When it comes to replacing an alternator, I don't like the japanese products. Hitachi and Denso may make fine goods, but they don't like to share the specs the way US makers do.
This is important because every alternator has a different output curve. Take three "55 amp" alternators. One may be rated 55A @ 4000 shaft rpm
, another 3000rpm, the last 5000 rpm
. Replace one with another at random--and you may lose or gain 20% power without ever knowing why.
in order to spec an alternator you need to see the output CURVES for amp output versus shaft rpm. Some alternators will put out 1/2 output at 2000rpm and full output by 4000rpm, others won't put out fully until 6500 rpm. That means one will give you good power at cruising speed while the other won't put out until you're at battle speed. Which would you want?
No specs? PASS ON IT.
And if you pick one that offers good output at low speed, and then you can either match the pulley to get you that speed at YOUR common engine
speeds (which will vary by the engine
type), or in the worst case have one machined to your spec, you can literally double the alternator output at your cruising (or idle) speed and forever cut your charging times in half.
And then there's one other important number: Maximum rpm for the alternator. If you set it up to run fast at cruising speeds, and then one day you run your engine at WOT for four hours clawing off a lee shore...make sure that alternator won't be hurt by running at top rpm. Some die at 10k rpm, others can run all week at 15k rpm. And sometimes put out the same
rated power at "cruising" speed.
Don't be afraid ofthe numbers, just the folks who tell you to ignore them.