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Discussion Starter · #1 ·
Performance degrade and engine knocking? Any long term damage? Just curious.

And btw, at 30,000 miles, what kind of maintenance besides the regular oil/filter should be done? How many miles should timing belt be changed?
 

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i did it a couple times back in the day when i was 16 and jobless. didn't notice anything, prolly did some bad though
 

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i've been meaning to make a thread about this.

my dad went to the dealer(honda) to get the crv serviced and the service tech told him that YOU CAN PUT 87 OCTANE IN THE CRV, ACCORDS, AND REGULAR CIVICS(non si).

i went and asked him if this was true. and he told me that for my car (01 5spd lude) that i needed 93 octane. he said s2k's , civic si's and ludes ...need higher octane cuz of the high compression pistons...and that if u use higher octane in the cars that dont need it it will leave carbon deposits and mess up the engine...

thats straight from the TECH'S mouth!!!

im gonna make a thread in o/t cuz this'll help some people and also i want a second opinion.
 

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minimum is 91 octane. says right in the owners manual. besides CA only offers 91 octane for their premium gas.


Using lower octane won't kill the engine....the ecu will retard the timing a bit and lose some MPG's and HP.

but I would run 91 octane. running higher octane won't do you any good.

87-100 octane gas has the same exact BTU's....same energy and offers no advantages if you run higher octane than needed.
 

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I've had to use 89 and 90 octane a few times when I was super broke. You can feel the performance difference, it basically feels like you're running shitty gas. I'd imagine prolonged use would do bad things to the engine.

I usually run 91, but on weeks with good $$$$ I run 93 or Ultra 94 from Sunoco, which is the best gas anywhere. 94 makes my 5th Gen as perky as an excited teenage girl. Def the best gas for street racing.
 

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the other day i filled up aand noticed that the gas was super cheap for 93 octane.....15 minutes later i iwas pinging like mad (running a hondata ecu with no knock sensor).....power is way down since they had the 87 octane with a 93 label :( i added a gallon of xylene to help it out some but id love to drain the tank....
 

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Gas for the S

I know that My Prelude S, with it's F22 engine hates anything other than low grade gas, it runs horribly, it bogs down more often and it definetly doesn't get the mileage out of it, i get around 385 out of a full tank of low grade unleaded, yet only 325 out of a tank of premium, midgrade was about 360. So, i think each car, and each engine type responds differently to the gas that you put in it. My old Grand Am only like Mid grade, couldn't stand the premium or the super cheap crap either, and i'm fairly certain anything V-8 needs premium.
 

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Discussion Starter · #8 ·
Is stock Prelude a H22 or F22? That's odd, it actually gets better gas mileage with lower grade fuel? Anybody else experience the same thing?
 

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plucky duck said:
Is stock Prelude a H22 or F22? That's odd, it actually gets better gas mileage with lower grade fuel? Anybody else experience the same thing?
which stock prelude?
 

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I know that a 4g Prelude Base its a F22, si H23, and si vtec is a H22 and 5g its a H22.

My Base 4g with the F22 hates 87, and 89, it only runs right on premium 93, No 91 octane around here.
 

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I always run 93 because I love my lude, but ive had many friends and many family members run regular octane when manuals and in the dash it says run premium, they have done it for years and over 100k miles, if I was broke I would have no problem running regular.
 

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Any 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.
 

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esp4p3 said:
Any 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.

Tell your coworker that he's moron, and then laugh ay him when his engine messes up. Besides if he has a mercedes I don't know why he is skimping on gas, not like he can't afford the premium i'm sure.

The owner's manual says you MUST use premium for a reason on an h22 prelude (4gen vtec, ALL 5gens). Honda is not out to make you spend more on gas than you have to. Your engine, as a (somewhat) high compression, high revving engine needs the extra octane not only for keeping healthy/prolonging the life of the engine, but also to give you the full capabilities of it without problems.
 

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SuperSeven said:
I know that My Prelude S, with it's F22 engine ... and i'm fairly certain anything V-8 needs premium.
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.
 

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Graph as promised:


The blue curve is a pressure map for your Prelude under normal conditions with 91 as the cylinder moves through its compression and power cycles. The cycles change at TDC, Ignition happens just prior. When you put 87 in your ECU / knock sensor will retard timing, moving ignition closer to TDC and shifting the curve to the right. The idea is to optimize the area under the curve post TDC.
 

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preludedriver99 said:
Can you explain this picture? Is this a car that has damage from long term knocking? Or no?
 

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no the block is scraped to shit. you don't get deposits on the cylinder wall unless you put it there after taking the head off
 
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