Octane requirement?

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gearheadE30

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The easiest way to find out is to run 85 and see if you hear it pinging. Unless you have a loud exhaust, you'll hear it if it happens. It's not like our trucks have much firewall sound deadening, and a tank of fuel isn't going to hurt anything. Don't make it harder than it needs to be, and with as expensive as your fuel bill will be with that engine, it is definitely worth trying the cheap stuff.

Yes, cylinder pressure is lower at altitude. That's why you have 85 and most of the country doesn't drop below 87. Especially with the cold weather in the middle of winter, risk is low. It's not like a TBI 454 is the pinnacle of performance-tuned engines pushing limits on CR or timing. I doubt you'll have a problem unless you have some other issue with your engine (distributor, plugs, carbon deposit-incited hot spots on the piston crown, weak fuel pump that can't keep up with demand, etc).

Lower octane fuel is more volatile, higher octane is less so which is what gives it a bit more predetonation resistance. I've had a few older cars (notably '70s and early 80s BMW stuff) that actually ran better on lower octane fuel, presumably because the ignition systems were weak enough that the lower activation energy actually helped combustion. I could definitely see a TBI engine falling into the category of engines that benefits from fuel volatility.
 

1992prime

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I read back further. my car says to use 91 and if in emergency, try to use as little 87 as possible and to avoid getting on the throttle since low manifold vacuum and in conditions not PCM commanded bypasssing, the supercharger is going to increase the compression but more importantly the temperature of the intake charge and the **** its cramming in the cylinders. Top end heat and temperatures is the problem being avoided when using low octane. its a low compression motor but supercharge makes heat and compression and then The late cooling fan strategy to keep the car at effieicent temp suddenly means spark knock possible in that way. also, Iridium and copper plugs of the same design and spec for heat range etc are going to move temperature out of the combustion chamber better than platinum. GM had tsb for cars with platinum plugs to go to iridum because people were chipping pistons with hot ambient temps, being on the throttle, and then underhood heat soak, the plugsbeing next to manifolds, no heat shields on half the plugs, etc andthen suddenyly you were having knock early because of what a diesel does.
The warnign is there because yes you can drive nicely and keep out of high load scenarios and high advancing scenarios to prevent preignition but if it does, it still had 2 knock sensors and a generous spark knock reduction programming(rip) but thats not because of your engine thats because of predetnoations effect on cat converters.
OBD2 misfire flashing is also only for a certain threshold of misfire/knock too, its not for stuff that can hurt your engine but fall low enough to pass the determined intensity for it.
HOWEVER even having 2 knock sensors, the idea to be nice until you have your fuel proper is goood because yes they are good at what they do but for your cars sake you wouldnt want to find out what happens when they dont prevent or fail to prevent oopsie. Basically dont be a dumbass and try to WOT if you have bad gas or see a large incline lol.

I would trust a TBI with knock sensors far more than old 80s ESC and janky components but i Would trust a 350 with 2 knock sensors more than 1

Also reducing gap on plugs would make for "Colder"(i know what it means but im not gonna break it down) spark that GM recommended .045 in small blocks that were equipped with .060 gap plugs as a means to reduce issues of load/misfire/chuggle(In transmission situations)

Gm also changed the LS iridium gaps to .040 or .045 on a TSB in the 2000s
You read back further in the thread and saw I had a supercharged car??? This thread is about n/a 454 TBI….
 

AuroraGirl

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You read back further in the thread and saw I had a supercharged car??? This thread is about n/a 454 TBI….
incorrect.

I was replying as to that reality but seeing more responses. My car was a personal experience I was conveying about gm, plugs, misfires, obd2, intake temps, octane, etc.
 

Cometman219

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Curious what I should be using. I have a 1995 K1500 and I've been using 93 octane because I was told it will run better and avoid clogs. 5.7 tbi. I live in the Midwest just outside Chicago so no elevation concerns.
 

AuroraGirl

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Curious what I should be using. I have a 1995 K1500 and I've been using 93 octane because I was told it will run better and avoid clogs. 5.7 tbi. I live in the Midwest just outside Chicago so no elevation concerns.
87. up to 10% would work but if your fuel system hasnt seen it and yours is original you may have things need replacing in future but thats not necessarily a for sure either.
 

someotherguy

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Curious what I should be using. I have a 1995 K1500 and I've been using 93 octane because I was told it will run better and avoid clogs. 5.7 tbi. I live in the Midwest just outside Chicago so no elevation concerns.
Stop listening to whoever gave you this advice.. at least in regards to anything mechanical.

Richard
 

RichLo

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Old thread but yea, no need for anything over 87 in these trucks unless you do internal engine mods.

When storing for long periods, you might be able to find a farm store/station that sells low octane non-ethanol for cheaper than 91/93 non-eth.
 
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