Octane booster... yeah, I know, I know..
 

So, I figured I'd give my $.02 on my experience with octane booster and this car. I have about 15 years of motorsports experience behind the wheel and turning wrenches, the majority of which involved subarus. I have thousands of hours of ecu tuning under my belt And I only use lucas oil octane booster because its pretty much the only store bought product that does anything anymore.

So...

I've noticed in the 9 mths or so I've owned the car that it seems to pull timing in the higher rpm's quite frequently. Sometimes due to ambient temps, sometimes to less than stellar gas and sometimes due to subarus oversensitive knock calibration.

After Installing a K&N filter and Works muffled axle back I noticed the problem happened even more frequently, even with doing an ecu reset after install. So I grabbed a bottle of booster and dumped about half of it in an empty tank with a fresh 10 gallons of 93.

I took the car out for a drive without an ecu reset with the expectation that the car would run a little smoother, hopefully not pull timing and power output would be more consistent as a result.

Wow. The difference was undeniable. It was very noticeable when the ecu started to see the higher octane fuel. Not only was the car not pulling timing anymore, it was actually advancing it to the point of entirely changing the exhaust note at wide open throttle. And before where the car seemed to run out of steam after 6000 rpm it now felt like it could have pulled to 8000 and made power the whole way. It genuinely felt like I had flashed the car with a tune.

Im sure once I get around to tuning the car it will be considerably better, Im sure the K&N and axle back is making me run a touch lean, but for the time being, its nice to know I can throw half a bottle in the tank for $4.50 and have that little extra I need when going to the track. Worth every penny.

Never underestimate how sensitive knock sensors are calibrated these days or how crappy some gas can be. I remember tuning one of the first US wrx's and watching the car pull timing as we hit bumps in the road. Its fun when you don't notice it for the first couple hours of tuning. :bonk:

In conclusion. This car wants 93+ and it means it.
If your running lean from a CAI and don't have the money for a tune yet this might be a temporary solution for you.

If I get around to running some logs I'll post them here.

Are you claiming that you're not reaching MBT with 93 AKI fuel?

There is no way to know without data logging but yes, I think its possible that our 93 here could be just under what the ECU is looking for to produce maximum timing advance in some situations. Again, this wasn't tested on a bone stock car and my mods, as subtle as they are, could have been contributing to a lean condition that was causing the car to pull more timing than just being light on octane would have.

Interesting!!

What Brand booster?

Most of them only change the octane by .1 or .2 at most.

On the other hand, I have seen the NOS brand work magic on a vishnu tuned 335i that was inadvertently filled up with 87 octane (by the owners wife) right before the dyno day that Shiv was installing and tuning the proceed's.

The lucas adds approx 60 points to 10 gallons of 91. This number will vary still based on quality of the gas, but the Lucas booster is pretty potent compared to most off-shelf chemicals.

I was surfing walmart the other day and found octane booster made by NOS!!! well, description says it bumps the rating up to 3.1 which is pretty good compared to other companies. I won't buy it anyways.. haha

Just buy a bottle of torco race fuel concentrate. I think it's around $20 for 48 ounce bottle. They have a chart of mixing ratio on their website. I used to use that with A4 2.0T 100 oct tune. I did feel a good difference.

Most "octane boosters", including the Lucas Oil stuff, contain a bunch of kerosene and a little bit of MMT (Methylcyclopentadienyl Manganese Tricarbonyl) to raise the octane, which is bad news for any car with a catalytic converter. During combustion, the manganese is liberated from the compound. This manganese vapor is then deposited on your spark plugs and in the fine mesh structure of your catalytic converters. The deposits in the cats can significantly obstruct exhaust flow and impede the ability of the cat to do its job with regards to NOx emissions.

MMT will not make your octane nearly as high as the feel of it in your engine would seem to lead you to believe. This is because MMT makes your fuel denser and burn slightly longer giving you additional torque than simply higher octane couldn't achieve. This process also can have the unfortunate result of contributing to gunk build up in the injectors and valves, especially if used in excess of .8 oz per gallon.

[ame="http://www.amazon.com/Torco-Accelerator-32oz-Best-Additive/dp/B004ZO3VN0/"]Torco Accelerator[/ame] is supposed to be the real deal, but it's more expensive.

I think I'm gonna buy a case of quarts.. I'll do a 104 tune next time i go to the dyno. Track days i'll just dump 8 or 16 oz into the tank when i fill up with 93 to bump the octane for good measure... a heck of a lot cheaper than buying 100 octane at the track.

This is only useful to those without a tune, right? I'm pretty sure that this will be of no benefit to me because I have a Unichip tune, but just want to make sure and confirm with the pros.

I have never been a fan of any kind of additives since you are placing your fuel system (and cash) in the hands of people saying "THIS WORKS... TRUST ME!".

Still, I had a very similar experience to the OP a few months back when I had a bad batch of gas in my car. I have NEVER seen a car that is so sensitive to bad gas before.

I basically did the same as the OP, I ran the tank as dry as I dared, added that 104 Octane booster (I think its made by STP), and filled the car up with 93 Octane goodness from my favorite, local Shell station. To say it made a big difference would actually be an understatement.

This goes against my "conventional wisdom" on the subject of additives and octane boosters but the difference at the top of the RPM band was definitely there. Also, in subsequent fill-ups without it, I did notice the car running the same as before the additive (minus the bad gas of course).

I would really like to see some dyno tests on cars with minor bolt-ons and no tune to back up my impressions.

Scott