Cam timing.. S50 (+ dynamic CR)

[Jhonno]

Looking at a cam data sheet, for the inlet (Vanos) cam it shows timing as

20-84 62-42

Now I am reading that as IO (Inlet open) 20-62 Deg Before TDC

IC (Inlet closed) 84-42 After BDC

Does this seem about right?

It is important in working out the dynamic compression ratio of the lump..

@84 ABDC it is ~ 8.25:1, however at 42 it is ~ 11.42:1 which is quite high. Anyone know if that would be ok with 97 Ron? Alot of the info online is based on Yank Tank lumps with cast iron heads, which says 8.0:1 is about right for a street lump, I assume on their shitty 91/93 Ron. Alloy heads require about 8.5:1 due to their extra heat conduction.. I can't seem to find much UK based, on modern, none carthorse powering, 4v lumps..

[glenn]

the s54 has a cr of 11.5;1 and the s85 has a cr of 12.0;1
both of them use 97 ron dan.
hth

[UweM3]

careful dude, US fuel numbers may be in AKI which is different to RON

90-91 AKI = 95 RON
93-94 AKI = 98 RON

[Jhonno]

Pretty sure it's referring to 'pump gas' which is 91-93.. I will check!

Glenn, the static compression ratio is very much a theoretical 'ideal' figure.. If the Inlet closes after BDC it reduces the 'effective stroke' and lowers the dynamic compression ratio