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The early motors had 9.25 to 1 compression and the late ones had 9 to 1.
The 74 mm Wiseco piston creates more compression with essentially the same dome volumn as the stock late piston because it is larger and has more swept volumn and because it is larger in diameter it's dome is shorter than the late stock piston even while both have 6cc's of dome volumn.
To make a long story short, a set of 74 mm Wiseco's in a early motor will make about 10.2 compression as advertised by Wiseco however in a late motor they will only make about 9.5 if everything is stock (uncut).
Originally posted by trbig
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Hey, Dan. Here's a pic of the domes of the early vs late piston on the same pin.
The 74mm Wiseco piston is domed somewhere between those two. I couldn't find my picture of it. Not as high as the late OEM, but higher than the earlier OEM. So, effectively, Wiseco will bump up compression over OEM on an early model motor, but decrease compression a touch on the late models.
I don't get it? Larger valves, but larger valve relief area and less compression than earlier models, even with the higher domed pistons. Was this a typo, or were you meaning that if compression was the same, the bigger valves win?
The 74mm Wiseco piston is domed somewhere between those two. I couldn't find my picture of it. Not as high as the late OEM, but higher than the earlier OEM. So, effectively, Wiseco will bump up compression over OEM on an early model motor, but decrease compression a touch on the late models.
I don't get it? Larger valves, but larger valve relief area and less compression than earlier models, even with the higher domed pistons. Was this a typo, or were you meaning that if compression was the same, the bigger valves win?
The 74 mm Wiseco piston creates more compression with essentially the same dome volumn as the stock late piston because it is larger and has more swept volumn and because it is larger in diameter it's dome is shorter than the late stock piston even while both have 6cc's of dome volumn.
To make a long story short, a set of 74 mm Wiseco's in a early motor will make about 10.2 compression as advertised by Wiseco however in a late motor they will only make about 9.5 if everything is stock (uncut).
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