A few friends of mine swear by putting in half a tank of 87 and then the other half with 93. They claim performance, gas mileage, and cost evens out really well doing it this way.

On the other hand, I've been reading around and so far the various internet sources say octane mixing is really bad on the engine. Anyone have first hand knowledge about this?

 

I think he's ending up with 89-90 octane gas. I heard once that stations with 4 or 5 grades available just mixes the mains mixtures of 87 and 93 to get the ratings in between. Of course the pump is computer operated. If you noticed most station now only have 87, 89 and 93, rarely 91 or even 92! Then there's shell 94 and some race gas at some other places. All I can think of low octane rating bad for engines is using lower octane than the engine requires. You'll get detonation. But then our cars have knock sensors to compensate, and then there's all these what if and how about... and blah blah. I don't think there's an issue mixing. Most gas stations sell mid level, 89 in between the 87 and 93 grades anyways for in between prices. Unless they are trying to get one extra octane for whatever savings they're getting, I think it's kind of pointless to go through all that trouble.

 

What kind of cars do they drive? Maximas? Geez I just put in straight 93.

Yeah.

Your "sources" don't sound very educated.

 

i would mix 93 and a higher octane for some kind of moonshine brew ! but mixing a for a lower octane ? i can understand saving a dollar or two but would never run anything lower than super premium

 

gas is gas. i only put 93 in my 89 cuz it sits around and idles alot, dont want knocking then. but my 93 is daily driven and long distances so it gets 87. the only thing lost is power when the computer retards timing to compensate for knock. if you are highway driving you will never notice it.
just my $.02

 

First off if they want a little less than 93 but more than 87 why dont they just buy the middle grade gas. The middle grade is a mixture of the two gases, i forget the percentage of 87 to 93 but i do know it is a mixture, being as i work for a gas station (really wasnt paying attention in that part of my training).

 

isn't 93+ octane IDEAL for 10.5:1 compression ratio?

 

I havent once put anything lower than 92 into my car. 92 is the highest I can get in my area unfortunatly. But yea I agree with you Big D, that is ideal. Hence the 91+ octane recommendation from Nissan for our cars.

 

I know that cause I was watching 2 GUYS GARAGE or HORSEPOWER TV last week and they built an engine with 10.5:1 compression and said to only run 93 octane and higher on such compression.

 

Look at Stillen's website about using the supercharger. They recommend 92 or higher. Not 91 but 92. The supercharger essentially increases the compression ratio in a sense more air compressed into the cylinder on top of the 10...:1 ratio. The reason the Ford Duratec and Honda V6 engines can get away with 87 on a 10:1 ratio engine is because they guarentee lower performance with lower octane gas. Of course the knock sensors would come into play. But then your engine already knocked. But their engine computers may have been programed to see 87 gas as the norm and if a higher octane gas is put in, then it will increase performance. I believe that is probably how those high compression engines can get away with 87 gas. The Mustang Cobra engines are 10+:1 compression and I think they need to use 91 or higher octane.

I also know that if you advance the timing even on a lower compression engine you may need to use higher octane gas to lessen detonation. Look at the 300zx engines, aren't the vg30 engines less than 9:1 compression? So basically the 3rd gen vg engines should only require 87 gas. I don't remember the 3rd gen's owners manuals saying 91 or higher octane.

 

So you're wondering why these cheap bast_rds are:
1) using something less than the highest octane (normal) gas available and
2) avoiding middle grade instead of mixing 93 and 87 and
3) not just mixxing 89 and 93 octane to get minimum recommended 91 average.

Answers (In Indiana we usually have 87,89,93 octane at $.10 marginal cost to upgrade one level) 1) We are, i mean they are, cheap.
2) A 50/50 mix of 87/93 yields 90 octane for price of 89 octane: I said we're cheap.
3) You too can save 1.66 cents per gallon:
If you put in 50/50 mix of 89/93 you pay base + $.15 per gallon to get 91 octane. If you put in 1/3 87 and 2/3 93 you pay base + $.133 to get 91 octane. Yes, at the gas station my wife has noticed, and hides her head in shame....

I figured if Nissan tuned engine for 93 octane they would have recommended 93 octane, but obviously 93 all the time is easiest, and delivers fine performance.