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voltage isnt critical to engine operation/safety at idle....it is at 6k and beyond.
But even at idle...it's not like the alternator isnt spinning like **** in either case.
Just get a good alternator, and it isnt an issue though. Or if really stuck, underdrive crank pulley and/or larger alt pulley if you were turning some very high engine rpm's and sustaining them
I went with the 160 truck alternator, but also have a 25% UDP so I'm sure I'm over the limit too.
I’ll go measure my buddies. He can’t find his tape measure.
it does the typical thing. Drops out at about 6600 WOT at the track. Volts go to 11.8. Fuel pressure drops, car goes lean.
According to Powermaster, output is not linear, so adding a different size pulley can affect output since the pulley installed on each of Powermaster's alternators is matched to it's output curve. So simply adding an oversize pulley might cause more harm than good not knowing an alternator's power output curve.
Powermaster states 20,000 rpm is max alternator speed compared to other sources that quote "18,000" rpm as max. Perhaps that's just for their alternators and not other alternator mfg's specifications.
Out of curiosity I searched for information as to what Nascar, Indy, Circle Track and other's use for an alternator when each spins the engine far north of 6500 RPM but haven't found anything.
Last edited by dlandsvZ28; 07-03-2020 at 08:43 AM.
Reason: edit content
I’ll go measure my buddies. He can’t find his tape measure.
it does the typical thing. Drops out at about 6600 WOT at the track. Volts go to 11.8. Fuel pressure drops, car goes lean.
With correct injector data and compensations...the volt drop shouldnt cause a lean condition assuming there is adequate pump etc. Although the OEM ecu is limited overall as to how it may deal with a large volt drop compared to a good aftermarket ecu.
Either way, it is not a situation that should be tolerated, it needs fixed.
According to Powermaster, output is not linear, so adding a different size pulley can affect output since the pulley installed on each of Powermaster's alternators is matched to it's output curve. So simply adding an oversize pulley might cause more harm than good not knowing an alternator's power output curve.
Powermaster states 20,000 rpm is max alternator speed compared to other sources that quote "18,000" rpm as max. Perhaps that's just for their alternators and not other alternator mfg's specifications.
Out of curiosity I searched for information as to what Nascar, Indy, Circle Track and other's use for an alternator when each spins the engine far north of 6500 RPM but haven't found anything.
Engine rpm is irrelevant....alternator rpm is. Honda's regularly see in excess of 9k.....but they wont use the same pulley sizes as an LS.
It's my understanding that two small 255 lph pumps can draw up to 28 amps when running simultaneously. Drop the amps required for the pump(s) to run at full capacity and you drop pump output simultaneously. So if voltage drops, then amps drop as well.
Racetronix appears to have done a lot of testing about this issue and as a result supply a 10 gauge wire in their harness's from alternator to the pump(s) and much larger capacity relays. Delphi also upgraded the bulkhead connector so two of the terminals of the four terminals in the upgraded bulkhead connector can handle up to 28 amps. The tiny terminals on the 98 bulkhead connector can handle only 14 amps. So any pump that requires a lot of amps requires upgraded components as well.
But we all know that when it comes to the wire harness but sometimes ignore that the power source (the alternator) needs to be adequate as well.
So I guess the question is: how much lag time is there between the time the alternator stalls at 20K max RPM or 18K (choose your flavor) and as a result the power supplied to the pump(s) drops as well?
FWIW, I have noticed during nighttime racing at poorly lit dragstrips when cars enter the burnout area and actually hit the rev limiter, the headlights dim, sometimes even go out, so there must be some correlation between alternator max rpm speed and amp output and that it happens pretty quick. At least that's with respect to the headlights, so assume the pump(s) react the same way - maybe.
Sorry - my bad. Amp draw is only about 19-20 amps at 14 volts at 58 psi. Maximum amps draw on my little Racetronix 510 dual pump system is 14 amps max per pump. The actual amp rate is probably about the same as the Walbro high pressure pump tested in the link below.
The point is that much larger higher capacity pumps draw a lot of amps and they need more than 11.8 volts to do so to be able to run at full capacity. Which is what Racetronix has shown with their testing and is available on their site. A Boost A Pump according to K Bell regulates voltage if the alternator can't maintain the desired voltage in order to get maximum pump output at 14 volts.
The tests in the link below confirm the difference in output when dropping voltage from 14 down to 12.5 volts (obviously lower if voltage is only 11.8). The reduction in output is about 30lph for the 255 at 58 psi when voltage drops only 1.5 volts.
Believe most of those 25% UD are 6.14". If stock is 2.25" on alternator.... 2.72 X RPM. Will likely still drop off line a bit over 6600. Summit has the 2.75" part # ASP-540084 (can get cheaper on ebay) That'd get ya over 7500.
You were correct on the balancer size. His upper pulley is 2.125”.
So where is cheaper than Summit? I can’t find any listings for it on EBay. Summit shows a few weeks out.....
I just looked on Ebay for a 17mm shaft alternator pulley. IT was under $20 shipped for the 3.19". My 1 wire 160a Fbody alternator charges just fine at idle near as I can tell. 14.1-14.2ish. Although I am sad to report it still drops voltage around 6k.
Just type "17mm pulley 6-Grooves" I needed a single washer behind mine and a 1" longer alt belt.
Scotty (2JZFC) mustang was fixed by dropping the total RPM. He had the same issue. Sounds like this is just a cheap alternator? My original equipment ACDElco Fbody alt didn't seem to drop off ever either. The last 7 alternators between the 2 cars have tho! lol
Which power master did you go with Ron? I'm to the point I'm just gonna buy something decent. My flare for finding cheap alternatives just isnt there these days! lol. No time with a 3 year old, just want it done and working!
It's PN 48206 I see the price actually dropped. dang, I want a refund!
I just went ahead and did actual measurements on my setup.
Balancer is a PowerBond C5 corvette UD.
So I measured the circumference around the grooves. Did the same for the Alt pulley. then did the math.
Balancer is 5.53"
Alternator is 2.23"
Ratio is 2.48:1
So the Alt hits 17,360 at 7000 rpm. maybe why I don't have issues?
Spoke with Power-master tech awhile. Super nice and helpful. He said none of the GM alternators are rated above 18k and the they shouldn't be operated there for long. He mentioned some of the nippon denso cores can go to 20k+ Also said there is a sweet spot. So my 1 wire "160a" alternator may only put out 160amps at 2500rpm. And then it drops like a rock with RPM. So it may just be out of juice before it hits red line. He said go with the most amperage alt I can find. Their 58242 is what he suggested. It's a 165a unit.
Also mentioned something sounds really off. And that they find belt slip is a huge issue with automatic tensioners. He thinks it's a belt slip issue and that my alt is likely fine. Feel like I have more than enough belt wrap with that massive pulley, really doubt it's slip. I ordered the 5824 powermaster unit to try. It was on sale for $200.
Last edited by Forcefed86; 07-09-2020 at 02:06 PM.
I purchased a 250amp alternator from JS Alternators. It came with a 2.65"(or so) pulley and I run a Corvette 25% UD pulley from Powerbond, but I run the alt off the a/c ribs. I rev to 8,000rpms. I haven't had the alternator long but I've done maybe 20 pulls to 8,000 and each log shows voltage stable at 14.6v up/passed 8,000rpm.
I lost an engine last year to a factory alt that could not keep voltage stable at 7800rpm. I only started having issues after installing (2) Derale huge CFM fans. I didn't notice the voltage drop until after the engine blew and I was looking back over video I took of the cluster during a pull a day prior. I was running the factory ECU at the time and did not have a way to log pulls. (3) fuel pumps, (2) derale fans going 100%, headlights/taillights, etc... After the engine blew, I set to ACC mode and voltage was showing 7 volts.
I purchased a 250amp alternator from JS Alternators. It came with a 2.65"(or so) pulley and I run a Corvette 25% UD pulley from Powerbond, but I run the alt off the a/c ribs. I rev to 8,000rpms. I haven't had the alternator long but I've done maybe 20 pulls to 8,000 and each log shows voltage stable at 14.6v up/passed 8,000rpm.
I lost an engine last year to a factory alt that could not keep voltage stable at 7800rpm. I only started having issues after installing (2) Derale huge CFM fans. I didn't notice the voltage drop until after the engine blew and I was looking back over video I took of the cluster during a pull a day prior. I was running the factory ECU at the time and did not have a way to log pulls. (3) fuel pumps, (2) derale fans going 100%, headlights/taillights, etc... After the engine blew, I set to ACC mode and voltage was showing 7 volts.
Is that the truck style alternator? OR the smaller cs130D fbodyr/vette car type? That's 18,867 rpm! assuming the standard 6.25" UD pulley. Good alternator for sure there! Likely more RPM as the portion of the pulley the belt rides on is likely smaller. I'm going to try the power master on my street car. May end up with something like that JS 250a deal on the race car. Thanks for letting us know!
Is that the truck style alternator? OR the smaller cs130D fbodyr/vette car type? That's 18,867 rpm! assuming the standard 6.25" UD pulley. Good alternator for sure there! Likely more RPM as the portion of the pulley the belt rides on is likely smaller. I'm going to try the power master on my street car. May end up with something like that JS 250a deal on the race car. Thanks for letting us know!
I bought it for my vette, so car type. I'll try to keep you updated as I continue to drive the car and make pulls, to see if it's staying consistent. I had contacted the company to see if they recommended a larger pulley and they told me that as long as the belt isn't slipping, I shouldn't have any problems. I know they sell different size pulleys but they were certain I didn't need it. Before I purchased it, I asked about spinning it high and they pretty much said, "It'll take 8,000rpms all day long". I will find out if that's true.
assuming the standard 6.25" UD pulley.
I drive the alt off the a/c portion of the pulley. That is a little larger than the main serp drive side. I don't know the exact size.
07-02-2020, 05:40 PM
