choosing pistons and cam 327 FI its complicated
03-19-2019, 02:34 PM
#41
Le Mans Master
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Location: Las Vegas - Just stop perpetuating myths please.
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The sky is the limit on blueprinting and expensive parts. If you can't live with old thumb rules like max compression for iron heads is below 9.5:1 c.r.. That and using published volume numbers instead of measuring volumes with lquid may or may not be good enough. It's up to you and your expectations. Modest performance with good drivability doesn't have to be rocket science as the stock engines where a good example when new 30 yrs ago.
But some just don't trust the published numbers for volumes and or need cutting edge blueprinting and that does take more time, skill and knowledge. Only you can choose what you really need for yourself.
Good luck.
But some just don't trust the published numbers for volumes and or need cutting edge blueprinting and that does take more time, skill and knowledge. Only you can choose what you really need for yourself.
Good luck.
03-21-2019, 10:48 AM
#42
Le Mans Master
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Location: "You may all go to Hell- and I will go to Texas- Davy Crockett
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St. Jude Donor '12
Nominal deck height is 9.025". The nominal sum of crank throw radius (1.625"), nominal rod center to center length (5.700') and nominal piston compression height (1.675") is 9.000", so nominal deck deck clearance is .025".
The biggest variable is deck height. As the broach tools wear, it increases. I've seen decks up to .015" high and .010" side to side variation. This is why deck clearance must be measured to accurately achieve a target compression ratio. Otherwise you're just guessing.
The best time to measure deck clearance is before the block is disassembled. Each cylinder should be measured to determine if there is any slope (usually it's not enough to be of concern). Then the new deck clearance can be determined using values for the new parts. Some replacement pistons like KBs have slightly higher compression height than OE.
If the left deck is higher than the right it can be machined down to equal the right side without consequence because the machine work is not visible once the head is installed. The right deck should not be touched to preserve the original stamped data and broach marks. Another alternative is to use different thickness head gaskets side to side to make up for any variation in side to side deck deck. This will help equalize SCR on all eight cylinders. I like to keep max variation to no more than 0.1 and 0.05 is preferred.
The above is why I am always harping about PLANNING and doing a FORENSIC TEARDOWN if you want a truly precision engine that maximizes performance and doesn't detonate. Just tearing down the engine and sending everything to the machine shop is a recipe for disaster and there are many horror stories on the Web. The final outcome will be directly proportional to your planning and forensic teardown effort, but all too many guys completely ignore this.
Duke
The biggest variable is deck height. As the broach tools wear, it increases. I've seen decks up to .015" high and .010" side to side variation. This is why deck clearance must be measured to accurately achieve a target compression ratio. Otherwise you're just guessing.
The best time to measure deck clearance is before the block is disassembled. Each cylinder should be measured to determine if there is any slope (usually it's not enough to be of concern). Then the new deck clearance can be determined using values for the new parts. Some replacement pistons like KBs have slightly higher compression height than OE.
If the left deck is higher than the right it can be machined down to equal the right side without consequence because the machine work is not visible once the head is installed. The right deck should not be touched to preserve the original stamped data and broach marks. Another alternative is to use different thickness head gaskets side to side to make up for any variation in side to side deck deck. This will help equalize SCR on all eight cylinders. I like to keep max variation to no more than 0.1 and 0.05 is preferred.
The above is why I am always harping about PLANNING and doing a FORENSIC TEARDOWN if you want a truly precision engine that maximizes performance and doesn't detonate. Just tearing down the engine and sending everything to the machine shop is a recipe for disaster and there are many horror stories on the Web. The final outcome will be directly proportional to your planning and forensic teardown effort, but all too many guys completely ignore this.
Duke
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cardo0 (03-21-2019)