View single post by Esprit2
 Posted: 08-14-2020 04:57 pm
PM Quote Reply Full Topic
Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 547
Status: 
Offline
I can't clearly identify them from the photo alone. But just to make the point... the early J-H 907 pulleys had solid centers with no holes/ spokes. Just say'n...

The 102 and 107 MOPs are curious since the geometry of the 40-tooth pulley doesn't support them co-existing on the same pulley with 110 & 115. Not unless there's a second keyway cut into the bore. Then, 102 & 107 can't co-exist on one pulley, so that would mean there would have to be three keyways cut into the bore.

If all that were the case, then there would also have to be some more indicater marks telling you which keyway to use with which timing marks.

115 MOP is the very early J-H emissions timing, and it reduces the power output. It can co-exist with 110 MOP, and was originally achieved by simply re-timing the stock 110 pulley. If you don't need 115 to pass a required emissions test, then you DO NOT WANT 115. With stock C-cams, the design-correct MOP would be 110.

Some Dave Bean aftermarket cams use a 105 MOP, and 107 MOP does co-exist on that pulley, if you know where to find it.

Late Federal J-H emissions 907s used a Blue dot, 100 MOP pulley on the intake cam. The 107 MOP co-exists with that one... if you know where to find it. That applies only to the pulley with a single Blue dot / 100 MOP. That was followed by a dual-MOP pulley with two timing dots, Red and Blue. On that pulley only, the Blue dot was really 97... a 'cheat' for the convenience of serving both needs with one pulley.

To find all 4 of those MOPs on one pulley makes me question how that was done, and the only answers that come to mind are...

1) multiple keyways in the pulley bore, or

2) one or two of the pulley's MOPs may be correct, but the others are approximations, and not accurate. If that's the case, then the question is, which one is accurate.

Since 110 & 115 were standard OEM MOPs, and can co-exist on one pulley, and if I were a betting man I'd bet on them being correct. Then, given the choice between 110 & 115, I would chose to use 110 MOP with stock C-cams.

107 is a non-standard MOP that was never used on any J-H or Lotus production cam.

Technically, 102 isn't standard either, but 102.5 MOP was used for the later Lotus E-cam. So what's half a degree worth in a polite conversation? If the 107 cam is a full step milder in the pursuit of improving low-end torque and driveability, then the E-cam was half a step in that direction.

*~*~*~*
If you're a racer tuning for track power, then you could build a case for timing the stock C-cams to a numerically lower MOP than 110... like 107 or 102. Doing so could improve top end horsepower, but any power increase would come at the expense of low end torque and driveability. Since so many J-H owners strive to improve low end torque and driveability, using those lower-than-110 MOP values would be counter-productive to their goals. So, what are your goals. One should be to get away from 115 Int / 115 Exh cam timing.

Regards,
Tim Engel

Last edited on 08-14-2020 05:10 pm by Esprit2