95' Del Sol S 1.5L takes unleaded premium?

[Northmont]

All our Toyota cars take unleaded regular but when I bought my Del Sol recently the guy who had the car has always used unleaded premium and says if you put in unleaded regular it will chug a lot. Is it ok to switch to unleaded regular? Thanks in advance.

[bingisSD]

anyone who tells you that you need higher than 87 octane on an american spec vehicle was misimformed. your engine is designed to run on 87 octane which to be sold in the united states must be a 'minimum' of 87, gauranteeing that the bare minimum is over 87. its actually 87.2-87.5. if you had a japanese motor or a HIGH performance motor like a b18c or b16a which are both the japanese spec versions, the american ones are b18c1 and b16a1/2/3, if the engine code ends in a number and not a letter its american and you dont wanna waste the extra money on the gas because the engine was not designed to benefit from higher octane gas.

now that Ive confused y ou, if you have a del sol s, just look on the engine code on the front of your block and it will say either d15b7. that is the confirmation that you do not need/want to put anything more than 87 octane in. in the very rare ocassion that somehow a d15b (without a number at the end) ended up in your car ou should thank the lord because its a rare motor, japanese spec, and it is a damn good motor.

[AudioGuy93DelSol]

Correct me if im wrong but also the ecu's fuel maps are "used" to the higher octance gas so when lower octane gas is put in it will run rough. Rite?

[bingisSD]

only in OBD-0 japanese spec pr3 and a few others, but not on all honda ecu's, especially not on an OBD-1 ecu. thats how i was told at least.

for the 5 miles per tank you might gain, you will pay an extra couple bucks, so youre not really going to gain anything. at least thats the way i read it in the november issue of like a import magazine i forget which one

[Plastic_Fork]

The Del Sol S and Si run just fine on 87 octane. The higher octane (91+) is necessary for the VTEC model because of the higher compression ratio for the B16A motor.

[bingisSD]

so it doesnt have anything to do with whether or not its a jap spec or OBD-0, simply because its got a 10.8:1 comp. ratio or whatever?

[Plastic_Fork]

Yeah. Something to do with the igniting ranges of the fuel because of the compression. I'm no expert, so here's what I remember. Don't take it as fact - I'm not sure I'm remembering it correctly.

At lower compression, you can run lower octane fuels because they will ignite at a lower heat range. At higher compressions, it's harder for the fuel to ignite so you need a higher octane to offset that so it will ignite (and consequently, different spark plugs as well with a higher heat range to adjust for the compression and heat).

Japan I believe sells 100+ octane at their pumps at normal gas stations. Their motors also have a slightly higher compression than the USDM motors (could be to take advantage of the pump gas there), but our emissions standards are stricter I believe. Either way, even the Honda shop manual calls for 87 for the S and Si and 91+ for the VTEC. Doesn't hurt to run premium though for a few extra bucks.

The Honda ECU's for the different models all have more than one air/fuel map. Each one takes advantage of the different ranges of octane and air intake and lack thereof. It's not really getting used to anything, it's just changing the map based on what the motor's ingesting. If you want to make sure it's using the right map, just turn the motor off, open the fusebox by the battery and yank the ECU fuse. Leave it out for about ten minutes or so, put it back in, and then start the car and let it idle under no load until the fan kicks in. Then turn it off and next time you start the car the ECU has re-mapped for your current conditions and will change accordingly. I did this when installing my air intake.

[Privatebigandrew]

Plastic fork, you are on the right track, and i think you know, you just might not know how to explain it. Its like this. Lower octane fuels ignite, or combust at lower temperatures than high octane fuels. When i say ignite, i mean without a spark or anything. So, a lower compression engine can run lower octane without preigniting the fuel because it does not create as much heat. Remember, higher compression engines create more heat due to creating more prsseure. Pressure=Heat. If you try to run low octane fuel in a high compression engine, the fuel runs the chance of igniting itself before the spark does due to the high temps. This is called preignition and is very bad for the engine. Higher octane fuel is acually bad for a low compression engine contrary to what all the commercials tell you. This is a theory that one of my instructors came up with. Look at it this way, high octane fuel burns colder than low octane fuel, it has to to cope with high compression engines. Anyhow, running a high octane fuel in an engine with low compression will create lower combustion temps than a lower octane fuel would. Over time, the colder temps will result in increased carbon deposits clogging up the valves and other areas. Something to think about. IT basically all has to do with heat. The higher the octane, the higher temps it can withstand before igniting itself.

[Plastic_Fork]

Yeah, that's the explanation I was searching for. Thanks for clearing it up.

[Northmont]

Sorry for the replies, thanks a lot. I have been feeding it unleaded for the past few weeks, works just fine