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| Joined: | 03-14-2005 |
| Location: | Atlanta, Georgia USA |
| Posts: | 406 |
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Your theoretical analysis of bearing dynamics mirrors my initial work. What opened my eyes was a technical article I read from Clevitte analyzing the performance of 180^, 270^ and 360^ bearing designs. Then I noticed the progression Lotus' made in main bearing combinations in later iterations.
The S1 Esprit essentially used JH bearings, but in subsequent years the middle bottom bearing changed to a plain bearing, then the top bearing changed to a plain bearing and finally the cross-drilled crank of the SE changed every bottom bearing to plain. Lotus' reasoning mirrors exactly what Clevitte said in that article and what every other major manufacturer was doing.
The progression of main bearing design further supports the prototypical nature of the 907 and why given the choice (and funds) it's a good idea to up-grade to later specs. To answer your question a 912LC "should" have iron liners (easily machinable) and a non-cross-drilled crank. Iron liners are attractive and if 912SE plain bearings are available at a reasonable cost the crank can be cross-drilled easily.
Is buying a 910/912SE worth the extra funds if a 912LC is available? Probably not considering the pain it is to re-plate the aluminum liners....except the crank will be forged steel and cross-drilled, but again that's not important for a <200hp build.
Posting dyno plots is a somewhat dangerous thing because the values don't really mean anything. Also the values are totally meaningless unless the same dyno is used for every combination. What ends up happening is everyone starts arguing who's combination has "the most" HP.
A more productive posting would be normalizing the graphs to show the relative shape of the torque curves. I have a graphs from various sources including LotusBits.com (focuses on the results of their porting techniques), but my ultimate goal is to get ALL of the various combinations on the same dyno. As a diagnostic tool such graphs can help everyone understand the differences in cam timing, ignition timing, cam duration, header selection and carb jetting.
Judson