Thread: 305 Update: new gaskets, Dieseling, misc

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First let's talk about your gasoline. "Dieseling" of a gasoline engine is a totally different phenomena from "pre-ignition". Dieseling is the condition where the engine continues to "run" with the key off, meaning the engine is igniting the compressed air/fuel mixture without any spark. Carbon hot spots can lead to dieseling, and having too much throttle makes it worse. This is the reason one of the guys suggested that you might use that AC idle solenoid in a different way, having it energized to establish your normal idle; and the de-energizing it with key "OFF" to totally shut your throttle. Pre-ignition is a condition where the air/fuel mixture ignites slightly before the plug fires when driving under load, and is evidenced by "ping", "clatter" or in the worst cases "spark knock". If you're running too much advance, or if you're running gas too low in octane you get pre-ignition under load, going up a hill getting into the throttle, but not enough for the tranny to kick down is the classic example.

Now for octane. The higher the octane the slower the flame path moves across the piston, reducing cylinder pressures and minimizing "ping". In short, you want to run the lowest octane rating that you can without pre-ignition. You're throwing your money away by going to 93 octane fuel unless you have to have it. Higher octane fuel doesn't pack more power, and in fact it packs less per unit volume. You go to premium because you've packed the extra power mechanically - higher compression generally. If you find that you have to have premium fuel (which I seriously doubt in your 305) do yourself a favor and go to the HyVee at 119th & Ridgeview. They're the only station in your area that has premium fuel without ethanol added, and if you're going to pay for premium you might as well get all gasoline instead of decreasing your energy input with corn.

By "straws" I assume you're talking about the pushrods? With those OEM stamped steel rockers I doubt seriously that you have anything very "special" in the cam. Once we're clear on whether you're chasing a "dieseling" problem (run on with key off) or "pre-ignition" (ping & clatter at WOT under load) the path will be clearer.

I'm sorry, I've heard it called dieseling/pre-ignition. Had no IDE of a difference.

Great info,
Really helped my understanding. I'm at 119th and ridgeview about once a month.

Yeah I typed the wrong word, yes push rod. Not sure what I said? And you guys would be able to tell better than me? Hydrolic lifters aren't as aggressive as solid lifters so yeah its a mild cam for sure. Maybe an RV cam like a 268h I think is what someone said? I just posted that so there is no confusion on solid or hydrolic.

Timing is 8.5*BTDC so it's not too far advanced because stock would be 5* and vacume advance adds 2-3*.

So should I run 91* octane? I can't make it to hy-vee every 1 1/2 weeks.

Thanks so much, as you can see I'm a little clueless on certain matters!