[Fot] What alternators are you using on a Spitfire?

[Tony Sheach]

Hi all

My experience is that if you are going to use one of these Nippon Denso derived alternators, you need to go for the OE part.

The various copies all have short lives, mainly because the diode set lacks up and usually starts overcharging the battery and causing the output voltage to vary considerably, usually upwards. I’ve had this happen and it’s not pleasant when a dry cell battery gets fat enough to pop.

You can buy diode sets for the original Denso units and these are a quick change ‘in the field’ so my view is to buy a decent one and a couple of spare diode packs (the assembly with the spade terminals on the end) and replace as necessary.

I have one 80amp unit that’s done 10 years and is going back in after the current refit. I appreciate that most don’t need this sort of output, but it’s usually wet and dark here so it’s everything on. The smaller 45/50 amp units are probably longer lived.

Best wishes to all

Tony



Sent from my iPhone

On 19 May 2025, at 16:12, Michael Moore via Fot <fot at autox.team.net> wrote:


Do you have the part number for the powermaster?

Have a Good Day
Mike

Michael T. Moore, CPA
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From: Fot <fot-bounces at autox.team.net> On Behalf Of JS Performance Motoring, LLC via Fot
Sent: Monday, May 19, 2025 10:21 AM
To: Mike Harmuth <ofracer at gmail.com>
Cc: FoTTriumph <fot at autox.team.net>
Subject: Re: [Fot] What alternators are you using on a Spitfire?

Mike,
       The mini-denso style alternators work great.  There is a difference in quality between the cheapest, bottom of the barrel options, and the more expensive options.

When my $10 Amazon special failed at VIR last year (had been in service since 2020), the backup unit I borrowed from Henry Frye looked identical, but weighed substantially more!  There's clearly a difference.

Currently, I'm running a powermaster brand and it seems to be well made.

I also like to run a larger pulley to slow things down.  Here in the states, you can get a 4" pulley sold as Powermaster p/n 182.  This is a direct swap onto the mini denso.

<image001.jpg>
<image002.jpg>

We were also watching the J500 at my house, did you catch the medium bore race, where under full course caution, the commentator shouted "Slow down, Henry!".  We about fell out of our chairs laughing!



Jason Sukey
JS Performance Motoring, LLC
440.984.7720
jason at jsperformancemotoring.com<mailto:jason at jsperformancemotoring.com>
www.jspmparts.com<http://www.jspmparts.com/>
https://www.facebook.com/JSPerformanceMotoring/


On Mon, May 19, 2025 at 9:01 AM Mike Harmuth via Fot <fot at autox.team.net<mailto:fot at autox.team.net>> wrote:
I'm getting tired of replacing the stock type alternators. They used to last a few seasons but now it seems like a few weekends is the norm.

 Like oil, I know there will be many different opinions, including running without one. That being said, any suggestions/part numbers/suppliers of a system that works for you?

BTW, I enjoyed watching the Jeff 500 last weekend on the VRG live stream (currently available on YouTube). Nice job against the 911 Mr. Frye.

thanks
mike h
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