3.5L Ecoboost Octane vs Mileage

[Eagleboy99]

JeffK gets it.

 

[MLA]

7 hours ago, Eagleboy99 said:

Sure - "dumb" motors.  Otherwise the computer manages the detonation.  But keep buying overly expensive premium.  Great for my 401K! 

My take, I do not want my ECM to manage detonation as a mater of habit, because I run too low of an octane fuel. I would prefer to run the suggested oct and NOT have any detonation that needs to be managed. 

[dlb]

8 hours ago, Nitrousbird said:

You need to educate yourself before making such "dumb" blanket statements.  High boost / high compression motors, at least more modern stuff, have low-octane fueling tables typically.  They pull boost (if turbo) and/or timing to compensate.  Kills power right where you need it; WOT and low RPM/high TPMS = lower fuel mileage.  You'll end up spending more on fuel while your car performs poorly.  

Motor in my boat requires premium.  I wouldn't dare trust the Indmar mapping to have a reasonable low-octane table.  Same motor in all automotive applications also recommends premium and has been proven to see performance degradation running 87.  Motor in my BMW has to have premium - I can tell a difference in max boost just simply on running 92 vs 93 octane (mind you I'm running mapping targeting 2x stock boost with logic that will adjust for octane).  Wife's supercharged Audi also recommends premium.  I'm sure it will run well enough on 87, killing fuel economy in the process.

The REAL answer - you should run the lowest octane possible that will allow the motor to run without detection of knock.  For many motors, 87 is fine.  Some, 91+ is what is needed.  Others might call for 91 but get away with 89 without knock detection.  Ambient conditions and elevation can also impact the ultimate octane need.    

Every motor we have gets the recommended octane, 4 cars, 1 SUV, 1 boat, lawnmower and a chainsaw as well.  Keeping them all straight is a task, 3 get premium, 1 mid grade except at the spring fill up, the others good ol’ 87.

The twin turbo’s in my wife’s ride get premium to keep them happy, she likes it that way,  and we all know the saying......

[Eagleboy99]

5 minutes ago, dlb said:

Every motor we have gets the recommended octane, 4 cars, 1 SUV, 1 boat, lawnmower and a chainsaw as well.  Keeping them all straight is a task, 3 get premium, 1 mid grade except at the spring fill up, the others good ol’ 87.

The twin turbo’s in my wife’s ride get premium to keep them happy, she likes it that way,  and we all know the saying......

IOW, you are RTFM- ing.  fancy that. 

[justgary]

On 9/30/2018 at 8:09 AM, oldjeep said:

Depends on where you buy your fuel.  Some brands like Holiday run a better additive package in the higher octane fuels. 

Around here, nearly every station gets their fuel from the same depot.  The same truck delivers to Shell, Exxon, BP, Citgo, and the non-brand local stations.

They may add different amounts or mixes of additives, but I suspect that they don't.  Fuel is a commodity.  So are additives.  YMMV!

I put 87 E10 in the cars and truck, but 89 or better non-ethanol in the boat and small engines.

[justgary]

1 hour ago, Eagleboy99 said:

IOW, you are RTFM- ing.  fancy that. 

Or R-ingTFM.

[dlb]

It is on the fuel door.....

[Nitrousbird]

17 hours ago, Eagleboy99 said:

Nice insult there pal. Real creative.  As you say "Motor in my boat requires premium" - why not run av gas in it then? I mean your thesis is that more (octane) is better right?

You obviously either did not read my post because you were too enraged I used your own term against you, or you simply didn't understand it.  Let me quote myself:

17 hours ago, Nitrousbird said:

The REAL answer - you should run the lowest octane possible that will allow the motor to run without detection of knock.  

How in the heck do you come up with "I mean your thesis is that more (octane) is better right?"?  

As for the motor in my boat, page 29 of the Indmar Manual:  
"WHAT TYPE OF GASOLINE TO USE All carbureted and standard EFI engines run on unleaded fuel of 89 Octane (R+M)/2 or higher. The LS1 requires 93 octane or higher"
http://www.themalibucrew.com/_files/engines/indmar_1994_2003.pdf

The sticker they put right below the pressure cap on the coolant tank of the motor also reflects the octane requirement.  Indmar is well known to tune overly rich and is quite possible they don't have a low octane table (or one that is well sorted).

"Premium" is just a term for the highest octane a pump offers.  In my state, it is typically 92 or 93...most being 93.  Sunoco used to offer 94 here but stopped a good 10-15 years ago.  E85 is common, which is typically around 100 octane depending on the blend, but you need the ECU and fuel system set up to handle E85; I'll run E30 blends in my BMW from time to time but the low pressure fuel pump needs upgraded before I can move up to a E50-E60 blend - straight E85 will require port injection to safely run E85 as the HPFP can't keep up.  I do see higher peek boost levels on E30 due to the higher octane.  Or is that just some magic and 87 octane would perform just as well, lol?

[Brett B]

Nitrousbird has it right. Forced induction engines are much more susceptible to knock and therefore have much more severe knock mitigation controls, i.e. lowered boost and drastically reduced timing at the earliest onset of knock. They will also often maintain these off-nominal maps for quite some time after the knock has occurred to keep the engine internals happy. If you are under heavy load on a boosted engine with 87 octane this can result in much worse fuel economy than if you had run the proper octane to prevent knock in the first place.

On topic for the Ecoboost, during light load highway cruising I can't see any way that the octane difference impacted your MPG that much. Knock typically occurs during heavy load, at peak torque which is also your peak Volumetric Efficiency (VE) and peak cylinder pressure. You will not be anywhere near a state where the engine knocks during normal highway cruising, so the ECM has no reason to pull timing and/or boost to degrade your MPG. In fact light load cruising is exactly when the ECM runs in closed loop O2 feedback mode to optimize MPG. As soon as you go to a heavy load state (such as high throttle position while going up a hill) the ECM drops out of closed loop control and reverts to the base fuel maps. It's much more likely that you had a slight headwind on one of the trips, cruised at different speeds, or even more likely that the factory MPG calculation just isn't that accurate.

A slight headwind and uphill grade causes my Tundra to lose 2-3 MPG when compared with a flat grade and a tail wind at highway speeds. Cruising at 75 mph vs 65 mph also causes a big difference. While towing my boat at highway speeds drafting a semi vs being out in the wind is a fun experiment too.

Edited October 30, 2018 by Brett B

[granddaddy55]

So your saying I should use 93 in my 2.7 eco on my long trip once a year mostly up hill  cause it will make a difference in the low numbers that were as low as 9.2 at 75++. Yes I read that under towing as you were speaking of my manual I think says run premium.  I just wanted one vehicle I didn’t have to run premium for first time in my 35 years of car ownership  

I wondered if it was more that I needed to lock out 6 gear cause when I was higher rpms in 5 gear up hill the whole dash and steering column didn’t rumble from the twin turbo like it did when in 6 gear

Edited October 31, 2018 by granddaddy55

[RyanB]

1 hour ago, granddaddy55 said:

So your saying I should use 93 in my 2.7 eco on my long trip once a year mostly up hill  cause it will make a difference in the low numbers that were as low as 9.2 at 75++. Yes I read that under towing as you were speaking of my manual I think says run premium.  I just wanted one vehicle I didn’t have to run premium for first time in my 35 years of car ownership  

I wondered if it was more that I needed to lock out 6 gear cause when I was higher rpms in 5 gear up hill the whole dash and steering column didn’t rumble from the twin turbo like it did when in 6 gear

You want better MPG while towing without using premium?  Slow down from your “75 ++” MPH speed. If that is your complaint, you will get a lot better outcome by following that advice than by running premium. 

And for the record, I’d be very happy getting 9.2 running those speeds. 

[Pnwrider]

1 hour ago, RyanB said:

And for the record, I’d be very happy getting 9.2 running those speeds. 

I’m sure your Cummins does way better than his 4 banger truck towing a much heavier boat. At least mine does... 

[RyanB]

39 minutes ago, Pnwrider said:

I’m sure your Cummins does way better than his 4 banger truck towing a much heavier boat. At least mine does... 

Nope. It doesn’t matter if i am towing or solo, my MPG drops like a rock at speeds above 70 MPH.  I’m between 8-9 MPG towing 75ish. Granted, those trips include I70 across the Rockies. 

But I don’t think 9.2 is anything to complain about towing above 75. 

[Pnwrider]

47 minutes ago, RyanB said:

Nope. It doesn’t matter if i am towing or solo, my MPG drops like a rock at speeds above 70 MPH.  I’m between 8-9 MPG towing 75ish. Granted, those trips include I70 across the Rockies. 

But I don’t think 9.2 is anything to complain about towing above 75. 

The pass I cross isn’t anywhere near as high as Rockies, but I saw mpg drop from 13 towing an older vlx to 10-11 towing 23 lsv on the same trip we always take for vacation. That’s with cruise set to 80. 

[carguy79ta]

I get 9.xxx with my Cummins (hand calcd) towing about 12k at 75mph. Do tow with the 200hp tune...I feather the throttle.  With the big tune, I get 1mpg increase across the board. 

[granddaddy55]

It really doesn’t get that much better at 65-70 with cruise control (11.5-12 and a good bit  of that was “downhill” on long trips , even uphill to 1000’ it’s 10-10.5 at 65-70) at best and I get tired of feathering the gas and let the cruise do it’s thing, you have to work to hard to get very little extra 

at home I go slow 60-68 on flat ground except bridges and am lucky to get 12 with 87oct

i used to get 8 on my ram 1500 5.9l having to run 89-93 to avoid uphill obvious knock, so I’m still happy but all of my figures are hand calculated , not quoting the lie o meter, and no knock on the EB

i did the long trip on purpose with 87, since that’s what I use at home snd don’t want to get premium for 50 mile pulls or wsy less.  No way the octane diff performance makes up for travel highway premium priced gas diff

next long  trip I do plan to use premium just to check the diff

Edited November 2, 2018 by granddaddy55