400i and 2 alternators

It may not be as simple as just replacing the stock 55A upper alternator with a higher amperage alternator as the stock V-belt system (using the smallish Gates 7M V-belt) doesn't have a lot of design margin (as proven during the 308 to 308i evolution) -- however, it was the correct original design choice because using bigger alternator V-belts would just increase the HP loss. If it was a situation of going from 55A to 65A, I'd go with "probably OK", but I wouldn't be hopeful that you could go from 55A to 110A. JMO.

Maybe I'm wrong, and others will be able to post their experience, but please do let us know how it works out.

Edit: Don't have access to the 400i schematic at the moment, but another factor may be the gauge of the wires going from the alternators to the battery -- if the same gauge as used on a (single alternator) TR = no problem. If significantly smaller = could be an issue.

 

Steve is correct. I changed the upper alternator to a larger one but it would destroy the belt on a regular basis. I went back to the old alternator but added adjustable voltage regulators that seemed to allow the units to come up to voltage at lower RPMs.

 

I believe the two alternator wires combine into one just inside the hood closure on the left side in front of the air filter box (400i). I am not sure but I think the combined wire is same as each individual, why would you need heavier wire in Italy?!?!
Ken

 

Ferrari engineers never really had a firm grasp of electricity until a few years ago.

 

Yes, that's a bit of an odd design decision The individual wire sizes are OK for 55A alternators, but the same size for two is marginal.

Mark -- What current level (single) alternator did you try?

 

I'm not sure. It was a while ago. I do remember it was from a truck. I had to build a custom bracket for it.

I put a really small pulley on to build voltage early. That may be why it kept eating bellts.

 

No good reason reason to convert to a single alternator, the dual alternator system works well, Ferrari used Bosch Alternators, they are reliable and parts are readily available to rebuild them if necessary
The 2 alternators provide redundancy in case of a belt failure.

 

Agreed, I like having two because a back-up is handy.

 

Do you have the Bosch Part numbers by any chance?

 

I have had on 2-3 occasions been on a long drive with AC on, with or without lights and wipers and when I stop I have a dead battery. Thee ae other posts about this but two 45 (?) Amp alternators are marginal for this car. Look at the power load: 3 fans, two fuel pumps, AC fan(s) and then add in lights and wipers and it is easy to come up close to 90 amps.

I am contemplating finding a 60 or higher AMP alternator to replace the top one, where the small belt wrap around is nearly 270 degree. Can anyone suggest an alternator, Bosch part #?
Ken

 

Are you sure that both alternators are working well? Can't say that there's anything wrong with your math, and the system doesn't have a lot of design margin, but has that been a widely reported problem for 400i?

What voltage do you measure at the battery terminals under different conditions? Say:

1. idle, no other electrics "on"

2. ~2500 RPM, no other electrics "on"

3. idle with AC "on", headlights "on", wipers "on"

4. ~2500 RPM with AC "on", headlights "on", wipers "on"

I wouldn't be totally freaked out if #3 was marginal, but if #4 isn't good = that needs help/repair IMO.