Alternator question

[grubsster]

Hi all,

I guess my question is similar to cwcarpenter98

My question is, I have an 8103-7 alternator which is rated at 105 amps. When my truck is in drive my engine rpm drops to about 550. At this rpm (when my Taurus fan kicks on) my amp needle is jumping like crazy and truck runs poorly unless I give it a little throttle. If I increase my engine idle RPM then my truck wants to lurch into gear. Probably need to change my torque converter again but it seems to drive great the way it is. Back to what I really hope someone can answer is, what alternator can I use at this rpm. I am running the stock crank pulley which I am not sure of the size? Is there an alternator out there that I can swap with or a pulley that will speed up the alternator I am currently running. I will also be adding a vintage air unit this fall.

Thanks in advance.

[gmc684x4]

I am not familiar with that alt number

What is your truck and engine combo?

I got rid of the external regulator on my 68 in 1990 for si style 105 smp alt
I still noticed my light dim at idle

Putting pops 72 on the road going with a cs130 altenator with serpentine belt setup

The cs 130 cs144 have a better output at idle

[grubsster]

Thanks for the reply. I think my current alternator is a cs130 type. The 8103 is the part number. It would have run on mid 90's cars with serpentine like a 94 Buick. I don't have serpentine I have a v belt. My truck is a 66' 283 with vortec heads that was built by a speed shop in Raleigh. Has a little bit of a cam so the idle is lower when in gear, about 550.. Would a cs144 bolt up to the stock brackets? I'm trying to determine which alternator would be the most effective at idle and not affect the output curve on the alternator at higher rpms?

Thanks

[gmc684x4]

I know cs144 is larger in size
I would think it has same output at idle as its little brother cs130

My understanding is the cs style has 80 % output at idle compared to a much lower si output

Si altenator is the previous version of altenator starting on 73 up c10 trucks

You can try a smaller pully on your alt to drive it bit faster

[gpgofast]

I have a similar alternator on my 1971 K20. It has a TPI motor out of 1986 Corvette, but the alternator is off of a 1990s Chevy Pickup. Running a serpentine belt. I have a 16 inch SPAL electric fan. My idle is computer controlled right at 750 RPM and I don't see any issues when the fan kicks on other than sometimes the AMP gauge needle dips on fan startup. 550 RPM is a really slow idle speed.

Have you tried just bumping the idle up?

[Pontiac1976]

The cs130 alt are smaller and they do not get rid of as much heat as the CS144. The cs130 much hard to repairs( take longer to repairs on a cs130, then a the CS144)
and the cs130's are know for bears going bad on the rear.

The CS144 have much better cooling more AMP selection can be taken apart easier then cs130.
The two draw backs are the CS144 Alt is bigger then the big SI 70-80 Caddy Alt.
And the CS144 weight is heavy of all SI-CS Alt.
CS144 is made more like the SI style for the most part witch makes it except for the in proved cooling better charging at low idle. And can be easy to add to most trucks set ups.
This link may help you.
https://bowtieguy.proboards.com/thre...t-grade-cs144d

[Steeveedee]

Originally Posted by grubsster

Hi all,

I guess my question is similar to cwcarpenter98

My question is, I have an 8103-7 alternator which is rated at 105 amps. When my truck is in drive my engine rpm drops to about 550. At this rpm (when my Taurus fan kicks on) my amp needle is jumping like crazy and truck runs poorly unless I give it a little throttle. If I increase my engine idle RPM then my truck wants to lurch into gear. Probably need to change my torque converter again but it seems to drive great the way it is. Back to what I really hope someone can answer is, what alternator can I use at this rpm. I am running the stock crank pulley which I am not sure of the size? Is there an alternator out there that I can swap with or a pulley that will speed up the alternator I am currently running. I will also be adding a vintage air unit this fall.

Thanks in advance.

One of the things that the manufacturers did back in the day was add a solenoid to kick the idle speed up a bit when the AC was turned on. No reason that you couldn't use one that was wired in with the fan so that the idle speed would pick up when it's drawing a lot of current. With the addition of AC, it's an even better addition, because the fan will certainly be running when the AC is on, for air flow at idle. Running a smaller pulley on the alternator may help, but it won't be enough to overcome the drop in idle speed when the AC is running, imo.