Ha, I almost wrote something like that in my last post.

In my opinion, most people who want a faster car should go get a different car that was designed to go faster. The consequences of modifications might be worthwhile to some people, but you have to be able to live with the drawbacks, too.

“I tend to have more faith in the guys at the factory”

I agree 100%.

My V50 is turbocharged but considering I started with an ‘86 240DL in college, I am already living high on the hog, as it were.

I do think it would be fun to have another 30 HP on tap, but I probably should just save the $1,500 to buy a faster car.

It should, sure. But if the performance is optimized to run on 93, then you’re going to lose performance when you use a lower octane fuel, which is the case that you have now.

In any case, I would be highly skeptical of chipping anything that doesn’t have a turbo. Most chips are a scam; when they do work, it’s primarily because you’re playing with the boost characteristics of the turbo. If you have a non-turbo Volvo, I wouldn’t even think of wasting your money.

That should make you wonder why the stock characteristics were set as they were in the first place. The engineers are usually shooting for some compromise between performance, durability, economy and visceral appeal, so if the chip ends up putting more stress on the motor and changing the idle characteristics, then it’s matter of choosing a different set of trade offs, not of making it a “better” car.

I tend to have more faith in the guys at the factory than some aftermarket shop, particularly the shops whose products tend not to work in the first place. I know that some guys like to tinker with stuff like that, but I don’t. Suspension mods are one thing, messing with the motor is something else.

“If you plan on driving out of state, you don’t want to have a car that requires 93 octane fuel, as you might not always be able to find it.”

I agree with your sentiments about the warranty. That is another reason why the $1,500 isn’t burning a hole in my pocket yet.

However, wouldn’t the knock sensor still compensate for the reduced octane if I had to use 91? I would assume that if you pay decent money for the re-flash, someone would have thought of that. But I also know what they say about making assumptions.

In much of the US, 91 is the standard octane level for premium; it’s not just in states such as Colorado, where elevation makes a difference, but elsewhere where that formulation is typical. If you plan on driving out of state, you don’t want to have a car that requires 93 octane fuel, as you might not always be able to find it.

If the car runs fine on premium fuel, then leave it alone. If it doesn’t, then there’s something wrong with the car that octane can’t fix.

I’ll share a few observations I have made in my various octane experiments.

I ran 87 octane gas in the car for about a year. I started to do it when gas prices shot up. The knock sensor compensated for the reduced octane level, of course. The engine clearly lost some power, but I felt like I had to bite the bullet.

A few months ago I bought a full tank of 93 octane when the station I stopped at was out of 87 and 89. On my way back into the city that evening on an EMPTY Edens Expressway, I found myself in a good-natured game of cat and mouse with some late model variety of MB C-Class.

The first time I really mashed on the accelerator, the car suddenly went like hell! I felt like I was driving KITT in Super Pursuit Mode. It was awesome.

I have found that mixing my own 91 just doesn’t produce the same results on a consistent basis. I had no idea that mid-grade gas is mixed inside the pump as it comes out of the nozzle. I’m guessing that is not a very reliable method, at least among the many thousands of different gas pumps in Chicago. At least that’s my story and I’m sticking to it.

I’m going to use 93 now. I’ll hold off on the ECU re-flash until I can save up some coin (it’s about $1,500 from ipd). It’s true that the extra power I get using 93 isn’t always necessary while plodding around the city, but I figure there’s no use having a turbocharged engine if you can’t take advantage of it when the time is right. Otherwise I should have just gotten the normally aspirated 2.4L.

I’ll probably use 89 on long road trips.

In some cases, turbo engines run with low octane fuel will overheat in one or several cylinders. This is due to series cooling systems forcing last cylinder on the loop to run hotter than rest – the manufacturer compensates by putting knock sensor on that hottest running cylinder.

Some Japanese brands, accustomed to running on 98 octane in Japan, run the ragged edge of pre-ignition even when they burn recommended USA fuel. Their reasoning is to keep mixture lean as possible so emission standards are met.

For those cars, the ECU may detect use of higher octane and actually advance engine timing to take advantage of it.

Engines always knock at least slightly. Normal knock is very mild, and isn’t audible externally. A knock sensor looks for preignition that is particularly loud or frequent, and signals the engine computer to retard the timing until the knock drops below a safe threshold.

An engine’s octane requirement varies a lot. It varies with altitude (octane requirements are lower at high altitudes), engine condition (older engines started to require higher octane numbers, due primarily to carbon buildup in the combustion chambers, not as much of a problem with modern engines), engine load, and temperature. If you’re climbing a hill or lugging in a low gear, the engine’s propensity to knock increases; if you’re cruising at a modest speed, it’s at a minimum. This is why the “shade-tree” method MadHungarian mentions above is not a great idea…the engine may not ping while it’s running in neutral without a load, but knock like mad going up a hill or a WOT.

Turbocharged or high-compression engines may not be damaged by 87 octane fuel, but it means you’ll be running with retarded timing all the time, which reduces both power and fuel economy. The reason such engines have knock sensors is not to let you cheap out by running regular fuel, but to prevent engine damage if you accidentally run a tank of regular, or if it’s the only thing available in a remote area, and you have no choice.

I would use premium. There are circumstances where using 89 probably wouldn’t make a significant difference (e.g., on a long highway trip at more-or-less legal speeds), but for the most part, if it’s recommended for your engine, not using it is a false economy. (Conversely, in the majority of cases, if the manufacturer recommends 87 or 89 pump octane, there’s nothing to be gained with 91 or 93.)

I thought that in most cases the best timing is right at that point, just before detonation occurs, and this is why the shade tree method of timing an engine is to do just that, advance until it pings, and then back off just enough to eliminate the ping in all conditions.

http://www.ipdusa.com/Volvo-850/Performance/ECU-Upgrades/p-72-143-2183/

I just noticed it last year when I tried their stations. No need to mix gas in this case IF you can find one in your area. :)

Maybe they have expanded this into other states 7 years on.

“Some 50 7-Eleven gas stations in North Texas and almost 100 in Florida…”
http://www.accessmylibrary.com/coms2/summary_0286-7431946_ITM

(Appears original article is no longer available)

2000 BMW 528iA (91 RON reommended).

When I had my Eclipse GSX the station near me (Poplar Grove, IL) had 91 octane mid-grade. It was nice to save 10 cents and get the right fuel.

Not true. Since the knock sensor is screwed into the block, it can “hear” the knock before you will. WELL before. Its like a frickin bloodhound, even hearing valvetrain noise on modified LSX V8s and cutting timing for no good reason.

I always understood that the timing is retarded on instruction from the Knock Sensor. So, for an adjustment to occur you gotta be knocking; never good for an engine.

Any thoughts, Piston Slappers?

You can use more octane than you need, obviously (although I’ve been told that you should not use excessive octane in a rotary; it supposedly causes problems, but that frankly makes no sense to me.)

If you would like to combine fuels on your own in order to get something between midgrade and premium, then you could certainly do it, assuming that you don’t mind wasting that kind of time just to save a few pennies. I wouldn’t.

The computer adjusts the timing automatically, of course, so it ran fine….

I went back to premium, as the reduced cost didn’t really offset the reduced mileage (as I recall).

YMMV