Cosworth Mk 12,13 and 15 Specs

[elj221c]

I have recently been digging through some Lotus related paperwork for a couple of our members, one of whom was after specifications for Cosworth twincams. I thought that the information may also be interesting to other members so with appologies (and thanks) to Cosworth, here they are.
The hand written notes on page two are mine and relate to the BRM cams I had installed at the time. (1975)

Roy
'65 S2

[Elanintheforest]

Great stuff, Roy. I started researching Sir John Whitmore's / Alan Mann racing Lotus Cortina which won the ETCC in '65, and had got as far as the car had either a Cosworth or BRM engine depending on the race. I only started last night! I think that your papers have answered a few questions....thanks very much!

Mark

[SJ Lambert]

I have recently been digging through some Lotus related paperwork for a couple of our members, one of whom was after specifications for Cosworth twincams. I thought that the information may also be interesting to other members so with appologies (and thanks) to Cosworth
Roy
'65 S2

Yes, thanks very much indeed to you too, Roy.

James

[SJ Lambert]

Do we still reckon 11:1 compression ratio would be the way to go with a bog standard Cosworth motor in an open wheeler??

[rgh0]

The fuel spec was the 100 octane pump fuel of the time for which around 11;1 was maybe the limit with the L1 cams they used. If running Avgas or modern racing fuels and depending on your cams a higher compression is possible in these days.

cheers
Rohan

[SJ Lambert]

So, with these "period" ground figures for the L1 cams, do we make the lobe centres as 106 on the inlet and 98 on the exhaust side with valve timing of 46/78 & 70/54 ?

[rgh0]

106 Inlet and 98 exhaust MOP's dont match modern recommendations for the cams. But you would think Cosworth knew what they were specifying

e.g.
Newmans Cams L1 equivalent for example are recommended at 108 In and 106 ex

cheers
Rohan

[SJ Lambert]

Thanks Rohan - Kent Cams look like they may be 106/106 as well - but I've marked up my wheel to the Cosworth specs and will see how that goes initially (and I've asked MODATEK what they recommend as to optimal settings on the period grind!)