Octane Recommandation

[95SHOATX]

Being new to this very informative forum I'm not sure if this topic has been discussed so I will ask the open ended question of what octane recommendation is the best for the SHO. I realize it states that premeium (93) is recommended but running 89 or even 87, pro's and con's anyone?

 

[AutoXSHO]

With the factory ECU calibration, I noticed no difference running 93/94 octane instead of 89. I just don't think the computer will advance the timing enough to take advantage.

With the LPM, running 94/92/89 there is a definite difference with the higher octane fuels.

John

 

[jthomas68]

I switch between 89 and 93.I`ve also used 87 for long thruway trips with no problems,but i wouldn`t use it for city driving.

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Jeremy Thomas
Juiced 91+
SHO Pic Of The Week:

 

[sdpatt]

The reasoning behind the higher octane recommendation is to optimize the performance potential of the engine under all conditions. The is achieved by allowing the electronic engine control (EEC) computer to keep the ignition timing advanced as far as possible under all conditions. If preignition is detected by the knock sensor, the EEC will retard the timing to eliminate the knock. This also reduces power and responsiveness of the engine. The higher the octane, the greater resistence to knock.

You could probably get by with using a lower octane fuel on highway trips where the engine is lightly loaded and you can do without the last ounce of performance from the engine. I can't. My more mature engine will ping under light throttle and high temperature conditions even with 93 octane fuel. The ping is only noticeable for a split second until the timing is ********, but I then know that the engine is not making the most of the engine control programming.

I run 93 octane all the time because I want the most out of my engine all the time. Now that I can get premium unleaded for $101.9 a gallon from Sam's Club, why should I try to be cheap?



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Scott

1991, 253K miles, glass hood, police grill, SVO shifter, Catz fogs,
K&N, 73mm MAF, Superchip, PP Y-pipe, Borla cat-back, 190 lph pump
Eibach/Tokico/polyurethane, SHO Shop front & rear strut braces,
16x7.5" Moda R1, 225/55ZR16 Bridgestone RE730, -1 deg camber x 4,
Class II hitch, Silver award at the SHOklahoma Car Show

 

[AutoXSHO]

Man, $101.9 a gallon!

Just kidding.

As Scott mentioned older engines often need higher octane to run properly due to carbon buildup inside the motor causing hot spots and detonation. My 135k mile 3.0 could get by with 89, but scott's needs 93.

YMMV.

JV

 

[fredhurderjr]

This subject came up a long time ago here, about carbon buildups. I have been told by other mechanics who work on SHOs that 87-89 octane gas typically burns hotter & faster, burning away more deposits, allowing the engine to run cleaner, but sacrifices performance (timing / knock sensor as mentioned above).

The opposite is true with higher octane - it burns colder / slower, leaving more buildup over time, but makes the most of the timing advances.

However, if you have buildup, you're going to rob power anyway (over time). If the only thing you do to clean your engine is your gas choice, perhaps doing what Jeremy does (switching occasionally to 89) will yield the best of both worlds.

I'll let you know what I find for deposits when we pull the heads off my old 72k 3.0L.

It's a moot point for me, as I HAVE to run at least 92 & up because of the blower.

 

[FordLover]

My 92 runs great with 87. So I rarely give it anything better unless I'm gonna be beating on it like track time or when I get together with other SHO guys. My 93 however pings just a bit when taking off from a stop, probably has to do with the lightened flywheel, and better clutch. The engine bogs down more from a stop in first than it would if it was stock. And that is when I notice the ping. So all it gets is 93 octane. Basically if your car will run fine with 87, then don't throw money away. But if it pings, eventually you will cause damage, so stick with higher octane.
-Martin

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My girl

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[89 Gary]

If you use less than the recommended octane(93?),then from what I recall reading is that you could cause detremental effects to your head/piston/valves. What these are I'm not sure but it was something related to what Fred stated and the extra "heat" in low octanes isn't good for the original design in the yamaha motor. I have an Expedition which calls for 87 but if you put in higher the computer sees this and adjust and you'll get more power! Why not just drive a regular taurus if you want lower octane -that's why we have SHO'S!!!! Let's do the math again (average driver)- 15cents more a gallon times 20 gallons- holy bazookas that's an incredible 3 dollars a week.

 

[Ric]

Is there an inexpensive way of checking the octane rating of the gasoline that you're purchasing at the pump? At times, especially during the so called "gas shortage" times, I'm sceptical about the grade of fuel I'm actually putting in my SHO.



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Ric & roughSHOd
93 3.2

 

[fredhurderjr]

Well, let's see...
89 has a more "fruity" flavor than 93, especially as it passes over the tongue. The higher octane tends to sour the palatte & has a more pungent aroma...

Seriously, no clue.

 

[Vazcular]

Originally posted by Ric:
Is there an inexpensive way of checking the octane rating of the gasoline that you're purchasing at the pump? At times, especially during the so called "gas shortage" times, I'm sceptical about the grade of fuel I'm actually putting in my SHO.

Good point. I notice my SHO runs far better on Exxon and Shell gas than Chevron. And all are "supposed" to be 93 octane.

 

[noSHO]

I don't really understand what the issue is here. At just about every gas station I've ever been to, there is a 20 cent spread from 87 to 93 (ie 87 is 1.03, then 93 would be 1.23). I doubt most of us ever let our gas tanks get so low that we must put in 15 gallons, but say we did. That would just be three dollars more that using 87. I guess it does add up over time, but I just don't understand the point of owning a performance vehicle and putting 87 octane in it. It isn't THAT much more expensive.

-Dave

 

[TwiceSHOwn]

There was a magazine article in c&d or r&t recently about this...as i recall cars designed for premium lost about 10% total performance on lower grade gas (m3 was the car i remeber). The computer is prob a bit better than ours at detection etc but i would think that 5% loss of power is reasonable to assume. that would be about 10hp and would cost roughly 1cent a mile (20mpg/20cents a gallon) so in 100,000 miles it would cost 1000 dollars for these 10hp not cheap but you do get 1 heck of a payment plan..3 dollars a week.

I get my gas at BJ's currently 105 for 93 regular is only 15 cents less at 90. So i figure put what was "recommended". For higway trips i have used 89 and even 87 on occasion without detriment however when i had the 80MAF and LPM on the car, it would throw check engine lights and report o2 problems when i did.

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********
93 Silver ATX 57K
LPM
80MM MAF
Y Pipe
Eibach + Tokikos
Front and Rear STBs
Cold air snorkel
TCE SHO stopper brakes
Recovering from its 60K...sigh

 

[NotoriusCSR]

(wonders where people find 93) where i live the highest ive ever seen is 91 so thats what i use.

 

[sdpatt]

The higher altitudes of Colorado have less oxygen per given volume of air and are less prone to preignition. They are also less prone to make as much horsepower due to this fact. Less fuel is injected per intake charge because the mass air flow sensor and barometric pressure sensor let the computer know that the air density is lower. The lower octane of your "premium" fuel is equivalent to the 93 octane of the lower altitude fuels.


------------------
Scott

1991, 253K miles, glass hood, police grill, SVO shifter, Catz fogs,
K&N, 73mm MAF, Superchip, PP Y-pipe, Borla cat-back, 190 lph pump
Eibach/Tokico/polyurethane, SHO Shop front & rear strut braces,
16x7.5" Moda R1, 225/55ZR16 Bridgestone RE730, -1 deg camber x 4,
Class II hitch, Silver award at the SHOklahoma Car Show