Saki GT

I'm surprised this didn't get posted before, but it is an interesting read - probably the most data-driven study on gas I've seen in a while.

https://www.freep.com/story/money/ca...ire/941532001/

lookstoomuch

Interesting and similar results to an article I read in some enthusiast magazine (Grassroots Motorsports maybe) using a Miata (I think) with a somewhat built engine and aftermarket ECU. They tried to squeeze as much power out of various grades of gasoline and the differences between pump gas (87-93) was surprisingly negligible, in the single digits. Since then I started throwing 87 in my K24 TSX even though it calls for 91, it's a DD spending 99% of it's life cruising the tollway. I do always put 93 in the S as it has a Gernby tune and spends most of its life on the track and try my best to stick to Top Tier certified brands.

Ok my google fu saved me from posting erroneous info: https://grassrootsmotorsports.com/articles/fuel-truth/

rob-2

I've run several cars from Honda that required 91 with 87 oc. Never saw much of a hit in MPG but loved the savings. About 250k in total over the course of 10 years. On the current motor is doesn't run right on non-top teir 91 so I've not played with 87.

vader1

I have a bp nearby and always buy the 93. That might be more than the required 91 for each car but the next step down at the station is 89 Ron. My bimmer has a minimum 89 octane requirement ( recommended 91 octane) but the difference in performance is significant. The car feels out of breath pretty easy on 89 and my per tank average mileage drops to about 26 instead of the average 30 mpg I get with 93 octane. The cost savings of the lower grade at this station does not make up for the lost mileage. I think 93 might be more than I need and might get identical performance on 91 octane but this station is right near my house and so I get gas there. But the drop from 93 octane to 89 is very noticeable on the bimmer . I won’t even try anything lower than 92 in the Cayman. My guess would be that turbos are more sensitive to octane than NA due to the use of fuel for cooling the intake charge.

HawkeyeGeoff

Lol all you're buying is detonation protection; on a car that isn't boosted or tuned it doesn't really NEED that octane until you're really pushing the motor (unless you decided to go with very high compression pistons). That said, I've run my big turbo Mazdaspeed6 on 87 without any KR readings...just stay out of boost (lol gas station ran out of premium....thanks Obama).

Chuck S

These "studies" occur like Ground Hog Day to some folk's surprise! The study notes using premium fuel where it's not required is useless.

Our cars require premium fuel according to the factory. But there's a "footnote" that anything better than 87 won't hurt the engine. Just makes the ECU and knock sensors work harder I imagine. Ford recommends premium fuel in their EcoBoost engines (like my 3.5 twin turbo Expedition), but does not require it, when or if more power is needed for towing, etc. The AAA study notes higher power and better fuel use -- but not fuel economy due to the 25% higher cost of fuel. Anything higher than 87 doesn't seem to make a bit of difference towing my 5500 pound trailer though.

Eons ago, in the First Muscle Era, I knew knowledgeable car guys who used to run Regular in their cars on road trips and Premium the rest of the time. They claimed the engines didn't care at 80 mph. The engines were well over 400 CID. Carburetors (sometimes multiple) and no ECU. Not having the money for engine repairs I ran Premium in my SS396 then and 93 octane in the S2000 now. As noted the Expedition drinks 87 even with the trailer on the back.

-- Chuck

mosesbotbol

Volvo recommended 87 for our S60.

electricmarauder

You saved $250000 in 10 years by using the lower octane fuel? How much do you drive?

Mr.E.G.

I thought he meant 250k miles without incident. I could be wrong.

electricmarauder

Yeah that would make more sense.