2009 Hyundai Genesis: A 790.2 Mile Run to the Snow Part 2

The one thing I'm wondering is if using regular gas instead of premium (which the engine allows) would decrease MPG or just negatively affect the HP/torque.

I don't think Hyundai's ECU can differentiate between the octane levels. The ECU on the Genesis Coupe, however, does.

All modern ECU can tell octane levels. It doesn't change MPG though, it just affect HP/torque output.

lazyhater, I think you might be right. I have a question though. Why do some automakers rate their HPs on premium while others on regular? Also, why do some automakers insist on Premium if ECUs can recognize the octane levels? This is a question which has intrigued me for some time.

The automakers who rate on premium have the engines optimized to run on premium with the higher horsepower numbers because of a higher compression ratio. When a car that is designed for premium runs on regular the engine fires the spark plug later so the engine does not knock but loses horsepower.

that response was for wobbly_ears

I have no real experience with extended driving at elevation, so perhaps that explains why I don't find those mileage numbers terribly impressive. I get 29-30mpg pretty consistently from my Altima SE V6 on highway family trips, and that car is only making 20 less hp than this Hyundai. The numbers aren't terrible, but I'd stop well short of "pretty good" for a V6 family sedan.

Can't wait to hear about the blizzard. Winter traction is kind of a big concern for me and the single biggest deterrent to getting a RWD vehicle.

Uphill driving with a car that's at least 300 pounds heavier and 20hp more powerful is a decent enough justification for putting it in the category of "pretty good."

I love how this car looks on the outside. The interior layout is a big goofy to me. I like the (more Infiniti-like) interior of the new Equus more. Hopefully they'll add some elements of that to this car as a MMC.

Anyway, if I was in the market for a sedan right now, this is the one I'd get. Great job to Hyundai for this one.

My grandfather just got one these in the V8 Model and from the one time I drive it, I am very pleased. But, one thing that I think they could have spent more time on was making the gauges more attractive. It just doesn't make any sense to met.

It's like the MB C300/350. They claim they spend 7 Years Engineering the new C-Class, yet they manage not to touch the engines, and just make them carryovers.

It's the same for the Genesis, except they spent all of this time making this car so great, but they just put bland gauges in it. I mean, they're legible, but noting is really too special about them like the rest of the car.

adavis2493, no offense, but your grandpa bought it?

Oh lord, I hope Genesis doesn't turn into a grandpa mobile like Azera. I'm 30 & bought my Azera for the luxury. But all the other Azeras seem to be driven by everyone over 70. Not too good for my image, ya see :((

As I said, no offense meant to grandpas.....

lenoroc, I presume it wasn't uphill there AND back.

wobbly_ears:

I'm adopted and my grandfather is only 55- don't feel that bad.

"All modern ECU can tell octane levels. It doesn't change MPG though, it just affect HP/torque output."

Its been dyno proven that 03-06 Accord V6 with the 6MT can gain 10WHP by the use of premium fuel and its MPG was slightly better.

My mothers former 2001 Ford Expedition 5.4 called for 87 but when 93 was used it had noticably more low/midrange power and fuel economy was better as well. The same with my grandmothers 1995 Toyota Camry XLE V6.

Modern engines that require premium can run off of 87 HOWEVER if you look in the owners manual it clearly states "the long term or extended use of low octane fuel can damage the engine". This can happen regardless if the ECU alters timing or not. If it says use premium....use premium. 20 cents a gallon isnt much considering the price of an engine.

The V6 does not require or ask for premium, only the V8 uses premium.

How do all the materials feel? Softness, sturdiness, etc.?

can an expert from Insideline enlighten us on the fuel grade detection issue? To my understanding, premioum gas does not have more energy per mass or volume. It only ignites at higher pressure therefore engine manufacturers can push the compression ratio to higher numbers getting more HP by doing so without pinging. So for an engine to detect and take advantage of the premium gas (assuming it was design to burn regular) the ignition timing has to change (done by the CPU of the engine ordering the spark plugs to ignite later) BUT most important the valve timing has to change too in order to keep them closed longer due to the shift of the ignition timing. How do modern engines change the valve opening sequence due to different gas quality? Is there a system like BMW's Vanos or Honda's Vtec with camshaft positions for the valve timing to change just for the case of better quality gas? I would appreciate an informative answer. Thanks!

There is so much misinformation in this comments thread regarding octane levels. Here are some facts:

1) Regular and super don't contain any more energy relative to each other. The longer branched hydrocarbons in super are more resistant to detonation (ignition due to heat of compression - remember the ideal gas law PV=nRT?)

2) High performance engines can achieve a cylinder compression to take advantage of super unleaded's resistance to detonation - this gives more power for the same amount of fuel

3) If you run regular in a high compression engine, the ECU will fire the spark plug EARLIER before maximum compression is attained - this is to prevent detonation.

4) With very few exceptions, engines made to run regular will not run better with premium

5) Conversely, engines for which premium is recommended can run regular without issues. The ECU will dial back the timing to protect the engine. Unless your owners manual says premium is required, you can run regular. Most high performance engines will RECOMMEND super, not REQUIRE it. There are a few exceptions though.

To some people above me:

The car does not detect octane directly, the car can only detect whether or not the fuel is detonating before the spark and then change the ignition timing (and, sometimes if applicable, variable valve timing and fuel injection timing) to prevent detonation before the ignition spark. Doing this, 99 times out of 100, causes a loss in power.

I think the confusion here is that Hyundai actually gave the Genesis V8 different power ratings depending on whether regular or premium fuel was being used. However, the V6 only has one rating and that is for the reccomended fuel, which is regular unleaded.

Retarding the spark timing WILL reduce both power and fuel economy.

With regards to a car that would normally run better on premium gas, lower compression as a result of a lower octane fuel means that you have less air packed into the cylinder at the time of spark ignition, therefore you get less power.

Is this not correct?

question for you octane-ecu experts.

if my car recommends premium (says so on the gas tank door) and i ran it as such for the first 3 or so years, but then when the gas prices started to go up-up-up i switched to regular for about 18 months. but now that gas is more reasonable again i have switched back to premium, 4 or 5 full tanks so far.

does it make sense to switch back to premium? or has my ecu permanently retarded itself because of using regular for so long? will my ecu realize that i am using premium again and give me back my HP?

I drive a 2004 altima v6 5spd btw.

chadwyck, you car is about to explode, get out NOW!

is there a stagg member from Insideline that can answer my question above? Thanks!

chadwyck, I could be mistaken. But I thi.nk you can use premium again. I think the ECUs adjust realtime & don't have 'memory' in this aspect.

There's a suggestion though. Whether it is premium or regular, use Top Tier Detergent brands though (which almost all major car makers suggest). I prefer Chevron/Texaco because even the cheapest regular has Techron.

Never EVER go for a cheap/no brand crap. We have enough trouble with the 10% Ethanol crap here in Texas

"or has my ecu permanently retarded itself because of using regular for so long? will my ecu realize that i am using premium again and give me back my HP?"

When you used regular gas the ECU detected premature gas detonation in the cylinder chambers during compression and therefore decided to ignite the mixture with the spark plugs sooner before the pressure was too high for the regular gas to ignite itself causing problems.

So you were missing some peak power when you used regular due to less compression of the mixture.

What I don't know and hopefully some engineering staff of this blog might know (where is The Mechanic when you need him?) is whether the valves are getting f@%$@ed with the premature detonation of the mixture even when the spark plugs ignite the mixture under the instruction of the ECU.

In general when running on regular do not push the engine too much...

Also don't get the cheapest 87octane. At least use the mid range 89 or 91 (to the states that 93 is the "premium" one).

@wobbly thanks for the reply, i usually stick with Shell or Exxon, the first 3 years it Chevron 93 only, but $71 tanks started taking their toll. Would Valero be considered cheap stuff? that's about as low as I've ever gone.

I can honestly say that since I have started running regular again I don't feel any particular improvement. I have 75k coming, I think I'll do a major servicing and replace the plugs and continue with the premium.

I ran 14.404 at a track back in 2004 when it had about 10k on the odo, I wonder what it'd run all these years later.......

chadwyck, we all went through that last year, didn't we..

The top tier gasoline retailer & refiners can be found here. Unfortunately, Valero isn't on the list. But the good news is that it is never too late to start using a good quality detergent fuel.
http://www.toptiergas.com/

"will my ecu realize that i am using premium again and give me back my HP?"

Your ECU will eventually retune things back to the original levels. You can speed up the process sometimes by disconnecting the battery and then stepping on the brake pedal (which will drain any remaining charge in the system) and then reconnect the battery. This will reset the ECU (along with your radio presets and clock in most cases :)) and let it start from scratch.

banhugh, as IL's enginerd on staff, I can say that eric_l and others have it right. High octane fuel allows more ignition advance, which ekes out power in certain engines.

Those engines are ones that run near the knock limit. That's the key part, really--only when an engine is operating near the knock limit can it benefit from higher octane. This means high octane has very little to no benefit during part-throttle operation. More ignition advance at part throttle increases peak cylinder pressure and can reduce power. Imagine that.

Generally, engines that can benefit from more ignition advance are high-compression normally-aspirated motors and boosted engines. Power-wise, boosted engines respond VERY well to more ignition advance. Better, in fact, than any other type of engine.

And lower-stressed engines like truck engines generally don't stand to benefit from advanced timing at all. Modern truck engines, though, are gradually becoming more sophisticated and running higher compression so perhaps this is changing.

Modern knock detection systems are pretty advanced. Its becoming nearly impossible to damage a stock engine due to knock, even ones that require premium and are fed something lower in octane. Not that I'd recommend doing that....

@wobbly, Thanks for that, I thought for sure Exxon would be on that list who knew? Shell and Chevron from now it is, good to know I on the right track with Chevron 93 only in the beginning.

@athatkur, I think I'll just let the ECU figure it out on its own, thanks for ECU reboot tip though.