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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
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Update that is a 910 engine not a 920..andMax_dvdt wrote:
We are in the process of fitting a 910 block+sumpGentlemen,
If you have a 910 already, then it's a good start. The 910's compression is 'turbo' low, so you'll need new pistons, but everything else is there, including a cross-drilled crank.
If you don't have an engine yet, then consider starting with a 912, preferrably a 912HC (high compression). That way it will come with useable pistons (LC = 9.44:1, and HC = 10.9:1). If you're dumping the 'turbo' anyway, and building a naturally aspirated engine, then the rest of the 910 - 912 differences aren't great enough to worry about for a street engine.
The late 910S is the ultimate 9XX 4-cylinder. It does have larger intake ports with improved shapes, and the intake valves are 1mm larger in OD. All the other/ earlier 910s have the same valve diameters as all the lesser, naturally aspirated 9XX engines.
All Turbo exhaust valves have sodium filled stems, which are larger in diameter, and require the otherwise same basic heads to be bored larger to accept the larger valve guides for the fatter stems. But sodium filled valve stems are not an advantage for a naturally aspirated engine, since they're not needed to deal with excessive heat; and the more slender, non-sodium filled stems are less distruptive and flow better.
A 912 would have the same wide Main Bearing Panel as the 910 (the only 'wider' part of the block ass'y) and matching larger sump. Block-ass'y strength is very similar.
Depending upon what your goals are for the build, a 910 and 912LC would come with two 107 cams, while the 912HC has one 104 cam on the intake, and a 107 on the exhaust.
No matter what the rest of your build goals are, buy a new set of steel, long-skirt tappets. The original chilled cast iron tappets tend to fatigue with age (iron does that), and they're all old by now. Also, it's not a good idea to run aggressive cams on the old cast iron tappets, regardless of their age.
Aggressive cams put more side thrust loads on the tappets, and longer-skirts help keep the tappets from cockng/ binding in their bores. Garry Kemp and JAE (and probably others) have aftermarket long-skirt steel tappets that are both better, and cost less than the Lotus cast iron tappets. They also have steel tappets with different crown thicknesses in order to compensate for re-ground cams.
Regards,
Tim Engel
PS... just to be clear:
910 = 2.2 Turbo.
920 = 2.0 Turbo.
Last edited on 09-27-2019 09:23 pm by Esprit2