Rise from the dead!

It's probably been covered in this thread already but just in case, recommended octane is simply what the vehicle is designed to run on with minimal correction. You can run higher, you can run lower, but the ECU will have to trim accordingly on this engine (not all high octane engines CAN run low octane fuel without damage). The VQ practically runs off the knock sensor anyways so it just pulls a few extra degrees of timing when running lower octane fuel. You can test this yourself by logging OBD2 data for timing advance and comparing tanks of fuel at WOT. I see a 5-7 degree loss in timing running 87 vs running 91, same ambient temperature/pressure.

Engine under light load will see practically zero difference, moderate load there is only a minimal difference.

 

Wow 5-7 degrees? I mean I knew it pulled timing, but it's cool that you actually data logged to find out how much. That's quite a difference.

 

Yeah I was a little shocked too, granted this was a 100% STOCK motor (revup) with zero mods at the time and I'm waiting until this spring to try it again with intake/exhaust mods.

 

We get 93 octane here. Run a half bottle of octane booster per tank when I'm in Arizona for city driving, don't worry about it if just freeway.

 

I never use premium

Telcoman

 

Honestly I don't think there's any standardized method the gas manufacturers use to define what octane rating the fuel actually is. I've legitimately had this motor run better on 87 fuel from a pump in Portland (dumb fuel attendant didn't listen when I asked for premium... I hate oregon and want to pump my own fuel gdi!!) than a 92 pump I went to in Seattle.

In my town I stick to a single fuel station and use their premium since I get +2mpg with their stuff for some reason?

 

Yeah, it's definitely not a quality issue. I'd trust shell or Chevron 87 over mom & pop 91. Easiest way to kind of explain what's happening is to put a 0 on the end of every grade and that's about the temp that it spontaneously combusts. So, 87 will self detonate at 870 degrees and 91 self detonates at 910 degrees. So, as long as your knock sensor is working, the grade will not matter and will be unnoticeable when we're talking about a 300hp car. Of course MY reason for using it is that I've spent a lot of money on mods and I wanna squeeze everything out of it I can, and I'm not gonna try to save $2/fill up after all that. Haha

Back to not feeling it, like I said, losing 5hp is gonna be unnoticeable at 300hp, but I know for a fact that 91 over 87 increases power, cuz in my insight I can definitely feel a difference cuz it's only 63hp. Losing 2-3hp when you only have 63 is noticable.

 

Pro tip: Top tier gas has enhanced detergent levels in all grades of gas. So as long as you purchase gas from a top tier station, even if you go with regular you get a better detergent package.

 

Correct. The grade does not denote the quality.

In that note, another pro-tip: I used to have that problem where my gas gauge would read funny and I couldn't "fill" it past the 3/4 mark (even tho it was full), and I added this royal purple octane booster/fuel system cleaner to a full tank of Chevron 91 and I haven't had the problem since. Gauge goes clear to the top every time now and gas gauge reads accurately ever since. This was about a year and a half ago, and still works great

That stuff was like $15 for a 10oz bottle, but worth every penny

 

I've stuck with Sea Foam for years, used a bottle today in fact, but I'm open to new products. Might give RP a shot in another 5k miles or so.

 

I found that regularly filling my car, especially the first road trip I took, fixed the partial fill problem. I think perhaps a lot of G35s developed this problem when gas shot up to $4 a gallon and people weren't filling their tanks and the sending floats ended up with a sticking point because of it.

 

I've gotta go to O'Reilly in the near future for a few things, I'll take a pic of the specific one I used (there's no long neck on the bottle, so you can't easily just stick it in your tank - I guess they're serious about the "off-road use only" designation). Of course if you're having success with sea-foam, then it may not be worth it, unless your gauge is still finicky. Either way, I'll take a pic. I believe it says it's good for 30 octane points too (3 grade numbers)