When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hey guys, just wanted to share my fix for overspinning my alt and floating the brushes over 6000 engine rpm. Every one knows to increase the alt pulley size. But finding 1 in a junkyard can be tricky.
I happen to find 1 off of a 99 mercury cougar 2.5 v6 car. The shaft size is exactly the same, right at 17mm iirc. I measured it and it seemed to put the belt in the right spot. This pulley is really close to 3 inches in diameter. Before my voltage would drop to low 12s when I got the engine over 6000 rpm. With the new pulley it holds strong at 13.5 up to 6500. It also sits at about 13.5 at idle. This is with using the big truck 145 amp alt.
This is new pulley with stock truck pulley next to it. This is a shot of new pulley. Upper hose isn't as close as it looks.
Moral of the story is you dont have to look at other gm cars to find little **** like this. Would be nice if we could get a list together of alternator pulleys that you have used to fix similar problems. If anyone wants to add theirs please list what it came from, the size, and which ls alt you were messing with.
Your problem here is your alternator. It has been well documented that some alternators are just **** and stop charging around 6k. Best to avoid them and get one that works fine.
The pulley in this instance is sort of a fix, but not the actual solution.
nah he's on the right track. the alternator shaft speed needs to stay under 18k max
Right with stock sized pulleys 7.5 crank and 2.4 alt at 6600 engine rpm the alt is spinning close to 20-22k. With this new pulley which is about 2.9 iirc puts me right at 17k.
Now I will agree after you have floated the brushes a few times it's prob cooked. Which is why I got a new replacement alt. But I installed this pulley on my old alt and it was wayyyyy better. Log showed voltage only dropped .5 volt. But the new alt is steady eddy with bigger pulley. Not willing to put the smaller pulley back on to test it tho lol
nah he's on the right track. the alternator shaft speed needs to stay under 18k max
No he isnt.
I've run stock alternators without issue to around 7300rpm without issue. 6k is **** all.
And I've run the exact same alternator after a local shop replaced the regulator on it.....and bam, it fucked up at almost 6k exactly. Exactly same brushes, rotor, etc etc.. Whatever part they changed it fucked up at 6k. Below 6k it'd be fine.
I tried changing brushes myself, and other items believing it was a similar issue...it was not.
Changed it to another alternator and it was fine again.
I now run an AD244 based unit and have seen as high as 7800rpm without any problems.
Yes a lower rpm may help if he actually needs to use sustained high rpm ( which 6k is not ), but his problem is that whatever alternator he is likely using, is not a proper GM unit. It's either a generic cheap copy or it has been tampered with at some point.
I've run stock alternators without issue to around 7300rpm without issue. 6k is **** all.
And I've run the exact same alternator after a local shop replaced the regulator on it.....and bam, it fucked up at almost 6k exactly. Exactly same brushes, rotor, etc etc.. Whatever part they changed it fucked up at 6k. Below 6k it'd be fine.
I tried changing brushes myself, and other items believing it was a similar issue...it was not.
Changed it to another alternator and it was fine again.
I now run an AD244 based unit and have seen as high as 7800rpm without any problems.
Yes a lower rpm may help if he actually needs to use sustained high rpm ( which 6k is not ), but his problem is that whatever alternator he is likely using, is not a proper GM unit. It's either a generic cheap copy or it has been tampered with at some point.
Wow, glad to hear you have been spinning this thing past 7,000rpm with no issues. I was told by a few alternator shops there’s nothing they can build that will last long even at 6800 rpm.
ill have to get one. Is it a direct plug-in for a 1998 factory harness...?
It's strange that the old man at Alternator Man told me multiple times to keep my alternator shaft RPM under 18K to keep it reliable, even with their unit. For awhile they were trying to create a hybrid CS130D that used the AD230 rear case, but now they won't sell it because they can't get the the CS130D rear air intake to mate with the AD230 rear housing. I still run a 2.75" pulley on my AlternatorMan 140A CS130D alternator.
It's strange that the old man at Alternator Man told me multiple times to keep my alternator shaft RPM under 18K to keep it reliable, even with their unit. For awhile they were trying to create a hybrid CS130D that used the AD230 rear case, but now they won't sell it because they can't get the the CS130D rear air intake to mate with the AD230 rear housing. I still run a 2.75" pulley on my AlternatorMan 140A CS130D alternator.
It isnt strange. And I doubt you're running a 24hr race with the alternator spinning at 18k in order for it to need to be reliable up there.
There's a hell of a difference with a brief few seconds barely touching 18k, which lets face it about 99% of people here will see......than actually running it continuously at 18k....if there are even 1% who would see that operation.
Much the same as those building a motor to run a sustained 8k...would be rather different than one that may just touch 8k from time to time.
TBH, there is little reason all round not to use a larger alternator pulley. Overall, the LS does use a pretty large crank pulley, so does have a higher gearing for the alt than some other cars might have ( at least compared to Jap/Euro stuff which tend to have quite small crank pulleys by comparison )
So clearly alternators dont need to be spun that fast to charge at idle etc.
TBH, there is little reason all round not to use a larger alternator pulley. Overall, the LS does use a pretty large crank pulley, so does have a higher gearing for the alt than some other cars might have ( at least compared to Jap/Euro stuff which tend to have quite small crank pulleys by comparison )
So clearly alternators dont need to be spun that fast to charge at idle etc.
What size crank and alternator pulley are you using?
Standard crank and a slightly larger alternator. Cant recall the size, but not much bigger than standard.
Ok, so 7.5" diameter crank pulley and maybe about 2.9" on the alternator...?
I'm talking to the people that sold you your AD244 170A.....they are asking me what I have for pulleys to make sure I'll be good with my planned rpm.
I assume since you are spinning upwards of 7800 with that AD244, I'll be way within limits and it should live for a long time at my planned red line of 6,800rpm.
kinda like when my race club ran track days, one of the "prep" items was to un-hook the wire for the AC clutch or pull the AC fuse before going on track, the WOT switch mode would disengage the AC under throttle ,, but re-engaging it when you got on the breaks would get you a LONG squeal until the engine RPM's got down under 4000. the clutches would be red hot after a couple laps.. And because of the fancy electronic temp controls in the cars, you could not totally disable the AC..
AN interesting check,, BMW E46 models, have a nice duct system that looks like it could be repurposed for other applications, it forces air from a CAI through the alternator on the upsized packages for the car.. 2006 3 and I believe 5 series had one..
kinda like when my race club ran track days, one of the "prep" items was to un-hook the wire for the AC clutch or pull the AC fuse before going on track, the WOT switch mode would disengage the AC under throttle ,, but re-engaging it when you got on the breaks would get you a LONG squeal until the engine RPM's got down under 4000. the clutches would be red hot after a couple laps.. And because of the fancy electronic temp controls in the cars, you could not totally disable the AC..
AN interesting check,, BMW E46 models, have a nice duct system that looks like it could be repurposed for other applications, it forces air from a CAI through the alternator on the upsized packages for the car.. 2006 3 and I believe 5 series had one..
I guess its easy enough to just remove the A/C belt when you get to the track for some runs.
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Slideshow: From wobbling harmonic balancers to failed EBCMs, these are the issues that define long-term C5 ownership and what repairs typically involve.
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Slideshow: A modern Camaro transformed into a retro icon, this limited-run "Bandit" build blends nostalgia with brute force in a way few revivals manage.
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Slideshow: Cadillac didn't just crash the high-performance luxury vehicle party, it showed up loud, supercharged, and occasionally a little unhinged...
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Slideshow: A one-off sports car that looks like a vintage Italian exotic-but hides a C6 Corvette underneath-just sold for the price of a new mid-engine Corvette.
Overspinning alternator, another option. 
