Cam technicals

thought i'd share with you guys. most probably already know this but a few like me don't/didn't.
i'm currently having my shop machine me some billet cam pullies to replace the steel/fiber ones. in doing the reverse engineering i noticed some very interesting things.
1. the cam pin holes are spaced out at 28*
2. the pulley pin holes are spaced out at 25*
3. the cogs/teath on the pulley are spaced at 12*

so by using the pin holes you have a 3* increament of retartd/advance. but you also have an additional 12* with a tooth adjustment. so bear with me i'll try my best to explain from here. looking at the cam center up the three hole, right/left and top. center the pulley hole so you have 2 tot he right and two to the left, as such pining the center hole would be 0* rotate the pulley and line up the two holes to the right and you'll have a 3* advance, from here it requires some math. lining up the far right holes on both cam and pulley will get you 22* advance but remember the pulley tooth is 12* so by rotating back the pulley 1 tooth you'll have 10* advance. i've been playing with the dwg in ACAD to see the different iterations and possibles with adding more holes or different spaced holes. and yes the pin holes are lined up to the pulley teeth.

just thought i'd share...

Sport tuner guy's have 2 piece Adjustable cam pulleys that use a slot and clamping bolts to set the timing degree's of the cam. Racing Chevys can use drilled offset bushings in bored larger, cam gear holes. You need to use a dyno to find what cam degree timing will produce.
But, I did not know about the offset holes on a stock Ferrari cam pulley. Great work, Thanks for posting your work.

1. the cam pin holes are spaced out at 28*
2. the pulley pin holes are spaced out at 25*
3. the cogs/teath on the pulley are spaced at 12*

With the 12* teeth on the pully and the 25* holes in the pulley, you should be able to find it possible to set the cams within (25* - 2x12*) = 1* of perfect.

true, but you're forgetting the 28* of the cam spacing which offsets those numbers by 3*. whats funny to get a 2* advance/retard you need to advance first by 10* then rotate back by 12* to get a 2* retard. opposite for advance.

it's easy to see how it can get screwed up.

new design boys...thought i'd share here also.

I spent the last two days going over fastners for proper torque and stress along with the vibrational issues they would indure. that was the biggest pain, the other pain was engineering around the small "real-estate". the neatest feature of all is that you no longer need to pull pins or jump teeth or even loosen the tension to adjust the cams.
these were designed based upon the cam adjustment pullies you'll find on hondas. however the similarity stops there. the honda based ones rely on tangs from the toothed wheel to transmitt torque to the cam. given the loads and speed of the 308 this wouldn't work. both parts of the pulley ride past each other at .001" across a .5" face on two sides. close for no axial movement but allows for degree adjustment.
the specs:
7075 aluminum, this is FAA certified aluminum; 95k tensile strength vs 45k for 6061-t6. Hard anodized
Custom spec'd ARP fastners M6x1.0 12point head, Helicoil inserts to negate shear.
Stainless Belleville washers double serrated DIN 6796

the pulley still retains the one pin that aligns the teeth and cam to 0*, the outer edge of both pieces are engraved with 1* increments from 0* to 10* for advance/retard to make adjustments easy to read. those marks don't show on the rendering, but would be found on the pad above the pin hole.
I'll have a physical part in 2-3wks.

now for the pic of the model....

thought i'd update for those not on the other board. all done here's a pic. amazing it took only 3 months but felt like forever!

oh and i changed over to a new belt design as well.

Very nice Scott!!!! You obviously put a lot of time and effort into this project. Do you have the new parts installed yet? Please post pics of the installation process.


JL

Scott, those look awesome. and very applicable. You need to add these to the Ferrari Mods section below.