What octance rating do you use in your car?

Mazda recommends 87 octane on their site, I read somewhere that if a manufacturer recommends a certain ocatane, and you use a octane higher, then you are just wasting your money...

Is this true?

 

I use 87 (the cheapest stuff) and it makes my pro 5 run best. I tried 93 and i got a lot less gas mileage.

 

You should always use the lowest possible octane that you can get away with.

Lower octane gas will burn more readily. Which makes it more efficient and will give you more power.

Now, once you start modding the car (really modifying) then you may have to move to a higher octane to keep it from knocking.

 

however, somewhere else on the board it seems to be showing that in the third gens it would appear that better gas mileage is being achieved with higher octane... nothing conclusive... just an observation...

http://www.protegeclub.com/forum/sho...&threadid=1022

 

i'm doing an experiment with the diff octanes in my P5...so far i've used 85, 87, and 89.....engine seems smoother with the 89 octain......just filed her up with 92, so i'll see how that goes

 

Here's a better experiment.

Does the engine have a knock sensor? If yes, then someone (with cash to spare) should connect the car to a datalogger and compare the timing advance curves while using different octane gas.

This will let us know if the ECU can actually detect the use of better gas and increase timing advance.

After christmas, I'll try to borrow my friend's pocketlogger (http://www.pocketlogger.com , I have one for my mirage, but it's OBDI) and see if it'll connect to the protege. If so, then I'll do these experiments myself.

 

"the magazine article" I've read thousands of magazines articles, be more specific. Magazine articles are just like TV News casts. You have to be selective of what you believe.

If the engine has a knock sensor then you can bet your house on the fact that the ECU is monitoring it. If the ECU is seeing knock then it's going to retard timing. I agree with you that the ECU can only downgrade performance from an optimal setting (my mistake for the miswording). However, just because the manual says run 87 octane we should NOT make the assumption that the ECU is running at the optimal setting from the factory while running 87 octane.

I'm not making any assumptions as to whether or not knock is present. Others have claimed that they've seen improvements with running higher octane. To be honest, I don't want to just believe these claims which is why I wanted proof through datalogging. (until I see proof then I'm sticking with 87) I'm simply stating a way of actually determining if 87 octane does cause knock in the engine. Do you have another suggestion or are you okay with believing the "manufacturing hype" that it's okay to run 87 octane because the ECU can see it and detune the engine for you? Trust me, the capability to run lower octane is a HUGE selling point for many buyers. (not myself)

If you monitor the timing curve (variables are sent out of the OBDII port) and notice that timing is getting retarded at high rpm, then there's a good chance that this is caused by knock. To go even further, if you put higher octane gas in the car and timing no longer gets pulled back at high rpm then you can be assured that the lower octane gas was causing problems.

Don't compare tuning strategies with a stock ECU to tuning with an Aftermarket ECU where you can play with ALL of the variables. That's an apples to oranges comparison in this case. With the stock ECU you have to tune with the idea of optimizing the limited ECU capability. With an aftermarket ECU you tune with the idea of optimizing the engine.

As for falling for "oil company hype" read my previous post about using the lowest octane gas that you can get away with. There's a reason I posted that.

btw, I do believe in Santa. :-)

 

I've been reading your posts concerning "good fuel system cleaner on a set schedule" and , unfortunately, using any fuel additive is not encouraged according to the owners' manual, and may void warranties.

I'm using 87 octane, and no additives. If I need an injector cleaning at some point, I'll gladly pay dealer labor rates once every few years for that good cleaning.

Until then, I'll leave it alone, like the manual says.

 

Okay, I had this long arguement worked out but I believe that you summed it up yourself.

If this is true then please explain this:
Why would you want to run mid-grade on hot-days if it's been "magazine proven" that there's no difference between the grades if your ECU is "designed" to run on 87 octane gas?

Let me give it a shot, it seems to me that you've made mods to your car that will only work effectively with higher-octane gas. The end result is more horsepower at the cost of more money at the pump. Sounds familiar to me. Maybe this "pipe dream" stuff isn't so bad afterall.

Your comment about adding "fuel system cleaner" had me laughing for hours!!!! Ye who doesn't fall for "oil company hype"!!! Who do you think produces those additives?? I honestly hope you don't believe they do anything. Almost all high octane gas contains these same cleaning agents, yet you still get buildup. The reason is because the additives are so diluted by the time they reach the spots, that need cleaning, that they are ineffective. If you want to clean your fuel system, then try replacing your fuel filter on schedule, and pull your fuel injectors out occasionally and clean them directly. That's the ONLY way they are going to get clean! As for carbon buildup, then I would suggest some kind of combustion chamber cleaner applied directly into the engine. Fuel additives! "It's a pipe dream guys."

I'm done with this arguement and back to where I stood before. If you want to know for sure whether higher octane gas is right for you, then invest in a datalogger.

 

You still have not addressed the fact that the 2002 Protege manual expressly warns against the use of fuel additives.

Is this only to get consumers to take the cars to the dealer for injector service?

Who will honor my warranty if Mazda says no after using any additives? Redline?? I doubt it.

Follow the manual if you care about the first 50,000 miles or 3 years of your car's life. After that warranteed period, maybe I'll use something.

 

I'm not sure how the warranty thing works out if you add additives in your car, but i'm pretty sure no amount of additive can produce actual damage to an engine (not that i've heard of).

The major problem with additives is that they might form deposits in the engine, so it may reduce performance, but still not enuff to cause total failure of an engine. And unless Mazda can prove that the additives cause the actual failure of an engine, I doubt that they can void the warranty.