So, I was wondering what are you guys using for fuel in your stock TPI...The 1st owner I got the car from told me he used regular grade fuel, and so was I the past few years that I've owned it, once in a while I used primium grade, but never noticed significant difference, however, I did saw that the owner's manual recommend using high grade fuel in the TPI engines.

 

That's what it says on my Mercedes near the gauge, Premium Fuel Required, on my Trans am it says Unleaded Fuel Only, I used 87 regular on my '87 Iroc and when I first bought my '92 Z28 I used 87, then switched to Premium (91) but then switched back to 87 89 & 91 and noticed it runs better on 91.

 

It does says unleaded fuel without reference to any grade near the guage, but if you have the owner's manual, look inside and you will see that they recomend going with 91, but they also say that you can use lower grade fuel but with reduced performance. I know mercedes require you to use primium, I think its because they use higher compression engines. I know if you use regular fuel in a mercedes, the check engine light will come on.

 

It's weird tho in my Grandmas Dodge Caravan V6 3.3L the owners manual says To use 87 regular for optimum performance and you would think that if you used 91 that would be even better right?, well the manual says the use of higher Octane 91 may result in poorer performance. That left me wondering. My Nissan Sentra runs on 87 and says Unleaded fuel only.

 

I guess each manufacture have its own settings for the fuel injection system which determines what gread of fuel to use. In the owner's manual they say you have the option to use regular fuel with reduced performance because of the electronic spark control system that the TPI has...I guess when you use regular gread fuel the ecm retards the timing a little bit.

 

93 oct

 

The octane rating of gasoline is basically a rating of how difficult it is to burn. Or really how slow it burns. The higher the octane rating the slower the flame front. For maximum power, it's best to use the lowest octane that is still safe for the engine. Our cars may loose power with lower octane fuel because the computer retards the timing to reduce detonation. That Dodge 3.3L looses power with higher octane fuel because the flame front moves slower, thus having less force against the piston. Or somthing like that.

 

To answer the O.P. I use 91. But, for emmission tests it's 87. Lowers the hydrocarbon count

 

91 octane for best performance

 

i do the same thing around smog time

 

It's good to know because when I went smog testing, I used to put 91. I thought it would run cleaner.... apparently I was wrong...

 

Yeah LB9 Hit the nail on the head, and not to be a jerk but 88I-ROC ur wrong on somethin else, using less then 91 octane fuel on a late model Benz will not turn on a check engine light. The computer will retard timing as needed to prevent pre ignition but no service light unless the gas is bad i.e. watered down and causing misfires or something else of the sort. I work on Benz and BMWs for a living and you would be surprised how cheap luxury car owners are about their car. We do try to advise them to use top tier gasoline and proper octane ratings all the time though to no avail...

 

you want to run the lowest octane that does not cause knock (retarded timing), and higher octane will not give any increased performance, except how fast your wallet empties.

also, with the price of gas I have found that premium fuel sits longer in the underground storage tanks and is more likely to be "bad gas" especially with the ethanol now in all gasoline.

 

Well, I'm talking from experience as well....My friend had a 2001 SLK and he used regular fuel for a while and he started getting the check engine light, only when he started using premium again, the check engine went away...

 

Probably because the car was designed for premium fuel. If it is designed for higher octane fuel (aka higher compression) then yes you will tend to knock with 87. But if your car was designed for 87 then there is no benefit from using higher octane fuel. The L98 and LB9 I believe are both 9.0:1 CR so there is no benefit to using anything higher than 87 unless you run higher than factory timing.

My vortec has 9.6:1 and I run a stock timing table and run 87 all day long. I have never had a hint of knock even on a 100+ deg day under heavy load.

 

Their 9.5:1

 

i use 89. it seems to idle smoother then when i use 93


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My car is a tbi but I'm running a little more advance than stock and it runs best on 93. Back when timing was stock I didn't notice any difference between 87 and 93 until I got on it and above about 3k rpm it would pull timing and kill power when running 87. Also gotta remember these cars are old and more than likely have a good bit of carbon build up which will make the engine more prone to detonation. I know here in FL 93 is around .20 more than 87 and if you put in 10 gallons thats only $2 more so the cost is negligible IMO. I always try to run Cheveron gas because of the Techron additive they use. The concentrate they make is the only fuel system cleaner I've ever used that actually works. Also, my wife used to work at Gate Petroleum and they checked their tanks daily for water and if it was contaminated they would stop selling that grade of gas and have a truck come pump out the tank.

 

That's true...but you don't necessary know that (knock) on a car with ESC because it's supposed to correct for that, but you can definitely see it in the knock counts and or spark retard.

 

Gotta be a bit careful though because different styles of heads react differently to compression ratios and octane.