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- 2019 CX-5 Signature
Comparing 87 to 91 octane for the 2.5L non-turbo engine
- Thread starter erhayes
- Start date
I don't pretend to have the answer, but if this is true, then why does Mazda list two different horsepower numbers for the 2.5 turbo? One for regular gas, and a higher number for premium gas?
I think what theblooms was stating is that changing to higher octane doesn't absolutely mean more power unless the system (engine/tune) can take advantage of it. The turbo does take advantage of that extra octane....at least above 4k rpm according to the graphs.
The naturally aspirated engine might not be programed to take advantage of the extra octane.
My archaic 1989 5.0 Mustang, with a stock tune, there would be no power gain over 87 if I used 93 octane. Now, a common 'free' mod was to bump up the base timing, which usually required 91-93 octane to combat pinging/knock. The net was something like 10hp by adding 4 degrees to the base timing.
Again, that's what I think he was saying.
Pardon me but I read it as 2 required fuel octanes to use and not just one recommended. Am I incorrect? Look at your highlighted important information.
I do find it interesting that Mazda only wants you to use their gas additives when looking into the ingredients less effective than 100% safe to use as per Chevron their fuel additives. I believe Shell is also the same not to mention many other brand names like STP, seafoam, Lucas etc.
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- 2014 & 2019 CX-5 Touring(s)
Read the highlighted part again. 87 octane [when measured by R+M/2 method] -OR- 91 Octane [when measured by Ron method].
For more info on these two ways of measuring octane, see: Gasoline explained - octane in depth - U.S. Energy Information Administration (EIA)
I really don't think it works exactly that way about the Turbo? I do know that the ECU programing can adjust for fuel type used based on values from sensors. You use 87 and you will not get the higher power output because the computer will in a phrase protect the engine from damage. Using higher octane will allow the engine to develop more power to a point where the ecu programing can no longer correct negative input and then it will go back into protecting the engine.
The normally aspirated engines ECU actually works the same way except obviously no Turbocharger. I think if any member contacted a ECU calibrator and talked to them they would have hundreds of before and after data logging to support this information.
Having owned a few Ponies I am a bit on fused about your Mustang as it was still in the era of OBDI not OBDII, which OBDII is currently want Mazda is using. Your Mustang used a knock sensor that did the same information sending as most other cars like our MAZDA only the ECU in your era Mustang was highly limited to what it could do to protect the engine. So driving spiritedly, competitively or just aggressively would necessitate the use of 93 octane to support the power output of the engine safely. Not sure why you did not feel any difference because it would have been at least 7-12 HP difference from 87 octane fuel to 93 octane in your year and engine size?.
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- 2019 CX-5 Signature
I read that as "don't use any additives". They can cause more harm than good. Just buy quality gas and forget about it.
Good information this a few other write up on that subject. Not to be rude but maybe go and read your provided article again? How a Mazda ECU programing is done and can be seen by entering and logging with a scan tool should be easy to see that using the higher octane fuel will and does support the engine to develop the claimed power levels by Mazda.
You have to wonder why Mazda just does not recommend 89 octane fuel with newer Mazda models?
Sorry for beating a dead horse I realize this is not a performance thread and most here seem to be just regular drivers so use what floats your boat. I just know I use the highest octane available in my Mazda, and in the few times I had to use other than that , the butt dyno alerted me to something was not as usual.
It clearly say to use MAZDA products. under the Caution section 3 .
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- South Carolina
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- 12 MZ5 13 CX-5
Let me be clear: it's not the higher octane that gives additional power, it's the ignition timing. The only thing the higher octane rating does is allow the additional timing without risking damaging the engine due to knock and ping.
Unlike old school Mustangs and Camaros (I had a 85 with a built 350), modern cars have knock sensors that are read by the PCM, which can constantly adjust timing to deliver max horsepower. Back in the day, we simply adjusted timing with a light, springs, and vacuum advance! Same exact thing though, it's just now computer controlled instead of a manual process.
For what it's worth, because of the way my Camaros timing was set, it ran like CRAP on 87. Hell, it barely ran right on 93. I usually ran 93 with a can of 104+ thrown in for measure.
Unlike old school Mustangs and Camaros (I had a 85 with a built 350), modern cars have knock sensors that are read by the PCM, which can constantly adjust timing to deliver max horsepower. Back in the day, we simply adjusted timing with a light, springs, and vacuum advance! Same exact thing though, it's just now computer controlled instead of a manual process.
For what it's worth, because of the way my Camaros timing was set, it ran like CRAP on 87. Hell, it barely ran right on 93. I usually ran 93 with a can of 104+ thrown in for measure.
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- 2019 CX-5 Signature
I stick with my theory based on the first 5 words that they began the statement with.
I was scratching my head and then it dawned on me. Because of your funny response and going back and re-reading everyone's responses. Its all how things are worded. I failed to use the word SUPPORT more in my responses having to do with octane values and engine power. DAU.
Sorry guys. Yes the use of octane values alone do not raise or lower the power out put of an engine , but if the ECU can adjust operating perimeters based on the input vales of sensors while using higher octane fuels than those high octane fuel can SUPPORT the engine developing more power and sustained power levels and in most cases without causing harm to the engine!Better?
clownshoes2
2017 CX-5 GT No Tech
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- CX-5
Can't we all just get along?
I think we're saying similar things, just different way.
At least on the turbo, the ECU is probably programmed for best performance with 93 octane. If someone uses lesser octane, the sensors and whatnot 'dial it back' to protect the engine.
As for my Mustang, it does not have a knock sensor. I don't think they had knock sensors until 96 when the 4.6 was added.
My Stang is essentially based on rpm and air flow (i.e. engine load), especially at wide open throttle. It does have O2 sensors for closed loop (part throttle) fueling, but anything more than about 1/2 throttle, it goes into open loop and looks at air flow vs. rpm and table lookups. Timing is all scalars, functions and tables, but no knock feedback.
Ok sure but I do not agree ECU are calibrated for octane values.. Rather they are limited by sensor input and how the mapping was done based on those same sensor inputs . Fuel octane effects those engine operation that the sensors pick up and send the information to the ECU which will adjust engine response accordingly.
As for the Mustang I never mention 02 sensors. But and don't take offence based on your interesting responses about it I suspect that you had your ECU calibrated for your performance needs.
Right on. Very minimal tech, inefficient power wise by today's standards and it was designed to run on 87 octane.
If you think about it, the stock Foxbody had 225hp, which was respectable at the time.
The new 5.0 is 460hp. That's over 2x the power with same displacement and yet yields as good or better fuel efficiency (I believe).
Technology has come a long way.
I guess what I mean by programed for 93 octane is that the ECU base values are based on testing with 93 octane. If you put higher octane than that, you don't gain any performance because the 'maximum' base parameters could be exceeded. Wonder if anyone has done any testing on Turbo 2.5 with say 98 octane (R+M/2) to see if there's any power increase over 93 without an aftermarket tune. I'm sure Mazda only publishes the 93 octane because that's the maximum you can find at most 'normal' gas stations.
My point on the O2 sensors in the stang is that's the extent of 'adjustment' the stock ECU does in a Foxbody Mustang. There is no ignition timing feedback for that ECU. If you take a stock Foxbody and fill it with 93, you will see no discernable gain in performance (power or mileage).....and could actually go the other way.
That goes back to the point that putting higher octane does not automatically result in more power. It can, but only if the engine/ECU needs or can take advantage of it.
And yes, I've modified the tune (timing) in my car to take advantage of the 93 octane that I run.
LOL! 91 Research Octane Number is essentially the same as 87 U.S. Pump Octane (the average of Research Octane Number and Motor Octane Number, two different ASTM test methods).
