Uprated Alternator?

[HJ2]

Uhm... What mechanic?

In the history of my S2 there is nothing of an alternator swap and it was tiny as it is. I can't be 100% sure, but i'd say 95% just covers it
The one i put in was the one i got out in the end. I will see if i still have the data of the bigger one that did not fit.
I did not reach in to grab the post of the starter motor, sorry. Just the alternator was enough for me.

Ever since i pray every evening that my starter motor won't give up!
I have plenty of pictures with the head removed so you can check if you want!

Greetings
HJ

[Elanlover]

Uhm... What mechanic?

I meant my mechanic when he put in my alternator.

[Elanlover]

So, the bench test on the stock alternator was interesting indeed. It maxed out at 60 amps at 6,000 rpm (engine speed). That's pretty pathetic really by today's standards and would be far less than that at most people's average driving speeds which would be anywhere between 2,500 and 4,000 rpm. At those levels we might be getting 30 - 40 amps. And that was on a stock alternator with only 8,000km on it so older alternators are probably delivering slightly less.

The alternator I bought a few years ago was a so called "equivalent" alternator from the lists here on LEC ('91 Isuzu Impulse) that is actually a tiny bit larger by 8mm in overall diameter. Obviously it fits since its installed but I'm sure there was some fiddling to do to get it in. That alt is rated at a max of 75 amps, puts out 70 at 6,000 rpm and about 49 at 4,000 rpm. They have one of these in stock now (the one that's larger) and are taking it to their high output bench to rewind it, replace the stators, etc. He told me he thought he could get around 100 amps at 6,000 which would represent a 43% increase over the already uprated one and getting close to double the stock alternator's output. It should be ready tomorrow and I'll post the results. The cost is $275 CDN which I thought was pretty good compared to all the other prices for high output alternators I've found on the web.

[Brit-Car-Nut]

What is the pulley ratio to the crank? The alternator pulley is probably smaller than the crank pulley so will be turning the alternator at a multiple of the engine RPM.

I will dig out my spare alternator later and try to quantify the ratio.

[Elanlover]

What is the pulley ratio to the crank? The alternator pulley is probably smaller than the crank pulley so will be turning the alternator at a multiple of the engine RPM.

I will dig out my spare alternator later and try to quantify the ratio.

All tests are done to simulate the actual engine rpm speed, not based on the alternator pulley speed. I'm told that the pully rpm is generally in the area of 3x the engine rpm.

[Elanlover]

Thread moved to correct forum area (as in this one).

[dapinky]

Is there a difference between LHD/RHD - obviously the power steering rack and pipes on a RHD get in the way a bit - but I have to agree with HJ - mine only just went in - and that was with lifting the engine with a jack just a few mil to get some extra clearance.

[Elanlover]

Is there a difference between LHD/RHD - obviously the power steering rack and pipes on a RHD get in the way a bit - but I have to agree with HJ - mine only just went in - and that was with lifting the engine with a jack just a few mil to get some extra clearance.

There either must be a difference or there's another way to do it. I can see how the steering might get in the way on a RHD car. The alternator that I have in there right now is an uprated version at 75 amps. Its the same one that is cited on the wiki as being a direct replacement in that it came from a '91 Isuzu Impulse. In this thread its also discussed but people are saying that its too big. Interesting that those saying it all appear to have RHD models. At the bottom of the page is a link to a Wood Auto product that is, in fact, the same uprated 75 amp model I have installed today. In this thread the very first post cites links to the same uprated and slightly larger alternator. In that thread we have people saying that it does fit and they all have LHD cars. You'll notice that at the bottom of the wiki page there is a reference to "Loren" who did the initial write up and may have referenced the replacement alternator part (they live in the USA it seems).

I'm thinking that we have solved the apparent contradiction of whether the '91 Isuzu Impulse alternator will fit on our cars. On LHD models it will but not on RHD (unless you plan on major surgery).

[hodge]

Fly in the ointment - I'm pretty sure HJ's car is left hand drive. He did a write up of his experiences with photos on his project thread. Found it very useful myself at the time as I had to replace one about a week later. I concur with Pinky - it is a very tight squeeze ! it's irregular shape needs to be oriented 'just so' thru an irregularly shaped hole. Altho small, it is surprising how quickly it's density apparently increases when held above the head, in a confined space, while lying on your back , (im)patiently going thru the options again and again. I had to stop for a cup of tea and fetch a bigger swear box. Sweet joy when it went in tho . . . mmm, what fun.

[Elanlover]

Having looked at a few pics in his thread I believe you are correct. So much for that theory then

[Elanlover]

I have picked up the alternator after its testing. Its rated at 108 amps compared to the stock version at 60-65amps and the uprated version now installed at 75amps. The math says that's between a 67% and 80% increase in output over the stock version at peak or between 43 and 48 additional amps at peak (6,000 engine rpm). I have a computer graph of the new alt and the one that's currently on the car (75amps). They are almost identical at idle at 36 vs. 39 amps (I'll bet the stock alt puts out only 30 amps or less at idle). Its not important, I feel, what the output is at idle or at peak revs since you typically don't have the stereo on full at idle with all the accessories nor do you drive the car regularly around town at the redline. What's important is the output in the "sweet spot" - the revs you are most likely to be driving at constantly which, for me, is around 2,500 to 4,000 rpm.

_RPM___Stock (60amps)___Uprated (75amps)___Custom Rebuilt (108amps)

idle.............15.......................36.........................39
2,000...........29.......................43.........................52
3,000...........45.......................59.........................78
4,000...........53.......................65.........................94
5,000...........56.......................68........................102
6,000...........59.......................71........................108

The alt has heavy duty stators, winding and a heavy duty regulator. The difference in the sweet spot should easily handle a decent stereo amp upgrade, seat heaters and other accessories as its anywhere between 20 and 40 more amps over stock. I will likely have some 2 gauge wire made up to replace the run back to the battery (need to "borrow" a spare alternator/starter cable so I can have one copied) just to be safe. Sadly, this alt won't get installed until the spring when I take it in for some work.

The guys who did the work have been rebuilding alts for 30 years and knew quite a lot about the aftermarket versions available that claimed higher output. I was told that, while its possible to get more output from them, they almost always have to go to larger bodies or, the stock alt was a large body version to begin with. I saw some examples and some of these alts are massive. Makes you wonder how they can fit them in the engine bay. There no way you could get more amps from such a small bodied alternator like ours without making the case larger. Even the uprated alt (75 amps) has a slightly larger case by 8mm I diameter that "just" fits. Also, many of these high output alts do achieve higher amps at the top end but sacrifice low end amps and deliver less at the low end than a stock alt does. It the sweet spot these alts may only be marginally better and quite likely less than the stock part. I'd advise against looking at these.