reducing compression

[pherako]

Does anyone know:
A. The distance between the the bottom oil scraper ring (when cylinder is at BDC) and the chamfer at the bottom of the cylinder itself.
B. How much thread engagement is necessary on the threads of the studs.
C. If anyone has dropped the compression on the GS by shimming the base up.
D. Other unforeseen complications as a result of doing this. (oil galleys being longer and resulting in more pressure drop or something and starving the head as a result (probably not ).)

Why: I don't know. Be able to run cheaper gas after upping the displacement. Boosting possibilities too. It's a theoretical question which may or may not have a practical application. I don't need the "its impractical, you're a retard" answer, I can give that one myself...

If I get some time I'll try to get my spreadsheet to spit out how x[mm] change in volume will affect compression while keeping swept volume (stroke) the same. See if it's even worthwhile. If i were to hazard a guess, 5mm shim at the base might drop compression 1 CR point. Gotta run the numbers to be sure.

Thoughts/opinions?

[ohgood]

there is a fella "ice" or something similar that has turbo'd a gs succesfully. do a search, he's rarely here, but active on other forums, and smart guy.

yes, i think you could reduce compression easily, but have no hands on experience myself, sorry.


good luck !

[trumpetguy]

The GS500 already takes REGULAR gas (cheapest).  Do you live in a place that sells a grade under regular?  Or do you just want a lower-performing engine?

[GeeP]

Beware the bottom end.  Stock GS crankshafts do not like much over 60HP.

As far as thread engagement goes, I'd be inclined to make longer studs.  I wouldn't change the stroke or rod length, just up the headspace.  Alternatively, deepen the head nut C-bores. 

You can calculate the necessary thread engagement if you know the tensile strength of the studs.

[ivany]

The compression ratio of the GS is already something like 8:1, you can run garbage in it and it will be fine. My GSX-R is upwards of 12:1 and takes 87.

[trumpetguy]

The compression ratio of the GS is already something like 8:1, you can run garbage in it and it will be fine. My GSX-R is upwards of 12:1 and takes 87.

Your GSX-R also has a four valve head and liquid cooling, both of which make it more detonation-resistant.  They're apples and oranges.  A 12:1 GS would blow up!  But you're right about the GS running fine on 87 octane.

[sledge]

Does anyone know:

D. Other unforeseen complications as a result of doing this. (oil galleys being longer and resulting in more pressure drop or something and starving the head as a result (probably not ).)

Camchain?
Moving the cams 5mm away from the crank will mean the chain in theory has to be 10mm longer (5mm either side). Is there enough slack in the chain and can the tensioner cope with it??......Dont ask me.....I dunno 

[yamahonkawazuki]

Extra or thicker head/base gasket?

[GeeP]

Does anyone know:

D. Other unforeseen complications as a result of doing this. (oil galleys being longer and resulting in more pressure drop or something and starving the head as a result (probably not ).)

Camchain?
Moving the cams 5mm away from the crank will mean the chain in theory has to be 10mm longer (5mm either side). Is there enough slack in the chain and can the tensioner cope with it??......Dont ask me.....I dunno 

Cam chain stretchers can be had, if you know where to look!   

[spc]

The compression ratio of the GS is already something like 8:1, you can run garbage in it and it will be fine. My GSX-R is upwards of 12:1 and takes 87.

As TG said, it's a completely different world.  My air cooled, two valve Duc is at 11.5:1 and isn't all that fond of premium though it works for getting around town.

BTW, anyone want to buy the Duc?

[hotrodstu77]

if your looking to turbo its really not worth it. i have been talking to the guy who turbo'd his, its a cool idea but its really difficult and you dont make much more power. it would be cheaper to just buy a 600 sport bike. the 600 would prob make more power then a turbo gs anyways.

[pherako]

my motivation wasn't for performance. I was thinking more along the lines of alternative fuels. but again, the question was theoretical. I appreciate all the responses.