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#1047396 - 01/22/17 09:08 AM LS swap alternator output  
Joined: Nov 2008
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jmireles Offline
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jmireles  Offline
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El Paso, Tx
Before I swapped the LS2 in the Monte, I'd notice the voltage drop below 12 volts (not confirmed by an external source) when a large voltage demand was placed on the alternator. So let's say while in drive, with the brake pedal applied, lights on, heater on (or A/C) and turn signal on, the lights would dim some and the blinker would slow to a crawl. Sometimes the blinker light would simply stay on and not cycle.
Now with the LS2 swapped in, I have been experiencing similar problems, although not as bad. If I lightly rev the engine, the blinker speed increases and lights don't seem as dim. Even though the motor is an LS2 from a '06 GTO the alt is from a '99 Camaro LS1. The different alt is used to clear the Monte's frame.

I would think the electrical demands of a '99 Camaro would exceed those of a '87 Monte, right? Is there no difference in output? Or are there other issues I may be having?

Thanks


-'87 Monte SS LS 2/4L65e Quick Perf. 9" w/disk brakes
-'89 Iroc Z28 Stock 5.7 Edelb. TES headers, Borla Exhaust90K
-'77 Trans Am 468(Stroked) Doug's Headers Flowmaster catback
B & M shift Kit 400 Turbo trans. Edel brock Performer
RPM Intake Sean Murphy built Rochester Carb. Restored
in '08. 3K
#1047403 - 01/22/17 03:13 PM Re: LS swap alternator output [Re: jmireles]  
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edward Offline
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phila pa
May need bigger alternator more amps ????

#1047404 - 01/22/17 03:41 PM Re: LS swap alternator output [Re: jmireles]  
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1owner83SS Offline
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Kenosha Wi.
look to the aftermarket, search for a alternator for higher output at idle.


[Linked Image]
1983 Monte Carlo SS our first new car.
#1047406 - 01/22/17 04:07 PM Re: LS swap alternator output [Re: jmireles]  
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jmireles Offline
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jmireles  Offline
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El Paso, Tx
I guess I need to research the amp output at idle. Although, at idle things are ok. It's when you're in drive with the aforementioned demands on the alternator that the problem arises.

I forgot to add the cooling fans are active as well.


-'87 Monte SS LS 2/4L65e Quick Perf. 9" w/disk brakes
-'89 Iroc Z28 Stock 5.7 Edelb. TES headers, Borla Exhaust90K
-'77 Trans Am 468(Stroked) Doug's Headers Flowmaster catback
B & M shift Kit 400 Turbo trans. Edel brock Performer
RPM Intake Sean Murphy built Rochester Carb. Restored
in '08. 3K
#1047407 - 01/22/17 04:27 PM Re: LS swap alternator output [Re: jmireles]  
Joined: Sep 2010
Posts: 376
steve40 Offline
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Windsor, Ontario
if i run both fans, i see a drop at idle in battery voltage, that is with a stock f body ls style alternator.

my friend was telling me there is a high output version used on the trucks, maybe the escalade and he was pretty sure it mounts in the ls f body location. not sure what accessory brackets you run, but maybe a ls1tech search can help you there

#1047412 - 01/22/17 07:11 PM Re: LS swap alternator output [Re: jmireles]  
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jmireles Offline
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jmireles  Offline
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Joined: Nov 2008
Posts: 645
El Paso, Tx
Thanks Steve, I am using stock GTO LS2 accessory brackets but using an F-body alternator. I read on the LS1TECH forum that you can run a high output truck alternator. You just cannot use the rear bracket. I am worried there maybe something wrong with the electrical system.


-'87 Monte SS LS 2/4L65e Quick Perf. 9" w/disk brakes
-'89 Iroc Z28 Stock 5.7 Edelb. TES headers, Borla Exhaust90K
-'77 Trans Am 468(Stroked) Doug's Headers Flowmaster catback
B & M shift Kit 400 Turbo trans. Edel brock Performer
RPM Intake Sean Murphy built Rochester Carb. Restored
in '08. 3K
#1047418 - 01/22/17 09:49 PM Re: LS swap alternator output [Re: jmireles]  
Joined: Mar 2000
Posts: 5,645
upflying Offline
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upflying  Offline
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Reno, NV
I am running 10 ga primary wiring out of the alternator, direct to the battery. No problems yet.


86 MCSS Notchback coupe, LS3, 4L65E, QP 9", Eaton Truetrac, 4 wheel disc, column shift, Dakota Digital, silver with maroon bench interior

#1047420 - 01/22/17 10:28 PM Re: LS swap alternator output [Re: jmireles]  
Joined: Dec 2007
Posts: 3,961
Monte_ExpreSS Offline
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Monte_ExpreSS  Offline
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Oshawa, Ont. Canada
Start simple, whats the voltage reading on the batt terminal of the alternator with the car running?

#1047438 - 01/23/17 03:37 PM Re: LS swap alternator output [Re: jmireles]  
Joined: Sep 2010
Posts: 376
steve40 Offline
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steve40  Offline
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Posts: 376
Windsor, Ontario
It's the truck alternator the one with the extra knob sticking out of the pulley?

#1047449 - 01/23/17 07:44 PM Re: LS swap alternator output [Re: jmireles]  
Joined: Apr 2011
Posts: 1,183
Hunter79764 Offline
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Hunter79764  Offline
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Joined: Apr 2011
Posts: 1,183
Grand Prairie, Tx
Yeah, I'd check voltages and start from there. But with fans running, blower on, fuel pump humming, computer running, etc... Is your car an '87 or a '99 as far as the alternator is concerned? It still totals the same amps. I would still think the stock alternator should handle it, though. Might check some of the main battery leads, run heavy gauge from the alt to the battery or starter (or both?), make sure the fans are running from a good source, consider running your headlights through relays if you haven't already, etc. When we do the late model swaps, we're now running 2000's era power through 70's era wiring, so some crutches may be in order.


Shawn

'85 MC with budget 5.3L swap, TH350 with stock 2.14 rear end
It ain't much off the line, but it's nice on the highway
#1047472 - 01/24/17 04:24 AM Re: LS swap alternator output [Re: jmireles]  
Joined: Nov 2008
Posts: 645
jmireles Offline
10+ Year
jmireles  Offline
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Joined: Nov 2008
Posts: 645
El Paso, Tx
The alternator is from a '99 LS1 Fbody. There is heavy gauge wire from the battery to the starter but maybe I should run heavier gauge wiring from the battery to the alternator. I also want to run some voltage checks:

1) At bat, no fans, no lights, in park at idle
2) Same but with both fans running, lights on, brake applied
3) Same as above but in Drive
4) Run same tests but at the Alt.


-'87 Monte SS LS 2/4L65e Quick Perf. 9" w/disk brakes
-'89 Iroc Z28 Stock 5.7 Edelb. TES headers, Borla Exhaust90K
-'77 Trans Am 468(Stroked) Doug's Headers Flowmaster catback
B & M shift Kit 400 Turbo trans. Edel brock Performer
RPM Intake Sean Murphy built Rochester Carb. Restored
in '08. 3K
#1047552 - 01/26/17 03:23 PM Re: LS swap alternator output [Re: jmireles]  
Joined: Apr 2011
Posts: 1,183
Hunter79764 Offline
10+ Year
Hunter79764  Offline
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Member

Joined: Apr 2011
Posts: 1,183
Grand Prairie, Tx
Go ahead and run the AC as well, blower on high. That should be pretty close to full load that you will ever see, while still being realistic (Growing up in Odessa, I know there's plenty of times you have AC on full blast at night in El Paso, and of course plenty of times you will go from full AC to full heat in the same drive).
If you get more than a tenth or two difference between Alt and Bat, you need to step up the wire gauge.
It would be a ton of points to test, but I would take your test #2, measure between Bat + and Bat - , then Alt + and Bat -, then Bat + and Chassis ground (alternator mount?), then Alt + and Chassis ground. With old wires and bad grounds, you might lose a half a volt on the positive side, then a half a volt on the ground path, then more resistance getting to the turn signals, and all of a sudden you are running 9 volts to certain components...


Shawn

'85 MC with budget 5.3L swap, TH350 with stock 2.14 rear end
It ain't much off the line, but it's nice on the highway

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