L4 cam spec?

[hansaxl]

Hi,

after a search here and on the web I cannot find the specification of the so-called "L4" cam. Could somebody please help me out?

Thanks in advance, Cheers,

Hans

[rgh0]

These are the specs for the Burton part "BLL4" - which is a copy of the original Cosworth L4 profile I believe.

3500-8000rpm. Valve lift .420". Duration 304deg. Timing 50/74/74/50. Timing at full lift 102deg ATDC. Valve clearances .008"/.009"

If using a camshaft like this you should get it drilled for long sprocket bolts and you also need to modifiy your valves and springs to get the lift to fit in.

There are better more modern profiles than this that fit the same or higher lift into a shorter duration and give you similar top end power but better midrange torque.

cheers
Rohan

[StressCraxx]

These are the specs for the Burton part "BLL4" - which is a copy of the original Cosworth L4 profile I believe.

3500-8000rpm. Valve lift .420". Duration 304deg. Timing 50/74/74/50. Timing at full lift 102deg ATDC. Valve clearances .008"/.009"

If using a camshaft like this you should get it drilled for long sprocket bolts and you also need to modifiy your valves and springs to get the lift to fit in.

There are better more modern profiles than this that fit the same or higher lift into a shorter duration and give you similar top end power but better midrange torque.

cheers
Rohan

We used those cams in a Twink in a Formula B Brabham BT18/21. The .420 lift requires the spring perches in the head to be machined deeper by about 0.050". Max lift on a stock head is .380 if I recall correctly. Rohan is correct about its useable rev range and specs.

Regards,
Dan Wise

[rgh0]

[quote="StressCraxx The .420 lift requires the spring perches in the head to be machined deeper by about 0.050". Max lift on a stock head is .380 if I recall correctly.
Regards,
Dan Wise[/quote]


Hi Dan
A stock head with stock springs is limited to around .380 lift like you say. However these days you dont need to deepen the pockets for higher lift. With the correct selection of component details (e.g. valve length, springs and retainers, thin buckets, cam base circle.) you can achieve 0.5 inch lift within the standard pocket depth.

cheers
Rohan

[StressCraxx]

Rohan,

Thanks! That's good to know. The machine work was very expensive, even in 1971.

Dan