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#1072329 - 10/28/21 03:44 AM SI 140 Amp Alternator  
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Ghost Car Offline
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Houston, TX
In the "Do-it-Yourself" forum, I read the good write-up on the CS144 Amp alternator conversion. With some work on the brackets, V-belt pulley and harness plug, it appears relatively painless.

I understand that the CS is the next generation and better alternator. Just wonder why not using a SI 140 Amp alternator, which was used in 80s trucks? I looked at the SI 140 and 150 alternators on Summit. The case appears the same as a stock SI 78 alternator and would be a direct bolt-on (brackets and plug-in). Electronics is my weakness. Does the SI 140 require some modification?

#1072332 - 10/28/21 03:35 PM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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mmc427ss Offline
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mmc427ss  Offline
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Pottstown, Pa
This is the 140A recently installed on my engine. Just a simple bolt in using stock 305 brackets. Only thing necessary is to upgrade the alt output wire to a #4 from the alt stud to an insulated + stud on the fender.

https://store.alternatorparts.com/7273m-a140-amp-12si-series-standard-regulator-alternator.aspx

Bob

#1072334 - 10/28/21 04:49 PM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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So I run the 140 amp 12si alternator from alternatorparts.com, I got the idea from Bob (mmc427ss). If I remember correctly he has the 10 si 140 amp. They are all the same frame size, I called and spoke with a guy at the above link and I will say he was very helpful and informative and answered all my questions, ive also purchased a starter solenoid from them since. I did have an issue when dual electric fans where full on (fail safe), ac on high, and headlights on while at idle with car being in gear (automatic) it sometimes would drop below below 13vdc and make my speedhut a/f ratio gauge fault, it has to maintain 13v or higher to operate. Below is all my readings, as long as you were driving it was fine. You could either adjust idle a little higher or I ended up putting a smaller pulley and it kept it above at 13v at all time.

Once I went to tkx 5 speed I removed the smaller pulley because it no longer pulls it down when pulled into drive. I am more than happy with it other than that one small glitch and it was really nothing it would only pull below 13v for a brief second when put into gear at idle. Also if I had too do it again I would. Usually it would only pull down too 12.8-12.9v and thats with all accessories full on. Also below is what alternatorparts.com says about 12 si and 10si.


Hooked to battery to check volts= Fluke 177
What i used to check amps =Fluke 374 FC

IDLE, no load, r.pm. at 800
Battery 14.43v
Alt. to Battery cable 10.1 amps
Battery to starter cable 12.3 amps

Idle, lights on, r.p.m. at 800
Battery 14.36v
Alt to battery cable 27.4 amps
Battery to Starter cable 24.3 amps

Idle, lights on, blower on high heat, r.p.m. 775
Battery 14.2v
Alt to battery cable 46.7 amps
Battery to starter cable 46.9 amps

Idle, lights on, blower on high heat, fans on fail safe, r.p.m. 725
Battery 13.6v
Alt to battery cable 67 amps
Battery to starter cable 41 amps
Fans in fail safe 22 amps

Idle, lights on, ac on high, fans on fail safe
700 r.p.m.
Battery 12.8 v
Alt to battery cable 59 amps
Battery to starter cable 42.3 amps
Fans 20.8 amps
Ac clutch green/white wire 2.6 amps

Idle, everything off except controller running fans. 800 r.p.m.
Battery 14.2v
Alt to Battery cable 21 amps
Battery to starter 8.5 amps
Fans ran by controller 9 amps

Idle, ac on high, fans ran by controller, 800 r.p.m.
Battery 13.7-14 volts
Alt to battery cable 54.8 amps
Battery to starter cable 33 amps
Fans ran by controller 18 amps
Ac clutch green/white wire 2.5 amps

[Linked Image]

#1072335 - 10/28/21 05:01 PM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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To add to what Bob said above i also upgrade my cables and had them built too order here. I also thought Bob had 10si but I was wrong.

https://ceautoelectricsupply.com/custom-cable-builder/

Last edited by 88ssBrent; 10/28/21 05:09 PM.
#1072339 - 10/28/21 08:24 PM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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mmc427ss Offline
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mmc427ss  Offline
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Pottstown, Pa
Went from the 78A stock many years ago to a 100A from another company, eventually it spun the front bearing in the housing. Did the stupid thing and bought a new front housing and bearing from my local alt guy. I should have checked the stator and rotor first, the noise i was hearing was the rotor rubbing on the stator, made it a junk alternator.

Brent being an electrician, who doesn't do houses, can really put a spin on how and what draws the load on the system, thanks.

If you don't have a large amp draw from an audio system or electric fans even upgrading to a 100A is sufficient. The reason i went o 140 was to reduce the surge when the headlights were on and dual electric fans were cycling. The headlights would dim for a split second, not a big deal, just annoying probably to other drivers.
Much better with the 140 now.

On my current system full load voltage will still be near high 13s, 14.3 at idle no load. And also the advantage of being a stick car.
Bob

#1072344 - 10/29/21 04:18 AM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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Ghost Car Offline
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Houston, TX
Thanks for the advice and info. The quick read is direct bolt-on. Visually the only difference is slightly larger vent holes in the back. Only concern is the gage of the wire from the battery to the alternator.

My car is stock. Only electrical draw is AC and lights at night. In the 90s when trying to get everything out of the 305, I installed an underdrive crank pulley, which doesn't help the stock 78 alternator. My car was running a little hot until I replaced the Edelbrock TES with ceramic coated Hooker headers. Really solved a lot of problems and coolant temp is back to normal with stock radiator and clutch fan. So, I don't have to draw amps for electric fans. Under the hood, I made it look the way it should have come from the factory (less a 350 ENG). I installed a Camaro dual snorkel air cleaner to include ducts topped with a 81 Corvette repop chrome lid. I had my original valve covers chromed which helps control the "electrical spaghetti" vs the GMPP valve covers previously installed. By installing my factory alternator pulley and placing a "ZB" ink code, a 140 alternator would look factory and I wouldn't have to watch the volt meter and tap the instrument panel when stuck in traffic...at night.

Thanks for the advice. This may be on my winter project list.

#1072346 - 10/29/21 09:07 PM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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Just to throw it out there the numbers above were using the stock pulley.

#1072350 - 10/30/21 03:38 AM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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Ghost Car Offline
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Houston, TX
Those are good numbers. Even with the under drive crank pulley, the 140 alternator should be a big improvement.

My current positive battery cable was manufactured by Lectric Limited, Inc. It is a repo 1970 Chevy cable that has the red terminal. I cut it down and soldered the ends to match the length of my factory cable. On Monday, I will call and get the tech specs to see if the alternator wire is 4 gage. If not, I can order one using the site recommended by 88ssBrent. I have recently installed a Delco Freedom II battery topper and like to have a positive cable with a red terminal and black wires.

#1072383 - 11/02/21 05:44 PM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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Ghost Car Offline
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Houston, TX
Called Lectric Limited. The main cable is 4 gage and the wire to the alternator is 14 gage. No need to change the positive battery cable. This weekend is the start of deer season. For now, I will have to put this project on hold. I got my current alternator from a local alternator/starter/electric motor rebuild shop 20 years ago. If still in business, I will likely purchase from that shop. Also, they could easily swap alternator pulley or match the pulley on the new 140 alternator.

Thanks for the tech help answers and supplier contacts.

#1072576 - 11/27/21 09:56 PM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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GNX89 Offline
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GNX89  Offline
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What GM trucks had the 140 amp alternator? Is there anyway to physically tell? Thanks

#1072586 - 11/29/21 12:14 AM Re: SI 140 Amp Alternator [Re: GNX89]  
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88ssBrent Offline
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Originally Posted by GNX89
What GM trucks had the 140 amp alternator? Is there anyway to physically tell? Thanks


I may be wrong but I've never seen a stock 140 Amp Si. Just ones that have been modified. Here is a list of cars and what came on them.
[Linked Image]

#1072600 - 11/29/21 11:36 PM Re: SI 140 Amp Alternator [Re: Ghost Car]  
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Ghost Car Offline
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Houston, TX
88ssBrent: I believe you are right about no stock 140 amp alternator on trucks. The 140 amp is likely an aftermarket upgrade. A month back, I found an online article about alternator upgrades for muscle cars. It had a chart on styles, years offered, and amps of various GM cars.

It also had a chart on minimum battery cable wire size for the starter and alternator. Per earlier comments, the wire from the alternator needs to be 4 gage with a 140 amp alternator, which is large like a starter wire. I did a search for 1984 Chevy truck positive battery cable. The trucks had three wires, a large starter wire, a large wire which must be for an electrical accessories/power box and a normal alternator wire. Basically, my current cable will not work, which was pointed out earlier. I wasn't tracking, but now on target. I could get a custom cable made (stock appearing black cables and red terminal) by the company that you provided.

Right now, I am putting this project on the back burner. I have to change out my water pump gaskets and I am still fighting a jiggle/squeak when hitting bumps. I ordered new front sway bar bushings. My bushings are original and dry rotted. Might not be the squeak, but need replacement.


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