Today my googlefu is strong
I started by plugging the known numbers into a compression ratio calculator from summit racing, but the swept volume wasn't correct, so I tried this one Omni Compression Ratio Calculator
Knowns
Bore 72mm
Stroke 82mm
Cylinders 4
Head Gasket thickness 1.4mm
Head Gasket Bore 74mm
Combustion chamber (STD) 45.1cc
Unknowns
(guesses that made the final compression ratio number look right)
Deck clearance 1.8mm the CROWN of the piston clears the deck by a couple of mm eye balled, I've asked if anyone in the Acclaim FB group has access to a short block to measure it, if not ill get the number as soon as I am well enough to pull the head off the spare engine that's sat on the floor in the workshop.
Piston dome size 0.5cc a total guesstimate as it's a very shallow dome.
This bought the CR out to 8.414:1 which is close enough to the 8.4:1 quoted everywhere.
Taking 5.54cc off for the 1mm skim gives a CR of 9.435:1 as frank sits now.
Fitting the larger pistons, +2mm bore = 74mm.
Swept volume of 1410cc with a CR of 8.904 on an STD head or 10.025:1 on Frank's skimmed head
Offset grinding the crank adding +2mm stroke = 84mm and +1mm to the deck height.
Swept volume of 1445cc with a CR of 9.96:1 on an STD head or 11.388:1 on franks skimmed head
This leads me back to my big takeaway from Dark Towers, the exhaust valve really could do with being a touch bigger.
And that's where I come to a complete dead end, I've not managed to find anything that's even close.
I started by plugging the known numbers into a compression ratio calculator from summit racing, but the swept volume wasn't correct, so I tried this one Omni Compression Ratio Calculator
Knowns
Bore 72mm
Stroke 82mm
Cylinders 4
Head Gasket thickness 1.4mm
Head Gasket Bore 74mm
Combustion chamber (STD) 45.1cc
Unknowns
(guesses that made the final compression ratio number look right)
Deck clearance 1.8mm the CROWN of the piston clears the deck by a couple of mm eye balled, I've asked if anyone in the Acclaim FB group has access to a short block to measure it, if not ill get the number as soon as I am well enough to pull the head off the spare engine that's sat on the floor in the workshop.
Piston dome size 0.5cc a total guesstimate as it's a very shallow dome.
This bought the CR out to 8.414:1 which is close enough to the 8.4:1 quoted everywhere.
Taking 5.54cc off for the 1mm skim gives a CR of 9.435:1 as frank sits now.
Fitting the larger pistons, +2mm bore = 74mm.
Swept volume of 1410cc with a CR of 8.904 on an STD head or 10.025:1 on Frank's skimmed head
Offset grinding the crank adding +2mm stroke = 84mm and +1mm to the deck height.
Swept volume of 1445cc with a CR of 9.96:1 on an STD head or 11.388:1 on franks skimmed head
This leads me back to my big takeaway from Dark Towers, the exhaust valve really could do with being a touch bigger.
And that's where I come to a complete dead end, I've not managed to find anything that's even close.
