Any benefits to high octane

We have 85 octane where i live and i use it all the time.

WIFE: How come you put that cheap gas in my car, then use the expensive stuff in your truck and motorcycle?

ME: The BOOKS says use 87 in your car...my truck calls for 89, the H.D. gets the highest the pump has to offer.

WIFE: You're high maintenance :B


OP: Just use what the MFG recommends. No need for "better" fuel, if it isn't going to provide additional benefits. My 89 octange was 17 cents more per gallon than the 87 (at pump TODAY).....why pay it if you don't have to.

eichacsj wrote:
No. Just keep running what you normally do. With today's ECM's they "learn" and it takes 2 - 3 tanks for it to balance back out, if you switch for a couple of tanks you will not get the results you are thinking about.

Also as said above, follow the MFG recommendations but as a note also stated above octane requirements go up depending on the compression ratio. You'll notice manuals with ratios around 10:1 or above generally requires premium.

Not true on my car with "today's ecm and not likely true on any.
Octane requirement aside, the "learning" involved, is instantaneous. A knock sensor or multiple knock sensors detect pre-ignition (detonation) as a certain frequency of vibration in the engine block. When that vibration is present, the knock sensor signals the ecm to adjust ignition timing to compensate. On newer engines, both 2 stoke and 4 stroke it happens instantaneously and silently.
My snowmobile actually has a light on the gauge that blinks when detonation occurs and it starts pulling timing. Great feature on 2 smokes. Saves a lot of burned up pistons.
Wifes SRT8 runs fine on low octane, but fuel mileage is down, low end power is down and it's generally rougher sounding/feeling if you floor it with cheap gas. Under the right circumstances can actually make it ping just a little. Put the octane back and it runs smoother and faster.
The 6.4 truck Hemi is designed to run on 87 or 89, from what I've read and will hand out a few more ponies on higher octane. Not sure if theres and advantage to running premium though.

Yes the PCM does adjust for lower octane, but it pulls out timing and other parameters to adjust which reduces power. And with the new fuel with 10-15% ethanol the engines from 10 years ago weren't designed for those operating conditions. My X used to struggle when I ran 87 like is recommended in the manual. Filling up with 93 made it much better to tow with. And running pure gas from WI was like adding a supercharger (well not quite) but you could definitely tell the difference! I now have it tuned for 89 octane with 10%ethanol and it drives better than it did when it was new!

Run the different grades back-back and you will be able to tell the difference! Both in mileage and power!

Ford recommends using ethyl in the 3.5 Ecoboost under rigorous towing conditions and some users report better power and cooler running pulling long grades in hot weather doing so. Some users report better mileage. My experience with the 3.5 Ecoboost towing in the southern Gulf and coastal plains and the southern Piedmont is that ethyl has no advantage over regular.


Next week I'm going north on I-77 across the Appalachians, I'll use ethyl.

I also notice my Excursion does better on mid-grade when towing. I know that vehicle well and when I am towing (especially my previous TT) I can feel when the PCM pulls out timing on long, hot grades to prevent pinging. Mid-grade I don't feel it as much. For a few extra bucks, why not?

BTW there is something called "inaudible detonation" so you might not even know when it is happening.

Adam

Switched from regular to mid-grade on my RAM 2500 because I found the manual recommend mid-grade. After 3-4 tanks I noticed I was getting about 1 MPG better millage.

drsteve wrote:
No. Computer controlled engines adjust their spark timing to eliminate preignition under heavy load.

That's only partly true.

Pre-ignition caused by too low an octane rating of the fuel is caused by compression ignition (diesel effect) and has nothing to do with spark timing.

Now....timing advanced too far will cause a knock too and the engine will correct for that. It will TRY to correct for the other condition too but really can't and your performance will nose dive as a result.

No. Just keep running what you normally do. With today's ECM's they "learn" and it takes 2 - 3 tanks for it to balance back out, if you switch for a couple of tanks you will not get the results you are thinking about.

Also as said above, follow the MFG recommendations but as a note also stated above octane requirements go up depending on the compression ratio. You'll notice manuals with ratios around 10:1 or above generally requires premium.

Winged One wrote:

tbolt2000 wrote:
Are there any benefit to running octane gas when towing? I had heard when towing use high octane gas.

Those days are gone.

I had a 70 Plymouth (liked high octane) that I decided to try a little mid grade in, just to see. Dear lord, you would think I put a bucket of screws down the carb's throat, for the fit it was throwing. Racing gas raised the octane enough not to kill the car.

You will know if you are running too little octane.

No, you probably won't know if the octane is too low. Horsepower, fuel mileage and engine life will suffer but you won't know without careful checking.