Jdm Engines On American Pump Gas

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flydelsolsi

Guest
jdm engines have higher compretion ratios since their higher octane gas prevents detenation, thus preventing engine damage and increasing horsepower. where i live in pa i get 93 octane and when up at school i get 94 octane. i know in japan they have like 100 octane. if i would do a swap, say b18 spec r for instance, would any harm result from the lower octane gas? would the car retard timing to compensate, thus lowering the horsepower to usdm levels, or would it stay at jdm levels? would it even be worth the price of the swap to go from usdm to jdm? high octane isnt a problem, i run 93/94 in my d16z6 anyways, just looking for input, when trying to decide what to swap.
thanks
 

asmallsol

Super Moderator
as for running that high octane gas on a d16z6, it is pointless. I have even herd of people having problems doing that because it makes some kind of coating on the pistons and when you run lower pump gas you run like shit. If you would have just ran the normal 87 octane from the start, when you put the higher stuff in, you would not see a diffrance.

About the jdm engines, in japan i think they run 98 octane, and when you put us gas in, you should run 91. Also you will lose a few horse but nothing real big, maybe 2-3.
 
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flydelsolsi

Guest
thanks for the input, appreciate it. as for the d16z6 octane, to each his own.
 

PhatHardy

Junior Member
too each his own I agree. However in this case asmallsoll is correct, putting that high octane gas in your car isn't going to make it run any better :( so really this has nothing to do with to each his own, unless that is let people be stupid because it's the nice thing to do, you asked for help and he gave you some, just my .02.
 

djextremity

Senior Member
To elaborate on why it can be bad to run such high octane gas on a low compression motor, let me make sure you know why you need higher octane gas on a high compression motor. Let's say you have a 12:1 compression ratio. Now on the compression stroke, the air/fuel mixture is going to be compressed to a volume 1/12 of what it previously was. So let's say at 180 degrees BTDC, your cylinder volume is .4 L. That means at TDC, your cylinder volume is .033 L. That's a big difference! Now during compression, a lot of heat is created due to the immense friction created between the air and fuel molecules which are now bouncing off of eachother at a much faster rate with such a little space in which to do so. High octane fuel takes more energy to combust, which assures the fact that it will not combust due to the compressing of the a/f.

Now to the problem with using high octane fuel in low compression motors. (I dunno the CR of the Z6, but this is a general explanation).

Imagine again your .4 L cylinder volume. Now with a 9:1 compression ratio, the cylinder volume at TDC is .044 L. It doesn't seem like much of a difference, but in reality, it is a 25% difference! Now with that 25% difference, there is a lot less energy being produced due to friction (I don't really know the proportion--someone feel free to insert it here). Now in the high compression motor, combustion could be occurring due to BOTH the spark from the sparkplug and the friction. But in a lower compression motor, the energy created by friction is not present (or at least isn't as strong). So some of the fuel may not combust properly. It then falls to the piston, and is not combusted on the next stroke (as more unburnt fuel is added). As fuel pools unevenly, it can unbalance the engine, and make engine emissions more rich due to occasional combustion of the pooled fuel.
 
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