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90T
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Here is why that high-current alternator may not be all you think it is. In order to keep the size the same there are fewer windings of the fatter wire to handle more current. That makes the low-rpm performance actually worse than the stock alternator. A road car spend most of its time at idle and low rpms so that is where you need the alternator to perform well. At idle stopped in traffic your fans are going full tilt and your alternator is barely turning. This graph explains it better. Below 2000 rpm the high current alternator performs worse than the lower current alternator.

264074
 

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1989 Sport Roof White Pkg 7M-GTE + mods
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Discussion Starter · #22 ·
You know, I used to know this stuff back when I was an engineering major 30 years ago. My brain has gone soft. So is the answer "Use two alternators?" or is the better answer "Get off the road until traffic clears?" I am getting a replacement 140A thanks to the warranty. Is a better solution to get the 90A Denso unit if the 140 fails?
 

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90T
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When the replacement 140A is installed with the fans running measure the battery voltage at idle. If > 13.4 volts then you are good. If its less then you may need something with more low speed current.
 

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Granted, I have a 2JZ with the 100A alternator, but I have had good luck with electric fans for the last 18 years. The controller is a DC control FK45 unit. It replaced a FK35 unit that was on there over 15 years before failing. PWM power-up on fans, so no current spike. A/C "on" terminal to run fans at 50% with the A/C running. No worries. Controller can be found here. They are built to order, so it may take a week or more to get to you. I've been happy with the guy's work. The controller runs some Flex-a-Lite fans. The Flex-a-Lite controller that I tried from Summit (after the FK35 failed) was a P.O.S., so I went back to the DC control unit (and moved it to a cooler part of engine bay).
 

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Catching up on this thread and the alternator aspect is of interest, as the one on my '89 looks pretty old and I may want to do some preventative maintenance by replacing it. Trying to figure out more details on the MR2 alternator option, and so far it does not look like a plug and play option, due to size and orientation differences.

A lot of threads point to the link below, but it's missing from the site. Anyone know why a write-up might have been removed or is there way to get it back? Was it moved? Just curious as I've run across missing posts a few times recently, and they don't seem like they'd be particularly controversial or anything.

The "Direct Fit" MR2 ALTERNATOR WRITE UP
 

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This thread seems reachable and has decent info. All the images are also online surprisingly enough. Might give this a squeeze myself, my alternator simply isn't up to the task...
 

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This thread seems reachable and has decent info. All the images are also online surprisingly enough. Might give this a squeeze myself, my alternator simply isn't up to the task...
Yeah, that's the thread where I first saw the link to the missing post. Just curious what that other post had to say. But from what I can see already, sounds like a bit too much fuss for my taste to try the MR2 "upgrade".
 

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Looking at it it doesn't seem terrible. My PCV hose is very compliant and the factory plug already sits near enough squashed against it anyway. I wonder if a slightly longer belt that allows the alternator to sit a bit further up might be a better solution. You can order belts in virtually any length you want.
 
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