gasoctane highcomp piston help

[kfx400isdashiz]

ok i just bought a 13.5to1 high comp piston for my 03 kfx400 stock comp is 12.2 to 1 iwas told that anything higher than 11.1 needs race fuel however in the manuel for the stock engine it says all it needs is 91 or greater octane so what kind of fuel should i use for a JE 13.5 PISTON

[GPracer2500]

When you hear "11:1 and over needs race fuel" that refers to air cooled engines--not liquid cooled. And it's only a rule of thumb, not a set-in-stone rule. Also, a stock KFX has a compression ratio of 11.2:1. That engine originated in the Suzuki DRZ-400E and it has a compression ratio of 12.2:1 but it's detuned a little in the DRZ-400S/SM, Z400, KFX, and DVX.

I would not run straight pump gas in a 13.5:1 KFX. Barring highly unusual circumstances you'll need something higher than 91 or 93 to prevent detonation. With that much compression I'd use something around 110 octane to stay safe. If your keen on picking up on the signals of detonation than you could experiment with lower octane ratings until you found the octane that prevented detonation from occuring.

[kfx400isdashiz]

i know i sound like a dumbass but what is denotation

[Over-land 450r]

run Vp C-12 u will be ok. its around 110 octane

[kfx400isdashiz]

could i use regular gas with octane boosters and be ok?

[GPracer2500]

Detonation is a form of abnormal combustion of the air/fuel mixture inside the combustion chamber.

When the spark plug fires the air/fuel mixture does not explode as we commonly think it does. It burns at a predictable rate starting from the spark plug and moving outwards towards the edges of the combustion chamber. As this burn is taking place, the expanding gasses cause the pressures inside the combustion chamber to climb very high. The temperatures in the combustion chamber also climb very high.

It takes time for the burning air/fuel mixture to reach the edges of the cylinder. As this burn takes place the pressures and temperatures continue to rise. This causes the unburned air/fuel mixture around the edges of the combustion chamber to chemically decompose into what are known as "end-gases". These end-gases are very unstable and if the pressure and temp is high enough the end-gas will spontaniously combust (explode) before the flame front of the normal burn has a chance to get there.

This explosion is detonation. It creates a supersonic pressure wave that bounces around inside the combustion chamber with extreme force. It creates a lot of additional heat and robs HP. If the detonation is extensive enough it will errode and crack the internal parts of the engine.

Detonation makes its self known by creating a knocking or pinging sound inside the engine. What you are hearing is that supersonic pressure wave smacking into the inside of the combustion chamber.

Octane rating is a measure of a fuels ability to resist decomposing into the "end-gases" that are susceptable to detonation. Most engines can tolerate a small amount of occassional detonation but prolonged or severe detonation will destroy the engine. Perhaps the most common failure mode is cracked and melted piston ring lands. But detonation can cause cranks to fail, heads to crack, valves to break, etc. The extra heat that detonation puts into the engine can also cause things to melt.

There are a number of things that contribute to an engine's ability to create detonation for any given fuel. Altitude, ambient air temp, engine temp, air/fuel ratio, ignition timing, cam specifications, and more. Compression ratio is probably the single largest factor though.

Hope that helps!

[GPracer2500]

Originally posted by kfx400isdashiz
could i use regular gas with octane boosters and be ok?

Unless you're adding tetraethyl lead or LOTS of tuelene you'll never get pump gas over 100 octane. Don't be fooled by what's printed on the bottles of off-the-shelf octane boosters. Their 1 point is actually 0.1 octane points. So if the bottle says it will raise your octane by 10 points, it's actually raising it by 1 octane point (e.g. 93 to 94, not 93 to 103).

Octane boosters are not the answer....

[jsmith2232]

I have always been told by any motorsports shop not to use octane boosters, I would just use 110

[rooster300ex]

If running straight 110 gets alil costly, i bet a 50/50 mix of some 93 pump will work.



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