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Better mpg on 87 octane than 93

3K views 18 replies 9 participants last post by  Smoke 
#1 ·
I have a Stock 13 GT manual trans with 6k miles on it. I drove the first 5k miles with 93 octane and was averaging 21 mpg. I recently switched to 87 octane and have been getting about 22.5 mpg average. I am on the highway more than local street and occasionally step on it taking off from a traffic light stop.

Do these results make sense? Better mpg with lower octane?
 
#5 ·
I would never put 87 in my car even if it gave me 3mpg more.

Also probably just your driving changed a little.
I agree with the changed driving but why would you not put 87 octane in your car?

According to the FTC studies, "It may seem like buying higher octane “premium” gas is like giving your car a treat, or boosting its performance. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage, or run cleaner. Your best bet: listen to your owner's manual."

Why would you not want to save $.30 a gallon if it was not going to do anything for or against you?
 
#11 ·
Do you own a 5.0? Owners manual tells you to run 91 octane. Not 87. Car will run on 87 but with a 11.0:1 compression you better baby the hell out of it.

I agree with what you posted. So should run 91. I run 93 octane because I am tuned to run 93. The 5.0 engine for optimal performance while stock should run 91 octane minimum.
You are exactly right, with the higher compression ratio, you need the higher octane. My 07 GT manual says 87 so that is what I use since I do not have a tune...YET. That is why you see a power increase with just a tune alone as stock is conservative enough to not cause detonation even with the lower octane. Key word you used, "optimal!" Stock is not optimal and that is what a tune is all about, trying to optimize the combustion.
 
#12 ·
You are exactly right, with the higher compression ratio, you need the higher octane. My 07 GT manual says 87 so that is what I use since I do not have a tune...YET. That is why you see a power increase with just a tune alone as stock is conservative enough to not cause detonation even with the lower octane. Key word you used, "optimal!" Stock is not optimal and that is what a tune is all about, trying to optimize the combustion.
Lol I said optimal performance while stock. I didnt say that was optimal performance for the engine in general.

For some wanting to keep the warranty they will want to run 91 minimum to keep the 5.0 running smoothly and easily without risk of damage.
 
#7 ·
The 5.0s computer can detect what octane it is and adjust to it, something the Mustangs before '11 couldn't do. That is why the 5.0s can actually see a small increase or decrease in power depending on what octane you put in. Now B52Bombardier what you said is correct about all Mustangs before 2011.
 
#8 · (Edited)
I am on the highway more than local street and occasionally step on it taking off from a traffic light stop.

:cool: So why didnt you just get the 30mpg 300HP model ?
Perfect for gas savings , more then enough for your ocassional 5 secound stop light blast,
and 87 octane friendly
With ALL the creature comforts of any GT if ordered correctly
Even Recaros and Pro Shaker Stereo, sounds like your saying,
I could of had a V6 ? :disgust:
 
#10 ·
:cool: So why didnt you just get the 30mpg 300HP model ?
Perfect for gas savings , more then enough for your ocassional 5 secound stop light blast,
and 87 octane friendly
With ALL the creature comforts of any GT if ordered correctly
Even Recaros and Pro Shaker Stereo, sounds like your saying,
I could of had a V6 ? :disgust:
Lol what? That was a mess to read. Second he wasn't complaining about the gas mileage. Why are you talking about it? He was confused he saw better MPG with regular. I don't think he once said he hated his MPG.

You need to read things before you post. Your posts are always cynical and wrong.
 
#17 ·
Don't we all...
 
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