Obviously lots of guys opinions differ... But as stated above a guy is running cheapest fast and almost has 200k. I run 89octane in CA and think it's sufficient.

 

I've run 93 octane since day #1 with my car. One day, i made the mistake of going to get gas when the low fuel light was on and filling the entire tank with 89 octane. I panicked, but since the G35 is premium recommended and not required, i didn't freak out too much.

I noticed no difference at all in performance. I prob did lose a few ponies, but my butt felt nothing. I ran a few tanks through and calculated out fuel economy and noticed nothing as well.

I went back to 93 octane, but find myself splitting my tanks now between 89 and 93 octane. I can't tell anything.

DO i want to try 87? Nope. But i'm not as hesitant now to try 89.

 

93 octane

 

This is not entirely true. Yes it's true that it is a mix. But it's mixed at the refinery, not the gas station. I worked engineering at a refinery for a while.

And no, higher octane does nothing but help with pinging/pre-detination. And it is recommended for our engines since they are higher compression. There is no extra cleaning agents in it. And if you have an engine designed to run on 87 octane, there is no benefit to running premium. Unless the gas station has premium that is 100% gasoline vs E10 or E15.

 

Bingo.


Higher octane is not "better". Just think of it like oil grades. If your engine required one oil, use it. If it requires another, you use that.

If your engine requires 87 octane only to achieve max performance, then that's all you need and you can save your $$$ on 91+ octane. There's no other difference in regards to additives and detergents within the same brands

 

You guys are correct to a very very good degree. On most more advanced engines (05/06 were getting there) though, the engine WILL correct for the gas being used by monitoring the KS and MAF, etc, etc.

On engines where that's the case running higher octane will actually net performance increase, and better economy. Though it may be hardly measurable.

Either way, I agree, run what's spec'd for the car. The 03.5-06 has the potential to run better on premium fuel but it's a question of gain/cost for sure.

 

Even if it's cheaper?

 

Still, if the engine was designed for max performance 87 octane, you won't get better performance from running 91 or 93. You can however get a tune for ANY engine for 93. The nice thing about older cars is, you can just twist the distributor a few degrees to gain some horses, haha.

If higher octane gas is cheaper, then by all means run it. It won't benefit anything in an engine designed for 87, but it won't hurt.

In the case of the G35, always get higher octance gas because that's what the engine is designed for. It has higher compression than your average engine.

 

Some good information on this thread.

 

certainly not trying to argue, but newer engines advance timing, etc when they can, this is in an effort to squeeze every drop out of engines. With stringent emission and fuel economy regulations, as well as customers wanting power and fuel economy in a very competitive market, manufacturers are designing cars to do things it may be hard for an old school mind to understand.

Things like them tuning themselves with more than just O2 trims. Variable camshafts, etc. And almost all manufacturers running wideband O2 sensors in order to get more accurate tuning. This includes the 05/06 G35 IIRC.

This allows them to run a much wider set of Maps. Rather than just a default rich-map and a lean-map, then your normal map that is around 14.7 AFR (what old narrowband O2 sensors read). This allows the engine to function, desire, and accurately measure a much wider array of operating conditions that veer away from 14.7 AFR, giving much more control of timing, etc, etc, etc. Running higher octane in these cars will net an increase in performance and likely fuel mileage. Again, might only be 5 hp. MIGHT be 25 hp. Depends on the car and it's setup.

ON THIS CAR, again, I agree just run what's spec'd. I posted the chart in this thread a couple times.

What's average? 10.3:1--->10.6:1 isn't a high compression ratio
Again, the chart I posted taken directly out of the Factory Service Manuals and Owners Manuals clearly disagrees, not all G35's need to run high octane, only certain models/years.

 

Again

2003-2004 6MT and 5AT SEDANS: 87, with 91 recommended for better performance
2005-2006 6MT SEDANS: 91
2005-2006 5AT SEDANS: 87 with 91 recommended for better performance
2003-2006 Coupe (all): 91

 

I'm not sure, but that may have to do with the target audience as well. Being able to run lower octane fuel is a great marketing point. I'm in engineering, and there are times when i have to design a product to suit a target audience, or some other aspect that is HIGHLY marketable.

Hate to say it, but G35/G37 sedans (the base RWD and AWD models, not the sport 6MT or coupe models) are marketed to "old farts". Most people don't care about performance. A car that can run the "cheap" stuff is very appealing in the eyes of many. Our cars were marketed as performance sport-luxury cars, the truth is they probably spend their early years (if you didn't buy new or near new) ferrying groceries and grandkids to and from bingo.

When i looked at new G37x's a few months ago (before buying a C300 4matic) the salesman even pointed out i could run 87 octane in the G37x vs 91+ in a benz, Lexus, AUdi, etc. Great point in marketing in my opinion. Running 87 octane vs premium is a free car payment for most people

Where im turning into a "old fart" myself, the ability to run lower octanes does look very appealing. Yes, i am well aware that it doesn't save much money, but when you factor in "old fart" stuff like paying for a mortgage, diapers, day care, preschool, hockey, gymnastics, etc etc, then you come to the point where the car starts to become an "appliance" and you toss in cheaper octane to help pay for more important activities and such. Plus i'm starting to not really care about performance. (even debating selling my modded Mustang because I'm losing interest) The person going out and buying a 6MT sedan now, may be a little more "free" from life's money draining issues and performance orientated. So going a bit aggressive on the timing and requiring premium fuel for 5-6 more HP makes a lot more sense with a young single guy with no kids. With that type of market, every HP counts. With grandpa...all he cares about is a nice car that can get him to bingo. If it can run 87/89 octane, than that might be just enough of an edge to keep him in an Infiniti and not get a Lexus.

Some may say that if you buy a nice car, treat it nice with "good" gas, but the truth is if the engine is designed to function on a lower grade of gas, you aren't "abusing it" by not runnin premium. You just might be missing out on a few ponies. It's all about what it was designed to do.

I've been running 89 octane in my G35x for a couple months now. I do about 500-600 miles a week of highway driving. I've noticed no difference in fuel economy when calculating it out, and the car still feels as quick as it did before. By my estimations, i'd save about $283/year by running 89 octane, and $425/year running 87 octane. Not a huge savings, and not one to cause me to risk damaging my vehicle over it. However, i don't feel that I am. I notice zero detonation at all, engine still sounds and rounds the same.

 

Nail on the head with everything above man, I literally would agree more than 100% if it was possible.

Not much point in runnign what isn't spec'd.

The tuning in these cars is very different from manual to auto and from early years to later years. Heck the Manual even has completely different cams!
The HP rating changes between 03/04, auto/manual, 05/06, auto/manual, coupe/sedan all fall in line with recommended fuel also. So in the G's case, I'd say there's some notable differeences in tuning and design between models and years. The most important thing is NOT to generalize this generation of car because of this. Following the chart above will do you fine.

If you're getting a Tune, step up to the highest octane you can consistantly get and stay there.

If you're just driving the car, follow the chart.

 

Newer engines designed to run on premium will run best on premium. Newer engines designed to run on 87 will run best on 87. If you have a 2012 Chevy Cruze, turbo, direct injection, it will run best on 87. It will NOT get better performance on 93. No matter how much the computer can correct, it will only correct using preset maps. Now, if the car had a map for 93 octane, then it would run better on 93. But it doesn't, and no cars that are recommended to run on 87 have maps for 93.

Lots of engines were in the 9s for compression. New direct injections are up around 11.

By the way, I'm currently an engineer for one of the largest automanufacturers. I'm not just making this stuff up. If a car ran better on 91, then that's what we would recommend. We recommend our cars run 87 because that's what they run best on.

 

There is never a dull moment when Gary comments. HA!