I have a mk1 Cortina with a aspirated yb. Specs of the engine are:
2wd cosworth sierra engine
accralite pistons that shall give a compression ratio of 11,7:1, 92 mm bore
Longneck valves and solid followers
L1 cams
Ported head
48 mm throttle bodies
Megasquirt

I have had some thoughts about the cam settings and compression. If I set the cams at recommended 47-79/79-47 giving 106 ATDC/ BTDC fully open the compression pressure is 18 (250psi) bars. I have advanced the exhaust cam 3dgrs and retarded the inlet cam 3dgrs and managed to reduce the compression down to 16 bar to be able to drive the car at all.
Still I have to retard ignition to 30 dgrs to make the knocking stop.

Has anyone any good ideas about what compression ratio to have in the engine with the cams set at more modern recommendations at in/ex 47-79/71-55 (fully open at in 106atdc and ex 98 btdc)?
Or any better ideas about the cam settings?
And also, any ideas about what compression pressure to have?

 

i would contact one of the following companys.... they all build nice atmo cossie engines

wpe (wacky performance engines0
vulcan engines
ht racing