H3 Put 91 octane in

[Kyle]

Okay so yesterday i needed gas and i remember reading some other forums about wether you can tell a difference in power, mpg etc. when running a higher octane gas. So for fun i filled up with 91 (highest in cali) and after about 30 miles or so the car started to feel just a little more peppier and the exhaust note changed a little bit, idk if its the placebo effect or not but the car also seems to be running cooler, it used to run between half and 3/4 now it runs just a little bit above 1/2!

Does someone else want to try higher octane in there 3 just to see if im actually going crazy or it actually does make a difference


Sent from the top of a mountain in my h3

 

[2010H3TAlpha]

Does anyone know if the 5.3L ECU has provisions to advance timing based on knock sensing? My '02 Grand Cherokee will adjust timing based on stereo knock sensors and will run higher HP on higher octane but will automatically retard timing if 89 or 87 is used. If the 5.3L does that, it would make sense that you'd feel a little power increase (my Jeep sees about 10% gains per wjjeeps.com). I am used to buying premium and may buy a programmer/tune if there is no auto-detect for the 5.3L just to squeeze a little more power out of the stock motor.

 

[Big2dabank]

If my owner gave me beer/whiskey instead of water I would also be be peppier. Honestly, I don't think it makes a huge difference, but I run premium in mine everyday and I can tell the difference, when I run regular I get also sorts of knocks and pings, of course I have over 160,000 miles and a custom performance tune.

 

[Panzer07]

I been running 91 most of the time in mine since i got it, however there's been a couple of time when i get to the pump they were out of 91 and i have to fill with the regular and i have to say i did noticed the truck decreasing in power, poorer milage and running a little hotter than usual. i talked with some people that know about fuel and what not, and they say it doesn't make a difference, and if you car is rated to run with a lower octane rating, and you use a higher octane rate you'll be just wasting your money because you won't get nothing out of it. but i believe it does makes a difference.

 

[ArtHummer]

Should be absolutely no difference from my experience. Hi octane fuel can handle more pressure before igniting, so it is needed for the engines with higher compression ration... So if engine is designed to run on lower octane fuel that means the compression ration is a bit lowered and it will make no difference if you will use high octane fuel, it will ignite at the same time. For engines with high compression ratio and low octane fuel, the fuel will ignite a bit earlier, this will screw up the timing and will result in engine knocking.
I tested this on my Nissan. It was rated to run on 87 but I always was running it on the 91. I ran several runs on the quarter mile with 1/8 of the fuel tank. When I had probably about 1.5 gallons left (it was on E but the light was not on) I filled up with 5 gallons of 101. After that I ran few more runs and the time was vertically the same.

 

[Chook]

87 is our regular gas here. We also have 91, 95, 98 at most stations (& some sell Shell Racing Fuel @ 100). Having tried them all at some stage in different cars the biggest difference is engine response as the octane level increase helps timing advance without knocking. I found the best use of higher octane fuel was most notable in small capacity, high revving engines (because of timing & knock). As far as the H3 goes it makes some difference (runs smoother & more responsive) but not enough to compensate for the price difference: performance ratio.

 

[Chook]

Tip: I find it good practice to alternate fuel fills 1 in every 4 as different companies have different additives & cleaners in their standard fuel. If you use the same fuel company/fuel type you will get a build up of gunk over time that brand doesn't cater for in its additives/cleaners. By alternating fuel brand/type you get a broad mix of additives/cleaners without having to add a specific fuel cleaner (which also only cleans some aspects).

 

[f5moab]

No, not from a stock calibration.

 

[f5moab]

Should be absolutely no difference from my experience. Hi octane fuel can handle more pressure before igniting, so it is needed for the engines with higher compression ration... So if engine is designed to run on lower octane fuel that means the compression ration is a bit lowered and it will make no difference if you will use high octane fuel, it will ignite at the same time. For engines with high compression ratio and low octane fuel, the fuel will ignite a bit earlier, this will screw up the timing and will result in engine knocking.
I tested this on my Nissan. It was rated to run on 87 but I always was running it on the 91. I ran several runs on the quarter mile with 1/8 of the fuel tank. When I had probably about 1.5 gallons left (it was on E but the light was not on) I filled up with 5 gallons of 101. After that I ran few more runs and the time was vertically the same.

I agree and personally never have believed in seat of the pants dynos.:giggle:

 

[cbetts]

I have felt the change in the seat of my pants, but it was from having a thinner wallet. Never noticed a difference running higher octane in the H3. I have noticed the difference on the Solstice, but that is because lower octane run like crap with the higher compression engine.

 

[Kyle]

it could also be because i have a cold air intake, and exhaust modifications. The thing that ive noticed the most is that it has better throttle response and the power carries through the entire rpm range. when i would run low octane i would notice that when i floor it the car goes and when i get passed 4500 rpm the engine cranks harder it feels like turbo kicks in or something, now thats gone and there is just a smooth power curve with power all the way through the rpm range.

 

[Mr_Rich]

I keep track of my gas mileage closely, and it appears to me that I get at least 10% better gas mileage using 91 octane vs. 89 octane. It begins to make financial sense to use the 91 octane in this case.

 

[ArtHummer]

I've seen a big difference on 350Z. It should use at least 91 but preferably 95 (if you can find it). The guy got a full tank of 87 in it... This thing ran like crap and it felt like engine was about to fall apart and it set all kind of codes. We had to siphon all of the gas out and add some octane buster to bring it back to life

 

[telemike]

I could have had PCMofNC optimize my H3 for 91, but I chose 87 for them to tune the PCM for best performance.

 

[SuperBuickGuy]

Does anyone know if the 5.3L ECU has provisions to advance timing based on knock sensing? My '02 Grand Cherokee will adjust timing based on stereo knock sensors and will run higher HP on higher octane but will automatically retard timing if 89 or 87 is used. If the 5.3L does that, it would make sense that you'd feel a little power increase (my Jeep sees about 10% gains per wjjeeps.com). I am used to buying premium and may buy a programmer/tune if there is no auto-detect for the 5.3L just to squeeze a little more power out of the stock motor.

There isn't a "provision" per se....WITH THAT SAID - the timing, shift points, and amount of fuel injected is changed by what the motor "sees" from its sensors.... thus, you could see better economy and power with higher octane fuel. But here's the kicker - you'll see those benefits if your in a situation where you need the additional knock retardation (higher elevations, towing, etc).

There isn't a "second" tune (I got in a huge argument about this with someone ages ago) in the traditional sense of the word.... YET, if the knock sensor detects a certain number of knocks - it will limit the advance curve; normally that "limit" is reset after 3 key starts and will kick in again if it detects the knocking. So you can either say it has 2 charts or a limiter - both have the same effect of artificially limiting the advance curve.

Which leads me to why your H3 cannot burn E85. Your injectors are too small; the rest of the fuel system is E85 compatible.... of course, that'd also mean a 30% decrease in mpg if you do upsize your injectors. And that point is important - just because you have better knock protection (higher octane rating, such as alcohol has), doesn't mean you'll automatically get better mpg

 

[SuperBuickGuy]

I could have had PCMofNC optimize my H3 for 91, but I chose 87 for them to tune the PCM for best performance.

I do EFI and I read those statements with quite a bit of "yes, but"s bouncing around in my head.

You can optimize the tune by changing the A/F ratio to a bit leaner and see better mpg, or conversely better power by slightly increasing the fuel ratio (we're talking going from 14.1:1 to 14.2:1) - but your mileage will vary because the tune is only as good as the description to the tuner. If you live in the midwest - you could see amazing mpg gains. Where I live, Seattle, with its hills and vastly varying altitude as seen on a barometer - it'd be a waste of money.

 

[backcountryislife]

Unless you raise compression, or change the tune to adjust timing, there is no advantage to running higher octane fuel.

Another thing that is a factor though, is altitude.

A vehicle that runs 91 at sea level, will run better on 85 up here. Running higher octane will decrease ignition temps, burn slightly slower and run a slightly cooler egt than lower, but the vehicle is intended for a particular octane in conjunction with a particular timing curve with the compression it's built at. As you go up in altitude you're changing that equation, you're giving it less dense air, causing less compression, so to get the same "fire" you need to lower the octane.

In motorsports, 2 stroke in particular, you can easily see the difference when someone adds race gas to a motor that doesn't need it... the bottom end falls on it's face. Often the placebo effect outweighs this, and the bump in power they feel as the lazy bottom end falls away is then taken as an increase in power rather than what it is... the motor recovering from too much octane on the bottom. The phenomenon is in large part the reason people THINK they gain power with the higher octane.

You're not "treating your motor better"... not even close. You're making it work harder to produce the same power.

Run the octane the motor is designed for, anything else is not only not helping, and costing you more, the lower temps increase deposits & can create other issues. Octane is a funny thing... we see a higher cost & think it's "better"... that's simply not the case.

Btw, I own three vehicles that run between 96 & 108 MON & mix race fuel all the time... finding the (safe) bottom is a BIG trick to performance. For us a lot of that depends on pull length more than anything else oddly enough. a vehicle that needs 104 can run on 91 for a second, 96 for 5 seconds, 100 for 30... etc.

If anybody wants to go SUPER fast... I've got a barrel of 112 I'd prefer not to store for the summer... I'll give you a good deal