big bore question

[drowningbird808]

wats the biggest you can go without making the walls to thin?

[spc]

I believe that 555 is the biggest you can go without replacing the sleeves.  I recall dgyver posting that 78mm pistons achieve this

[drowningbird808]

yeh and the only way to get them is to buy a kit for a kz1000 or something

[spc]

kz1200 I believe..........but if you find someone to split it with..........

[spc]

I believe this is the thread you're looking for:
http://gstwins.com/gsboard/index.php?topic=14401.0

[drowningbird808]

so 78mm are 541cc
theres still no claimed power gain or dyno charts to prove it
for all i know i can be interseted in biulding a 541cc time bomb

[ben2go]

It works, he has it in a bike as we speak.The kz pistons raise the compression quite a bit,because they have a raised dome on top of the piston.You have to use hi grade fuel and rejet or use 34mm or 36mm carbs.

[dgyver]

79mm is the largest you can bore stock sleeves but the walls get thin and risk cracking. 79mm pistons are very rare, still have one waiting on locating another. As for power, I never dynoed my first 555 but a guess would be around 50-55hp with Megacycle cams. This is number partially based on other bikes I raced against. 1/4 lap behind and walked down a R6 in 3 laps. Rider has a lot to do with it as well.

Larger displacement + higher compression = more hp & torque

Yes, the 78s are in a running motor. It used to be a race motor that I pulled from my track bike for my 92 street bike until I build another motor, either a 569 or the GR. The 569 has 80mm pistons and the cylinder has been resleeved. No problem with thin walls.

Any motor modified beyond its original design has the risk of destroying itself. The 541 I have spit a shim and punched a hole in the head. This was due to over reving. No problem to rebuild.

Any motor can fail. Heck I have heard of more stock motors failing, mostly due to owner stupidity or incompetence. But if you do not know what you are doing, it probably will fail. If you are afraid that the motor will blow up, then do not build one.

[Mk1inCali]

dgyver-

Did you swap carbs or do any port work?

[dgyver]

The 541 head (with the hole) was ported for 34mm round slides, sadly I sold them but it has 36mm CV carbs installed for now. Currently it has stock cams and a basically stock head...necked valves and cleaned up the casting lines. The ported head has been fixed and is planned to go on the 569 motor along with the Megacycle cams, after they get repaired (now that I found them). I have a set of 36mm flat slides that may find their way on to the 569 or they may fuel the GR motor. I am looking for another set of bigger carbs so it all depends on what I find.

The 555 ran 33mm carbs. I had to sell the bike prior to getting bigger carbs.

[The Buddha]

Hey dgyver ... quick Question ...
On a GR motor, can I fit the GS carbs.
Same bore spacing & dia and manifolds or ... I need GS manifolds ... or GS head
Cool.
Srinath.

[dgyver]

Dunno. I have not tried to fit any carbs. Probably will not since I will be installing GSXR head.

[drowningbird808]

my bike says it has 34mm carbs

[ben2go]

my bike says it has 34mm carbs

Your bike TALKS?That's so kool.   

[dgyver]

my bike says it has 34mm carbs

uh ok