:bow :bow :bow :bow :bow :bowscottigee said:wow... no offense dude but these are incorrect and ignorant statements, respectively.
Here we go....
In the compression stroke the sparkplug fires a set number of degrees of crank rotation before top dead center (TDC). This happens as the pressure within the cylinder is rising, and after ignition the pressure heads quickly to its maximum. Cylinder pressure peaks several degrees after TDC which means the piston is already on its way back down the cylinder at peak pressure. Imagine that curve. (I'll post a graph)
Using a lower octane gas shifts the curve to the left because peak cylinder pressure is acheived earlier in the power stroke. The majority of the work in the power stroke occurs between TDC and when your exhaust valve opens (the rest of the work happens between firing and TDC, but that is minimal)
So when you shift the curve to the left you reduce the area under the curve post TDC, which is where all your power is. Also, consider it as decreased relative pressure as the volume of the cylinder is increasing, which basically means that gas is just filling the space the pistion leaves behind, rather than forcing it back down.
A knock sensor looks for earlier peak pressures and retards the ignition timing accordingly. Your ECU wants the mixture to mount pressure later to get the 87 pressure curve closer to the curve for 91. That's theory....realistically every ignition system is advanced as far as possible to match its other components and that becomes the upper limit of the range of octanes your engine can handle. That is why putting 91 in your CRX HF gets you jack dick, other than closing the gap between what the gas station sells you (85ish) and what 87 really would be.
Then depending on the ignition system's spark distribution system (spring, vaccuum, oil line...) there are limits to how much ignition retardation your system can do. So it will retard timing within a range, and that becomes the range of octanes you can use without pinging.
That said I am tempted to believe that Honda would give us at least an 87 to 91 range...but that is untested as by me.
Short story long - I think you can use 87, but despite all my blathering, I don't know.
EDIT - your best bet is to empty your tank and put a gallon of 87 in to test it. If it pings, fill her up with 91. If you just lose power then that means 87 is within your engine's ability to retard timing.
And there you have it.esp4p3 said:I happened to look in my 98 Prelude's owners manual. (Imagine that)
I found a paragraph that says something to the effect:
use 91 octane gas but if you can't find 91 then a lower octane gas is permissable. The computer will automatically adjust for the decrease in octane and you will notice a small decrease in hp.
But getting anything above 91 wouldn't benefit our engines anyways. But it would be nice to pay less for 91 in southern cal. Damn everything is more expensive here.ludejohnny said:is there not one place in all of california where you can get gas above 91 octane? It seems stupid that we pay more than anyone else and get shittier grade gas... I need to move
I own a 5th gen. just rebuilt it back basically stock. The only difference is i put farrea 5000 flat head valves in the head. The guy i bought it from almost ruined the whole entire engine but i managed to save it. But when i first filled the car up i used regular not realizing it took 93 only. It does ping and it has my timing 42 degrees advanced so it lacks major power if you try to really get in it and it has alittle hesitation but if you just granny shift it and ride it like a normal car without using vtec it seems to do ok. It does drink the gas pretty quick and threw an o2 b1 sensor codeAny people who own 4th or 5th gen ludes that have consistenly used 87 octane gas? And what did you notice? Was there a knock? Or a reduction in mpg or hp? Any engine damage?
I am very curious because I am having a heated debate about this very subject with a co-worker. He says that I am getting taken by buying 91 even though I told him the prelude says 91 only. He says that his mercedes says the same thing and he uses 87 and his car has never knocked or anything. I tried to tell him that with a higher compression ratio you need a higher octane to prevent knocking. He says that may be true for a race car but not for my car. I am convinced that he is damaging his car over time but he says he uses 87 all the time.
Does anyone have some technical documents that back this arguement up? I would love to show him something.