KilerTA

iTrader: (70)

I have a 232/234 cam in my car with heads and some other mods doign 432 rwhp and ever since i did the cam swap i drove it for about 4k miles with no problems and then my alternator went out so i changed it and then 4-500 miles later it gose out again i take it back thinking it was just a bad one and to i put the 3rd one in and it lasted 4-500 miles then i put the 4th one in and it last a grand total of 4 miles lol talk about bad luck. My question is spining your car up to 6800 rpm is whats taking the alt out.. I know some are gunna say ther is a bad ground but ive checked them all ive event ohmed im and they all check out anyone have an idea of what might be causeing this?



PS i dont have a under drive pully

ProjecT 9

iTrader: (6)

i used to have a F14 and when i spun my car to 6800 i would take out alts too. i quit spinning my motor that high and noticed i kept altenators on my car for longer periods of time. now i have a F13 and my shift light is set at 6200. not a problem so far. just dont spin it as high and I'm sure youll be fine.

Phil'sC5vette

iTrader: (4)

interesting.

68chevypu

iTrader: (18)

an underdrive pulley would helop prevent htis though right?

Krab

iTrader: (28)

I would assume so. An underdrive pulley is supposed to prolong the life of all your accessories.

68chevypu

iTrader: (18)

cool thanks

bad2000z

iTrader: (4)

I haven't heard of this before, but the underdrive pulley sounds like a good idea.

warp10

iTrader: (5)

Did you replaced the heads as well? If you did, did you reconnect the ground wires at the back of the heads?

ILLINTENT

iTrader: (4)

Hey guys, Matt here from Powermaster tech support, we are not a sponsor, but the tech in this post could be applied to many products that are supplied by site sponsors, so hopefully it won't get deleted.

The common accepted RPM limit for your family of alternator is 18,000rpm.

You can easily calculate the actual RPM of your alternator by figuring your pulley ratio and multiplying that by your engine RPM.

Simply measure the diameter of your crank pulley, and divide it by the diameter of the alternator pulley. For example-

Say your damper/pulley is 6" in diameter, and your alternator pulley is 2" in diameter. 6 divided by 2 = 3, or a 3:1 pulley ratio. This would mean that the alternator is spinning 3 times faster than the crankshaft. (engine RPM)

Once your pulley ratio is found, just multiply that by your max engine RPM -

3 x 6,800 = 20,400 RPM, or 2,400 over the safe limit.

Obviously, that is just an example, you will have to measure your pulleys to know exactly what it is spinning. There are many companys that offer a smaller diameter damper/pulley, or a larger diameter alternator pulley; either would slow down the alternator. If you find that your alternator is not spinning faster than 18,000 rpm, you may just have had a run of poorly rebuilt units.

Be advised however, that the slower the alternator spins, the less current it will produce. When slowing down your alternator, you will often notice that your system voltage will fall slightly at low or idle speeds, which can sometimes cause problems for electric accessories on the vehicle. Like anything else on a high performance street car, it is always a give and take scenario.

Hope that helps.
Matt

99 Black Bird T/A

iTrader: (4)

3 x 6,800 = 20,400 RPM

if the safe limit is 18,000 rpm for the alt. would it be over by

2,400 rpm not 4,400 rpm

If it's only over by ~2,400 wouldn't a 10 percent underdrive would probably take care of the issue.

I have an ATI dampener which is 10 percent underdrive but I shift around 6,300. No problems, with the alt. I've never had a charging problem with the 10% underdrive on the ATI.

ILLINTENT

iTrader: (4)

Thanks for the correction, hit the wrong button. You can still just divide diameters to find you actual pulley ratio with the 10% underdrive.

According to the math, the 10% underdrive would do the trick, but you have to be carefull as some rebuilt alternators have slightly smaller pulleys on them. The best bet is to always measure and know for sure

...the charging problems that can sometimes occur with underdrive pulleys are completely dependent on the vehicles amp consumption at idle. A vehicle equipped with an electric waterpump, twin A1000 fuel pumps and a nitous bottle heater is going to have a much greater amp consuption at idle than a more or less stock LS1, for example.

The system voltage will only begin to drop when the vehicle is consuming more amperage than the alternator can produce at a given RPM.

98mysticZ

iTrader: (11)

i dont hhave a problem with the alt.. i keep blowing out the power steering pump seal then it takes my alt out

Steve Gunn

I have a similar cam and underdrive. The alt had 140,000mi's when I did the motor. It now has 170,000mi's and gets spun to 6800 daily. It's still going strong, but has been on the ragged edge of low charging on the guage since the swap.

LS1Beginner

Good post. Just to add to the data, I lost my alternator about 2 weeks ago after spinning up to 6500+ a few times. I am looking into slight underdrive.
For now I'll try to keep revs below 6K

JimMueller

iTrader: (9)

I have around 115K on my original alternator. Rev limiter's been set to 7200 for 3-4 years and I'm easily riding that limiter a dozen times each month at autocross. My PS pump does leak a bit and the alternator needs a good application of Summers Eve.

I did install a ASP underdrive pulley a few years ago and didn't get the alternator overdrive option (not because of the issue in this thread, just due to cost). I considered getting it after I was having some battery charging issues, but re-attaching the little wire on the alternator took care of that

BIG BAD BLACKSS

iTrader: (4)

Stop buying autozone rebuilds! Im assuming thats what it is since your from ohio and autozone electrical is the absolute biggest pile of junk ever put on a shelf. I have story after story about autozone and electrical items.

99NMB

iTrader: (7)

Thats funny... I keep having the same problem.

5.3LJimmy

iTrader: (10)

HaHa. I was gonna ask if they were from autozone too. If they are then the 500 mile lifespan is perfectly normal. That's what the lifetime guaranty is all about. I guaranty you'll be changin it once a week for the rest of your life.

gillbot

iTrader: (27)

+1, i've never had an issue with an alternator on either car here. I would only get factory alternators though.

KilerTA

iTrader: (70)

so whats im gathering is dont get the autozone speical and just go to gm and get a brand new one from gm if that keeps blowing out im thinking off just getting a 10% underdrive pully