enough to correct those other voltage issues too. They're really not all that troublesome in a well maintained system -- witness the many millions of one-wire alternators running today.

Ken H.