Z32_5.3

Alright, so I made a video of 2 logs I have. 1 is on the dyno in 4th gear, second is on street with 3rd gear.

I tried to log one clip of 2,3,4 gear at once. Datalog kept shutting off when it went off limiter in 2nd gear during spin. Anyways, my voltage does indeed drop decent amount at high rpm and duty cycle is up there.

I have 525 pump, 93 oct. 80lb dekas, M1 spray turning on at 140-150kpa. I recorded videos at .01X for speed so easy to see whatever.

https://youtu.be/ZVwH_JdrrTg

https://youtu.be/WYMA8szZ7lE

Z32_5.3

Z32_5.3

LetsTurboSomething

You might have the issue I did where the factory alternator stops making any power after a certain RPM. Mine cut out at 5500RPM so I put a larger pulley on it and that made it work up until about 5800RPM. Each unit its different.

I eventually just installed a 17.5v Kenne-Belle boost-a-pump which feeds 17.5v to the pump no matter what voltage the the alt puts out. That solved my issue for $260. You could also go with a better quality alternator like a Mechman that's good for 9000RPM. I just went with the boost-a-pump so I didn't have to screw with figuring out new serpentine belts, mounting the alternator, etc...

A 525lph at 11.4v is probably only about 350lph at 40psi.

But the 400LPH at 17.5v on deka 80's runs 70% duty cycle at 80psi of fuel pressure on 22-24psi of boost. It's gotta be 1000hp at the crank now.

Boost-a-pump it in my opinion, Walbro says the pumps are good for 17.5v constant.

Forcefed86

iTrader: (4)

The other option is another pump in parallel. Inline style aem400 is cheaper than a boost-a pump and nets you more volume.

Also FWIW I had issues with the small magnafuel boost-a-pump I had. It doesn't like being starved for input voltage either and gets pretty hot. I stepped up to a much larger and more expensive MSD unit. It seemed to hold up just fine. (I actually still have it if your interested)

You can also get a 3-3.5" alternator pulley these days pretty reasonably. Also not a bad idea if you're going to be revving it to have an SFI aftermarket crank pulley anyway. Might as well get an under driven one.

Z32_5.3

ended up buying this one


Advertise it works up to 7500 rpms.

Forcefed86

iTrader: (4)

hmm I'd have to call BS on that. But hope it works for you. They probably say it can work at "up to 7500" with the proper smaller crank pulley.

It's pretty simple to calculate the RPM.

https://powermastermotorsports.com/power_pulleys_a.html

Crank pulley diameter divided by alt pulley diameter X RPM. So stock is 7.5".

7.5/2.85= 2.63 *7500 = 19,736 RPM

Delco style alternators MAX rpm is 18k. And I've had some (remans) drop off well be fore that. Some junky autoparts stuff falls off line at 16k or less. So I'm not sure what magic they are using to keep that alt charging to 20k. All that said some have great luck with OEM alts. Not all are created equal and some will run 20k and charge no problem. I was just never that lucky.

Z32_5.3

once it comes in, I’ll let you know for sure. Hoping for the best.

Z32_5.3

Just got this in the mail. Installing today. The ribs are super sharp lol. Feel like I’m going rip belt off over tighten.

2.85” we see if it handles 7000rpm without voltage drop now.

Z32_5.3

Update on the pulley:

my voltage is around 12.9-13.6 whole time and my lowest voltage while revving up to 7,500 rpm is 11.7

so it did help but my voltage was always around 14 normally driving and now it’s much lower. The 11.7 isn’t ideal either so it’s no way a fix to issues but my it got my duty cycle from 104 down to like 92 at the 6800rpm.

Z32_5.3

notice big lack of power in the car. Went on dyno, tq is being killed mid rpm band.

pulled the datalog, voltage is 10.0 around 4500 rpms. Anyone know quality alternator that can keep up to 7500 rpm? I have a slightly larger pulley to throw on it already to help.

also ignore my fall off of power at end, it’s cause boost falls off. Car needs some timing and tuning for the higher rpms still. Haven’t worked on that since I found out alternator problems

LetsTurboSomething

mechman is one...there are a few though. But they ain't cheap. I still say get a kenne-bell boost-a-pump. You have the same problem I had and the boost-a-pump is how I fixed it.

Z32_5.3

the boostapump won’t fix the meth pump from lower voltage though.

89mulletbird

iTrader: (1)

Your symptom looks much different than the famous LS high RPM alternator cutout. When that happens you see the voltage instantly drop from 13s down to 11s.

Z32_5.3

im going to get the better alternator and hope for the best with this new pulley. I’ve talked to bunch people today saying no issues with voltage at 72-7300 rpms. So idk honestly. Maybe I’m chasing things for no reason. The whole 18k rpm thing may just be fantasy 🤷🏻‍♂️. Can’t even find pulley for 3” to get under 18k rpm so finding it hard to believe other people are doing things the “right” way and keep alternator rpms low. Even under drive pulleys from texas speed have them same 7.5” diameter so only hope is to change the alternator pulley but it’s 2.85” or 3.5” is all I could find.

89mulletbird

iTrader: (1)

This is what you want, with a 2.5" pulley. I went through all the same steps you did before buying this.

89mulletbird

iTrader: (1)

What kind of ground do you have from the battery to the frame, engine to the frame, etc... I think you have other issues besides the alternator.

Forcefed86

iTrader: (4)

Usually several factors involved. Check your voltage at the battery posts at idle, then at the back of the alternator. Shouldn't be more than a .2v difference. If there is, you should have larger wire. (or add additional wire).

Next the alternator quality itself is huge. reman alternators are junk.

You don't need a $400 alternator either. Its simple math. Doing the alternator pulley alone usually isn't enough. I did the math for ya on the pulley you ordered. You're still spinning it to damn near 20k.You need a smaller crank pulley.

Do you run an SFI pulley? Or are you on the factory stuff? If your on the factory crank pulley, you need an SFI to be legal anyway. Not to mention its a good idea. I've had the factory crank pulleys come apart. Its not fun when they do! Grab the standard jegs 25% under drive 6.22" pulley for $185 w a good oem new alt. Use your new alt. pulley, and be done.

6.22/2.85 = 2.18 * 7500 =16,350

I've heard folks having good luck with Mechman alternators as well for higher RPM ($400+) But There's no reason to be zinging an alternator to 20k IMO. Esp when you need an SFI crank pulley anyway.

Z32_5.3

I didn’t realize crank pulley was a tech thing. I’ll have to look into that crank pulley. Rather spend money towards the crank pulley than stupid alternator lol.

Forcefed86

iTrader: (4)

Yea, has to be SFI 18.1 rated for 10.99 or quicker I believe. After you've had to pull one off that exploded, you'll never install a cast wheel again IMHO.