Jump to content

94-amp AC-Delco Alternator Swap Details


Recommended Posts

I had originally tagged this onto another thread but have completely rewritten it with updated information, hence the new thread...


There are other posts on doing the Delco Remy (GM) alternator swap on an L6 engine, but I thought someone might want to see some pictures of what we did on all three of our 280Z's.


Other alternator swaps have their advantages and this particular swap isn't for everyone. My reasons for going with the Delco alternator were:

  1. The exact Hitachi replacements for the 1976 280z or the 1978 280z's were not in stock.
  2. The old external voltage regulator could be eliminated on the '76 Z.
  3. A GM alternator can be had anywhere, anytime for cheap. One less thing to worry about on a long trip.
  4. Higher output rating. The Delco Remy 10si/12si comes in 63A, 78A and 94A ratings. Summit sells chromed 140A alternators (part SUM-810350) for around $120. (Of course, the higher rating doesn't mean much unless the wiring is up to snuff.)
  5. We saved about $20 and ended up with a high rated alternator.
  6. It was fairly easy to do with the tools I have.
  7. On two of our Z's, the bolts holes at the front of the mount were stripped and the bolts were missing. The swap solved that problem as well.

Click here for a great website with info about the Delco Remy 10si/12si alternators.


There are three methods of mounting the Delco 10si or 12si alternator that I am aware of:

  1. Mount the alternator upside down. The place on the alternator where the adjustment bolt normally goes will bolt right up to the existing mount with no modification. The trouble is that some people have said that the thin metal on the alternator eventually bends.
  2. Buy or fabricate a new alternator bracket. The mounts I've seen advertised were $80 to just over $100.
  3. Modify the existing bracket. This allows the alternator to mount to the engine much like it does in GM cars.

We went with option #3 since it seems to be reliable, inexpensive and fairly easy to do.


Here are some of the tools used:

  • Reciprocating saw or hack saw
  • Bench grinder
  • Drill bits from 1/4" to 13/32"

Parts used:

  • Delco Remy 12si alternator rated at 94amps (Autozone Duralast Gold DL7294 at $70 with lifetime warranty or Valucraft 7294 at $50 with 1yr)
  • M10x113 bolt (HELP! Part #45636)
  • M10-1.5 hex flange nut (Dorman 982-010)
  • M10 spring washer
  • M10 flat washer
  • 5/16"-20 bolt for ground strap
  • GM alternator plug (Calterm 08602)

Basic procedure:

  1. Remove Hitachi alternator and alternator mount.
  2. Shorten mount and drill a through-hole.
  3. Move the v-hub from the original alternator to the GM alternator.
  4. Install the modified mount and GM alternator.
  5. Change Field/Sense plug and put on larger ring-terminals.

This is the third time I've done the swap. It takes between 2 and 3 hours to do the job if the parts and tools are all lined out.


A picture of the new AC Delco alternator with modified mount next to the old Hitachi alternator with original mount:



A picture of bolt and flanged nut:



Now to the work. First, we removed the alternator mounting bracket from the side of the engine and cut about an inch off the front mounting surface. We didn't want to accidentally cut too much off so I left the bracket a little long and then mounted it to see how much more needed to be cut off. I started by cutting off 1.25". This placed the alternator pulley too far to the front. I used a bench grinder to do the fine adjusting. To get the alternator pulley was in perfect alignment, the bracket had to be ground so that it was exactly 1.7" deep.



Next, the rear bolt hole needs to be enlarged and extended through the front of the bracket. The M8 threaded bolt hole needs to be enlarged to accept an M10 bolt. We used a 1/4" drill bit inserted into the rear bolt hole and drilled through the front. I worked up to larger drill bits and drilled the entire bolt hole until it was 13/32", which is just big enough for the knurled shaft of the M10 bolt. Actually, my drill set did not include a 13/32" drill bit, so I worked up to a 25/64" bit and hogged the hole out to make it large enough for the M10 bolt. For me, drilling the mount was the hardest part of this little project. Keeping the drill bit from grabbing while drilling straight is difficult without a drill press. Still, it only took about 20 minutes to get the mount modified.



Here is the modified bracket mounted to the engine:



Here's a picture showing the V-hubs (pulleys) of the AC Delco 12si and the Hitachi:



The V-hub on the GM alternator is slightly more narrow than the one on the Hitachi. Even though the narrow hub seems okay, the belt rides higher in the groove and causes the alternator to turn too slow, so I decided to swap hubs. They came off easy with an impact wrench.



The spindle is larger on the GM alternator so I mounted each half of the Hitachi hub in a vise and used a step drill to enlarge the center holes. Here is the Hitachi hub mounted on the 12si.




Here is the final mechanical installation. This picture shows a cheaper 10si 78amp alternator without swapping out the hubs. I lost my picture of the 12si with the Hitachi hub.



I’ll add some more info about the electrical hookups in a follow-up post.


I hope this helps somebody out there.

Link to comment
Share on other sites

The electrical mods are a breeze on the later Z's and ZX's since they don't use an external voltage regulator like the 1977 and earlier do. The T-connector needs to be changed to a GM-style connector. The "+" and ground ring-terminals need to be a little larger to fit the studs on the alternator. That's it.


If you have an earlier Z, there are articles on converting from an external voltage regulator to an internal one like on the 280ZX alternators. The only difference when using the GM alternator is that a different connector is used. Click here for info on the electrical mods needed to use an internally regulated alternator on Z's made previous to 1978.


One thing I should mention is that the wiring harness that carries the wire from the alternator to the main battery wire is often fried on old Z's. The wire probably gets fried when the battery isn't tied down and the + terminal of the battery shorts against the chassis. I've had to rebuild this harness on three different 280Z's and I chose to run a new 8-gage wire in both cases. Even if you know your harness is in good shape, I think it is a good idea to run an extra wire from the alternator BAT stud to the alternator fuse or fuse link. It doesn't do much good to install an alternator rated at 94amps if the wiring won't support it.


Here's a picture of the GM connector that replaces the Hitachi T-connector.

Red -> White/Red

White -> Blue



I replaced the ground terminal with a larger one so that it would screw onto the back of the alternator:



For reference, here are the connections for the GM alternator plug:



Here are the connections for the Hitachi alternator T-plug.


Link to comment
Share on other sites

  • 9 months later...

An update to this old post. I replaced the alternator/fan belt today and decided to go with a slightly smaller belt since the alternator was only 1/4" away from the outer end of the adjustment bracket.


Instead of using the Gates 9350 (listed as stock replacement on a 1976 280z), I used the 9345 which is 1/2" shorter. It wasn't as easy to get on, but it left 3/4" adjustment either way.

Link to comment
Share on other sites

  • 1 month later...

I've got the same 12si alternator rebuilt by Champion.


There's two things I'd like to mention about buying this alternator.


1) I've read that buying a rebuilt alternator may not give you an alternator with the same amp output as the alternator it once was, as sometimes, the rebuilder would use the same internals or small parts from the lower output alternators to rebuild the one you are buying. I don't think that's true, as I'm sure they test it so that it's within an amp or two of the factory rating if it is to be sold as a specified rating.


2) My friend who gave me the alternator told me something that I would believe to be more true (he's a GM Nut!). He ensured me that the older the casing is before it's rebuilt, the better it is. And he's had this alternator in the garage for a couple of years now, and it's brand new, in box. Reason being is that the old casings were cleaned up better from factory, and they don't have any of the casting-flash from manufacturing.


The new casings were made in china and use newer, yet somewhat less well-refined castings, and have flashing on the inside of the case castings. So even after they're rebuilt, casting flash tends to break off from the inside of the alternator, and build up on the innards of the unit.



Just something I thought I'd mention.



Link to comment
Share on other sites



i did the swap, mounted upside down, did some mods to the upper bracket, and it works. it works real good.


the only thing is, at idle, it will only put out like 12.2 volts. constant. Its a reman one, an 80amp, made by Worldwide (remy)


whats up? you think its just a bad one? im going to switch to the 100amp (thd different looking fan) and try that.


i cant figure it out. ive got good wiring...hmmmm


i left the smaller pulley on the new alternator, so that should help it spin faster, right?

Link to comment
Share on other sites

  • 6 months later...
Guest Iansstud

I have the same issue as bubbleguinea, No charge at idle.... I have new wireing, and everything looks good, but no charge at idle, Any advise?

Link to comment
Share on other sites

How ironic....


I just searched for the Delco alt swap info last night and came accross this thread, now there's been a new reply in it not 24 hours later.


I talked with my alternator guy (yes, I have an "alternator guy", since I build a lot of electrically taxing audio systems), and he's going to set me up with a newer CS alternator, rated at 130 amps peak, and said I will have about 100 amp idle charge. I'll document the install and results.

He said he could build the alternator to be a higher peak output, but I really don't need it for this car, since the audio system will be small. I just noticed last night after installing a volt gauge in my dash in place of the ammeter, that the charge voltage was low (13V after a good rev at idle, and peaked at about 14V, at about 2500 engine RPM). For the EFI swap I want a SOLID 13.6V at least at idle, and 14.4V above idle.

Link to comment
Share on other sites

I think there was a thread that discussed the no charge/low charge at idle.


If I remember correctly these alternators are not capable of making full charge at idle. A quick search could bring up the thread


First of all, I just want to say that HizandHerz did a great writeup of this alternator install, and I think this should be made into a sticky!


Now, with regard to alternator output at idle, I found a website with output vs alternator (not engine) rpm for the GM 10si, 12si, CS130D and CS144:




Here are the graphs:










To summarize, you can see the 94A 12si only puts out 50A at 2000 rpm. If your idle speed is 1000 rpm, this would require a 2:1 crank pulley to alternator pulley ratio. It's been a while since I measured the pulley diameters, but I think it's less then that with the pulley supplied with the 12si, and it's even worse if you put the Z pulley on, since it's slightly larger. So this means that at idle, you're looking at less 50A, maybe less than 40A if your idle is low, and it will get even worse as the alternator heats up. A smaller pulley will help, but I don't know how small you can go before it becomes a problem for the belt.


The 105A CS130D (1994-2000, the earlier CS130 is not considered as reliable) can put out 70A at 2000 rpm. It's similar in size to the 12si, but there appears to be a variety of cases and "clocking" orientations for the mounting tabs. I haven't found a site yet that shows what year and make would be the best for us.


The 140A CS144 can put out 95A at 2000rpm! But it's somewhat larger than the 12si, so I'm not sure if it would fit. Has anyone tried this alternator yet?


12si case dimensions



CS144 case dimensions




'73 240ZT

Link to comment
Share on other sites

  • 3 years later...

I have a '79 280zx, with the Hitachi alternator and built in regulator. The original alternator lasted ~29 years, and then the car blew through two rebuilt hitachi's in a year. They always blew at the worst time. When I tore each down to find out what failed and it was open diodes in one and the regulator in another. I didn't think these alternators were well designed for heavy use. The cooling for the diodes isn't great. Though the rebuilt's had lifetime warrantees I got sick of swapping them out. I was also sick of the fact that the replacements were special order and took 3-4 days to get. I did a really thorough check on the wiring harness and electricals to make sure it wasn't my Z that was blowing the alternators.


So I purchased a 63A Delco-Remy (10SI type) and did the swap. I toyed with a higher capacity Delco-Remy, but my electrical demands are modest and I didn't want to spend the extra $50-60 plus the more expensive core (that I'd eat because I don't have a core to return). I left the very slightly smaller diameter pulley on the Delco-Remy alternator, figuring I'd have better charging at idle, and thinking the smaller 10SI rotor would tolerate my pretty infrequent red-line acceleration runs.


This was a great retrofit guide and I wanted to say thanks to the author for putting this post together. Here's some tips I'd like to pass along to "pay it forward": The 1979 280zx alternator bracket appears identical to all the earlier Z brackets, and I was able to trim it down to 1.7 inches wide by putting it in a good vise, and hitting it carefully with a fresh hacksaw blade and lots of oil. It can be done. A handheld hacksaw will cut very accurately if guided carefully. I suggest scribing all the way around with the help of some T & combo squares, so that you can keep the hacksaw aimed properly. Use the same care drilling the hole. I ran drills through it starting with 7mm, then 8mm, then 9mm, and finally 10mm - again lots of oil. From opening the hood to cleaning off the tools it took 5 hours using just hand tools and lots of elbow grease. I would have saved a good 1/2 hour if I'd had a metal chop saw, and another 1/2 hour if I hadn't wanted to lengthen the wiring harness a little and solder all connections.


As far as the wiring, I didn't have the Delco-Remy alternator connector, so I just used individual crimp on female spade connectors. I did completely cover them with shrink tubing to prevent them from shorting out to the alternator frame if they bent. I also soldered the connections as the alternator is low enough that I worried about road splash.


My parts store only had the alternator variant with the 9 O'Clock connector orientation, but there was plenty of room for the wires to clear the block. Plus that variant was the least expensive @ $49 with lifetime warranty (core was only $15).


I noticed that the Hitachi's tended to regulate at 14.1V, where in typical GM fashion, the Delco-Remy was close to 14.7V. This results in the dash mounted voltmeter needle pushing close to "red" on the gauge, but otherwise this is not an issue. The car runs far better at 14.7V than it did with a busted alternator and a battery at 12.8V or less. I ran it with a dead alternator for the summer using no accessories & charging at night till I had time to get into this. My drive to work was short so I never used more than 5-7 AH from the battery and it isn't any worse for the wear.


I'll report back if anything odd happens, but I highly recommend this swap.

Edited by altair
Link to comment
Share on other sites

  • 2 years later...

Well, seven years after I wrote this I came back to look up the information for getting another alternator because the cheap AutoZone 10SI that I put on my wife's '76 280Z went out after probably 20K miles. The 12SI on my '78 280Z has worked great for the same amount of time and over 50K miles. I'll be replacing the bad 10SI with a non-remanufactured 12SI.

Link to comment
Share on other sites

  • 7 months later...

Hi guys I did the GM 12si swap last week, real easy and works great...except I didn't drive the car for a week and the battery was dead. Checked for a draw and the alternator is pulling .354 amps when not running. And yes I confirmed it was the alternator; anyone else experience this. My 240 is a 1973 if that makes a difference.

Link to comment
Share on other sites

I followed the instructions here..http://www.atlanticz.ca/zclub/techtips/alternatorswap/index.html


Built the two jumpers based on the picture of the '73 regulator plug shown to bypass the regular, checked for switched power when done and it works. Sorry I probably shouldn't have posted the question here, as the wiring instructions came from somewhere else.

Link to comment
Share on other sites

The specifics on that page are for the 1977 model.  He added the other material as a bonus, but it may not be complete.  Some of the other models have relays that end up powered all the time if you just follow the instructions.  1976 for example.  If you hear a click when you connect and disconnect the battery, with the key off and a charged battery, that might be your problem.

Link to comment
Share on other sites

I've been running a 12si for years on my Chevy V8 260Z. But I started experiencing dead battery problems. Tracked it down to a bad parasitic draw from the alt. Took it to Oreillys for a check, came back with Lamp/Diode Trio FAILED. Took it home, cracked it open to verify, NO Diode Trio in this thing!? Only the Bridge Rectifier, brush holder and regulator. The bridge rectifier diodes all checked OK, the stator windings, OK, the rotor, OK. Anyone have any experience with a 12si like this?

Link to comment
Share on other sites

  • 1 month later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...