Alternator Pulley Size

[Oblithian]

Hello, I am new to this forum. So far, I have found the search function doesn't work as well as some other forums I am on. So if this topic has been beaten to death I apologize, but I did look (both on here and through google).

As many posts here have acknowledged, the stock alternators on the S30 leave much to be desired (particularly at idle).
I found sites discussing swapping to smaller diameter pulleys, but only in a generic sense. Therefore, I don't know what the alternator on a 1975 280z can handle ...or if it would even help.

Has anyone tried putting a smaller pulley in to increase the idle alternator RPM?

What are your thoughts and what size might you suggest?

Obviously, it will wear faster and I don't want to over spin it. On the note of wear, what do you think of swapping for a clutched pulley while I am at it?


If no one answers, I will just try swapping in a internally regulated 70-Amp alternator from a 1986 300zx.

Edited August 14, 2016 by Oblithian

[Chickenman]

Go with a newer style Internally Regulated alternator. Spinning an alternator faster does not increase the maximum overall output and can blow the windings off the rotor at high RPM's. More modern and efficient alternators generate more output at idle by design and that is the way to go.

 

I used the 1985 300ZX 70 amp alternator and it works great. Remy part # 14655 from Rock Auto. It's a smaller frame Mitsubishi style. You could also use an 80 amp 1985 Maxima alternator, but you may have to switch pulleys.

 

The Mitsubishi uses a different type of connector than our Datsun Z cars. . Mazda uses the same type. I went to the Autowreckers and snipped one off.  Common on Mazda Protege, Miata's and other models.  I used Deutsch DT  connectors to connect the old and new alternator  harness together. 

 

On the V/Reg side there are two ways to connect the wiring. I prefer the Z Car creations method as it connects terminals  1 and 5 and 3 and 6. Atlantic Z Cars method connects 1 and 5 and 3 to 2. the difference between #6 and #2 is that #2 is a constant +12V from the battery and #6 is a switched ( Ignition )  +12v. Using the switched connection assures that the alternator stops charging when the ignition is shut off.

 

http://www.zcarcreations.com/howto/voltreg.htm

 

I just used the above connection method on my 1976 280Z and it works great.

 

Nice to have the reliability of an Internally regulated alternator with modern Solid State components instead of the old mechanical V/Reg and it's 40 year old technology. I previously had a new 60 amp ER 280Z alternator on the Z. But the 2 year old mechanical V/Reg started to act flaky on a recent trip.

Edited August 14, 2016 by Chickenman

[Chickenman]

Couple of other tips to help you out. the old alternators have a " T " terminal. The horizontal connection is the Sense wire. Also called an N wire or sometimes IGN wire.

 

The Vertical connection is the Lamp connection. Also called F ( Field ) connection.

 

Here is a chart for the different types of alternator connections. Our Datsuns are a Type 1. The 1985 300ZX Mitsubishi alternators are a Type 5. Note these are viewed as looking at the end plate of the alternator.

 

 

Edited August 14, 2016 by Chickenman

[Oblithian]

Thank you. Any thoughts on the clutched pulleys?

[Chickenman]

Clutched pulleys? What are you referring to?

[Trevor]

Dodge/Chrysler uses an over-run clutch to prevent the serp. belt squealing if there is a load on the alternator while accelerating.

The clutch will slip and then allow the alt to gradually speed up to the crank and belt speed.

[NewZed]

I've seen a lot of variance in output at idle among different alternators.  The auto store reman I had was weak up until it died after 9 months.  The two old junkyard Nissan alternators worked fine at idle, although I do have my idle speed up by about 100 RPM.  

 

The Maxima 90 amp alternator swap is popular, it bolts on but needs a pulley swap and wiring change.  That 300ZX 70 amp swap looks good, I've not seen it before.  Looks like just a wiring change, if the pulley lines up.

 

Hard to tell what you'll get at idle though, the maximum output doesn't always follow idle output.  The 10si curve shown in this link gets around the internet.  http://corvaircenter.com/phorum/read.php?1,572964,573043

[Oblithian]

Thank you guys for the information. The Maxima alternator bolts right in?

[NewZed]

It bolts on but there is some work to get the pulley aligned correctly.  The pulley it comes with is for the ribbed belt and the replacement v-belt pulley needs adjusting, using spacers  

 

The 300ZX with the v-belt pulley is probably the easiest, assuming the pulley is already aligned.  Just figuring out wires.  There's only two.  Were I starting from scratch I'd probably go that route.  Odds are the few extra amps, 60 up to 70, are enough.

[Oblithian]

Hmmm, using the described method at http://www.zcarcreations.com/howto/voltreg.htm sounds like it would cause the car to run while the key is off, while the Atlantic Z method would cut power when the ignition is turned off... though perhaps brute force. Maybe I will give the Diode a try.

Edited August 26, 2016 by Oblithian

[NewZed]

 the stock alternators on the S30 leave much to be desired (particularly at idle).

A diode isn't going to change output.

[Oblithian]

You mean in terms of the supposed solution to the car staying running when the key is off?

[NewZed]

No, I mean in terms of what you said you were trying to do.  As far as the thread shows you still have your 1975 alternator with external regulator.  

 

The run-on problem is not a big deal, the least of your worries.  Down at the bottom of the atlanticz page the diode solution is described.  It's actually described all over the internet, on various Z car forums.  The atlanticz page is dead now anyway.

[Oblithian]

Oh, After chicken man's comment and yours I was looking at a swap. I picked up a 300zx alternator, plopped it in now and threw in the diode. The linked page is a bit confusing but for anyone doing this later:

 

I left the old voltage regulator hooked up (So I can convert it back to original easily). Connections wise, L from the old (WB) to L in the new. IG (Y) to S (See chickenman's pic of connectors above).

Aside from that, everything new goes on the same as it was (The new post 12v post is wider, so you need a wider end). You can pull the leads out of the old T and slide them right into the new connector (used an old keyring and hammered the tip flat for a tool). Lastly, the line on the diode goes toward the alternator in the L wire (WB).

[Tony D]

My 0.2¢... If you drive like a geriatric then a VW diesel might be a good Hybrid Idea....

 

I blew apart my alternator windings with the stock pulley....

 

If you access JeffP's Extreme 280ZXT page on Angelfire, go to his alternator section. If you physically increase the diameter of the alternator you mechanically gain some generation advantages. Because of his electrical demand he needed something producing more amps at idle than most stock 240 alternators delivered at 4,000 rpms! He accomplished it.

 

The pulley will spin it faster, but that is not the answer. If you seriously need serious amperes at idle, a larger diameter alternator is your answer. The rpm limit of 7,000 puts the alternator at 10,000+

[Chickenman]

Oh, After chicken man's comment and yours I was looking at a swap. I picked up a 300zx alternator, plopped it in now and threw in the diode. The linked page is a bit confusing but for anyone doing this later:

 

I left the old voltage regulator hooked up (So I can convert it back to original easily). Connections wise, L from the old (WB) to L in the new. IG (Y) to S (See chickenman's pic of connectors above).

Aside from that, everything new goes on the same as it was (The new post 12v post is wider, so you need a wider end). You can pull the leads out of the old T and slide them right into the new connector (used an old keyring and hammered the tip flat for a tool). Lastly, the line on the diode goes toward the alternator in the L wire (WB).

I used Z Creations wiring method and did not have to use an extra Diode. I believe most modern IR alternators already incorporate circuitry to make sure that alternator field output is killed when  an Ignition switched 12v source is used .