The Clarity has been my daily driver for the past 18 months and it has been great. I hope Honda keeps developing this platform for another generation, and hopefully make it a hatchback with 2.0L engine and 20kWh battery. But for the current Clarity, the only issue that I had with the car during long road trips in the mountains was engine power in higher elevation and for steep grades. I wish the engine had more power. Therefore I was thinking maybe using premium gas can result in some extra power. Now usually Atkinson cycle engines work better with low octane gas (older Prius models for example), but with Clarity having relatively high compression ratio (13.5:1) is it possible that you can get extra power with premium gas? Now being an Atkinson engine the effective compression ratio is probably lower than 13.5:1, but still it could be high enough to benefit from premium gas. What you think? Has anyone tried to measure engine power with regular and premium gas?
Premium Gas
- Thread starter Agzand
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JFon101231
Active Member
No idea in Atkinson but for a regular engine higher octane doesn't give you more power unless there was knock-induced ignition timing retard happening.
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In general I agree, but I do perhaps 4 trips like this each year, if the car performs better it worth the $12 difference in fuel cost. It is a different matter than using premium on an ICE car every time you fill up. That can add up to significant money.
For ICE cars it really depends on the engine. I had a 2016 VW Golf Sportwagen with 1.8 turbo engine. The recommended fuel is regular, but the car clearly performed much better with premium. I am not talking about meaningless metrics like 0-60 or horsepower, the engine just ran much smoother and had better throttle response with premium. You could tell from the moment you start the engine. Personally I believe turbocharged engines work much better with premium gas.
The Gadgeteer
Active Member
My approach to steep climbs is put in sport mode and stomp on the accelerator. No issues so far. Yes, I know Sport mode only changes the mapping of the accelerator but it helps me psychologically. I do not use HV or HV Charge during the climb.
I won’t debate what fuel to use in your Golf. That said, I’ve never owned a vehicle with a turbocharged gasoline engine that didn’t require premium fuel. That’s 91 Octane in many parts of the US. That includes a Volvo and 2 Subaru’s, in addition to a normally aspirated Audi, which required 91 octane.
The US version of the Clarity PHEV is designed to run on 87 Octane. You certainly can run a test on the next trip with a higher grade fuel. It’s unlikely that there will be a measurable difference.
ClarityBill
Active Member
Turbocharger, with the higher cylinder pressures would benefit from the anti-knock properties of premium fuel.
The Atkinson engine is almost an anti-turbocharger, using lower cylinder pressures to gain efficiency.
I tried to use an OBDII to track Atkinson mode, and only saw the Clarity out of Atkinson during warm-up: I was surprised it did not revert to normal operation when more power was required.
People like me, who use ethanol-free gasoline (when I last filled up our Clarity many months ago it was a whopping $4/gallon vs sub $2 regular gas) for its longevity also get whatever possible (almost certainly none) benefit of its higher octane. So you can have two shaky justifications--less degradation and more power--for buying this expensive gasoline.
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craze1cars
Well-Known Member
Higher octane = cooler burn. Lower octane = hotter burn. All things being equal, an engine makes the most horsepower out of the lowest octane fuel it can handle without knock. I’ve done a bit of engine and fuel/ignition tuning in my life, and on dyno and track tests, in almost all cases the lowest octane fuel the engine can handle makes the most real world horsepower. Until octane drops to point of detonation, which causes engine wear or damages.
But all things are not equal. And all modern cars have dynamically changing fuel and ignition maps. So nobody here has any idea how Honda designed the Clarity fuel/ignition map. Without that knowledge, nobody (including myself) can make a valid fuel recommendation. Only Honda can.
My last Honda Civic was a 1.5L turbo. Specifically tuned by Honda for 87 octane ethanol blend. Premium not required nor even recommended for max performance. So all turbos don’t need premium either. Many do.
As this is a Clarity forum, my final recommendation is for Clarity. Back to my earlier statement that nobody here on this forum can make any valid fuel recommendations: Honda can. Owners manual clearly states the car is designed to run on 87 octane Top Tier oxygenated fuel In concentrations as high as 15% ethanol. No additives mentioned, no benefit to ethanol free fuel mentioned.
That’s the fuel Honda designed this car around to allow it to to run at its peak. That is the fuel Honda recommends. So that’s what I do, and that’s what I recommend. 87 octane E10 or E15 with no additives is the best choice. Until someone shows me a full dyno result chart for Clarity proving that premium or non-ethanol fuel works better in some fashion, I will flatly say that such a result is HIGHLY unlikely. If true Honda would have recommended different fuel for the fuel/ignition maps their engineers created for this car.
Certainly when I modified fuel flow and ignition curves vintage cars which were originally designed for now unavailable/obsolete fuels, I designed them around a certain modern fuel, and I sure has heck didn’t then tell the owner to run a different fuel than I set the car up to run best with! So why the heck would Honda? They wouldn’t. They’re not all that dumb.
Run the fuel that Honda recommends folks. Don’t add stuff to it. Don’t deviate. It ain’t that hard.
But all things are not equal. And all modern cars have dynamically changing fuel and ignition maps. So nobody here has any idea how Honda designed the Clarity fuel/ignition map. Without that knowledge, nobody (including myself) can make a valid fuel recommendation. Only Honda can.
My last Honda Civic was a 1.5L turbo. Specifically tuned by Honda for 87 octane ethanol blend. Premium not required nor even recommended for max performance. So all turbos don’t need premium either. Many do.
As this is a Clarity forum, my final recommendation is for Clarity. Back to my earlier statement that nobody here on this forum can make any valid fuel recommendations: Honda can. Owners manual clearly states the car is designed to run on 87 octane Top Tier oxygenated fuel In concentrations as high as 15% ethanol. No additives mentioned, no benefit to ethanol free fuel mentioned.
That’s the fuel Honda designed this car around to allow it to to run at its peak. That is the fuel Honda recommends. So that’s what I do, and that’s what I recommend. 87 octane E10 or E15 with no additives is the best choice. Until someone shows me a full dyno result chart for Clarity proving that premium or non-ethanol fuel works better in some fashion, I will flatly say that such a result is HIGHLY unlikely. If true Honda would have recommended different fuel for the fuel/ignition maps their engineers created for this car.
Certainly when I modified fuel flow and ignition curves vintage cars which were originally designed for now unavailable/obsolete fuels, I designed them around a certain modern fuel, and I sure has heck didn’t then tell the owner to run a different fuel than I set the car up to run best with! So why the heck would Honda? They wouldn’t. They’re not all that dumb.
Run the fuel that Honda recommends folks. Don’t add stuff to it. Don’t deviate. It ain’t that hard.
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Here’s another approach. On steep grades the ICE will be operating as a generator, providing up to, and perhaps more than, an additional 60hp to the electric motor. The batteries provide up to 121hp to the motor.
While it is unlikely that we will ever obtain meaningful data from Honda, documents for Onan/Cummins gasoline powered generators indicate that they will deliver their rated output up to elevations of 3,000’-5000’, depending on the model. Above those elevations output will be reduced 2-3% for every 1000’ increase in elevation.
At 10,000’, it’s possible that the output from the ICE/generator is reduced 10-20% or 6-12hp. Less oxygen, less fuel, less bang. Additionally, under high load, some of that sauce may be getting sent to the batteries rather than the motor.
Keep the $12 in your pocket.
While it is unlikely that we will ever obtain meaningful data from Honda, documents for Onan/Cummins gasoline powered generators indicate that they will deliver their rated output up to elevations of 3,000’-5000’, depending on the model. Above those elevations output will be reduced 2-3% for every 1000’ increase in elevation.
At 10,000’, it’s possible that the output from the ICE/generator is reduced 10-20% or 6-12hp. Less oxygen, less fuel, less bang. Additionally, under high load, some of that sauce may be getting sent to the batteries rather than the motor.
Keep the $12 in your pocket.
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David in TN
Well-Known Member
I think that the primary concern for steep grades would be the battery charge.
A few weeks ago I was on a trip, and purposefully let the battery deplete. I have a ScanGauge II, and it typically shows STC (state of charge) ~ 10.4% when the engine starts. On this trip, whilst going up some grades, I saw the STC as low as 4.6%.
If I were going to be encountering significant climbing, I'd make sure that I had the battery at the most charge that I could get it, even if I had to invoke HV Charge.
I'm fortunate with my job, where I travel locally - the furthest place that I go is about 63 miles from my office. Most locations that I visit have RV plugs on the outside of the building that I can tap into while there. (I have a 16-amp EVSE in my car -- full charge in about 4 hours on 240 volts.) I've filled up in January, February, and June so far this year.
A few weeks ago I was on a trip, and purposefully let the battery deplete. I have a ScanGauge II, and it typically shows STC (state of charge) ~ 10.4% when the engine starts. On this trip, whilst going up some grades, I saw the STC as low as 4.6%.
If I were going to be encountering significant climbing, I'd make sure that I had the battery at the most charge that I could get it, even if I had to invoke HV Charge.
I'm fortunate with my job, where I travel locally - the furthest place that I go is about 63 miles from my office. Most locations that I visit have RV plugs on the outside of the building that I can tap into while there. (I have a 16-amp EVSE in my car -- full charge in about 4 hours on 240 volts.) I've filled up in January, February, and June so far this year.
Yes, I think this is a good way to drive up very steep climbs. You want to force the engine to run but at the same time use some battery to supplement engine power. I have to try it on a real climb and see how much battery it will use.
Requiring or even recommending premium gas for a non premium brand is a sales killer in US market. So carmakers recommend 87, even though it might not be the best grade (case in point my VW 1.8t). I am pretty sure your Civic would have run much better on premium as well.
craze1cars
Well-Known Member
@Agzand, I did not test this with my Civic, so could you please share your dyno or track result chart for Honda Civic to prove this statement? Here’s Car and Drivers test result for same engine in a CRV, which contradicts your certainty:
https://www.caranddriver.com/features/a28565486/honda-cr-v-vs-bmw-m5-ford-f-150-dodge-charger/.
They found 93 actually made the car slower than 87 octane at the track...
I’ll remind this is a turbo car that is specifically tuned to run on 87 octane by Honda, disproving that there is benefit to premium in this particular turbo car.
Their direct quote/summary: “The modern CRV.... makes the same argument: don't waste your money on premium. Switching from 87 octane to 93 yielded a 7-hp gain on the dynamometer, but that advantage was lost in the noise at the track. There, the CR-V's zero-to-60-mph and quarter-mile times both tracked a tenth of a second slower on the expensive stuff. While fuel economy at 75 mph ticked up from 27.3 mpg to 27.6 mpg on premium, that's a 1 percent improvement for a 21 percent higher cost.”
I have no idea what VW recommends for your 1.8T...but I recommend not deviating from their owners manual recommendation, whatever it is, cuz they will tell you the fuel that’s best for that car’s tune. If they want to not lose US market by recommending premium, they can just re tune their turbo to run best on 87, as Honda did with their turbo for the US. It is just a simple computer reflash and some testing these days...
https://www.caranddriver.com/features/a28565486/honda-cr-v-vs-bmw-m5-ford-f-150-dodge-charger/.
They found 93 actually made the car slower than 87 octane at the track...
I’ll remind this is a turbo car that is specifically tuned to run on 87 octane by Honda, disproving that there is benefit to premium in this particular turbo car.
Their direct quote/summary: “The modern CRV.... makes the same argument: don't waste your money on premium. Switching from 87 octane to 93 yielded a 7-hp gain on the dynamometer, but that advantage was lost in the noise at the track. There, the CR-V's zero-to-60-mph and quarter-mile times both tracked a tenth of a second slower on the expensive stuff. While fuel economy at 75 mph ticked up from 27.3 mpg to 27.6 mpg on premium, that's a 1 percent improvement for a 21 percent higher cost.”
I have no idea what VW recommends for your 1.8T...but I recommend not deviating from their owners manual recommendation, whatever it is, cuz they will tell you the fuel that’s best for that car’s tune. If they want to not lose US market by recommending premium, they can just re tune their turbo to run best on 87, as Honda did with their turbo for the US. It is just a simple computer reflash and some testing these days...
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craze1cars
Well-Known Member
https://newsroom.aaa.com/2016/09/u-s-drivers-waste-2-1-billion-annually-premium-gasoline/
Another independent test flatly saying that Premium fuel is higher in octane only, NOT higher in quality. And any car that has not been tuned to benefit from higher octane will see ZERO benefit from using premium fuel.
Clarity is no different. Premium in this car will be a 100% waste of money. There is no other way to state it, and no documented proof otherwise...
Top Tier brand fuel, however, offers benefits. Make sure the fuel station you buy from is Top Tier branded. Again this is a direct Honda recommendation, and also proven beneficial in independent tests.
Everyone should use the fuel type that your car is specifically tuned for. This is clearly spelled out in every owners manual...
Another independent test flatly saying that Premium fuel is higher in octane only, NOT higher in quality. And any car that has not been tuned to benefit from higher octane will see ZERO benefit from using premium fuel.
Clarity is no different. Premium in this car will be a 100% waste of money. There is no other way to state it, and no documented proof otherwise...
Top Tier brand fuel, however, offers benefits. Make sure the fuel station you buy from is Top Tier branded. Again this is a direct Honda recommendation, and also proven beneficial in independent tests.
Everyone should use the fuel type that your car is specifically tuned for. This is clearly spelled out in every owners manual...
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craze1cars
Well-Known Member
https://us.etsracingfuels.com/blogs/blog/guide_to_racing_fuels_the_octane_factor?loc=us
Additional good and accurate octane info for those interested.
Additional good and accurate octane info for those interested.
craze1cars
Well-Known Member
Another extension cord thread? Thought this was octane discussion...
Well, in the article that you posted they say in controlled environment (dyno) they gained 7 hp, so the premium actually improved performance. The 0-60 or track tests are a fluke probably, maybe the temperature or driver mood was different. However, I was clear in my statement that numbers like 0-60 are meaningless for a car that has adequate power in day to day driving. My car was running smoother and had better throttle response with premium, qualities that you can feel and enjoy in day to day driving. With regular you could feel a split second of choking when you push the gas pedal, kind of like turbo lag. If someone has a Civic maybe they can try and report back if they see the same with the 1.5t engine. I am quite certain they can feel the difference.
Regarding the owners manual, you give too much credit to entities that brought dieselgate, ignition switch fiasco, resisted seat belt laws, etc. They write anything in the owner's manual as long as it will increase their profit. If I am not mistaken the first year of 1.8t engine they recommended premium gas, then the following year they changed recommendation to 87, the engine kept the same HP and torque rating, which means they did not change the engine tuning.
Finally, my point is that unlike my VW, with Clarity even 5 HP can make a difference, because the engine power is so marginal when you climbing. So it worth experimenting if someone has the means to test it.
It is octane. Could be towing. Just an observation on my part of when others choose to follow or ignore the Owners Manual.
Conclusion is, people tend to quote the manual when they agree with it.
I was also under the impression that there aren’t strict guidelines on this forum to stay on topic.