Regular or Premium fuel? [merged]

[Eclipse_98_RS]

Hi guys, my car is an all-stock RS, but I'm going to start doing some mods to it. Right now I just use regular unleaded gas, but when should I start going up in the octane? After intake/exhaust, or beyond that? I don't want to screw up my engine but I don't want to have to shell out more cash on fuel than I do now. I know, I'm a cheap bastage.

 

[staticbrainwash]

I don't know why this is even a thread really, why wouldn't you want to run your car for optimum performance. You will get the most power and the most economy out of the car running it at the correct octane.

 

[DSMunknown]

I don't know why this is even a thread really, why wouldn't you want to run your car for optimum performance. You will get the most power and the most economy out of the car running it at the correct octane.

First off, this is the first time I've seen this thread. I agree Geoff, there really shouldn't be a thread on this topic; people just need to do a little research.

However, you don't know what you're talking about when it comes to octane ratings at the local pump (Regular vs. Plus vs. Premium). These three types of fuels only differentiate when it comes to "fighting off" detonation or pre-ignition. That is it.

Premium fuel will not give you better gas mileage, better performance, cleaner emissions (aka burn better), better idle, or any other BS people claim. The only difference most people will see is under hard loads and WOT (or near WOT), assuming everything else is in proper working order and appropriate for the given application. "Normal" driving will be uneffected if one were to use 87 octane in his turbocharged DSM.

What does "normal" driving mean? Driving like the folks or grandma, to put it simply.

Filling up with Premium fuel is nice if you "romp" on your car at least once a week. But for people who use their (turbocharged) DSMs for daily use, and drive like the level-headed everyday citizen, paying for "the best" will just make your wallet take a turn for "the worst".

 

[staticbrainwash]

I know what i'm talking about. What i simply meant was the you will get the best performance for the best mileage as per the ecu's factory settings. It's meant for at least 91 octane. Not running that means you will have pulled timing to recuce knock, ect. Therefore not getting the performance you want making you possibly pull the car harder reducing mileage.

If i'm wrong i'm wrong. But i don't think it's as simple as you put it. There's a lot of thing that factor into how the ecu reads gas.

In the end this is still pointless, just run 91+ and deal with it. Quit smoking, or drinking, or driving around so much with no purpose. Seems like an easy fix to me.

 

[tkelly27]

As much as I'd love to give up drinking to run premium, the factory knew morons like me would disregard the sticker on the tank. I don't seem to get knock in my cars, but I dink around with the tune and the plugs and have been super lucky so far. If I were to boost past stock, I'd get premium, no questions asked. For near stock boost, I stick with regular gas. It's cheaper and I drive a lot, sadly. If you were so incredibly concerned about performance you'd go ahead and get the $5 a gallon 100 octane. A complete waste of money on the street if you ask me, you shouldn't be speeding on the street anyways!

Why would anyone run pump regular? For some people these aren't the end all, be all performance mobiles in their life

If you change your tune (actually, compression ratio is the best to change) to deal with it, you can get close to the same gas mileage from E85 as you get from regular gas. When you find me 110 octane gas (that's what alky is, isn't it?) for $3 a gallon at a pump station, then you can tell me it sucks.

So far everything I've read has lead me to the worse gas mileage conclusion. If yours didn't change, I completely believe you. There are a lot of variables to deal with, but your test could be just as valid as any others I've seen.

 

[coolwata34]

hey guys, well after sitting in the car yesterday i noticed this little pain in the @$$ lettering on the speedometer that said"premium unleaded only" now with gas at $3 a gallone right now that sucks ... but anywho what octane would that be? 93 octane? which is the highest... or the one right in the middle? thanks

 

[wret]

93 or the highest you can find.

 

[dsm91TalonTSi]

I run nothing but 93 in my 91 TSi, cept when i get gas from sunoco, and then i get 94. It's only like 2 or 3$ more on a fill. In fact, there's a local station that sells 104, but ive yet to use it.

 

[theycallmedalgo]

93 octane all the time.

I was getting gas the other day, and this dude didn't speak english too much, and I said premium so he starts to put in regular. Im like NO, PREMIUM! V-POWER! so he mumbles some stuff and switches it. Then he proceeds to walk away and says "same shit." Same shit eh? Maybe you would understand if you had a high perfomance engine fed by a turbo. People......

 

[DSMunknown]

I finally remembered to copy a quote and post it up. I'll put it in bold so everyone will see it nice and clearly.

There are two different schools of thought about which octane grade to use during dyno testing. One says that you should test and tune to the octane you expect to run on the street. The logic is that you should tune as you intend to drive it. There is no use dyno tuning a car with 100+ octane race fuel if it is only going to see 91 octane when operating on the street. The other camp advocates running much higher octane than stock --perhaps race gas-- to help ensure against detonation while dialing in A/F mixtures and ignition maps. Remember that octane is basically a measure of a fuel's resistance to detonation. The higher the octane [rating], the less sensitive the engine will be to pre-ignition and detonation.

And he goes on to say:

Detonation: a spontaneous auto-ignition and combustion of the A/F mixture inside the combustion chamber that occurs apart fro the normal flame front. Detonation occurs after regular ignition has been initiated. The result of detonation is very high local temperature and pressure spikes that can cause damage to the piston and cylinder head. Detonation is often heard as a characteristic "pinging," "tinking," or "knocking" sound.


Pre-Ignition: the premature ignition of the A/F mixture in the combustion chamber before the regular ignition spark occurs. Often cause by excessively high pressure and/or hot surfaces inside the combustion chamber.

 

[Zaku III]

Seen the question asked a few times, but never when making it clear that it's completely stock. Not to say it won't be modified in the future, but right now I only have the money for the car.

So anyway, I'm looking at buying a '95 GST with 77,500 miles and wanted to know if, while stock, regular gas is ok. If performance suffers, that's fine really - I'm used to an 88 horsepower station wagon.

 

[big_d]

Use the highest octane you have available. I know you Californians have trouble getting your higher octane fuels at some pumps ...big_d

 

[GofaST4life]

yeah def. use the highest octane...the car will just run better in general...

 

[snowborder714]

Use the highest octane you can.

Less octane = more knock (which isn't good)

Here's a few links on 'regular gas' (which I'm assuming to be about 87 or 89 octane):
http://www.dsmtuners.com/forums/newbie-forum/207182-89-octane-gas-96-turbo.html
http://www.dsmtuners.com/forums/tuning-engine-management/172947-performed-log-89-octane.html
http://www.dsmtuners.com/forums/newbie-forum/248974-friend-put-87-octane-gas-my-dsm.html
http://www.dsmtuners.com/forums/newbie-forum/134403-87-octane-oops.html

 

[DSMTalonTsiAwd]

I wouldn't Put regular gas in. You might save a dollar or two, But in the end you will be putting that money you saved right back into your car for repairing it! So i would Advise using Premium.

 

[tqmx1]

You can but don't plan on running to much boost. My wife does it all the time as a commuter car (not trying to get every last HP out of it) Between a light foot and the detonation sensor we have got 179K on the stock bottom end. 91TSI FWD.

Second thought she has a lead foot! and the silly thing still gets 26MPG

 

[turbosax2]

My owner's manual says:

All cars equipped with a turbocharged engine;
Your car is designed to operate on premium grade unleaded gasoline having a minimum octane rating of 91 [(MON+RON)/2], or 95 RON. If premium grade unleaded gasoline is not available, unleaded gasoline having an octane rating of 87 [(MON+RON)/2], or 91 RON may be used. However, the performance level may be reduced.

MON: Motor Octane Number
RON: Research Octane Number

 

[Zaku III]

Right, right. So, get some more hours at work. Gotcha. Much appreciated.

 

[BoostFrenzy]

Yeah, you might have noticed that inside the fuel door, there is a little sticker that says Premium only. I think that's a pretty important sign. But yeah I know how you feel. Gas went up this last month or so but it is just starting to slide back down. Just wait and it should get a bit better. Or worse...

 

[ToDdErDoDdEr]

i really dont notice a difference on my stock TSi.. use 87 for now if its more conveniant.. its pretty safe to assume that the previous owner(s) probably did all its life.. yea i know its supposed to be premium.. but when you are tight on cash its nice to know you can dump cheaper gas in.. hell next time i fill up in gonna use 20% ethanol fuel in (91 octane) cheaper and higher octane..

 

[BoostFrenzy]

i really dont notice a difference on my stock TSi.. use 87 for now if its more conveniant.. its pretty safe to assume that the previous owner(s) probably did all its life.. yea i know its supposed to be premium.. but when you are tight on cash its nice to know you can dump cheaper gas in.. hell next time i fill up in gonna use 20% ethanol fuel in (91 octane) cheaper and higher octane..

Still, not good. But the reason you "don't notice a difference" is because you have a 1G 6-bolt. 6-bolt engines have a lower compression ratio then us with the 7-bolt variants of the 4g63. Higher compression means the higher the octane needed. And if that octane number isn't used, then we get knock.

I can't remember where I read this (probably the DSMLink Wiki) but it says that you'r car actually monitors what it believes your octane rating is. So once it sees that it is not a "premium" gas, it retards your timing or something to that extent. This is so you don't go blowin' your motor.

 

[tlikethedrink]

the difference is less than a bottle of octane boosters that your only hoping will raise your octane. just throw premium in... if your just using the car to get from a to b and your going for broke, use regular. just dont try and save $ by using regular to buy mods as they will be useless when your having to fix your car.

 

[snowborder714]

I was just looking at gas prices in Santa Rosa and was just a bit curious as to how you really couldn't afford to run Premium vs. Regular. First off, I got my gas prices from gasbuddy.com and the prices are for a Arco gas station (not sure which one everyone goes to, but I chose to use this one in my calculations).

On average, I put 13.3 gallons in my Eclipse GST when I fill up.

Regular - $3.19/gallon
Premium - $3.43/gallon

Fill up on regular (for 13.3 gallons) - $42.43
Fill up on premium (for 13.3 gallons) - $45.62

A difference of $3.19. Now, I think the octane levels are lower in Cali (here I run 93 octane), but with that little of a difference, you can't even really buy a bottle of good octane booster for that. With regular driving (not using it daily and not beating on it), I fill up about 2 or 3 times per month. So, if you were to go with the regular, you'd be saving about $10 or so per month (unless you really like to drive it hard).

Is it really worth it to run the cheaper gas?

 

[Zaku III]

Actually 'bout .10 more, but it's not saying I can't afford it - just didn't want to if I could avoid it. I eat cheaply, and that $3-$4 is a meal for me, hence my asking.

 

[Defiant]

My owner's manual says:

Tell us the part about how fuels containing MTBE must never be used.

 

[DSMopar]

Tell us the part about how fuels containing MTBE must never be used.

Uh whu...? WTF