cantw8forg8

I picked up my new G8GT 5 days ago and just filled it for the first time. I've been following the threads on this site and a couple of other G8 sites recently and seen some recommendations for premium (that I just put in) but wondered if there was any specific benefit in terms of dyno numbers or mpg difference that I could use to support my expensive habit (actually was only a 15c difference between the grades where I filled up so I thought it was worth the experiment). BTW, best car I have ever had.....haven't felt this way about any car before and I've owned a few!

Blackbirdws6

iTrader: (7)

Honestly, there is a lot of argument back and forth about it at the moment. I am putting premium in mine just because the fuel is a bit cleaner than regular. If it was a lease, I would throw in regular just like it says to use. I may be pissing away $$ at the pump this way but I like to tell myself it picks up a few HP from doing it.

-Brian

dltv

Here are some numbers I've collected from various forums. (first post guys!)
If someone cares to add or edit please do.


Updated 4/16/2008


Running 87 Octane - Mustang Dyno - Patrick G LS1TECH Sponsor
279 rwhp, 299 rwtq - stock
313 rwhp, 328 rwtq - tune only (stock intake)
https://ls1tech.com/forums/showthrea...tune+87+octane

Running 93 Octane - Mustang Dyno - Vector Motor Sports
304.8 rwhp, 315.3 rwtq - stock
335.1 rwhp , 348 rwtq – tune only
http://www.g8board.com/forums/showpo...0&postcount=14

Running 93 Octane- Dynojet Chassis Dyno - Mike @ New Era
298 rwhp, 322 rwtq - stock
317 rwhp , 336 rwtq – tune only (stock intake)
309 rwhp, 327 rwtq – stock + New Era Intake
324 rwhp , 341 rwtq – tune + New Era Intake
http://www.g8board.com/forums/showthread.php?t=1851

Running ?? Octane- DynoJet - So1is
306 rwhp, 325 rwtq -stock
http://www.g8board.com/forums/showthread.php?t=1880


Running ?? Octane – DynoJet – Kelly @ PCMforless
310.37 rwhp 328.16 rwtq - stock
http://g8gt.com/t3385/

Mr. Sandog

Too many variables. Need same vehicle, same dyno, same day, same temps, etc. with different gas.

If the vehicle is not tuned for higher than 87 putting anything higher in it will be wasted.

BADSZ28

iTrader: (39)

These are great finds man. Thanks!

skywalkrNCSU

iTrader: (3)

definitely not enough data there to say there is a significant difference...there are a lot more factors that need to be taken into account (sorry statistics major here who just got out of experimental design )

20SS07

Usually you should just use what's recommended. If it's not tuned for higher octane you're probably just throwing money away. Were those dyno numbers all on the stock tune? If so well then obviously there would be some benefit to putting in premium.

skywalkrNCSU

iTrader: (3)

one would think this but especially due to the fact that these are probably different vehicles, it wasnt a randomly done experiment, there werent multiple runs with each, we dont know the mileage at the time, etc, etc. there is actually no way you can say that it is statistically evident that the two will differ on average.

i could explain it more but it would take a long time especially considering i have been taking an entire course this semester on just the basics of designing an experiment to produce statistically significant results.

Vega

Yea there is a performance difference. In today’s modern fuel-injected vehicles, engines are designed to be use with specific octane rating, usually correlating an engine’s compression level to the grade of gas (higher compression level, higher octane grade).

If you car is engineered to run with an octane rating of 87, using 91 will result in no real benefit. In some instances, you may even accumulate un-burnt fuel into your emission system, which can end up collected into your catalytic converter — eventually stressing the system. If your car is designed to use octane 91 gasoline, you definitely should fill the car up with 91 octane. If you happen to pump 87 or 89 into your car — don’t worry, it’s not blowing up — the onboard computer will generally dial back your engine’s performance to prevent knocking. In some cases (such as the Lexus RX 330), a car’s owner manual may even specify that you can either use 87 or 91 octane, with 87 for economy and 91 for performance.


I can use 87 octane for my LS1 and its not going to explode. I will have a decrease in performance because you cannot compress 87 like you can with 91. There is a difference between premium (91 octane) gas and regular (87 octane) gas — BUT, not because “premium” gas is a “better” gas. Grades of gasoline are base on octane rating, which in a nut shell, measures the resistance of gasoline to premature combustion, aka engine knocking. (Going kaboom before it should go kaboom by a spark plug).

(Paraphrased because I'm le tired)

Johns98TA

iTrader: (2)

Watch out for ethanol blends. Every city is different. Here in Omaha, our mid-grade 89 octane is 10% ethanol, while our standard grade 87 and premium grade 92 octane are both 100% gasoline. So the 87 octane fillups cost more than the 89, but you get better mileage and better performance from the 87 octane (vs 89). If I cross the river into Iowa, several gas stations blend 10% ethanol into ALL of their grades, 87, 89, and 92. So buying premium gas 5 miles away in Iowa will give me less performance than buying the "same" premium grade at a local gas station here in Omaha.

Buyer Beware!

Slayn

How do you figure out how much ethanol is in your gas?

dltv

I just wanted to point out that the EPA numbers for MPG were taken from 93 octane testing. So those HP numbers that pontiac is bragging about was not on 87.


Check the gov website.


Its been looked at that the table for the G8 actually runs better on higher octane. The timings increase and performance is better.

cantw8forg8

I'm still confused.......looks like there is no real data. I'm not a statistician but have a science background and realize that although the numbers from DLTV appear impressive the numbers aren't from the same vehicle, same mileage, same elevation, etc. I did try to get info from pontiac but just got a phone operator trying to read out of the handbook which I already have and then advised me to contact the dealer. BTW handbook states 87 octane but the quick reference the car comes with states 93 for maximum performance. I have emailed pontiac for some specifics, I'll post the answer if I get one.

Slayn

I am pretty sure almost all new cars ( especially performance cars ) change the timing based on the gas you use, so using higher octane will make the engines computer be able to change the timing for a little more horsepower. I know on the Corvette forums I have read have stated this time after time that they get much less hp from 87 but they can run it without problems, but the newer Corvettes also are made for premium. I am pretty sure on newer cars the computer knows what octane you are running and can slightly change the timing, but I doubt its a big deal.

In CA we have 87, 89, 91 and I always use 91. Gas is about $3.50 for 87, $3.60 for 89 and $3.70 for 91. The cost is not worth putting 89 in for me at all, I would rather always put in 91 even for peace of mind. $52.50 for a 15 gal tank of 87 vs $55.50 for 91, I will spend the extra $3.

dltv

While i would love to agree with your statement slayn we just cant be sure without some confirmation from a Pontiac Engineer or someone who does an accurate dyno on the same day.

But any info i get ill share with you guys.