View single post by Esprit2
 Posted: 06-02-2019 04:59 pm
PM Quote Reply Full Topic
Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 512
Status: 
Offline
cjwilson wrote:
When I purchased this car years ago, I remember the PO saying something about upgraded cams. I am wondering if I have the 2.2 upgrade?The 2.2 liter 912LC used 107-cams on both the intake and exhaust.
The later 912HC (high compression) used a mix of the street-hot 104 cam on the intake, and the 107 cam on the exhaust.

Both of those cams required the use of Lotus' 104° MOP pulleys (green timing dots). 104° MOP doesn't co-exist with any other Lotus MOP on any pulley... there's just one green cam timing dot per side. Since your photo of the pulleys shows multiple timing dots, then they're the 110°/ 115°/ 97° pulleys ('ALL' other Lotus pulleys are single MOP). Taken on faith that someone knew what they were doing, that would indicate the cams are not 107s, or 104s.

Yours are probably stock C-cams, but they could be Lotus D-cams, which were also designed to run at 110° MOP. When Lotus started using the 907 in their own cars, Federal emissions models got the C-cam (same as the JH), and all other markets got the D-cam. There isn't a big difference.

C-cam . . . D-cam
0.340" . . . 0.350" . . . Lift
26° . . . . . 25°. . . . . . In. Opens, BTDC
66° . . . . . 65°. . . . . . In. Closes, ABDC
66° . . . . . 65°. . . . . . Ex Opens, BBDC
26° . . . . . 25°. . . . . . Ex. Closes, ATDC
52° . . . . . 50°. . . . . . Overlap
272° . . . . 270° . . . . . Duration
110° . . . . 110° . . . . . MOP, Design Correct

OEM Lotus cams are marked on the bit of exposed cam between the front of the cam carrier and the back of the pulley.

C-cam = no mark
D-Cam = one groove cut all the way around
E-cam = two grooves cut all the way around
107-cam = 7777777... stamped all the way around
104-cam = 4444444... stamped all the way around.

Aftermarket copies or alternate cams don't follow that ID convention. They may not even be marked.
All 'stock' JH 907s, in all markets, have the C-cam.

A numbered cam name (104, 107, etc) refers to the last three digits of the Lotus part number.
A numbered pulley name (100, 104, 110, 115, etc) refers to it's MOP timing.
It's only a coincidence that a 104 cam requires a 104 pulley. Don't read too much into that.

Regards,
Tim Engel

Last edited on 06-02-2019 05:59 pm by Esprit2