What about gas mileage running car in 6th gear compare to running it in 5th gear going around 60-70 mph? RPMs are lower from. My Xfire is a daily driver and I commute 80 miles roundtrip.

 

RESULTS:

After a few tanks of regular gas, I got some results and driving experience that I want to share with everyone who wants to know.

Gas milage:
with top tier (Shell) Premium 91 octane gas, I get average about 23.5 MPG (ranging between 22.5 - 24.5 MPG depends on driving conditions). During the 5 tanks of top tier (Shell) regular 87 octane gas, I still get average of about 23 MPG. (First tank 23.9, second 23.3, third 22.6, 22.5 and 22.7 MPG) I found the data quite interesting, I'm pretty much getting the same MPG on both premium and regular gas, difference is minimal.

Performance and driving experience:
On the first 100 to 200 miles switched to regular gas, I can feel the engine running a little rough at idle, but I don't feel that anymore after the first 200 miles, well, maybe once in a while but that's is normal. I think this is the time while the knock sensor and computer gets to work.

Regarding the horsepower, I don't have any equipment to measure, but on my regular driving experience, I don't really feel any difference, it drive the same way. But I have to point out two interesting feelings: 1, sometimes I feel the lack of power with regular gas when going on high RPM. 2, I think the up shifting is delayed with regular gas (mine is an automatic). But I don't know if this is real or just my imagination, since I know what gas I have in the tank and so my psychology may affecting my sense.

Does regular gas do any damage?:
I did some research and found there are two theories. Therory A says that low octane gas used on high conpression engines will cause early explosion causes knocking engine, the wrong timing and extra heat energy may damage the engine. Therory B suggests that new engine like ours have knock sensors to retard the timing and the engine will run with no problem. I believe in both, and my suggestion is if you drive like an old man, regular gas would works on the crossfire, but if you drive it like a sport car like wht it supposed to be, go with premium gas.

 

I have been running 89 (in the Dallas area that is the in between octane) and get consistantly 26mpg. So, no problems, have had the Crossfire for 5 mos, runs great and fast. Anyone is the Dallas area like together for drinks?????

 

not a good idea to use regular gas!

 

Just curious.....have you priced out catalytic converters yet?

 

I have used regular once when i was in a hurry and picked the wrong nozzle. since the new engine 1 time....god she runs great!

 

This experiment may hold valid for a base coupe, but trying it in an SRT6 is highly discouraged.

If you ever have to fill with anything less than 91 RON, then stay out of boost.

 

i just have to ask.. does your name mean anything or is it just a random palindrome? I thought it was sonorous for a while but just tried to figure out what it means.... but anyway I've been getting 19 mpg on premium.. kinda sucks compared to the 23 on regs I see.

 

downwardspiral,

The screen name is nonsense. I actually did choose "sonorous" at first but I thought it would be too difficult to remember so I made a nonsense palindrome using as much of the word as possible, hence, sonoro(nos).

For some reason it's easier for me to remember than a real word. Here at work we have to change passwords every 64 days so we get used to playing these kinds of games.

 

The whole reason for Octane rating is actually the ability of the fuel to NOT detonate (i.e. EXPLODE) based on "pressure" ! If squeezed hard enough, the fuel ignites WITHOUT using a spark - i.e. Diesel engine principal. The higher the octane rating, the greater the ability to withstand detonation. As mentioned, the computer will retard the timing and reduce the power, etc. . . . you won't really have an issue with your engine, other than lack of power. However, the one thing that still happens, even though you CAN'T HEAR it, is detonation - or as some have suggested - higher cylinder tempurature. There is still potential for KNOCK with the lower octane . . . hence the recommendation for minimum 91 octane.

Fuel mixtures are very poor these days, lots of "oxygenators" (spelling?) in them to help promote clean burning. However, these are not the greatest burning fuel - leave fuel in your car for a year to see how everything gums up etc. . .YUCH !!! I have found that going from my "altitude" (3500ft) to lower really screws up my carburated vehicles - they would run WAYYYY rich at sea level. Even though we have the computers for our cars, and fuel injection, the constituantes that make up the fuel, determines alot of how they will run. Personnally, for a few cents more a gallon (or litres up here), I run the 91 + octane. Cheapest in the long run !

Cheers

Mark
A12Rag

 

One thing is for sure, when the government mandated switch to ethanol from MTBE as an oxygenate occurred, we all suffered in the MPG department.

 

I wonder what we are going to feed our cars 10 or 20 years down the road... ethanol... corn oil... vodak...

 

My experience with building and racing engines, mostly motorcycle, is that you match the octane to the need. If you experience "knocking" you increase the octane. Running higher octane than needed does not improve performance and increases cost. I run medium grade Shell in my NA rdstr. Mileage returned in avg of 28. Performance is normal and I drive in a "sporting" fashion. The old days of 105 octane, tetra ethyl lead and carburetors are long gone..

 

Oxygenated fuels (such as in CA) wil yield lower mileage, the consensus is, that it's about 10% lower.
The technical knowledge of this group is just plain low to non-existent. Using regular gas in this engine will not be detrimental under normal driving conditions. This engine is designed to cruise at sustained 100mph+ (autobahn) and to endure hard accelerations (loads). Those are the conditions for knocking and detonation. The average highway speed in the US is only about 70mph, fairly gentle driving will not induce knocking even with regular, and there is the knocking sensor to save the day. The carbon build-up notion is just plain stupid. Carbon is the result incomplete combustion. A lower octane gas is actually more volatile than the higher octane. In fact, it's the higher octane gas fed to a lower compression and lower load engine will produce more carbon, that's why grandma's car with her "gentle" driving (low speeds, low accelerations) looks like a miniature coal mine when disassembled.

 

a motor will in theory make more power on 87 since it burns faster, however it also burns hotter which makes detonation a deadly possibility

the reason people use 93 in high power motors is it burns slower and colder.. which eliminates detonation (to a certain power level)
i'll bet you 100 dollars that your motor is atleast pinging at high rpm's...

 

I would expect the ECU to adapt to that, since it appears to have adapted at lower RPMs, lower loads.

 

yes.. its pulling tons of timing
reducing power and killing gas mileage

 

Exactly, which is why I'm surprised there wasn't much of a drop in mileage... it's probably not knocking except under high load, which is why it doesn't show up in regular driving. I'm more curious about how long it takes for the fuel maps to recover after you switch back from regular to premium... but it's definitely a good idea if you don't plan to wring out your car regularly...

 

it doesnt take long, the new obd2 ecu's are pretty good about remapping within about 15minutes of driving

it wouldnt work for me... i drive my car like it owes me money

 

When your engine blows, post another thread and we can say "I told ya so".