compression how high
Thread Starter
|
Intermediate
Joined: Dec 2005
Posts: 25
Likes: 0
From:
compression how high
hi there are there any out there who know if the compression on my 2007 street bob is geting higher if i do a 103 big bore i thing the stock is 9,2:1 if it does how mutch, would the se204 cam be ok with stock heads?
Road Master
Joined: Jul 2005
Posts: 1,061
Likes: 5
From: Fort Worth TX
RE: compression how high
Yes your compression would go up due to the fact you are increasing bore volume and the head chamber is still the same size ,. so you are going to be compressing more area into the same area. I based this on a 85 CC chamber ( stock is from 84-88) you would be at 9.9.1 range with a .040 head gasket. That type of compressin I would suggest a larger cam to keep thing in check. Have you looked or thought about cam other than SE?? There are several that would offer great power in the 103 . I would increase the comp level some and use a andrews 55 or a woods tw7 cam. I run the 204 to a limit of 9.8. If you where to use a .030 gasket you would be in the 10.1 range and that would work with several other cams. Head porting would be of huge help with your build to really know what cc range you are in as well getting the heads to flow more .
We did a set of heads for a 96 inch bike with 204 cams, and slip ons that made 90 hp and 105 tq that is a very nice gain over stock numbers
We did a set of heads for a 96 inch bike with 204 cams, and slip ons that made 90 hp and 105 tq that is a very nice gain over stock numbers
Road Warrior
Joined: Dec 2005
Posts: 1,950
Likes: 2
From: Colorado Springs, CO
RE: compression how high
Static compression will remain essentially the same, as the swept area does not change. Like he said, the head chamber volume doesn't change, so there will be an increase, but it will be slight.
Static compression isn't nearly as important as dynamic compression; AKA Cold Cranking Pressure. DC takes in to account static compression, head chamber voulme, cam timing, altitude, boost, etc. A good street rider will have a pressure around 190'ish. Anything greater than 200 will require a stronger starter and compression releases to be reliable. It will also require premium fuel.
I have a static compression of 10.25, and use a 204 cam. Since I live at 6,400' ASL, the bike runs great on regular fuel. I was tempted to go 11.5, but the bike would be pretty much unridable at lower altitudes.
The RB Racing web site has an excellent calculater for dynamic compression.
Static compression isn't nearly as important as dynamic compression; AKA Cold Cranking Pressure. DC takes in to account static compression, head chamber voulme, cam timing, altitude, boost, etc. A good street rider will have a pressure around 190'ish. Anything greater than 200 will require a stronger starter and compression releases to be reliable. It will also require premium fuel.
I have a static compression of 10.25, and use a 204 cam. Since I live at 6,400' ASL, the bike runs great on regular fuel. I was tempted to go 11.5, but the bike would be pretty much unridable at lower altitudes.
The RB Racing web site has an excellent calculater for dynamic compression.
Thread Starter
|
Intermediate
Joined: Dec 2005
Posts: 25
Likes: 0
From:
RE: compression how high
thanks HDWRENCH and BOBCOWAN for the reply i have to use the SE stuff and i have to use bolt on things, when the CR is 9,9:1 on a 103cid 2007 model whit stock heads is it better to use the se211 cam, it has a longer open time but same lift ,keep in mind i am having my heads done next vinter there are no good shops in denmark so i will send the to the US it is still at a lower cost than a pair of SE heads here.
Road Master
Joined: Jul 2005
Posts: 1,061
Likes: 5
From: Fort Worth TX
RE: compression how high
We do a ton of over seas shipping drop me aline see what I can do. The 211 would work better but type of riding , amount of two up riding all play apart in that set up.
Thread
Thread Starter
Forum
Replies
Last Post
Jay Guild
Engine Mechanical Topics
23
Oct 22, 2019 07:20 AM
blksoftail
Exhaust System Topics
7
Jul 15, 2011 11:30 AM
