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> Jensen Healey & Jensen GT Tech > Engine & Transmission > Section TDA, 1983-87 Lotus Turbo Esprit Manual |
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> Jensen Healey & Jensen GT Tech > Engine & Transmission > Section TDA, 1983-87 Lotus Turbo Esprit Manual |
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| Section TDA, 1983-87 Lotus Turbo Esprit Manual | Rating: 
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| Posted: 11-03-2005 04:46 am |
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1st Post |
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Esprit2 Member
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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 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 06-17-2019 12:56 am by Esprit2 |
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| Posted: 11-03-2005 03:05 pm |
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2nd Post |
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Mark Rosenbaum Member 
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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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3rd Post |
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Esprit2 Member
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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. ONLY on the 110°/100° "DUAL"-MOP pulley, the 100° MOP blue-dot is really 97° MOP. The pulley's geometry/ math simply does not support 110° and 100° co-existing on the same pulley. So Lotus cheated the 100° timing dot over to the nearest whole tooth, and that was 97° 100° = 100° on a Single-MOP, blue-dot pulley. 100° = 97° on a "Dual"-MOP 'cheater' pulley. If you're just timing factory-stock pulleys with blue-dot/ 100° MOP timing marks, then just align the dots and don't worry about the details. If you're trying to check the cam timing with a degree wheel, the Dual-MOP 100° blue-dot will throw your math a curve... it's really 97°. Apparently, for the 110°/100° "Dual" MOP pulley, Lotus thought it would be less confusing to just stick with the same old blue timing dot (blue = 100°) rather than have to explain what 97° was doing in the mix. However, in the long run, their little 'cheat' seems to have caused more confusion that it has saved. There are minor dimensional differences between early and later pulleys (rim centering on the hub, etc), but they are inconsequential to fit, and they don't alter timing. Interchange to your heart's content. Lotus timing dot colors: 110° MOP = Red Dot 104° MOP = Green Dot 102.5° MOP = Yellow Dot 100° MOP = Blue Dot 115° MOP was JH-only. Lotus never used it, so they didn't assign a timing dot color to it. But whenever I have seen a paint color with 115° it has been white. Regards, Tim Engel Last edited on 06-17-2019 12:57 am by Esprit2 |
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