EGIan

Okay, this might have been talked about in previous posts, but nothing good enough to satisfy me. Down in Montreal, the saying goes that if you don't put the highest octane gas available at the pump, IN YOUR JDM ENGINE, you're literally f*cking your engine to it's death. I've studied chemistry, still am, and I was wondering what the f*ck would 87/100 compared to 91/100 do to your engine that would be that bad ? The saying goes specifically for JDM engines, like mine.

Okay, if more octane entered the pistons for combustion, alright, more power, less residues. But, I have a practical mind and 4/100 more octane just doesn't make any f*cking sense fto me. Certainly not giving up an extra 3.00 - 5.00$ for nothing that I've ever noticed.

Unless the 4 extra octane molecules are actually superduperoctane, what's the point ?

EGIan

Looking at this from another angle :

Good stuff - (91/87)*100 = 4.6% increase ( I would'nt really give a sh*t )
Bad stuff - (9/13)*100= 31% decrease ( hmm ... yeah makes more sense )

... WHATEVER !

ddd4114

The anti-knock index is resistance to detonation. If you don't notice detonation with fuels of a lower anti-knock index , there is no advantage to running higher octane fuel.

ddd4114

What...?

SOHC_4dr

the most common diff between the JDM and USDM engines is that the JDM engines have a vary slight increase in compression (.2 ish on most). so a higher octane rating would resist detonation better but i think it isnt needed on the factory JDM engines unless it calls for 91 instead of 87. unless someone is that concerned about detonation, then 87 is fine factory

Jo$e L@go

idk wat the hell those numbers mean but finally someone knows wat they are talking about when it comes to this whole gas situation


the only different between 87 89 and 91 is the process in which the gas is made.87 doesnt go through as much "thining" if you want to call it that.basically in ENGLISH WHAT IAM TRYIN TO SAY is that 87 is just a little thicker then 89 and a little thicker then 91


so thats why if you;ve noticed that when you fill up your "buckets"/"moms cars" with 87 gas seems to last better its because its thicker then 91.but its such a SLIM difference its not gunna kill your engine if you put 87 in say a JDM engine that swears up and down that you have to put 91/93 octance in your car of you'll MESS it up.

EGIan

The number, at the pump, is the number of octane molecules versus other less valuable hydrocarbons. You know what I mean.

EGIan

Yeah, okay, I was aware about the thickness issue, but the goal was to know if it was really worthwhile and that critical.

Thanks a bunch,

ddd4114

The number at the pump is the average between RON and MON. It's otherwise known as the anti-knock index. It's does not indicate the actual amount of octane molecules. Rather, it provides an equivalent.

If you can get adequate power from your engine on 87 octane, that is fine.

blinx9900

Not true, gasoline does not actually have octane in it anymore, at this point its simply a rating system.

trustdestruction

87 is fine. The compression on the D15B isn't that much higher than a D16Z6.

jdm_ekcivic

I'm sticking with premium.

ddd4114

Why is that?

2slow4stock

Your dead wrong, please don't post if you have no clue what you are talking about. The higher the octane doesn't mean ****, when it comes to burning. Octane is only there to help with combustion. ALL GAS 87-93 BURN AT THE SAME BTU. Which means, it all burns the same. It's people who are smoking crack that think they are getting better gas mileage out of 93, in a car that doesn't need it.

But if you have high compression yes, you would want to run 93. But in a d15b 87 is damn fine enough for it. No point in wasting money unless you have some power mods that you would want to run a high octane so you don't detonate.

romerosi

you have to run higher octane in jdm motors only if ur running the j spec ecu, there is alot more timing advance and differant fuel trim on the jdm ecu, in japan there min octane is 101. if u run a usdm ecu ur fine

[713]

so ur tellin me if i run low 87 in a CTR swap its gonna downgrade its performance?

lcsej1

The antiknock quality of a gasoline is indicated by its octane number. The higher the number, the more resistant the gasoline is to detonation. The octane requirements of an engine are determined by combustion chamber design and compression ratio. However, the octane requirement changes with weather, altitude, and driving conditions. It can also be affected by changes in the mechanical condition of an engine:

*Reduced cooling system efficiency.
*lean air/fuel mixtures.
*over-advanced ignition timing.
*increased compression ratio.
*failure of an EGR valve.

So if your using a high octane gasoline with a car that doesn't need it you are wasting money.

and btw i was wrong on my last comment.

lcsej1

srry man no need to flame. thank God we have smart people like u here at H-T to fix the misinformation ppl like me give to others! we love you man!

F20B-CX

iTrader: (1)

Japan does have higher octane fuel; the general figure I've seen passed around is 95 octane minimum. One must be weary, especially when buying a car that's been tuned, running said car in North America. Too much timing, not enough octane = detonation. Even in my beater Neon the octane requirement is 91. If I put 87 or 89 in it, at low RPM and a good amount of load, it detonates like crazy. This is in a car with 9.6:1 compression. Imagine 11.0:1 with a mean timing map. If you can get away with absolutely 0 detonation, fine. It might be an idea to learn what detonation sounds like. Don't cheap out and risk a motor otherwise.
FWIW, Octane is RESISTANCE to ignition. Detonation is when the fuel gets ignited before the spark plug fires. Putting 91+ in a car that can't detonate even on 87 is a waste. You might even lose mileage and power because you are effectively retarding your ignition timing.

teamworxek9

iTrader: (5)

Ill add my two cents, i know my car runs much better with 93 tham 87. Im boosted and have seen the difference when my brother borrowed my car and filled it up with 87.

trustdestruction

FYI
Japan's 100 = Our 95 (well, if we had 95)

trustdestruction

on boost you're supposed to run premium, that's why you notice a difference.

teamworxek9

iTrader: (5)

Yes i am aware of this. was just putting up my experince. Ff a car manufacturer says you should use a high octane the use a high octane.

xsaxisx

i have a jdm d15b in my 92 and here in Ontario i have always used 89

efchris

i had a single cam with a decked head and it was at around 11.5.1 compression and if i didn't put 93 in it it woud run like **** and spark knock all the time so maybe thats what they were tlaking about cause spark knock isn't good and if it has higher compression it might mess something up.