View single post by Esprit2
 Posted: 10-10-2016 07:52 pm
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 337
qwerty wrote:
(Snip)... I doubt is has a different Cam but i will check do i check?
On the stock, OEM cams, there were marks on the bit of exposed cam between the pulley and the cam carrier's front seal. The first marks were grooves cut around the cam, none, one, or two grooves. Later, the grooves gave way to a series of numbers stamped around the shaft.

No mark = C-cam, the J-H OEM cam, 272° duration, 0.340" Lift, 110 MOP. This was also the original Lotus cam used for Federal 907 engines.

1 Groove = D-Cam, Orig Lotus Euro 907 cam, 270° Duration, 0.350" Lift, 110 MOP.

2 Grooves = E-Cam, Later Lotus Euro 907 cam, 260° Duration, 0.344" Lift, 102.5 MOP. The 907 was designed by the same motorsports enthusiasts who brought us the berzerker Seven, Elite Mk 14, Elan and Europa, and the Lotus-Ford Twin Cam engine. And they were still in berzerker-mode when they designed it. They did not anticipate that their new customers for the 3rd Generation cars (4-seat Elite-Eclat, and Esprit), would not appreciate having to drive the cars with their foot mashing the throttle to the floor.

When they began to see the light, the E-cam was their first attempt to make the 907 more mild, with a stronger low-end torque curve... at the expense of top-end, balls-out power. It's the same design philosophy use in the later 107 cam, but the E-cam was a smaller step in the mild/ torque cam direction. The 107 took the idea further.

7777777... stamped all around the cam = 107-cam, 912LC & 910 cam, 252° Duration, 0.378" Lift, 104 MOP. This cam goes even further in the direction of improving low-end torque and driveability in commuter traffic, but at further expense of top end power. A 9XX engine with two 104 cams will still reach redline, eventually, but it clearly starts to run out of breath above 5000 rpm... definitely above 5500 rpm.

4444444... stamped all around the cam = 104-cam, 912HC Intake cam (along with 107 on exhaust), 272° Duration, 0.410-0.420" Lift, 104 MOP, 64 Overlap.

5555s, 6666s & 88888s indicate the 105, 106 & 108 competition cams that are not appropriate for street use.

The trouble is that a lot (most) of the non-stock cams now found in 907s are re-ground. Some vendor took an original C-cam and re-ground it to meet E-cam, 107 or 104 specs. And most of them didn't bother to alter or add an identifying mark. You really can't tell just by looking what it is. In that case, measuring the "Lift" will give you some clue whether the cam is stock, or something else. If something else, then does it match the lift given for one of the other 'Lotus' cams given above. If not, and it's a totally different aftermarket grind, then your guess is as good as mine.

Early on, Lotus used one part number for all cams, but with a different Alpha prefix identifying each cam... hence the C-cam, D-cam, E-cam naming. Later, Lotus changed the part number format, and each cam got it's own discrete part number, and the common name became the last 3 digits of the 'serial number' portion of the part number... ie, 104 & 107 cams. The fact that the 104 cam also has a 104 MOP is purely coincidental. The C-cam, etc, also got new part numbers, but the fans still use the old alpha-names.

(Snip).... The Notes to the bottom left are:
Here's your notes with some info added:
RED DOT ....... 110 MOP = design correct MOP for C-cam & D-cam
BLUE DOT ...... 100 MOP = Federal emissions timing for C-cam & D-cam
YELLOW DOT .. 102.5 MOP = design correct MOP for E-cam.
GREEN DOT .... 104 MOP = design correct MOP for 104 & 107 cams

EUROPEAN SPECS .. INlet ....... 102.5 ATDC .. YELLOW Dot
............................. EXhaust .. 102.5 BTDC .. YELLOW Dot
That's the yellow-dot pulleys for the early Euro 'torque' cam, the E-cam.

NORTH AM SPECS .. INlet ....... 100 ATDC ..... BLUE Dot
............................. EXhaust ... 110 BTDC .... RED Dot

That's the red-blue dot, dual-MOP pulleys for the Federal emissions 907s, with the C-cam. The Red-Blue pulleys could also be used to time the D-cams to 110 MOP.

Tim Engel

Last edited on 07-11-2017 05:29 am by Esprit2