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Section TDA, 1983-87 Lotus Turbo Esprit Manual  Rating:  Rating
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 Posted: 11-03-2005 04:46 am
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Esprit2
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This probably amounts to waste of bandwidth by double-posting;  however,  I felt posting this info in the Engine & Transmission forum made more sense.   It was originally posted in a carburettor message that ran wide of the topic.

Tim

*~*~*~*~*~*~*~*~*~*

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 son's website:

http://www.tc.umn.edu/~enge0214/lotus/     (TDA.pdf  and  TDB.pdf)

There is one bit of a caveat for J-H owners using Lotus data...   cam timing specifically…

There is a difference between early J-H cams & pulleys and the Lotus versions of the same parts.   In matched combinations  (JH/JH  &  Lotus/Lotus)  the nominal timing events are the same;  however, the hardware is different by a small change in the angular placement of the keyways.   The same difference is applied to both the cam & pulley in each pair so that the J-H pulley & cam together give the same nominal cam timing as the Lotus cam & pulley give together  (nominal being 110°).   But installing a Lotus pulley on an older J-H 907 cam will increase the MOP 7.5°, and installing a J-H pulley on a Lotus cam will reduce the MOP 7.5°.

On either engine, 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.   Similarly,  the Lotus dual MOP pulley gave 110° & 100°.   In order to produce those different combinations,  different keyway locations were required on both the cams and pulleys.   Later J-H engines also used the 110° / 100° pulley and from that point on have full cam/pulley compatibility with Lotus.   Prior to that time,  care is required not to mix and match similar looking sibling parts.

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 (the alternate 115° & 100° MOP's are both for playing emissions games and not desirable) and would both be at some risk of an MOP-error if used with early J-H pulleys.   All other Lotus cams listed in Section TDA have different MOP's and require different matching pulleys  (E-cam/ 102.5° pulley, 107-cam/ 104° pulley, 104-cam/ 104° pulley),  so there's little chance of mixing-n-matching there.

Other than that, there shouldn't be any land mines hiding in Lotus Section TDA waiting to pounce on J-H owners.   Indulge in good health.

Tim

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 Posted: 11-03-2005 03:05 pm
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Mark Rosenbaum
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So... if I understand you correctly, you're saying that if I have a pulley with, for example, the markings 'IN 110' and 'EX110' actually cast into the metal by the factory, and with no strikeouts of nor alterations to those markings, the pulley might in fact not actually offer that cam timing???

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 Posted: 11-05-2005 03:39 am
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Esprit2
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Mark,

Yes.  (Snip)...




Edit 5-31-2009 by Tim Engel


No.   As it turns out, there's no difference between the J-H and Lotus versions of the cams and pulleys.   The 100 MOP blue-dot pulley is really 97 MOP.   For some unknown reason, the factory rounded this one off,  while all others are correct as marked.   The difference was thowing off my calculations.   In a recent conversation with Lotus Cars,  the engineer told me the correct value is 97 MOP.   Given that into, everything adds up.

There are minor dimensional differences between early and later pulleys, but they inconsequential to fit and don't alter timing.

Interchange to your heart's content.

Tim Engel

Last edited on 05-31-2009 08:17 pm by Esprit2

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