Camaro9969

iTrader: (12)

So i have been dealing with this since last year tried everything from new 160amp alternator to using larger gauge alt wire Car has a relocated battery to the trunk
Volts when cold are amazing 14.5 but after a few passes at the track i am seeing 13ish idle and when running down the track 12.5ish car def has a lot of draw
twin 255 pumps one off hobbs gauges all over the car just installed the Alky Control kit which i tried a pass without it and they were a little better but only about .5 so still some concern. I am thinking a couple things. One is heat under the hood with the turbo is just killing the alt, maybe i'll change the wiring from the back of the alt for power on the 2 pumps to straight to the battery. Any help would be great i gotta figure this out.

1 FMF

iTrader: (1)

the normal voltage the alternator regulator holds at is 14.5 volts +/- a little. I'm not sure exactly on the LS1 but over the years various cars had temperature compensation built in to the alternator charging/output such that as temperatures got hotter the alternator maintained system voltage less than 14.5 and possibly as low as 13.0 in order to not cook the battery. so if you have a turbo and have excessive underhood temps that may be causing part of your problem, if it is a problem.
the other thing is heat kills alternators, specifically the 6 diodes that make up the rectifier within the alternator. once you start losing diodes voltage output from the alternator becomes reduced especially at low rpm's and you start to notice flickering of various lights on the car.
from what info you gave, it is a little vauge and it doesn't sound like you have a real problem based on the numbers.
for the 12.5'ish volts you say you see that doesn't make sense to me and my thoughts are
- running down track how accurate is your measurement of 12.5, how are you measuring that?
- i assume your "twin 255 pumps" and everything else is running at idle before you launch and engine is under load at high rpms? if so and they draw high current when running you would have the low voltage problem whenever they are running, there's no reason for them to operate differently any time is there? these are fuel pumps? really the only thing that will draw more power when rpm's are higher is the ignition system and coil packs.

1 FMF

iTrader: (1)

other thing forgot to mention is i believe if you take the alternator to get bench tested you can check for failed diodes in the voltage rectifier. now whether places like autozone have the knowledge to do that i don't know, all they know is connect a couple of wires and push a button so their machine may or may not bet set up to check that so specifically inquire.
under a normal basic test the alternator will work but you're specifically looking for AC ripple on the alternator output.

Camaro9969

iTrader: (12)

I actually tried another alternator the truck one 145amp and I thought it was better but after a pass it was actually a little worse. It's gotta be because of heat and really have no clue what to do about that. Twin 255s one on a Hobbs switch boost refrenced regulator so as there is more boost the pumps are ramping up. also the meth injection pump is a progressive system so that also is working harder with more boost.
As for measuring voltage I'm logging with hp tuners.

Camaro9969

iTrader: (12)

Went to an ASP Alternator pulley and it def has helped a lot with volts. Will try it at the track soon and see how much of a difference it has made.

chrysler kid

iTrader: (14)

You don't need that many volts once the battery is fully charged. Alternator should only be putting out high numbers after starting to recharge the battery

Daniel Richards

iTrader: (1)

this reminds me of one time when I was "showing off" my radio to one of my mechanics one day, by the time I was done the voltage reading on the gauge was damn near down around 12 and it took several minutes of driving after that for the charge to "build back up" to it's normal voltage level, what you have is excessive voltage draw combined with the heat effecting alternator output, you may want to look at adding a second battery in the trunk.

Camaro9969

iTrader: (12)

That would be crazy and a lot of weight imo maybe just go to a yellow top optima. So far so good just haven't had much time to change it

2nd Gen Fl 'bird

iTrader: (13)

Doesn't heat cause resistance? Two pumps and alky system for a very short demand shouldn't do that, I wouldn't think. Are the grounding points solid?

Camaro9969

iTrader: (12)

I believe it's the under hood temps from the turbo that are causing the issues. But has been much better with the overdrive pulley