Will it simpply adjust the timing and work OK or is this a bad idea because the car cannot self adjust adequately?

Yes I know it will have less performance.

Bob S.

 

Yes, as part of the OBDII requirements, modern engines must have knock sensors. They will detect knocking due to lower octane gas and retard timing and/or bosst to prevent damage. Higher compression engines, turbo charged, or supercharged engines tend to require higher octane gas and may show a larger loss of performance with the use of lower octane gas.

 

you can run it without performance loss with alcohol injection. The alcohol injection will more than make up for the lower octane. There's been a few magazine articles on this recently.

 

I was just curious if anyone had done this on say a long highway trip where you're cruising most of the time and wanted to save a little coin.

Bob S.

 

You won't save any coin because the timing will be changed in order to deal with the lower octane. It's a really bad idea because you get fewer cleaning additives in lower grade fuel and you are significantly increasing the chance that you might knock.

 

+1

91 octane +. I wouldn't do anything lower. My wife did it once, once. She will never make that mistake again, I was not happy about it.

 

91 is the highest i can get out here....easily

i used to run 93 in it when i was on the east coast.

 

I don't know, perhaps, but if your not running the engine hard it's not going to knock so I doubt the timing will be retarded. However, the practical question is if I really can alter my driving style because I have a hard time doing it in my turbo cars ... ;>))

I don't agree with that one. Maybe if you're buying Hugo Chavez's fuel and I just won't.

Bob S.

 

I could be wrong, but the only time I see timing pulled on my car is when the knock sensors or IAT triggers it. As long as he's got his foot out of it, I don't see any difference that is going to occur. The car won't know that lower octane is in it.

 

But when a car is fun to drive I've frequently been accused of having a permanent case of lead-foot-itis so maybe it's a moot point?

With my turbo cars I can turn the boost way down which is also very nice in slippery weather.

Bob S.

 

C16 is all I put in the STR.....Who uses 93??!?!?!?!?







































Who thought I was serious

 

Thats strange, I cant even get 91, its either 87, 89, 93. When I was in Colorado it was 85, 87, and 91.

Who runs 85??? I was shocked to see that available.

 

It will be retarded. Why? Because the lower octane fuel will tend to detonate early in a high compression engine. Even at idle.

Lower octane fuel has fewer additives. Statement of fact. I have a 2000 Honda Civic that I drive during the winter and I've rebuilt that motor. Using lower octane fuel from Shell for 8 years left deposits on the valves....

 

Here is my take on it - there is only a $0.20 spread (in MN at least) on Reg vs. Premium. Since I fill up at around a 1/4 tank, the most I would buy is 15 gals. That works out to a price difference of $3.00 per fill-up. I usually fill-up 2-3 times per week (say 2.5x for arguments sake), for a total of about $390 per year. Now $390 is still quite a bit of money, but for the peace of mind that it provides in knowing that my car is happy and healthy, more than makes up for it. The supreme performance is an awesome bonus, along with 28mpg on the highway.

Now if the R were a N/A auto, I wouldn't be as hesitant to try Reg gas. But with the way a supercharger works, combined with the different engine set-up, I wouldn't want to try it, especially given the insane number of electronics on this car. To me, the $390 is also offset by a worst case scenario analysis - the cost of fixing something.

Just my 2¢.

 

Agreed....


BUT how the HELL are you getting 28mpgs??? I had the AC OFF yesterday, new fuel filter, recent oil change, 93 Octane, windows pretty much up, NO Sport Mode, and the best I could do was 25ish. Now, this was all highway driving, and I drove like a 95 year old woman with arthritis in her right foot. Literally.

I cant imagine getting more than 22 and change driving like I want to, spirited, not like an A hole.

 

I wonder if they change the settings for different countries. In Canada, we use the Imperial gallon and I see 28-31 on the freeway. The Imperial gallon is larger than the US and would certainly make for a significant difference between the two...

 

i get 27-28 on the flat out here in the desert running at 72 mph with the cruise on.

 

Imperial gal 5/4 US gal. On motorway (hwy), I get about 35mpg (2004 STR) so that's about 28mpg using US gal.

Keep windows up and a/c on if you're hot, because windows cause a lot of drag. But an STR is never gonna be fuel efficient, I mean c'mon!!

Oh, and YES, they do "calibrate" the PCM for different places (laws, fuels, etc).

 

OK statement of fact ...
Come back in 8 years after you've rebuilt it again after using the Shell higher octane rated gas and I'll have a look at it. Your ideas of proof are interesting.

Honestly I don't want to argue the point I just wondered if anyone had
tried this on a long trip of hi-way driving. Obviously I'm not I'm not talking about doing this full time.

With respect to the "high" compression ratio.

11.0:1 (normally aspirated)

9.1:1 (supercharged)

If you think it's going to knock at idle well ...

I assume you meant that the ignition will be retarded yes?

Bob S.

 

At first I too was skeptical of the others who claimed this kind of mileage, but I have been achieving it with some consistency. The key is flatness, no wind and cruise control. Any sign of a hill or anymore than a slight breeze and mileage drops to 22-25mpg. Road surface is another overlooked factor; on the brand new roads around here, I am getting 31-32 without trying while on the older roads its drops off. One other factor is tire pressure and proper alignment - which from past posts, I am sure you are very familiar with.

I too bought the STR knowing full well it was not a gas sipper, but I am shocked that this 400hp beast can pull that off. At first it was hard to drive with the cruise control and let other cars pass me by, but I have noticed dramatic increase in mileage as a result. This is not to say that I don't have my share of fun with the bimmers and ricers , I just pay the price for it in potential tickets () and fuel cost - which going back to the OP is a result of using premium fuel!