Re: 300hp Motor rebuild....
IIRC the early 300 HP engines had an advertised CR of 10.5, but it was dropped to 10.25 in later years, possibly due to the larger chambers of the 462 heads, which elimnated the plug side quench zone of the 461s, but as was typical, "as built" these engines, and all engines of that era, were probably a half a point lower.
I believe steel shim gaskets are available, but can't quote any sources.
"Advertised" CR always includes implicit assumptions, and it's too bad they are not more explicitly stated. This applies to both OE and aftermarket.
A piston advertised as XX.X:1 CR ASSUMES several dimensions. Usually on a SB a nominal deck height of 9.025" is assumed, but most were machined high at Flint as I previously stated. Also, the advertised CR assumes a particular head gasket thickness, which is often not specified, and a chamber volume is assumed or stated.
So what's the piston compression height, volume, assumed deck clearance and gasket thicknesss for the specified range of CR for your proposed pistons.
Like I keep saying, it's all in the details. The difference between a shim gasket and a composition gasket - 15 to 20 thou - is half a point! And typical high decks cut the actual CR another quarter point or so relative to "advertised".
That's why I keep harping about measurilng deck clearance prior to disassembly. It tells you if the decks are parallel to the crankshaft axis and how high they are relative to nominal specs, and with this data you can compute the CR of the engine prior to disassembly assuming you have the compression height and volume of the installed pistons. Combine the measured deck height with the compression height and volume of the new pistons and you can compute the new CR with various head gaskets.
Combine the above with your prior experience with the engine. Did it have a tendency to detonate? If so, lowering the CR with a thicker gasket may be in order.
Is one deck side higher than the other? If the LH side is high it can be cut down to equal the right and achieve a consistent ratio side to side.
In order for you to achieved the "advertised" CR of you '64 327/300 I can just about guarantee that you would have to deck BOTH sides of the block, which would wipe out the stamp pad, which is definitely not a good idea. And you would have to used a thin shim gasket. And I can also just about guarantee you that this set up will detonate unless you ran a very lazy advance curve, which will lower the torque curve, especially at the bottom end.
The highest actual CR I recommend for your engine is 9.75:1 and with a composition gasket, OE or equivalent piston compression height, and typical deck height I doubt if the assembled engine with exceed this value, but start with the teardown measurements, calculate the CR of the existing setup, a new proposed setup and go from there.
Duke
IIRC the early 300 HP engines had an advertised CR of 10.5, but it was dropped to 10.25 in later years, possibly due to the larger chambers of the 462 heads, which elimnated the plug side quench zone of the 461s, but as was typical, "as built" these engines, and all engines of that era, were probably a half a point lower.
I believe steel shim gaskets are available, but can't quote any sources.
"Advertised" CR always includes implicit assumptions, and it's too bad they are not more explicitly stated. This applies to both OE and aftermarket.
A piston advertised as XX.X:1 CR ASSUMES several dimensions. Usually on a SB a nominal deck height of 9.025" is assumed, but most were machined high at Flint as I previously stated. Also, the advertised CR assumes a particular head gasket thickness, which is often not specified, and a chamber volume is assumed or stated.
So what's the piston compression height, volume, assumed deck clearance and gasket thicknesss for the specified range of CR for your proposed pistons.
Like I keep saying, it's all in the details. The difference between a shim gasket and a composition gasket - 15 to 20 thou - is half a point! And typical high decks cut the actual CR another quarter point or so relative to "advertised".
That's why I keep harping about measurilng deck clearance prior to disassembly. It tells you if the decks are parallel to the crankshaft axis and how high they are relative to nominal specs, and with this data you can compute the CR of the engine prior to disassembly assuming you have the compression height and volume of the installed pistons. Combine the measured deck height with the compression height and volume of the new pistons and you can compute the new CR with various head gaskets.
Combine the above with your prior experience with the engine. Did it have a tendency to detonate? If so, lowering the CR with a thicker gasket may be in order.
Is one deck side higher than the other? If the LH side is high it can be cut down to equal the right and achieve a consistent ratio side to side.
In order for you to achieved the "advertised" CR of you '64 327/300 I can just about guarantee that you would have to deck BOTH sides of the block, which would wipe out the stamp pad, which is definitely not a good idea. And you would have to used a thin shim gasket. And I can also just about guarantee you that this set up will detonate unless you ran a very lazy advance curve, which will lower the torque curve, especially at the bottom end.
The highest actual CR I recommend for your engine is 9.75:1 and with a composition gasket, OE or equivalent piston compression height, and typical deck height I doubt if the assembled engine with exceed this value, but start with the teardown measurements, calculate the CR of the existing setup, a new proposed setup and go from there.
Duke
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