how bad is it to be running a 93 Octane tune but using 87 gas?

[MercNasty]

Am I harming the car by doing this? should i change the tune to 91 to be safer or should i just change it to 87 since thats what im using. The car is my dd and i drive about 50 miles daily round trip so im not even thinking about putting a higher grade of gas in it right now due to the price of gas. Let me know your thoughts.

[SpartaPerformance]

You run the risk of detonation which can blow your motor. If you're going to run 87 then run the 87 tune.

[RF Overlord]

^^^what he said^^^

The knock sensor can pull timing just so far...if you exceed that limit then you get to pull your engine and put another one in.

[Bluerauder]

Am I harming the car by doing this? should i change the tune to 91 to be safer or should i just change it to 87 since thats what im using. The car is my dd and i drive about 50 miles daily round trip so im not even thinking about putting a higher grade of gas in it right now due to the price of gas. Let me know your thoughts.
Since you asked .....

You will NEVER drive the car far enough to save enough money to cover the cost of the engine WHEN it fails. I'd suggest that you park the MM and get a daily driver that runs on 87 that can do the duty and not break your bank. The owners manual says "Minimum 91 Octane" .... anything less and you are pushing your luck. The 4.10 gears are probably costing you 1-2 MPG (about $2.00 per day) ... put the 3.55 gears back in and you may be able to afford the 91/93.

Worst case scenario is to sell the MM and get something more in line with your current situation. I suggest doing it before the engine blows. You asked. ;)

[IwantmyMMnow!]

Worst case scenario is to sell the MM and get something more in line with your current situation. I suggest doing it before the engine blows. You asked. ;)

If saving $$$ on gas is of great importance to you, I agree with Charlie...park or sell your MM and get a 4-banger to DD with. Running 87 octane on a car that requires 91 minimum AND running a 93 tune sounds like the perfect storm for eventual engine-go-boom.

[MercNasty]

Thanks Sparta and RF for answering my question lol Bluerauder's response was a lil far fetched. I think ill just change the tune to 91 and start putting 91 gas in there. I think i can pay for 91 with a food stamp card.

[Bluerauder]

lol Bluerauder's response was a lil far fetched.

Do the math if you think my response was far fetched? :rolleyes:

[IwantmyMMnow!]

Thanks Sparta and RF for answering my question lol Bluerauder's response was a lil far fetched. I think ill just change the tune to 91 and start putting 91 gas in there. I think i can pay for 91 with a food stamp card.

You asked for our thoughts/opinions about your situation...you may not like what you hear. :depress:

[Hadamustang1]

Do the math if you think my response was far fetched? :rolleyes:
$2 to $3 bucks a tank.. x how many tanks . new motor cost?

I think he was right on the mark..

[MercNasty]

i didnt any questions regarding any math or what i could afford or if i should park, sell or get another DD. I forgot how extra some of the comments can be on here. Thanks again Sparta and RF for answering my question.

[a_d_a_m]

I think i can pay for 91 with a food stamp card. ...are you serious?:flamer:

[MercNasty]

lol no man that was a joke.

[a_d_a_m]

...phew! Good!

As others have said you're best off running what your car is tuned for.
And if you do the math, you'll see that it really isn't much more expensive to be running 93 vs. 87. Here, assuming a 16gal fillup, that'd be $3.20/tank. Better than an engine rebuild.

[03sport007]

Trust me I'm not advocating this at all but if the op was very gentle on the throttle and avoided lugging the motor wouldn't he be ok? I would stay away from heavy acceleration or big hills but I would think driving on flat terrain with grandma starts should be doable.

Again not something I would personally do or suggest she speaking hypathically.

[MercNasty]

Thanks Adam, now thats some math that ill consider. I guess there isnt that big of a difference $62 for a fill up with regular and $67 for super. looks like i start putting 93 in it.

[marauder410]

you put 87 in your MM areeee you seriousssss wowww thats not good i use only 93 from bp or shell thats itttt and only them twooo if ur running 87 that cheap gas when ur motor is not gonna last long

on the spoeedomter is SAY PREMIUMM ONLYYY

[marauder410]

if uve been putting 87 in ur car after it say premium only just sell your
MM and jus get a 4banger honda

suprissed ur motor hasent blown yet

[RF Overlord]

Trust me I'm not advocating this at all but if the op was very gentle on the throttle and avoided lugging the motor wouldn't he be ok? I would stay away from heavy acceleration or big hills but I would think driving on flat terrain with grandma starts should be doable. Maybe as a one-shot to get home or someplace safe in an emergency, but everyday driving is too unpredictable to depend on that.

[IwantmyMMnow!]

Let me know your thoughts.


i didnt any questions regarding any math or what i could afford or if i should park, sell or get another DD. I forgot how extra some of the comments can be on here. Thanks again Sparta and RF for answering my question.

:confused: Kinda left the door wiiiide open....just sayin'. I'm glad you got the answers you wanted and it appears that you realize paying the extra $3-5 per fill-up is worth it. I understand where you're coming from...the first 9 months I had mine, I was traveling at least 1,200 mi each month to see my kids, spending at least $100 on gas each trip I made, so yeah, it does take a chunk out of your wallet. Hell, I put 30K on mine in the first year! That's approx 1,500 gal/$5600. But being an MM owner and part of this great club we have is worth every penny that gets put in my tank. :)

[Juice]

A little food for thought... In the spirit of saving a little extra money over the next few months I have been driving the MM very easily. Simply changing your driving habits a little bit can go a long way in fuel economy. Just by staying near the speed limit and accelerating/braking at a very conservative rate, I've been able to take my AVG fuel economy from 14.5mpg to 20mpg. That's an extra ~105 miles per tank that I am able to drive, saving me about $50 a month (for my distance driven).

[Chevyguy]

Trust me I'm not advocating this at all but if the op was very gentle on the throttle and avoided lugging the motor wouldn't he be ok? I would stay away from heavy acceleration or big hills but I would think driving on flat terrain with grandma starts should be doable.

Again not something I would personally do or suggest she speaking hypathically.

Factory compression ratio of 10.1:1 requires 91 octane minimum. Should only use less in emergency situations.

[fastblackmerc]

A little food for thought... In the spirit of saving a little extra money over the next few months I have been driving the MM very easily. Simply changing your driving habits a little bit can go a long way in fuel economy. Just by staying near the speed limit and accelerating/braking at a very conservative rate, I've been able to take my AVG fuel economy from 14.5mpg to 20mpg. That's an extra ~105 miles per tank that I am able to drive, saving me about $50 a month (for my distance driven).

But I bet it's not as fun as driving it like you stole it!

[Juice]

But I bet it's not as fun as driving it like you stole it!

I beat the piss out of the Mustang on the weekends, so that's a small consolation.

Also, the MM is going to the track again at the end of the month, so she'll be screaming again in no time. :D

[MyBlackBeasts]

I don't know about where you live but by me the 87 has 10% ethanol in it. I stopped running it 2 years ago when I found running the 91 with 0% ethanol gave me 5mpg more. The simple math showed by spending a few dollars more to fill the tank = many more dollars saved by better mileage (not to mention how much better the car ran). :coolman:

[PonyUP]

Thanks Adam, now thats some math that ill consider. I guess there isnt that big of a difference $62 for a fill up with regular and $67 for super. looks like i start putting 93 in it.

Well, the owners manual says premium fuel only, which leaves 87 out. Best rule of thumb I can offer, follow the recommended maintenance as written in the owners manual and everything will be fine.
Running 87 in an emergency will get you by, but it is definitely worth adhering to the prescribed fuel



Pony seal of Approval

[SC Cheesehead]

Thanks Adam, now thats some math that ill consider. I guess there isnt that big of a difference $62 for a fill up with regular and $67 for super. looks like i start putting 93 in it.

Yup. ^^^^^ When you do the math, you soon find out there's not a whole lot of difference.

You can get 24 mpg out of these cars, but it takes a VERY discipleined right foot; hard to do with a DOHC V8... ;)

[IwantmyMMnow!]

You can get 24 mpg out of these cars, but it takes a VERY discipleined right foot; hard to do with a DOHC V8... ;)

It appears I misplaced mine about 1 year, 2 mos, 26 days ago...:banana2:

[MercNasty]

ill be using 93 from here on out and I will work on my driving habits like Juice recommended, thats gonna be hard tho since i like hearing the aero's and being the first one off the line.

[SC Cheesehead]

It appears I misplaced mine about 1 year, 2 mos, 26 days ago...:banana2:

what, your foot or your mpg? :confused:

[Ozark Marauder]

Just wondering........How bad is it to run 94 octane on a completely stock motor? Weren't they tuned to run on 91 from the factory? Does running the higher octane than factory recommended octane just a waste of money?

Sorry for the :Offtopic: Just wondering. All the premium gas here is the same price. Octane comes in 3 grades, 91, 93, & 94.

OZ

[Juice]

Just wondering........How bad is it to run 94 octane on a completely stock motor? Weren't they tuned to run on 91 from the factory? Does running the higher octane than factory recommended octane just a waste of money?

Sorry for the :Offtopic: Just wondering. All the premium gas here is the same price. Octane comes in 3 grades, 91, 93, & 94.

OZ

No, it won't hurt. For those of you who don't know, the octane rating describes how prone the gasoline is to spontaneously igniting when compressed. The lower the number, the more susceptible the gas is to this. So 87 will ignite at a lower compression pressure than 91. Since our motors have a higher compression ratio (the compression stroke compresses more air in the cylinder) than the average car, we are required to run a higher octane gas.

The only thing you're hurting by running higher octanes is your wallet.

[RF Overlord]

Does running the higher octane than factory recommended octane just a waste of money?In a word, yes.

As Juice explained, gasoline's octane rating is a measure of its resistance to detonation. Because of this resistance, it has a slower flame front when ignited, therefor you don't get as big a "bang for your buck". The general rule is to use as low an octane rating as you can get away with, while still maintaining a safety margin. IOW, if the book says 87, use 87. If the book says 91, use 91. All other factors being equal, there's no performance benefit from using a higher octane than the engine needs.

[MyBlackBeasts]

In a word, yes.

As Juice explained, gasoline's octane rating is a measure of its resistance to detonation. Because of this resistance, it has a slower flame front when ignited, therefor you don't get as big a "bang for your buck". The general rule is to use as low an octane rating as you can get away with, while still maintaining a safety margin. IOW, if the book says 87, use 87. If the book says 91, use 91. All other factors being equal, there's no performance benefit from using a higher octane than the engine needs.

True, the only caveat is the wild card of ethanol in the fuel. If your 87 contains ethanol and the higher octane does not, you can see a significant increase in fuel mileage running the higher octane. This can put more cash back in your wallet than the extra going out from the increased per gallon cost (especially on smaller less powerful engines). Try 3 or 4 tanks of higher octane with no ethanol and compare your specs to what 87 w/eth gives you.

I learned this with my Tbird. 87 w/eth gave me avg 17mpg and engine was dog (would stall if a/c was on coming to stop), 2nd tank of 91 w/o ethanol = 21mpg, 4th tank = 22/23mpg, more power & a/c ran with no issues. :burnout: