Fuel Question

cop1976

Member
:
2002 Protege 5
Hi All...I yet another question for my fellow MP5 owners. This question concerns fuel for the MP5. I was wondering what you all use and suggest for your car. The Brochure I have says regular unleaded fuel. Are you guys using regular or are you using middle blends or premium? I have heard using premium can actually work against you because the engine isn't made for high performance. Thanks for your replies.
 
Do what the brochure says. The P5 has 9.1:1 compression so it certainly does not need higher octane fuel, unless of course, you don't want your fuel to combust as completely. ;) This has been discussed too often. Search for octane and you'll have more info than you can possibly read. Some people but premium in their cars anyway and say it is better. I think that is the placebo effect.
 
Sure it's been discussed. However there was no definite answer.

Mazda's website for the Protege5 specs shows:



Recommended Fuel Unleaded regular, 91RON

Does 91RON not mean 91 octane? I thought so until I took a closer look, on the same line it says "Unleaded Regular". So what the hell does "RON" mean? I saw this before I bought the car, so I always bought premium (92 octane here), until I saw the "Regular Unleaded" part. I switched to 87 octane regular unleaded, and noticed the car started to seem "drowsy". Do you think the ECU retards and advances the timing based on octane? If I always ran 92, then switched to 87 and my ECU picked up the difference and retarded the timing to guard against pinging, wouldn't that explain the loss I felt? Besides the guess of it being placebo effect.
This is what I mean by no definite answer. You're guessing, I'm shooting in the dark for en explanation, and Mazda can't even make up thier mind on their own website. I guess we're looking for someone with a brain at Mazda to give us the whole scoop on this topic.
 
It's a tricky topic. But all the info I've read explains that octane prevents premature combustion, therefore octane does not combust as easily. So with such a low compression as the P5, I don't see anything more than regular being needed. Regular is 87 octane everywhere in North America I think. I ran 91 octane a couple times and had no difference, besides a higher cost.
The ECU should not be able to identify the octane level of the gas in the car. If it could, that would be hella cool.

We need an expert for the definitive answer.
 
RON (Research Octane Number) is an octane rating system they use in Europe and other parts of the world. An octane rating of 91 RON is equivalent to 87 RON+MON/2, the rating system we use in North America. So, on Mazda's website they ARE telling you to use regular gas, not premium. That's the definite answer. As to whether or not the engine will actually perform better on premium, that's really for each individual owner to test and figure out for themselves, if they're curious. Personally, I'm happy to have a car I can just put 87 in -- my previous car needed premium.
 
Sheesh, finally a real answer. Thanks for the info on RON, that makes sense now.
But about the ECU, I read some posts (just from people on the forum, not like Mazda dsegners or head techs or anything) about the MP3 ECU vs. regular 2.0l ECU's (Pro5, ES). Someone said they found out that Premium is recomended because the MP3 advances the timing to aid in the extra 10 HP (I don't think that could give it all 10 HP, but I could be wrong). If regular 87 is used, the ECU can sense something (knock sensor?) and retard the timing to regular specs.
Now, assuming that this is true, how about this idea (just shooting in the breeze here):
Being a penny-pincher car (under $20G) it would make sense that Mazda would not want to totally re-do the ECU for just 1500 cars, so I'm wondering if they designed all ECU's for ther 2.0l to give the extra HP for premium fuel, and regular power for reg. gas? I mean, the MP3 is the only one recommending premium fuel, the only one with the extra HP, and without the better fuel, no extra power, right? So Mazda puts the same damn computer in all cars, tells MP3's to use premium, and there. Problem solved. Now the owners like me who put 92 in, well, they just happen to get the extra HP without even knowing it.
Aaahhhhhhh, one can dream, right?
 
it's a very interesting idea. Making a different ECU for only 1500 cars does seem a bit strange and expensive.
 
I don't think it would be much more difficult or expensive. All they would need to do is put the prototype engine of the MP3 on a dyno hook up the ecu to a pc, tinker with the fuel, timing and other stuff and voila program for mp3 engine.

All they do is make different proms for it. I'm sure the ecu's are identical, just the program it runs is different.
 
Just a note~~ no ECU will give 10 hp. I am also finding it difficult to understand where the 10 hp difference is?? Ok, premium fuel, different ECU, Racing Beat muffler?? All that adds up to MAYBE 5 hp @ the crank. I know it may have been dynoed and shows the 10 hp difference (or does it?) Or is it the wing that gives the 10 hp~~sorry , had to get that little rib jab in there. I tell you what~~ I have a P5, and will not think twice about racing a MP3, i am pretty sure that the difference would be so negligable, that it would be hard to tell who won.
 
Racer 5 said:
I tell you what~~ I have a P5, and will not think twice about racing a MP3, i am pretty sure that the difference would be so negligable, that it would be hard to tell who won.

Yeah I think it would be pretty close too, I mean you wouldn't really lose by much to a MP3... :D :D :D

Seriously though, I think it would be a close race. A friend of mine has a Protege5 and we both drove around Houston a bit last week. I was leading the direction with my MP3 and every time I'd rev up to pull away he would be pretty much right there behind me (two passengers each). I don't know how much he had to pedal it, but I have to say I never did pass the 5K RPM mark (I like my new car too much and not easy to do within city limits on crappy roads with other cars in the way).

Overall the MP3 has quite a bit of unecessary weight when you compare it to the other pocket rockets. The heavy wheels, sound dampeners, and sub are some I can think of. MP3s are more for show than for race... but hey, I knew EXACTLY what I was buying so I got almost exactly what I wanted (although who wouldn't want more HP?). Love it! Love it!
 
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