Can anyone help me find a 6PK 89.75" or 90.0" belt?

[Jon K]

I need it for my car, custom supercharger setup. An 89.5" belt i fitted tonight worked, but my alternator was putting out 12.2v, the belt was real hot (sign off over tight slipping), so I swapped a 90.5" belt on and it was too loose. So I am thinking of an 89.75" belt or a 90.0" belt... that converts to 2279.7mm (89.75) or 2286mm (90.0"). Can anyone help?

[Jon K]

I need it for my car, custom supercharger setup. An 89.5" belt i fitted tonight worked, but my alternator was putting out 12.2v, the belt was real hot (sign off over tight slipping), so I swapped a 90.5" belt on and it was too loose. So I am thinking of an 89.75" belt or a 90.0" belt... that converts to 2279.7mm (89.75) or 2286mm (90.0"). Can anyone help?

bump

[Martin in Bellevue]

Is the supercharger belt running double duty with accessories?

The e36 m3 Dynan supacharger with the updated pulleys on the vortech, uses napa 25-060535. This is a 6 rib belt.

I have a set of pulleys for the update kit; turns out the newly purchased car had the updated pulleys already.

[ryan roopnarine]

did you mange to find an alternator with reverse fan or did you reverse the fan on your alternator before you put your setup together?

[Jon K]

did you mange to find an alternator with reverse fan or did you reverse the fan on your alternator before you put your setup together?


I am trying to run the belt system such that the alternator runs forward.

[SRR2]

AS long as the engine is running the same direction as before, how would the alternator NOT run the same direction? To reverse any belt-driven load you'd have to have the belt twisted twice over itself somewhere.

[SRR2]

I've seen you refer to "over tight belt slipping" before. This is a new concept to me. Can you explain for us ignorati what "over tight belt slipping" is and how it happens?

[Martin in Bellevue]

The worn-out supercharger belt on the m3 slips. Dinan updated the pulleys, partially for this reason. The tensioner can't really be overtightened on it, but maybe Jon is doing something else to tension the belt. That was why I asked if he was using 1 belt to turn the supercharger & the alternator. I wouldn't expect the alternator belt tensioner to hold enough tension for a supercharger belt.

I've seen you refer to "over tight belt slipping" before. This is a new concept to me. Can you explain for us ignorati what "over tight belt slipping" is and how it happens?

[Jon K]

The worn-out supercharger belt on the m3 slips. Dinan updated the pulleys, partially for this reason. The tensioner can't really be overtightened on it, but maybe Jon is doing something else to tension the belt. That was why I asked if he was using 1 belt to turn the supercharger & the alternator. I wouldn't expect the alternator belt tensioner to hold enough tension for a supercharger belt.


Theres a hydraulic tensioner on the M50. It is more than enough to tension belt on M50. The Alternator is now running backwards, still making 14.3v and the fan seems to cool it enough still because i drove about 100 miles like this now. The blower is BLOWING hard.

[ryan roopnarine]

Theres a hydraulic tensioner on the M50. It is more than enough to tension belt on M50. The Alternator is now running backwards, still making 14.3v and the fan seems to cool it enough still because i drove about 100 miles like this now. The blower is BLOWING hard.


power output change should be negligible in either direction, only certain designs of alternator will SLIGHTLY output less (ie 13.7 instead of 13.8) when ran backwards because the design of the brush holder/regulator produces a modicum of lessened tension. if running it backwards improves performance you either have a problem inside of it, or a belt tension problem outside. there's no such thing as a fan that blows in the same direction regardless of rotation, and you have a bleeding edge (for 92) alternator that puts out 140 amperes and NEEDS the cooling. I'd either do a small time rebuild (disassembly for rebuild is covered in the etk) to check the condition of the comm./slip rings (&c. &c) or have an auto electrician do it, or sort out your belt tension issues. i have no doubt that it will leave you on the side of the road if you don't seek a resolution for this.

[Jon K]

power output change should be negligible in either direction, only certain designs of alternator will SLIGHTLY output less (ie 13.7 instead of 13.8) when ran backwards because the design of the brush holder/regulator produces a modicum of lessened tension. if running it backwards improves performance you either have a problem inside of it, or a belt tension problem outside. there's no such thing as a fan that blows in the same direction regardless of rotation, and you have a bleeding edge (for 92) alternator that puts out 140 amperes and NEEDS the cooling. I'd either do a small time rebuild (disassembly for rebuild is covered in the etk) to check the condition of the comm./slip rings (&c. &c) or have an auto electrician do it, or sort out your belt tension issues. i have no doubt that it will leave you on the side of the road if you don't seek a resolution for this.


I hear you ryan. The voltage output is the same as before as it is after. I've felt the alternator after the 1.25 hr drive from home to school and noticed no rise in temperature compared to before. I know the fan doesnt spin the same way. However, if you take a computer heatsink for example. I have one that says to blower out from the heatsink, temperatures are lets say 45 degree C. If I test and flip the fan around, blowing down through the heatsink, temperatures were 46 degree C. I know this is relative, but I am saying whether you induct or expel air, the air is moving inside the alternator. It's an enclosed fan in there, you can barely see it as there are not very large openings in the housing... so my thoughts are that the alternator does not require THAT much cooling, else it'd have the M30 style open fan and more open alternator. Regardless, I have ordered a 100" belt and will be running it properly later this or early next week, no fears ;) But I found it interesting that this works very well as-is.