premium fuel in a DI engine

[dave5358]

Originally Posted By: sciphi
Originally Posted By: dave5358
Originally Posted By: Finz
JHRZ2... How is this determined by a DIY'r?

JHRZ2 may jump back in with more specific information. Try to find a website / forum that pertains to your specific vehicle model or engine - someone there might know from experience.

Or, look in your owner's manual/ask a dealer technician for recommended fuels. If they say 93 octane fuel, then the advance curve will accommodate that advance. If it's only 87 octane, then probably not.

The problem sometimes arises when a person has a vehicle clearly designed for regular gas (87 or 89 octane). The manufacturer doesn't bother to include an advance curve for anything beyond that, so if you run a tank of 93 octane fuel, the extra energy is pretty much wasted. It runs okay, but not much benefit.

For the turbocharged Cruze at least, this is incorrect. It's pretty heavily detuned to run acceptably on 87. Exhibit A: a Trifecta or Vermont tune picks up 25-27 hp and 45-50 ft/lbs on 93 octane with no other changes made to the engine/intake/exhaust. Those tunes are fairly conservative to account for slight production and regional fuel differences. But when 18% more horsepower and 30% more torque can be gained on a 138 hp/148 ft/lb engine just by a reflash, that says that there's a lot left on the table in the stock tune.

The owner's manual may say 87 octane. Being turbocharged, it will run better on 91+ octane. Less knock means it can run less enrichment to prevent knock.

The surprising part of that is that your manual says 87 octane for a turbo car. My turbo Forester manual say 93 octane. It will run on 87. It just doesn't run as well, but the ECU can handle it.

If I fill my wife's Corolla with 93 octane gas, it runs well enough, but there's no real benefit - there's no 93 octane map in the ECU - the advance curve doesn't go there.

 

[badtlc]

Originally Posted By: sciphi


For the turbocharged Cruze at least, this is incorrect. It's pretty heavily detuned to run acceptably on 87. Exhibit A: a Trifecta or Vermont tune picks up 25-27 hp and 45-50 ft/lbs on 93 octane with no other changes made to the engine/intake/exhaust. Those tunes are fairly conservative to account for slight production and regional fuel differences. But when 18% more horsepower and 30% more torque can be gained on a 138 hp/148 ft/lb engine just by a reflash, that says that there's a lot left on the table in the stock tune.

The owner's manual may say 87 octane. Being turbocharged, it will run better on 91+ octane. Less knock means it can run less enrichment to prevent knock.


You just described every stock tune out there. Look at the VW GTI. It is stock tuned for 91+ octane, but just by flashing a new tune, you can gain 50+ HP using the same 91+ octane. That is a sports car that comes "detuned". The focus ST is the same way.

 

[Finz]

Badtic.., my nephew just passed 4,000 miles on his '13 GTI. he's looking to get more power so what I think you just mentioned is exactly what he should look into... I think

Problem is, I don't fully understand. FLASH a new tune? Is that along the lines of a chip upgrade or software patch?

Would you elaborate please?

 

[badtlc]

Originally Posted By: Finz
Badtic.., my nephew just passed 4,000 miles on his '13 GTI. he's looking to get more power so what I think you just mentioned is exactly what he should look into... I think

Problem is, I don't fully understand. FLASH a new tune? Is that along the lines of a chip upgrade or software patch?

Would you elaborate please?



Just tell him to checkout APR and Unitronics. They both have top notch tuning and both have DIY flashing hardware. You just buy the product, pug it in to the ODB port and flash the new ECU programming. It is very simple, massive gains and easily reversible. He will enjoy it.

 

[Finz]

Thank you...

 

[sciphi]

Originally Posted By: badtlc
Originally Posted By: sciphi


For the turbocharged Cruze at least, this is incorrect. It's pretty heavily detuned to run acceptably on 87. Exhibit A: a Trifecta or Vermont tune picks up 25-27 hp and 45-50 ft/lbs on 93 octane with no other changes made to the engine/intake/exhaust. Those tunes are fairly conservative to account for slight production and regional fuel differences. But when 18% more horsepower and 30% more torque can be gained on a 138 hp/148 ft/lb engine just by a reflash, that says that there's a lot left on the table in the stock tune.

The owner's manual may say 87 octane. Being turbocharged, it will run better on 91+ octane. Less knock means it can run less enrichment to prevent knock.


You just described every stock tune out there. Look at the VW GTI. It is stock tuned for 91+ octane, but just by flashing a new tune, you can gain 50+ HP using the same 91+ octane. That is a sports car that comes "detuned". The focus ST is the same way.


Keep in mind that GM rated the 1.4T on 87 octane, and then included a high-octane map that keeps more of that power around under less than ideal conditions, such as summertime. Nice little Easter egg for the curious owner.

The reason GM has 87 octane listed in the owner's manual is because the Cruze's 1.4T is so detuned in stock form. In the compact class, cost of ownership is everything. Americans being the dollar-foolish cheapskates we are, a mainstream compact requiring 91 octane would be a non-seller. Even when it ended up being cheaper per mile than other compacts requiring 87 octane, folks would look at the cost to fill up and wonder why it costs $40 instead of $36. So they took some MPG's and performance off the table to make it feel cheaper to own.

 

[Benzadmiral]

As I think I mentioned, my Regal has a fairly high compression, 11.4:1 or something like that. This weekend, out of curiosity, I filled up with 93 non-ethanol. The car seems quite nimble, but then it usually does. I'll report on whether I see any better mileage.

 

[Benzadmiral]

Originally Posted By: Benzadmiral
As I think I mentioned, my Regal has a fairly high compression, 11.4:1 or something like that. This weekend, out of curiosity, I filled up with 93 non-ethanol. The car seems quite nimble, but then it usually does. I'll report on whether I see any better mileage.

To which the answer is: Nope -- not enough to pay for the surcharge on the premium. I saw only a 6-7% increase in mpg, and the premium around here runs a good 15% more than regular.

Today I filled up with 87 again, and the Regal seems to drive about the same. I may try midgrade in the near future -- but even that tends to be about 10% higher in cost than regular, so I'd need to get 10-12% better mpg on it.

 

[badtlc]

Originally Posted By: Benzadmiral

To which the answer is: Nope -- not enough to pay for the surcharge on the premium. I saw only a 6-7% increase in mpg, and the premium around here runs a good 15% more than regular.

Today I filled up with 87 again, and the Regal seems to drive about the same. I may try midgrade in the near future -- but even that tends to be about 10% higher in cost than regular, so I'd need to get 10-12% better mpg on it.


Sounds like your answer is YES, not "nope." You did see improve MPGs. Obviously that didn't break even for you $ wise but it is misleading to say the answer was no.

 

[Benzadmiral]

Originally Posted By: badtlc
Originally Posted By: Benzadmiral

To which the answer is: Nope -- not enough to pay for the surcharge on the premium. I saw only a 6-7% increase in mpg, and the premium around here runs a good 15% more than regular.

Today I filled up with 87 again, and the Regal seems to drive about the same. I may try midgrade in the near future -- but even that tends to be about 10% higher in cost than regular, so I'd need to get 10-12% better mpg on it.


Sounds like your answer is YES, not "nope." You did see improve MPGs. Obviously that didn't break even for you $ wise but it is misleading to say the answer was no.

Quite right. "Yes -- but not enough to pay for the surcharge on the premium."

 

[UG_Passat]

Originally Posted By: badtlc
Originally Posted By: Finz
Badtic.., my nephew just passed 4,000 miles on his '13 GTI. he's looking to get more power so what I think you just mentioned is exactly what he should look into... I think

Problem is, I don't fully understand. FLASH a new tune? Is that along the lines of a chip upgrade or software patch?

Would you elaborate please?



Just tell him to checkout APR and Unitronics. They both have top notch tuning and both have DIY flashing hardware. You just buy the product, pug it in to the ODB port and flash the new ECU programming. It is very simple, massive gains and easily reversible. He will enjoy it.


Actually, this is incorrect. The ECU needs to be opened up initially for a special grounding procedure to bypass the security encryption. All software is uploaded by the APR or Unitronic distributor.

 

[oilotaku]

my 2012 focus has DI never ran anything other than regular in it did fine and got 45mpg on one trip

 

[turboseize]

Originally Posted By: JHZR2
The question you need to have answered is what is the maximum spark advance that the engines in question will support.

For example, I know that my saab (not DI) will advance to the point of utilizing AKI 90 fuel. Beyond that, it's a waste.

In NJ we get 93, but in some places I see 91 as premium.

So DI or not, the question is about spark advance really.

DI adds some combustion cooling characteristics, so there are some benefits there, but it's all mapped and the OEM knows what the design can take advantage of. That's what you need to figure out!


How old is your Saab? A classic with distributor timing or does it already have a DI (witch is the Saab abbreviation for direct ignition. The only direct-injection Saab engies are to be found in the extremely rare second genaration 9-5 of 2010) or even Trinic?. Trionic Saabs will not exceed their max power with better than recommended fuel (but reduce power and mileage when the fuel is worse). Classic, analogue-APC-Saabs won't get better mileage with higher octane fuels, but will allow significantly higher boost pressures and thus have more power.

The reason better fuel will not change power if Trionic Saab lies in the engine manegements boost table. Boost values listet there will not be exceeded, even if you car does not detect any knock. If you want to mor power, you'll have to hange these... However, DI/Trionic Saabs can paly with timing to a considerable degree, thus improving efficiency with higher octane fuel.
Classic Saabs with distributor timing cannot adjust timing according to knock, and their analogue APC (boost controller) has no fixed boost tables... it just cut's back boost when knock is detected.

Whith a trionic 9-5 oder 9-3, you can actually have a look at knock events and real boost pressure (the gauge in the dashbord is a bit inaccurate) via "live SID". I'd say you have "overdone" it on octane when no single knock is counted... Until then, you're benefitting from higher gas, as in response to knock the trionic will retard timing.
Whether this improved efficiency will be significant in daily driving or even lead to cost savings is an entirely different matter, though.

 

[Silverado12]

Probably will get beaten up by suggesting this, but I blend 87 octane with ethanol E-85 to make a 20% blend. This gets you approx 89 octane cheaply. Gas mileage difference is not much less than running plain 87 gas. I'm a big believer in ethanol, as it burns cleaner, cooler and can be run in newer non-flex fuel vehicles at this mixture w/o tripping the CEL.

 

[badtlc]

Originally Posted By: Silverado12
Probably will get beaten up by suggesting this, but I blend 87 octane with ethanol E-85 to make a 20% blend. This gets you approx 89 octane cheaply. Gas mileage difference is not much less than running plain 87 gas. I'm a big believer in ethanol, as it burns cleaner, cooler and can be run in newer non-flex fuel vehicles at this mixture w/o tripping the CEL.


it also produces combustion byproducts that cause lung diseases. cleaning burning at the expense of your health.

 

[wemay]

Can't say we've noticed any mpg difference in either vehicle where 93 vs 87 is concerned, although we often use 93 in the turbo anyway.