Running Premium Fuel w/ N/T?

[DSMOCTANE]

-I am working with a 99' Eclipse with the 420a engine. I have bolt-on's including a short-ram cold air intake and a full header and catback exhaust system. On my rebuilt engine, is it truly beneficial to run premium 93 fuel? I know the fuel gauges in the gs-t and gsx insist on only premium, but will higher octane give me much more power for a n/t? I also heard fellow mechanics speaking of higher octane resulting in more efficient fuel economy and more mpg. What do you guys think?

 

[CanadianTalonTC]

The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, methane, propane and butane are all hydrocarbons. Methane has a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.[/I]

So 110 Octane is comprised of 110% Octane... .

Joel

 

[Colt4G63 also]

So 110 Octane is comprised of 110% Octane... .

Joel

Cool, then it should only take 10 gallons of 110 octane fuel to fill an 11 gallon tank.

 

[DSM1G90]

Well what if you ran 93 from the get-go after the rebuild? Wouldn't that naturally reduce major carbon build up from the start?

No, not as long you didn't change your compression ratios - like planed the head, or added domed pistons to increase compression ratios.

Let me clear up things a bit with carbon buildup: If you just do a lot of 'slo-mo' driving, shift quick to 4th and add throttle, or any low speed driving in any car and horribly advanced timing (or, incorrect timing in any form) rich A/F ratios, you WILL get carbon buildup in the compustion chamber to where, when you add throttle, you'll get knock, or the knock sensor will retard the ignition for you.

I've seen it many times where drivers will start adding higher octane fuels to eliminate knock. BUT, if they just ROMPED on the throttle in a lower gear, got the thing up to 70 in that one gear quickly, that right there will blow out the carbon buildup on the pistons and chamber.

My father would lug his pick-up down (chev with a 350) so many times where it would ping like crazy. That when I got in it, I would romp that thing up to almost 80 in third, and you should see the massive black soot come out of the tailpipe .. that was all the carbon that was built up inside that motor being blown out..and guess what? Truck ran great after that hi-speed, low gear run.

Better off doing 85/87 from the beginning since these fuels are cleaner and burn hotter than 93 which is so full of additives(to raise octane) that it's actually a 'contaminated' fuel. And, if you go slow with that "polluted" fuel, it's gonna carbon up stuff real quick since it can't burn off quick enough, thus coating everything in site with carbon..and guess what you got: carbon buildup.

Remember that the octane level is only to prevent knock by slowing down the fuel ignition process - why the more additives to retard this ignition.

Lower the octane level, the more prone for knock - why of the lower compression ratios.

The old flathead motors of yesteryear with 5.5:1 to 6.75:1 can run on octane levels much lower, yet these lower octane fuels of yesteryear, were so clean and it ignited very quickly. It was almost like using "white gas" - no additives what so ever.

But, when compression ratios started to increase, esp with the introduction of the OHV motors, octane levels had to increase to 'retard' the ignition of the fuels.

For economy's sake, the majority of the motors built had compression ratios between 8.2:1 up to 9.5:1 where they can operate with 85 fuels without any problems and simply due to correct ignition timings less than 10*BTDC (the 4G63turbos can run 85 if the turbo was disabled since the stock 6bolt compression ratio is a low 7.8:1 and it has only a 5*BTDC base timing - can't knock this motor with this low compression and light timing settings..).

Take the Bugatti Veyron W-16 motor: With quad turbos to pump out 1001HP, it needs 100 road octane at 8 bucks/gallon. Simple, single engine, piston engine aircraft uses 108 low lead octane since the oxygen levels are lower up there than on the ground.

Save your money. Run 87 on the rebuild, esp for a 420A motor..and there is nothing wrong with having a 420A: they're doing the best as they were designed to do: to get the vehicle down the road effectively.

The 420A was a drastic improvement over the older 2.2L that were in the "K" cars - those old SOHC motors had serious head problems-coolant passages weren't the best and head would get cracks like crazy...and they're still in use in China - Some company over in China bought the plans for the motor to be used in some manufacturer's vehicles.

Good luck - DSM

 

[Skorcher]

Nice, thanks for the info.
I learned something today.

 

[crazytsiawd]

no gains and no point

 

[T is for TURBO]

So 110 Octane is comprised of 110% Octane... .

Joel

No. Octane is a hydrocarbon, which has 18 isomers. One of those isomers is 2,2,4-trimethylpentane (iso-octane). Iso-octane is what is used when they test the octane rating in fuel. However, since iso-octane is not the the most knock resistant fuel available, the octane rating can actually be higher than 100. If 2,2,3-trimethylpentane would be used in the fuel instead of 2,2,4-trimethylpentane, the octane rating would be higher than 100.

I'm not a chemist by any stretch of the imagination, I'm just trying to regurgitate what I have learned on my own and what I have been taught by my close friend (who is a chemist).

I hope this helps

Also, gusu is correct, other countries rate their fuel differently, so that has to be considered, but that does not make the info meaningless.

Skatershawn- The original quote was from howstuffworks.

 

[importracr317]

Anything higher than 87 octane in your car is a waste of money.

 

[NeMiZiS]

I run premium fuel in every vehicle I own.
But the highest Octane is only 90 here.
I've always felt like it helps the gas mileage.

 

[thomcasey]

I always run 93 premium for 1 tank in ANY vehicle I own for the first tank of a long trip (2+ hours of hwy driving). Premium also has more detergents, so it runs real nice after the tank. I use it rather than use fuel system cleaners.

 

[re-rx7]

Its this simple. 87 burns easier which in turn will yield better mpg's, You can buy 85 octane in colorado you know why? Because the air thinner up in the Rockies. Lower octane is easier to ignite. So 87 wil lgive you better mileage for it will give a better burn.

 

[eclipse420ags]

All this goes against everything ive ever heard I have 8.8 compression (Eagle/JE combo), what should I use?

 

[silicosys4]

I always run 93 premium for 1 tank in ANY vehicle I own for the first tank of a long trip (2+ hours of hwy driving). Premium also has more detergents, so it runs real nice after the tank. I use it rather than use fuel system cleaners.

Premium vs. Regular | Car Talk

 

[synthetek]

All this goes against everything ive ever heard I have 8.8 compression (Eagle/JE combo), what should I use?

If you are turbo you should probably use higher octane but that will depend on your tuning. On a stock car like the OPs you should use what the manufacturer calls for.

 

[re-rx7]

Turbo? If i FI always use 91+ even if it stock Turbo/supercharged

 

[thomcasey]

Premium vs. Regular | Car Talk

Regardless of what they say, my 2002 Mountaineer (172k miles) and my 98 Buick Park Avenue (215k miles) Run better AFTER a full tank run on a trip, period. Verified by me. Better than after using a fuel system cleaner. I do NOT see better mileage with that tank, but they run smoother AFTER that tank has been run through.

 

[synthetek]

Turbo? If i FI always use 91+ even if it stock Turbo/supercharged

You use what the the manufacturer of the car requires for your car, If its a factory turbo, supercharged, high compression or aggressively tuned car and your manual / gas cap/dash says use premium fuel only than thats what you use, if your car does not require premium fuel than you will get no benefit from using it.

 

[importracr317]

You use what the the manufacturer of the car requires for your car, If its a factory turbo, supercharged, high compression or aggressively tuned car and your manual / gas cap/dash says use premium fuel only than thats what you use, if your car does not require premium fuel than you will get no benefit from using it.

Well said. /thread.

 

[re-rx7]

You use what the the manufacturer of the car requires for your car, If its a factory turbo, supercharged, high compression or aggressively tuned car and your manual / gas cap/dash says use premium fuel only than thats what you use, if your car does not require premium fuel than you will get no benefit from using it.

BTw ow the hell did you only manage a 13.6 with 300whp? those are good power numbers.

 

[synthetek]

BTw ow the hell did you only manage a 13.6 with 300whp? those are good power numbers.

That 13.6 was before It was tuned and didn't have the same mods. I haven't been back to the track since I dynoed & tuned it. That HP was also on a 16G since then I have upgraded to a 20g, cams etc.. so it needs to be tuned and dynoed again the I will go back to the track

 

[Abe'sGST]

Back when i was in college, the instuctor told us that premium fuel WILL give you better gas mileage, maybe not a big difference but it will. In all 3 of my cars, one premium is required and the other two i put premium in them. I feel a difference in gas milage and also feel like my cars like it better, they run a bit smoother and the idle is a little better. With that being said, it's up to you if you want to run premium, i think it would help a little and it's worth the few extra bucks, just my .02

If you are turbo you should probably use higher octane but that will depend on your tuning. On a stock car like the OPs you should use what the manufacturer calls for.

On n/t models it says "unleaded fuel only", doesn't say "regular unleaded fuel only"

 

[synthetek]

On n/t models it says "unleaded fuel only", doesn't say "regular unleaded fuel only"

It does not say premium either, I have 3 cars that require premium from the factory and they all say it on the gas gauge, in the manual on the gas cap. If it does not say premium it does not need it.

 

[re-rx7]

Your instructor was wrong. 93 simply does not burn like 87. 87 will ignite easier and more through than 93 on a regular engine. On cars calling for premium the 93 burns better because the C/R or Cfm calls for a fuel that will burn/resist burn bettter at a higher level.

Synthetik-so the 13.6 wasnt run on 296whp?

 

[synthetek]

Synthetik-so the 13.6 wasnt run on 296whp?

No it was before that tune and before the jmfab manifold and some other stuff but it was on the same turbo (big 16g) that made the 296whp.

 

[re-rx7]

I was wondering cause i was like that cant be right. Lol

 

[95twinturboawd]

93 is more explosives then 87 right? and all i know is with my old 4g63 n/t i would get 36mpg with 93, and 30mpg with 87, plus it would run a lot better and start better. and its only $.20 more a gallon so that's $3.00 more for 15 gallons, why not have a better running car for $3.00