Hi everyone,

Long time lurker i think i've posted once or twice. Anyways on to the subject..

I've tried to search for answers but only bits and pieces come through. What I'm looking to do is bump the compression up a bit. clean up the valve ports and possibly carve just a bit out of the carbs.

About the bike 87 600F1 Cane
40k on the clock, Burns oil ( thinking rings ), Timing chain rattles like a snake (already checked tensioner), and has an aftermarket jet kit in it stage 3 maybe?

The motor is comming out friday to get a tear down inspection and fix. I toyed with the idea of shaving the head or getting a thinner gasket. My cousin warned me about that its a dumb idea and that I'd need race gas all the time. Stock we sit at 11.5:1 and run 87 gas right?

Is there validity to his concern or does it depend on how much compression we squeeze out? Can i combat the possible detonation with water injection?

Please ignore considerations of everyday use / cash limits.

only other mod i'll be using next riding season is the +6 timing sprocket

Thanks in advance

 

Alex,

I would advise against increasing the compression ratio on the CBR unless you are planning on competitively racing it. There would be zero benefit on a road bike and it would likely make it more difficult to start and get tuned properly. The stock compression ratio is 12:1 which is pretty high as motorcycle engines go.

If you are just looking for more HP you should look at a later year bike.

A few things to consider. First, the stock configuration is based on the engineering of the time. If you raise compression it puts additional force on all of the internal components. In a race engine the components are beefed up in order to withstand the additional forces. On an engine with 40K on it that would not be a good idea...even on a new stock engine it would be questionable.

Also, just raising the compression ratio doesn't really give you much without a different cam, larger valves, lighter pistons, balanced and stronger crankshaft and special rods. Porting and increasing the flow are also important. Carbs would likely need to be bigger...just changing jets probably wouldn't be enough.

Finally, an increased compression ratio could result in all sorts of unwanted problems just in basic running of the engine. Increased heat, difficulty starting (higher compression results in more force required to turn the engine over and the starter may not be up to it). Higher running temp could result in detonation and backfiring...all unwanted problems.

I could go on but hopefully you get the idea. That little 600 has plenty of get up and go as it is. I would spend my money on getting it running the best you can as it is and have fun with it.

 

I had my head decked when it was ported and polished. The stock pistons, rods, and crank are more than capable to handle the increased load. The starter does take a slight beating with the 13:1 compression I run and turns a little slower than before. The carbs can handle the increased airflow requirement if done correctly. However the 91 f1 carbs are 1 or 2 mm larger and slightly better for airflow after doing the same mods.
I have to run at minimum 91 now to keep from detonation. That being said, there is VP race gas at the pump here and I usually run a 50/50 mix with 91. When I used to race it, it got C16 race gas exclusively.
It does run a little hotter, but a lower temp thermistor or a switch on the fan takes care of that.

 

Drakito,

You pretty much said most of what I thought would be the case with the exception of running stock rods and pistons.

Having to run higher octane fuel (race gas is some spendy stuff), also adds to the equation. I'm thinking Alex wasn't planning on racing this bike so special fuel is another problem to add to the list.

I think you meant F2 carbs in your comments above...how do they fit on an F1? I thought the spacing was different.

 

@Drakito: Yes i plan only to "skim" the head enough to ensure a smooth flat connection maybe .015" ?

@Dennisgb: Correct I do not plan on "racing" the bike but if the safe and open on ramp / highway presents it self i wouldn't mind a little extra snap. I'm not expecting anything huge. Also do you think that much damage will occur to the springs/valves/rods/pistons if left stock?

I'm a modest rider and the bike is for having good safe fun. Do i like to roll up along newer RR models and play along with quick accelerations from time to time? Sure. Did I change the front -1 and the rear +2 for playing with bigger bikes of the line? you betcha. But I will never race unless on the track which i will use 106+ gas.

 

.015 is within factory rebuild specs for flattening the head. The motor is more than well designed enough to handle all that I have done and still run fine. The stock rotating assembly is standard Honda fare, Bullet proof. Same can't be said about the RR and stator, the shift star, and the electrical connections. The rings, pistons, rods, springs, valves, etc can handle the stock rev limit, higher CR, etc all day long. Just make sure and keep the oil and coolant topped off with quality stuff.


Dennis,
Thanks I had a brain fart, 91 was f2 as well.
The f2 carbs don't line right up. The 89-90 non California carbs were a running change and went up just slightly in size at the throat and had a slightly better design in the internal air horn. The cams were also revised and the valves slightly unshrouded in the head. Total change was like ~4-5hp from the 87-88 to the 89-90.