• Required reading for all forum users!!!

    Welcome!
    Register to access the full functionality of the GSResources forum. Until you register and activate your account you will not have full forum access, nor will you be able to post or reply to messages.

    A note to new registrants...
    All new forum registrations must be activated via email before you have full access to the forum.

    A Special Note about Email accounts!
    DO NOT SIGN UP USING hotmail, outlook, gmx, sbcglobal, att, bellsouth or email.com. They delete our forum signup emails.

    A note to old forum members...
    I receive numerous requests from people who can no longer log in because their accounts were deleted. As mentioned in the forum FAQ, user accounts are deleted if you haven't logged in for the past 6 months. If you can't log in, then create a new forum account. If you don't get an error message, then check your email account for an activation message. If you get a message stating that the email address is already in use, then your account still exists so follow the instructions in the forum FAQ for resetting your password.

    Have you forgotten your password or have a new email address? Then read the forum FAQ for details on how to reset it.

    Any email requests for "can't log in anymore" problems or "lost my password" problems will be deleted. Read the forum FAQ and follow the instructions there - that's what we have one for...

  • Returning Visitors

    If you are a returning visitor who never received your confirmation email, then odds are your email provider is blockinig emails from our server. The only thing that can be done to get around this is you will have to try creating another forum account using an email address from another domain.

    If you are a returning visitor to the forum and can't log in using your old forum name and password but used to be able to then chances are your account is deleted. Purges of the databases are done regularly. You will have to create a new forum account and you should be all set.

How much comp before race gas?

  • Thread starter Thread starter speedy400
  • Start date Start date
S

speedy400

Guest
Hey,
I have a 82gs850, and I'm trying to bump up the compression a tad, (for street use), I'll be having a oil cooler on, high perf. cams as for heat wise on my bike. But I am wondering how much can I get milled off the head to get to 10.5 to 1 comp? I thought I heard someone say about .009 inches? Thanks-darren
 
Last edited:
Before I'd do anything take a compression check. If it's below oem limits I wouldn't do anything until it's fix, worn rings or valve's??

Depending on what cams you use some require more compression due to valve timing, maybe 11-1, 12.5-1??

If you do mill the head be sure to check your valve to piston clearance, cause it's going to change, get smaller. Adjustable cam sprockets work great for this.
 
Speedy, I don't know how much to mill to get 10.5:1 compression but I personally wouldn't mill the head to achieve higher compression. I would use some Wiseco pistons which will bump your compression and also freshen your performance because of better ring seal (new rings are included). At 10.5:1 you won't need race gas. You MAY need to slightly retard your ignition timing which can be done by changing the position of your ignition plate and the 2/3 pickup but you could also pick up a Dyna 2000 or newer Dyna ignition (not a Dyna S) where they build in several advance curves that retard igniton. At 10.5:1 you may need to retard just a bit but you will likely be fine on 93 octane.
 
I would love to get wiscos, but A. I cant find a set anywhere for stock bore for my 850, and B. I can get the milling done for free compareds to ~$200 for a set of high comp wiscos. Also my stock rings have been sealing real well, its only got 13,000 miles on her. Thanks though, sounds like 10.5 to 1 is a good number to shoot for. Thanks again-darren
 
I am running 10.75:1 on premium pump fuel with no problems. I decked the head and block a total of 12 thou. to bump my 10.5:1 piston kit compression up.
 
motorcyclemodeller, Thank you! Exactly what I was looking for!-darren
 
You must log in or register to reply here.

Similar threads

KiwiAlfa156
Retarding Ignition Timing
2
Replies
25
Views
561
rphillips
R
roeme
Replacing a "Spark Unit" / "Igniter" / CDI (OKI MPS-200) on a '80 CB650
Replies
16
Views
370
roeme
roeme
garyS-NJ
Sources for Race Tech FEGV-S3301
2
Replies
29
Views
6K
dorkburger
dorkburger
G
GS750 Rebuild options?
Replies
14
Views
1K
Chuck78
Chuck78
P
78 GS550: 650e topend or complete engine swap?
Replies
1
Views
200
Chuck78
Chuck78
Back
Top