Motor is a 454 chevy with 15:1 compression
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Raising CR with restrictor plate is going in correct direction !
but , are you really sure you actually have a measured 15:1 CR ??? because its very hard to get that knid of CR on a BBC 454 cid engine size even with decking and angle-milling
unless you are using other than OEM conventional valve angles/tilt and chamber design .
Many years ago i used the highest CR Speed Pro and TRW
pistons available for BBC-454
TRW and SP said their dome volumes were 50 CC ,
i was coming up with 44.5 CC at most ...it took about
half an hour to actually talk to an engineer at Speed Pro=Sealed Power ..he said they use a term called Effective Dome Volume ...which he said means they pour the dome with clay filling up valve notches ..and so the domes look better than they are .
So during that week many years ago , i also poured Manley's Pro Series Dome for BBC-454 ..they said it was 52 CC,
i told them i was coming up with 48 CC ....about a year later in Manley's next cataloge , i noticed the dome was rated at 50 CC ...another few years later in a newer cataloge , Manley rated the same dome to 48 CC
don't trust the piston people on dome volumes ..pour the domes yourself .
you'll be very lucky to get 15:1 CR with angle-milling and block decking and no flycutting, and small duration spread-center cams ,...thats what it will take to get 15:1 actual on a conventional head 454 Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers