Gas octane

[Mosey]

I have a Craftsman lawn tractor with a 15.5 HP Kohler (is that spelled right?) engine. I've always used 87 octane gas in it. I tried some 90 octane in it, only because that's what I had on hand at the time, and it seemed to run a little stronger and faster. Maybe it was just my imagination. Will 90 octane hurt the engine?

 

[Solo]

Mosey
I run 93 octane in all my small stuff. It burns cleaner. I was told to run that by my chainsaw dealer. It does'nt build up as much carbon.
Solo

 

[hazmat]

Oh boy, get to use my $100K eduction again (thanks dad)

Octane is a measure of gasoline's ability to resist premature detonation or "knocking". In simpler terms, it can get hotter without burning. Higher octane allows you to use higher compression with out knocking. The higher compression generally speaking gives you more power. This is why some of the higher end cars require premium gas (MB BMW etc, they run higher compression engines for more HP).

Carbon deposits cause hot spots on the cylinder wall, causing the knocking. Higher octane resists this knocking. Higher octane does NOT prevent carbon build up.

Unless your engine is designed with higher compression, you will not get more HP out of it with the high octane gas. If you've got a carbon build up problem, the high octane gas will eliminate or minimize the knocking.

You're owners manual should state the min octane rating. For 4 cycle outdoor power equipment I've seen as low as 77. Unless your engine is knocking, I'd stick with regular gas.

 

[MikePA]

<font color=blue>This is why some of the higher end cars require premium gas (MB BMW etc, they run higher compression engines for more HP).</font color=blue>
My wife's 2000 VW Turbo Beetle Owner's Manual specifies premium gasoline. However, it also indicates we can use regular if we have to. It'll just produce less power. I imagine (I haven't researched it) the on board computer does such things as ****** the timing, changes the fuel delivery profile, etc. when it senses the knocking that would come with lower octane gasoline. So, if the engine has no capability to auto-adjust, then using higher octane is a waste of money, unless the engine is already knocking in which case it might fend off damage that might arise therefrom.

 

[hazmat]

<font color=blue>I imagine (I haven't researched it) the on board computer does such things as ****** the timing, changes the fuel delivery profile, etc. when it senses the knocking that would come with lower octane gasoline. </font color=blue>

Usually the first step the "black box" takes is to ****** the timing.

Car & Driver did a test a while back to compare HP with regular vs. premium fuel. If I remember correctly, about 1/2 the cars they tested that specified premium fuel didn't produce any extra HP. No gains were noticed on cars that ran on regular.

 

[Thomas]

High octane in HD touring bike..indeed what a world of differents...smoother ride & more horse power. /w3tcompact/icons/smile.gif

 

[fishman]

I have a 96 neon which specifies premium. The couple of times I forgot and put 87 octane in it was very noticeable. Just my observation of one specific car, but for it, premium is definitely important.

 

[s1120]

<font color=red>Unless your engine is designed with higher compression, you will not get more HP out of it with the high octane gas.</font color=red>

Hazmat has it right. The higher octane burns slower. I did a test back in my drag racing days with a stock 351W Ford. With stock pistons, and slightly bumped timming, I ran 87,93, and Cam2 race fuel. The higher the octane, the slower the car went. By about 2 tenths per change. With the timming realy bumped high, the 93 was the quickest, 87 pinged bad, and cam2 slowed me down. Now when I went to 10 3/4 compression, I need all the octane I could get.