Hello All and Happy new Year.
I am in the process of rebuilding my MK3 850. I swapped out the stock cam for a Megacycle 560NR cam, and went with .040" over JCC pistons in the cylinder barrels, so it's a true 850 CC's. After carefully measuring (and matching) the combustion volumes in the RH4 cylinder head I came up with 51CC for both sides. I am now trying to decide on the thickness of my copper head gasket. I have both a .030", and a .040" thick gasket to choose from. When I do the arithmetic with the .030" thick gasket I get a theoretical 8.79 compression ratio, and if I use a .040" thick gasket the ratio drops to 8.62.
Conventional wisdom says to up the compression ratio with a hotter cam to make up for the increased open valve duration, but how much do you increase compression? Megacycle's 560NR cam is their mildest grind with only .030" added lift and 10 degrees more duration. I am worried that the higher compression ratio may be too high and lead to detonation. I will be running 32MM twin carbs.
Any thoughts from users in the know would be greatly appreciated.
Rick
I am in the process of rebuilding my MK3 850. I swapped out the stock cam for a Megacycle 560NR cam, and went with .040" over JCC pistons in the cylinder barrels, so it's a true 850 CC's. After carefully measuring (and matching) the combustion volumes in the RH4 cylinder head I came up with 51CC for both sides. I am now trying to decide on the thickness of my copper head gasket. I have both a .030", and a .040" thick gasket to choose from. When I do the arithmetic with the .030" thick gasket I get a theoretical 8.79 compression ratio, and if I use a .040" thick gasket the ratio drops to 8.62.
Conventional wisdom says to up the compression ratio with a hotter cam to make up for the increased open valve duration, but how much do you increase compression? Megacycle's 560NR cam is their mildest grind with only .030" added lift and 10 degrees more duration. I am worried that the higher compression ratio may be too high and lead to detonation. I will be running 32MM twin carbs.
Any thoughts from users in the know would be greatly appreciated.
Rick