When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Attached are some renderings of a proposed modular crank pulley. Each of the three primary sections are separate, allowing for quick-changing the external multi-rib pulley section without removing the crank (could be useful for supercharger or auxiliary load applications), as well as using a custom center section to replace the v-belts.
The middle and rear sections are fastened together with M4 screws that also serve the purpose of engaging the casting ribs in the damper - locking them keyed damper to the crank pulley eliminating the potential for the pulley to slip on the bolt, and combat bolt backout issues.
The front section is held with M6 capscrews.
All the sheaves have been redesigned to the proper standard, the factory crank pulley was stamped/spun and does not have the proper sheave dimensions, which does cause belt problems under some loads.
Hans - fantastic, I am very interested in this. Are there any standards for modular pulleys that would allow you to access existing accessory pulleys - or do you need to make all the modules yourself?
I am especially interested in larger diameter alternator pulleys with wider extra ribbed belts. I'd like to increase the alternator ratio by increasing the crank end diameter and decreasing the alternator end diameter (so for friction area: trade diameter (patch length) for effective width ). I think this would be a good solution for many in very hot climates where temperature derated alternator output is a concerning summer issue. More alternator RPMs is the easiest solution - and I don't really like a much higher idle.
I'd also like a different ratio for my vacuum pump (in place of the air pump).
...
I am especially interested in larger diameter alternator pulleys with wider extra ribbed belts. I'd like to increase the alternator ratio by increasing the crank end diameter and decreasing the alternator end diameter (so for friction area: trade diameter (patch length) for effective width ). I think this would be a good solution for many in very hot climates where temperature derated alternator output is a concerning summer issue. More alternator RPMs is the easiest solution - and I don't really like a much higher idle.
...
I assume the alternator has a max RPM spec, is that a concern?
Why the need for the purple bolts? Maybe have on or two as a place holder during assembly. After that, the mid pulley section will hold it.
Those screws are inexpensive, less than the added mill operations to add similar drive bosses. The heads are used to capture the ribs in the factory damper, and will interlock with the damper and leverage its keyway eliminating any potential for the pulley to rotate independent of the crank.
Hans - fantastic, I am very interested in this. Are there any standards for modular pulleys that would allow you to access existing accessory pulleys - or do you need to make all the modules yourself?
I am especially interested in larger diameter alternator pulleys with wider extra ribbed belts. I'd like to increase the alternator ratio by increasing the crank end diameter and decreasing the alternator end diameter (so for friction area: trade diameter (patch length) for effective width ). I think this would be a good solution for many in very hot climates where temperature derated alternator output is a concerning summer issue. More alternator RPMs is the easiest solution - and I don't really like a much higher idle.
I'd also like a different ratio for my vacuum pump (in place of the air pump).
Alan
Metco makes several different pulley rings, so it would be possible to modify my geometry to use those, but they are fairly large compared to the range we would want. 150mm would be pretty big for us, and I really cant see using anything larger than 175mm.
Those screws are inexpensive, less than the added mill operations to add similar drive bosses. The heads are used to capture the ribs in the factory damper, and will interlock with the damper and leverage its keyway eliminating any potential for the pulley to rotate independent of the crank.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
I assume the alternator has a max RPM spec, is that a concern?
There are max RPM specs for the alternator of course - these are a little hard to find documented.
I think that a 10% ratio change is very reasonable for the stock alternator and you can alternatively swap to alternators that have a wider RPM range. My case is a bit special - I'm not really thinking of the stock alternator for this usage (but I do think it could help for that too). It's probably always better to have a bigger crank pulley and the same or only slightly larger alt pulley to ensure no slip anyway if you are going to improve the ratio a bit. Then you can add a freewheel style alt pulley like a Litens OAD pulley for less dynamic (belt) loading.
There are max RPM specs for the alternator of course - these are a little hard to find documented.
I think that a 10% ratio change is very reasonable for the stock alternator and you can alternatively swap to alternators that have a wider RPM range. ...
Right. Given the poor alternator performance at idle when it's hot here in Arizona, I'd be willing to risk shorter alternator life for a 10% (or so) higher output at idle. Granted, I'm banking on an assumption that Porsche's design had a large enough safety factor that a 10% ratio change would not noticeably decrease the life of the alternator for most drivers.
Even if that's not the case, given that I seldom have the opportunity to rev the car anywhere near red line, I doubt the life of the alternator would be shortened even if the alternator's max RPM spec would be exceeded with the motor running at 6,500 RPM. Unfortunately, with an automatic transmission and Phoenix traffic, I seldom get the car above 5,000 RPM. So, I think increasing the ratio 10% would give a welcome boost of output at idle with no real effect on the life of the alternator.
Hans - did this idea go anywhere? I'm seriously interested in a modular crank pulley config now. Different size pulley for the air pump (now a vacuum pump for me) and a different ratio & wider belt for the alternator section.
I found a shop that was able to turn my supercharger crank pulleys from a single chunk of billet at a reasonable price, so wen that direction for my kit.
However, the first batch of pulleys had an issue, so I had to "scrap" them. They are not usable for my application, but asked the shop to hold onto them so I could repurpose them for a different design. They would be great blanks to machine the modular pulley from. Alternatively, Its easy enough for me to just put in an order for pulleys if there is enough demand.
09-09-2016, 02:55 PM
Modular Crank Pulley
