Any info on installing a 37/33mm valve Scrambler head onto a 350 bottom end with stock piston, re compression ratio? Does it go up, down, stay the same?
I know about fitment details. I'm just looking to understand whether a stock piston will work well, or if I need to buy something more agressive for decent performance.
I surely want something better than Sebring performance, and I'm afraid the bigger ports alone might not do properly.
Thanks, Joe
Ducati 350 NC with 250 Head Compression
Hey Joe,
The 250/350 narrow case heads are basically the same and will all interchange. The 350 is only 2mm larger in bore size than the 250. There is no significant difference in the combustion chamber volume of the various heads. The difference is in the port sizes. The Sebring (and Monza) already have 37mm intake valves. The SCR actually has a 36mm intake valve but the port is bigger to match the SS127 carb used on the SCR vs. 24mm UBF on the Sebring/Monza. The Sebring has the lowest compression specification of all the N/C 250/350's. The piston crown is basically flat. But, Dr. T may have had a good reason for this: The N/C kickstarter arrangement was notoriously weak. The 350 (and only the 350) came equipped with a compression release (actually just an exhaust valve lifter) for starting, probably in recognition of the marginal kickstarter system. Was the low compression on the Sebring also a compromise due to concerns over starting? If you're going to install an SCR head, larger carb and use the SCR cam, you'll need to bring the compression up to realize the full benefits of this specification. Longer duration cams always demand more compression. Also, brush up on your "run-and-bump" technique...
The 250/350 narrow case heads are basically the same and will all interchange. The 350 is only 2mm larger in bore size than the 250. There is no significant difference in the combustion chamber volume of the various heads. The difference is in the port sizes. The Sebring (and Monza) already have 37mm intake valves. The SCR actually has a 36mm intake valve but the port is bigger to match the SS127 carb used on the SCR vs. 24mm UBF on the Sebring/Monza. The Sebring has the lowest compression specification of all the N/C 250/350's. The piston crown is basically flat. But, Dr. T may have had a good reason for this: The N/C kickstarter arrangement was notoriously weak. The 350 (and only the 350) came equipped with a compression release (actually just an exhaust valve lifter) for starting, probably in recognition of the marginal kickstarter system. Was the low compression on the Sebring also a compromise due to concerns over starting? If you're going to install an SCR head, larger carb and use the SCR cam, you'll need to bring the compression up to realize the full benefits of this specification. Longer duration cams always demand more compression. Also, brush up on your "run-and-bump" technique...