So when I had my motor built I was supposed to be right around 10.5 compression and I had manual compression release installed. I never use them to start the bike and never had an issue, but my question is does that mean that maybe Im not running that compression but actually a lot lower one? Or is 10.5 compression really not that high?

 

Does the bike ever back up against the stock starter??

 

What's the intake close on the cam your running???You could go to Big Boyz website & enter your info.It will give you an estimate of what your running!!!Where your heads CC'd??How thick is your head gasket??

 

Just like Arealinvestor said; get the numbers and go to BigBoyz website.

Also,your starter may have enough nuts to turn it over without issues. I'm at 10.4:1. I have manual decompression and I hardly ever use them. My calculatated PSI is 198. I've never measured it.
I believe Harley upgraded their starters in the early 2000's. Can anyone answer that for me?

 

Thanks for the answers. Ive been running this setup for almost a yr and no issues. Went to big boys and said I was at 10.4. Not a big deal just wondering why some people have to use there release everytime and some people dont when the compression is the same

 

Static CR doesn't tell you much; you need to know cranking compression. When cranking compression hits about 200psi, it's time to start thinking about compression releases and heavy duty battery cables. It will also depend on where you live/ride; sea level is different from Denver.

If you haven't had any kick backs on a 100* day after a gas stop, you cranking compression isn't all that high. A lot of guys, myself included, install compression releases on any performance build just to extend starter and battery life.

 

JITB,
It mostly has to do with when the intake valve closes. A lot of builders think that 165 psi cylinder pressure is the threashold for hard starting. I've never had a hard start.
Most of the time, hard starting is a problem directly related to tuning/ timing, fuel quality and fuel delivery problems.

 

Im pretty much with you on the hard starting related to tuning, I was at my buddys shop this past weekend, he was dynoing a 103 with motor work, and he was using the new powercommander 5? anyway, he can pull timing and add fuel just on start up, pretty neat stuff i thought, wonder why more harley guys dont go that route. chad

 

I live at 4500' elevation but when I start riding down to sea leval this summer on hot day I'll have to see how she acts on a nice hot day and if I need the releases to start her. Everyone thanks for all the info just trying to get more knowledge

 

WARNING! For those that don't know any better (or maybe I'm just an idiot - very likely)
I read this thread and thought the Big Boyz website sounded interesting. So I went to bigboyz.com. It's not a motorcycle site! Next thing I know there are 50 pop up adult websites on my screen and counting and I can't shut my computer down. So I just unplugged it. This is at work and supposedly through a firewall, so be careful folks...for anyother people like me that may not know any better.

Compression releases. The hotter the bikes gets, the harder it will be to turn over. I am at 220 psi and always use my compression releases. Even so I still eventually fried the stock starter. Now I have an aftermarket starter with more power and looks way cooler too - all quality chrome.