So, I spoke with Tman Performance this week, initially about using their 590PS-2 cams in my build, but the conversation quickly turned to everything related to my build. Because I live and ride at 3000 ft elevation, I am fighting an uphill battle to get my corrected compression and cold cranking pressure in line with the performance that most people who live at sea-level enjoy automatically with a straight up build. Since I am learning a foreign language with all of this, I believe that I was told that I should utilize a high compression piston (their oversized 4.127” 5cc pistons) rather than take too much out of the heads to try to achieve most of my desired compression, and then zero deck the heads, port/polish/flow them, and install larger intake valves (2.10”) and better springs. They told me they would hone the cylinders I get with the kit for the oversized pistons, and that try to build to 200-205 cold cranking pressure, and that my elevation is going to require at least 11:1 static compression to get near that. I’m not sure I want to go to 11:1 compression, as I do want a street-able and reliable machine.
I’m figuring that if I’m running ~192 ccp at 3k elevation I’ll probably be just fine and happy, but to get there it looks like I will need to start with approximately 10.9:1 compression at a minimum, assuming my head volume is about 95cc to start.
The Harley guys tell me it’s better to mill the heads for compression, than it is to use HC pistons (and I’m not really sure that I understand why that is…) but if I get .032-.040 into the heads it doesn’t seem like there is still a lot of room for oversized valves, or a lot of meat left for reliability. I’d like to be able to ride on pump gas (91 octane with ethanol) without any issues. I’d like to be able to ride down to sea-level and not have to worry about low rpm manners in traffic, over-heating, and what quality gas is available.
I am trying to build a 130/130 relatively flat torque curve motor, but I want that motor to behave exceptionally well at low speeds, and be drivable. I’d love to avoid lurching, missing, popping, ticking, detonation, knocking, reversion, etc… I’m afraid if I take the compression to 11:1 or beyond I am just asking for all of that to be my reality.
I know I’m overthinking this, but I’m just trying to understand it, so that I can actually convey to those involved what I want to do, and make some well advised decisions.
Any input here would be SUPER helpful. Please and thank you!