What gas do you run in your kat?

[Jreid843]

Is it okay to run regular gas in pre kat 600. I use premium but i always wondered if it made a difference. I do get 45-50mpg don't know if octane makes a difference. I was told the higher the octane the less ethanol mix. Well all pumps just say may include up to 10% so i dont know how true that is. What gas do you run in your kat?

[Stumpy]

I just use the cheap regular stuff. Occasionally I'll fill her up with BP or Shell premium stuff - but that's mostly just pointless It does stink less than the cheaper stuff though.

[MEngineer]

Pretty sure the manual says to run regular.

[dano68]

Kats run fine on regular ogtane fuel. They are not set up to run on higher octane so you are pretty much waisting $.

[numus]

Meh I was advised to run 89 when I put the ignition advancer in. It isn't exactly a lot more than 87.. Also I try to buy non-ethanol whenever possible.

[rockat]

I have a post and I run 87. I have been running Sta-Bil in my tank on every fill up the past few months and I swear it runs phenomenally better with the Sta-Bil.

[Mopar-Man]

I have an advancer and I run 93. I tried 87 and heard it rattle TWICE at low rpm pulling away from a light. I should add that I live in Florida and it was 90 plus in slow traffic both times. This makes a HUGE difference because as you know the Kat is oil cooled with NO fan.

[numus]

I have an advancer and I run 93. I tried 87 and heard it rattle TWICE at low rpm pulling away from a light.

Try 89... I don't have a problem with it.

[blitz2190]

if you advance you timing you need higher octane, but the kat was tuned for 89 octane i believe, no higher octane will give you more hp, the only advantage is reducing knock, by allowing a more controlled burn preventing pre-detonation, which is the rattle you heard

[muffinman]

Regular 87

[Kreylyn]

if you advance you timing you need higher octane...

Higher Octane retards the explosion.

Ignition advancer moves the explosion timing forward.

Doing both pretty much defeats the purpose of the other.

Jus sayn.

Krey

[arsenic]

Higher Octane retards the explosion.

Ignition advancer moves the explosion timing forward.

Doing both pretty much defeats the purpose of the other.

Jus sayn.

Krey

[numus]

Higher Octane retards the explosion.

Ignition advancer moves the explosion timing forward.

Doing both pretty much defeats the purpose of the other.

Jus sayn.

Krey

Ya... Not really.


What the increased octane does is increase the activation energy required to ignite. Sparks (which is how gasoline engines work) far exceeds the activation energy of almost any octane gasoline. But temp ignition is only 1 way gasoline can ignite. The other is pressure (compression). What higher octane does is increase the required pressure for ignition. Most standard gasoline engines don't have compression anywhere near the ignition threshold (also known as autoignition), but higher performance (and motorcycle) engines do.

All the ignition advancer does is change what state the piston is in when the gasoline is ignited.

This is why diesel engines do not have spark plugs (or anything really). They are such a low octane that they rely on autoignition.

Edit: To clarify the statements. Pressure does have a temperature component (compression increases both). Just stated pressure to emphasize the difference between spark and auto ignition.

[Kreylyn]

Ya... Not really.


What the increased octane does is increase the activation energy required to ignite.

It also slows down the burn when activated at relative compression.

Meaning... if compression = same, then the burn from ignition to complete consumption = slower for higher octane fuels. That's the point of increasing the compression when building an engine. More compression with more fuel = bigger bang when it's needed.

You can get overly detailed to explain and pick a single aspect to say your right, but it it's really very easy to prove... higher than 87 octane in a Kat engine will = less performance when measured on a dyno.

The same applies across the board for any similar engine setup. This is only going to change when you have a EFI with a modern much higher tech electronic ignition system that can auto adjust for the change in fuel.

Anything more than 87 is a waste, and the only reasons it would give false improvements is when your bike is improperly tuned. The most common reason for that is over lean due to the way the carbs work. Dirty carbs and air leaks = lean mix that a higher octane would then "hide" by preventing the "ping" or pre-detonation that occurs because of that. This still leaves you with less fuel than the engine could be using and burning and = less power.

Krey

[TRPUT]

Any benefits from running advanced timing and higher octane fuel are reduced or even negated as you approach the redline - hence a poor result on a dyno if all you are measuring is max HP. The benefits are most noticeable in the lower half of the RPM range (touring rather than sports) when the timing advance will have a greater influence on the whole fuel ignition process, as will a higher octane fuel's role in slowing the explosive effect of combustion and preventing pre-detonation ... which you tend to get at low speed and under load. (The standard Kat 5* advancer is a huge advance in an otherwise non-modified engine.) Ambient temperature, altitude, humidity ... also play a role.

If your style is to bounce the needle off the redline, you will probably see little benefit from an advancer or premium fuel (unless premium = no ethanol). If you tend to spend most time in the low-mid range in 100*F temps, you may very well see benefits.