View single post by subwoofer
 Posted: 01-31-2014 09:16 am
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subwoofer

 

Joined: 04-01-2008
Location: Sandefjord, Norway
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MOP is also known as LCA, Lobe Centre Angle.

For 260 degree cams and 110/110 timing, you will have the following timing:

Ex: Open 60 degrees BBDC, close 20 degrees ATDC
In: Open 20 degrees BTDC, close 60 degrees ABDC
Overlap: 40 degrees

Same cams, 115/115 timing:
Ex: Open 65 degrees BBDC, close 15 degrees ATDC
In: Open 15 degrees BTDC, close 65 degrees ABDC
Overlap: 30 degrees

I am no expert, but large lobe separation angles are by some (like David Vizard) claimed to be a band-aid to make too-long-duration-for-the-purpose cams behave on the street. His claim is that the ideal lobe separation angle is an engine characteristic and that cam duration should be chosen for the desired overlap at this particular LSA (or (MOPex + MOPin)/2).

Since later 907s and 912s came with 104 degrees LSA, this could be considered to be a good choice. Vizard claims that too narrow LSA is preferable to too wide LSA, and that the ideal value varies in the interval 110 to 100 degrees depending on valve geometry and head flow.

So for streetability, that theory would indicate that you need short, high-lift cams at 104MOP. The 107 cams did just that, shortened duration and higher lift compared to C, D and E cams.
--
Joachim

Last edited on 01-31-2014 09:17 am by subwoofer