The Real Difference Between

[don corleone]

srk i dont know everything about engines (too much to know if you ask me) but i know the basics, charging system basics, engine function basics, etc. and i am not a noob i used to go by ko90ls but i forgot my password. recently i've been studying the honda b18a/b (stock integra engine) + vtech (any honda B series vtech head) mod and in my research there have been numerous warnings about the compression change if you add a vtech head with higher cylinder roofs then the stock unit. basically the stock Integra LS compression is 9.6:1 or something around that. the GSR and Type-R engines with vtech have higher compression 10.5:1+ (dont quote my numbers check yourself) but the lower compression engine (LS) can run fine on 87. the GSR is recommended on 91. if you add the vtech head on the LS block then you would need to either use higher octane fuel or upgrade the pistons to the stock GSR pistons, which are slightly longer than stock, to correct the compression diff. if not the you can blow your engine. but regular honda b16's can run fine on 87. i tend to agree with import tuner and like the way they preview parts run dynos and show the latest and greatest builds on exclusive cars.

[AZ Mike]

In my research, the vast majority of so called experts suggest that there is absolutely no value to using a higher octane than is recommended for your engine. Remember that octane is the ability for gas to withstand predetonation; it is not a measure of power. Yes, newer cars that recommend premium can generally get away with regular due to the ECU's ability to !Removed! timing in order to avoid pinging. However, this will often be accompanied with a decline in optimum and result in slight decreases in horsepower and fuel economy. This has to do with the ECU adjusting things to accomodate the lower octane, and not the fuel itself. So no, using higher octane than is recommended does NOT improve mileage and power.

[Marklouis]

srk i dont know everything about engines (too much to know if you ask me) but i know the basics, charging system basics, engine function basics, etc. and i am not a noob i used to go by ko90ls but i forgot my password. recently i've been studying the honda b18a/b (stock integra engine) + vtech (any honda B series vtech head) mod and in my research there have been numerous warnings about the compression change if you add a vtech head with higher cylinder roofs then the stock unit. basically the stock Integra LS compression is 9.6:1 or something around that. the GSR and Type-R engines with vtech have higher compression 10.5:1+ (dont quote my numbers check yourself) but the lower compression engine (LS) can run fine on 87. the GSR is recommended on 91. if you add the vtech head on the LS block then you would need to either use higher octane fuel or upgrade the pistons to the stock GSR pistons, which are slightly longer than stock, to correct the compression diff. if not the you can blow your engine. but regular honda b16's can run fine on 87. i tend to agree with import tuner and like the way they preview parts run dynos and show the latest and greatest builds on exclusive cars.

Most everything you read in car magazines is based on some good knowledge but mostly trial and error runs. there was a article on a guy that tried to run a huge Quad turbo system on a Chevy big block - and the poor fella never got it to run - it would just sit there and crank. He did all the math, blue print, balance, compression ratio, and he was a MIT guy of some sort. it was just a nice conversation piece that he put $10k into - a good semester worth of college tuition today. the only way if you really want to learn the difference in regular and premium is to do your own trial and error experiment - I had no choice during the Fuel shortage we had 5 months ago, no one had Premium, only 87. so i put $15 of 87 in my LS400 with a bottle of high octane booster from auto zone, and there was still a lack of acceleration, and the mileage dropped - i drove like grandpa that week for sure. of course the flashpoint is different between 87 and 91 - and im sure the ECU compensates the difference and you kinda drive around with your car engaged in safe mode to prevent any (pre-det) damage. i also have a 69 mustang 302 4 barrel (no ECU here) that if i put premium in that thing, it will lack HP and Torque, because it was built (compression wise) with 87 in mind.

Go Longhorns! Thats for you ko90ls! Dem Buckeyes are goin' down!

[Penquins'97LS400]

I've always said its just a few bucks more... I wouldn't put anything less that premium in my cars. Like the first post said its 4 bucks diff!!!

[AZ Mike]

Based on people I have talked to and reviews that I have read, it is a one way street.

1) Use of regular unleaded in a vehicle that recommends premium may result in loss of power and fuel economy

2) Use of premium unleaded in a vehicle that recommends regular typically yields no beneficial results, and some argue negative results.

I.e., you may have negative results stepping down from recommended, but do not get positive results when stepping up from recommended.

[jcrome04]

Using HIGH octane fuel in a vehicle that requires LOW octane makes NO DIFFERENCE!

Use what fuel the owner's manual recommends.

High octane fuel DOES NOT make more power on cars that require regular. That is absurd.

Once again. Octane is the fuels ability to resist ignition.

[SRK]

Actually it is the fuel's ability to resist "self-ignition". Self-ignition can be caused by things other than octane, like overheated spark plugs, excessive chamber temperatures (overheating engine), carbon deposits glowing (not common since unleaded fuels) and lean mixtures. If self-ignition occurs before the spark plug has fired then it's "pre-ignition" and if after "detonation".

If a second flame front does develop, and it's the result of low octane, then cylinder pressures must be relatively high - like more than half throttle. Low cylinder pressures, such as idle, cruise, gentle acceleration, do not promote this condition. Light load "ping" is normally not damaging, and in some engines is simply the computer "probing" the max ignition advance and listening for ping.

So as Mike says, one can experience a reduction in power using a lower octane fuel, but if fuel economy is the goal, and a light throttle foot is being used, then low octane will have little, if any effect on mileage.

Octane ratings are critical in engines that operate at high cylinder pressures - boats and airplanes are examples - or racing engines where full throttle is the norm.

I have said this before, I'll say it again, if you are just gliding around town driving gently, low octane fuels will NOT harm these engines at all. Use high octane if it makes you feel better. Remember that the engine can't read the cam covers and it doesn't know that it's a Lexus and that some owners derive some superiority from that. It's just an engine, and will respond as any engine does to the combination of mixture, spark advance, fuel octane, and temperature.

My LS gets 89 as the wife drives it. My GS gets 92 as I drive it. 94 is available in my area, and I NEVER USE IT.