Different Octane Gas

[brandon_guzzo]

I was just wondering if you use a higher octane gas in a gm vehicle with piston slap will it help it or is it worse for the engine. GM told me that i should stick with the lowest octane or the highest and not to go with the medium grade. so i guess what im asking is will a higher or lower grade gas help piston slap in my engine. Thanks for the response.

[ZZ327]

if youre knocking you can try a tank of high octane gas to see if it helps. I think them not recommending medium grade is BS

[brandon_guzzo]

i only experience knocking for 15-20 seconds on very cold mornings on initial startup then its gone but i cant really tell because i start it with my remote start but thanks zz327 ill have to try it come next winter. has anyone else experienced a difference when using different octane's

[66nova]

For the piston slap issue you are describing you will not see any improvement with higher octane.

 

If you are experience detonation under a load then you may need to step up to a higher grade. But unless your truck actually calls for high octane there really is no reason to run it. If you are experiencing detonation (and your doesn't call for 91+) then there is a problem somewhere (carbon build up, sensor problem, bad gas, etc)

[Alljackedup408]

For the piston slap issue you are describing you will not see any improvement with higher octane.

 

If you are experience detonation under a load then you may need to step up to a higher grade. But unless your truck actually calls for high octane there really is no reason to run it. If you are experiencing detonation (and your doesn't call for 91+) then there is a problem somewhere (carbon build up, sensor problem, bad gas, etc)

 

+1

[brandon_guzzo]

Thanks for the response 66nova thats what i was getting at. i wasn't sure if it would help or not .thanks

[Genuinefine409]

I was just wondering if you use a higher octane gas in a gm vehicle with piston slap will it help it or is it worse for the engine. GM told me that i should stick with the lowest octane or the highest and not to go with the medium grade. so i guess what im asking is will a higher or lower grade gas help piston slap in my engine. Thanks for the response.

 

 

my truck used to make noise, at 160,000+ it is quite. I started using chevron techron injection cleaner. I was putting two bottles in at each fill up for a little while then just started doing it on oil changes after it got quiet. after a year it is still quiet, no more slap.

[pinky93]

I was just wondering if you use a higher octane gas in a gm vehicle with piston slap will it help it or is it worse for the engine. GM told me that i should stick with the lowest octane or the highest and not to go with the medium grade. so i guess what im asking is will a higher or lower grade gas help piston slap in my engine. Thanks for the response.

 

 

my truck used to make noise, at 160,000+ it is quite. I started using chevron techron injection cleaner. I was putting two bottles in at each fill up for a little while then just started doing it on oil changes after it got quiet. after a year it is still quiet, no more slap.

 

 

 

Actually, you were experiencing pre-ignition due to the carbon build up. It actually pre-ignites the mixture before the spark plug, so it actually lights off before it is supposed to. This causes a higher pressure than normal as the piston comes to the top of the compression stroke, causing the noise perceived as piston slap. You did exactly what you should have, in that the the additives you put into your tank cleaned up the excess carbon, eliminating the hot spots causing the pre-ignition.

 

Detonation is usually under full throttle and is very audible and VERY destructive. It is more of an un-controlled burn, with VERY high pressures.

 

Back to the original question in the thread, the higher octane fuel actually just burns slower than the lower octane variety. This slows combustion and prevents the detonation under full throttle. This is definitely more evident when an engine is under more load, say pulling a trailer or with more advanced ignition timing. Whoever told you not to run the mid-grade was full of zhit.

 

Hope this helps......