Rykers Require 87 Octane - Not 92!

[CENTAUR]

Compression ratio on Ryker is 11:1. Doesn't that call for 91oct even though book sez 87?

[Aufgeblassen47]

Compression ratio on Ryker is 11:1. Doesn't that call for 91oct even though book sez 87?

Not necessarily! Compression is only one leg of a 3-legged stool. The other two legs are spark and fuel injection timing. In the bad ole days of carburetors, premium was needed much more often, as the was no such thing as injection timing.

A possible 4th leg could be valve timing, for engines with VVT.

[BajaRon]

Stand corrected. Since we can no longer delete a post, error pulled.

[IdahoMtnSpyder]

Now, with fuel injection, the fuel does not enter the picture until just before the spark plug fires.

I don't think that is correct. The EFI injectors inject the fuel into the intake ports of the cylinder head, which means the fuel enters the combustion chamber along with the air. If the fuel was injected just before the spark plug fires that would mean the fuel would have to be injected directly into the combustion chamber, like a diesel engine. Look at the Fuel System section of the EFI chapter of the service manual (2014 RTS in my case).

I think one of the main reasons predetonation isn't the problem it used to be is that combustion chambers have been designed to maximize air/fuel mixing, plus there are probably no sharp corners or other small bits of metal that can get hot enough to retain heat and cause the next air/fuel charge to ignite prematurely.

[Aufgeblassen47]

I don't think that is correct. The EFI injectors inject the fuel into the intake ports of the cylinder head, which means the fuel enters the combustion chamber along with the air. If the fuel was injected just before the spark plug fires that would mean the fuel would have to be injected directly into the combustion chamber, like a diesel engine. Look at the Fuel System section of the EFI chapter of the service manual (2014 RTS in my case).

I think one of the main reasons predetonation isn't the problem it used to be is that combustion chambers have been designed to maximize air/fuel mixing, plus there are probably no sharp corners or other small bits of metal that can get hot enough to retain heat and cause the next air/fuel charge to ignite prematurely.

WHATEVER the reason, NO pre-ignition means your octane level is just fine and a higher number does NOTHING!

I've been a diesel owner since 1984, and owned many makes & models. Dieselheads are the exact same way about CETANE, they think a higher number (than actually needed) makes it run better, smoother, faster. Totally false. The "placebo effect" affects those guys too. A minimum cetane number is needed to START a diesel engine. If your engine starts right up, you have adequate cetane - period. Adding a "cetane booster" to your fuel does ZERO if it already starts w/o adding one.

[BajaRon]

I don't think that is correct. The EFI injectors inject the fuel into the intake ports of the cylinder head, which means the fuel enters the combustion chamber along with the air. If the fuel was injected just before the spark plug fires that would mean the fuel would have to be injected directly into the combustion chamber, like a diesel engine. Look at the Fuel System section of the EFI chapter of the service manual (2014 RTS in my case).

I think one of the main reasons predetonation isn't the problem it used to be is that combustion chambers have been designed to maximize air/fuel mixing, plus there are probably no sharp corners or other small bits of metal that can get hot enough to retain heat and cause the next air/fuel charge to ignite prematurely.

I stand corrected. You are correct. We do not have direct fuel injection. My error. Thank you for pointing this out.