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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
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Tim
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I think every naturally aspirated 9XX owner (Lotus or J-H) should have a copy of Section TDA (Technical Data A, Naturally Aspirated 907/912… and optionally, TDB – Turbo 910) to supplement their Workshop Manual Technical Data Section. I've posted them in PDF format on my Dropbox folder, here:
https://tinyurl.com/y32bdnyk -- TDA, Naturally Aspirated 907, 911, 912
https://tinyurl.com/y3e6x558 -- TDB, Turbo 910
There is one bit of a caveat for J-H owners using Lotus data... cam timing specifically. And not so much a caveat, as you need to know what you're doing if you're going to play around.
Increasing MOP Advances the exhaust and retards the intake. Reducing MOP retards the exhaust and advances the intake.
J-H used a dual MOP pulley that gave 110° or 115° MOP depending upon which side of the pulley faced forward. On that pulley, both MOPs are accurate as marked.
Similarly, another Lotus dual MOP pulley gave 110° & 100°. However, in that case, the pulley's math doesn't support having 100° MOP co-exist with 110°. So the 100° timing mark was moved to the closest whole-tooth timing position that did co-exist, 97°. It's a 'cheat' to force 100° MOP onto the same pulley with 110° MOP. The Spec 7 emissions timing is going to seriously screw-up how the Federal 907 runs anyway, so what's another 3° ? :-/
On a single-MOP 110° pulley, and on a single-MOP 100° pulley, both MOPs are accurate as marked.
However, on a dual-MOP 110°-100° pulley, 110° is accurate as marked, BUT 100° is really 97°.
On a dual-MOP 110°-115° pulley, both MOPs are accurate as marked.
All other Lotus pulleys are single-MOP, and accurate as marked.
Both 115° and 100° were Federal emissions cam timing settings, and neither are desireable. J-H's 115°/115° timing reduces the output by 10+ horsepower and makes the engines seem... well, less than awake. The 110°/100° is part of Lotus Spec 7, the worst of the Federal Emissions specs, and responsible for the "Torqueless Wonder" moniker. Given a choice, you don't ever want to use either 115°/115°, or 110°/100°, so discussing either setting any further is a waste of bandwidth.
The early J-H cam/pulley's timing events match those of what Lotus called it's C-cam. The Lotus C-cam and D-cam both use a nominal 110° MOP. All other Lotus cams listed in Section TDA have different MOP's and require different matching pulleys. If you wish to install either 104 or 107 cams, they you must also purchase new 104° MOP pulleys to go with them. You can NOT 'adjust' your stock C-cam pulleys to work correctly with either of those cams.
Lotus' Design-Correct Cam Timing:
C-cam = 110° pulley (115° & 100°/97° were for emissions only, and are NOT design-correct)
D-cam = 110° pulley
E-cam = 102.5° pulley
107-cam = 104° pulley
104-cam = 104° pulley
115°, 110° & 97° all exist on the same pulley, whether they're all marked or not. If your J-H's cams are timed to either 115° or 100°, and you wish to re-time to 110° Int / 110° Exh, you don't need to buy new pulleys. Just figure out where the 110° should be, and re-position the pulleys as required to give 110°/110°.
The following represents the timing mark locations as they would appear on your J-H 907's pulleys with the cams timed to 115°/115°.
. . 97° IN --- 97° EX, one tooth above the centerline between the two cams
. 115° IN --- 115° EX, aligned ON the imaginary centerline between the two cams.
. . .Tooth --- Tooth (blank, no timing marks)
. . .Tooth --- Tooth (blank, no timing marks)
110° EX --- 110° IN, three teeth below the centerline between the two cams
NOTE that the IN & EX marks next to the 110° timing marks are reversed compared to those next to 115°. You can NOT simply slide the belt off, rotate the pulleys three teeth, and re-install the belt. It's not that easy. In order to re-time from 115°/115° to 110°/110°, you must first remove the pulleys, flip them over front-to-back, re-install them, then rotate them three teeth to align 110° IN & 110° EX on the imaginary centerline between the two cams.
What you want to see is:
. 110° IN --- 110° EX, aligned ON the imaginary centerline between the two cams.
. . .Tooth --- Tooth (blank, no timing marks)
. . .Tooth --- Tooth (blank, no timing marks)
115° EX --- 115° IN, three teeth below the centerline
. 97° EX --- 97° IN, four teeth below the centerline
Other than needing to know how to correctly apply the cam timing specs, there shouldn't be any land mines hiding in Lotus Section TDA.
Regards,
Tim Engel
Last edited on 06-16-2019 11:56 pm by Esprit2