Is high octane fuel a requirement for high-compression engines?

Question

I own and use a 2005 Chrysler Crossfire SRT-6 as my daily commuter vehicle. I'm not interested in trying to eek out a few extra miles on a tank, I want to keep the vehicle and its engine running as long as possible. I do all the proper maintenance (e.g. change the oil every 3 to 6 months with a synthetic 0W-40W, proper air pressure, change the brakes, wash the exterior once every to one to two weeks).

I'm primarily concerned with the engine: it's quite expensive to replace, and I don't want to damage it. Is it absolutely necessary for me to keep filling it up with premium (octane >91) fuel?

Answer 1

The problem is, the crossfire isn't just high compression, I believe its supercharged as well. Forced induction motors like octane - the high pressure, high compression, and most importantly high combustion temperatures make you more prone to detonation.

There are enough electronics in the engine (knock sensor for one) to realize that something is amiss and it will usually pull (retard) engine timing to compensate as a safety measure. As a result, you will lose horsepower - a significant amount.

However, it can only reduce timing so much. If you're running low octane fuel and push the car hard enough, its conceivable that long term damage can still be done.

bottom line: manufacturers recommend high octane for a reason.

Answer 2

This is one of those eternal debates that have very few definite answers.

My view is:

Try lower octane gas, if you notice either knocking or decreased performance then you should stick with the higher octane fuel.

Try midgrade first, then if everything is good, try regular. My mother had a Mazda Miata that recommended Midgrade but would run fine on Regular.

As far as engine life goes, I believe the extra 'cleaners' in many premium gases amount to a negligible difference in engine life. Other maintenance makes a MUCH larger impact than fuel choice (ala regular oil changes, fuel system maintenance, etc).

I found a PDF article that says the 2005 Crossfire SRT-6 has a compression ratio of 9.0:1 which I believe must be when the supercharger is NOT running. Many of my naturally aspirated cars had that compression ratio or higher and ran on Regular fuel.

I believe that sometimes the recommendations by manufacturers (not just automobile makers) are a best-case scenario. For the absolute best maintenace/performance you should follow their guidelines, but oftentimes 90% of people can't tell any difference between the two maintenance practices.

As a rule of thumb, I put fuel system cleaner through my cars every 5,000 miles to make sure I have clean injectors, fuel pump, et al