crazy compression question
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Road Master
Joined: Aug 2008
Posts: 1,181
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crazy compression question
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?
Road Warrior
Joined: Oct 2009
Posts: 1,251
Likes: 1
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?
Road Master
Joined: Jun 2008
Posts: 868
Likes: 1
From: Trenton,N.J.
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?
Road Master
Joined: Jan 2008
Posts: 853
Likes: 5
From: Mnpls MN
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?
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?
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Road Master
Joined: Aug 2008
Posts: 1,181
Likes: 2
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
HDF Community Team
Joined: Jun 2006
Posts: 12,774
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From: san antonio
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.
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.
Road Master
Joined: Jan 2008
Posts: 853
Likes: 5
From: Mnpls MN
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.
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.
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Road Warrior
Joined: Oct 2009
Posts: 1,251
Likes: 1
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.
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.
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Road Master
Joined: Aug 2008
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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.
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.
Cruiser
Joined: Sep 2007
Posts: 157
Likes: 0
From: South Carolina
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.
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.