Engine knock/pinging on 89 octane

[Ramjack]

I'm thinking of installing a catch can to reduce pinging, wonder if anyone here has tried that with good results?

I installed a catch can at 1,000 miles with hopes of slowing carbon building up enough to prevent pinging in the first place. Once pinging has started, installing a catch can is not likely to help much.

 

[silver billet]

I installed a catch can at 1,000 miles with hopes of slowing carbon building up enough to prevent pinging in the first place. Once pinging has started, installing a catch can is not likely to help much.

I forget where, but at one point on a forum I read that the catch can catches vapors which would otherwise interfere with the clean air/fuel mixture, making pinging worse. So if that is true, it might still help? Might not just be a carbon thing, but keeping the fuel mixture as clean as possible. I really have no idea how true that is, wish I could find the post back.

 

[Drewster]

I forget where, but at one point on a forum I read that the catch can catches vapors which would otherwise interfere with the clean air/fuel mixture, making pinging worse. So if that is true, it might still help? Might not just be a carbon thing, but keeping the fuel mixture as clean as possible. I really have no idea how true that is, wish I could find the post back.

Yeah, the general thought is that all the random crap lowers the effective octane. However, I have never seen a single paper that backs that up definitively.

To me it makes logical sense that reducing crap in the intake would help with timing - the more randomness, the more likely you are to get knock and pull timing... but again, that's subjective.

 

[GKIII]

Yeah, the general thought is that all the random crap lowers the effective octane. However, I have never seen a single paper that backs that up definitively.

To me it makes logical sense that reducing crap in the intake would help with timing - the more randomness, the more likely you are to get knock and pull timing... but again, that's subjective.

There is some logic to it, the auto-ignition temperature of motor oil vapors is around 400F (give or take 20-30F) which is significantly lower than even 87 octane gas.

 

[silver billet]

There is some logic to it, the auto-ignition temperature of motor oil vapors is around 400F (give or take 20-30F) which is significantly lower than even 87 octane gas.

Well that does it then, going to try a CC!

 

[Drewster]

There is some logic to it, the auto-ignition temperature of motor oil vapors is around 400F (give or take 20-30F) which is significantly lower than even 87 octane gas.

Exactly - it's logical.. but no one has ever proven *what* that octane is, exactly how much of a difference it makes, etc.

 

[GKIII]

Exactly - it's logical.. but no one has ever proven *what* that octane is, exactly how much of a difference it makes, etc.

In short an octane rating the ability of a fuel mixture to resist combustion under compression when compared to a reference mixture of 2,2,4-Trimethylpentane (more commonly known as iso-octane). Basically an 87 octane fuel blend will have the same auto-ignition characteristics of an 87/13 iso-octane/heptane mixture.

The only thing I said in my previous post was that oil vapors will ignite under compression before even 87 octane gasoline will due to it's lower auto-ignition temperature. Now do I know if there's enough oil vapors passing through the RAM's intake system and mixing with the fuel-air mixture to make much of a difference in terms of effective octane rating? No idea, but that is certainly something that can be experimentally measured. It would not surprise me if every modern vehicle manufacturer has done such an analysis.

Edit: I re-read this and realized I missed a word in your reply and thought you were saying nobody knew what octane actually *is* lol. My bad. Leaving up the explanation for other's benefit.