Mixing Gas

[CuttySup]

Is it okay to mix 87 octane with 89 in the same tank? This may sound silly, but I'm thinking my car had 89 in it when I bought it because I've noticed a slight decrease in performance since I've been putting regular 87 into it. I want to start putting 89 into it to see if I can get the missing power back. Would this create a problem?

[Prospeeder]

no its fine

[3pt1lumina]

i dont believe it would cause a problem. I have 87, 89, and 93 in my Chevelle at the moment ... if it is bad I'm screwed

[supreme_style21]

What does the 3.5 recommend you run for gas? I have a feeling this is one of those 'in your mind' things.

[THe_DeTAiL3R]

My car seemed faster when it was "new" (my last car being a 2.8 GP) but now it feels slow. So it's possible there might be a power difference from the gas or your ass dyno might have been re-calibrated.

[gp90se]

as long as it isnt 104+ octane (leaded stuff), mix away.

[digitaloutsider]

My Cutlass constantly goes from 89 to 93 to 89 to 93 to 89 to 93. I can never constantly afford premium

[Prospeeder]

My Cutlass constantly goes from 89 to 93 to 89 to 93 to 89 to 93. I can never constantly afford premium

 

does it even need premium, i was aware the 3.4 runs perfect one 87

[94CutlassSLCoupe]

does it even need premium, i was aware the 3.4 runs perfect one 87

 

It does...we run our '94 3.4 'Vert on 87...runs great

 

As does our '90 Quad 4 DOHC HO (LG0)...but that one has a sticker on the visor that says "This vehicle is equipped with an electronic fuel injection system. Regular Gas may be used without damage, but Premium Fuel is recomended for Maximum performance."

 

Honestly, that car does run real good on 87...even gets like 35+ MPG highway

[CuttySup]

I'm thinking that because the older (as in pre-VVT era) Northstars run on 93, that maybe my 3.5 needs at least 89, seeing that it is the "Shortstar."

 

I distinctly remember accelerating really hard the first night I had it, and there was a major surge in power in the 3500 rpm range that doesn't seem to be as prevalent.

[JNGTP94]

it does run good with 87, but i do feel like mine runs alot better ( smoother ) with 93 in it. I would have to agree with your butt dyno just getting used to the car

[digitaloutsider]

I'm also chipped, and you definitely feel the difference from 87 to 93.

[chadz34]

I'm also chipped, and you definitely feel the difference from 87 to 93.

Will agree with digitaloutsider, when I use 87, the 3.4 has a noticeable amount of power loss compared to 91 or 94. It runs smoother with higher grade fuel.

[ToroToro]

I'm thinking that because the older (as in pre-VVT era) Northstars run on 93, that maybe my 3.5 needs at least 89, seeing that it is the "Shortstar."

 

The 93-99 N* were required to run premium. In 2000 when they lowered compression and went to the coil on plug setup, they could run on regular.

 

A good rule of thumb with the 2000+ N*, and all Shortstars is that they'll run good on regular 75% of the time, and not so good 25% of the time, wheras the 93-99 motors would run good on regular on 25% of the time, and bad 75% of the time. Sounds sorta strange, but I've been told that by numerous N* techs and enthusiasts.

 

I've always noticed on all 3 of the N*s I've had/have ( 95,99,03 ) that they run much better on premium then regular, especially the 95 and 99.

 

Bottom line...you might be leaving a little on the table running regular, but it shouldn't be that big a deal.

[19Cutlass94]

Doesnt running high octane gas burn out your fuel injectors faster, or is that only if you run like 110+ or something absurd like that? Maybe tomorrow Ill put some 93 in the olds, see what see runs like, even though I have no real mods that it could benefit from lol

[JNGTP94]

only with 110 i would think

[gp90se]

only way your gunna burn an injector is running leaded fuel, methanol or to many cleaners thru them, anything you get from the pump wont hurt the injectors.

[chadz34]

even though I have no real mods that it could benefit from lol

It doesn't matter about mods. The engines just run and accelerate better. My Z34 runs like shit on 87, and it guzzels gas. At least on 91 or higher grade fuel it runs smooth and is easier on gas.

[DaveFromColorado]

as an engine gets older, the "motor" requirement goes up.

 

what does this mean you wonder...

 

Can you get additional benefit by using Premium? Probably not. If you keep your motor in good shape, you will not have "pre-ignition" with regular, just as you won't have it with Premium. (Pre-ignition, or dieseling," or "knock" is what "octane" prevents). In fact, you normally get better fuel economy with Regular because it has a higher "heating value" in BTUs per gallon than does Premium.

 

What causes the confusion is the way octane ratings of gasoline are displayed. (R+M)/2 simply means "the average of the Motor and Research octane numbers." Without getting into the differences, for conventional refined and blended gasolines the Research number ® is about 9 or 10 octane numbers higher than the Motor number (M). They are both determined using special "knock" engines, but the "Motor" determination is done under more severe conditions thus you get lower numbers

 

so basically if you are feeling a power loss when running the lower graded fuels this is probably because your engine is in one of the more severe states, and it's more then likely your knock sensor robbing you of that power by pulling timing and changing the fuel maps ... after all, Octane rating is literally just an "anti-knock number".

 

--Dave.