It’s been suggested that in some Saturns (both S and Ion) that the car runs better on premium unleaded (91-93), and I wish to properly test this theory to end the debate once and for all...

the theory anyway, is that due to more knock resistance in the fuel the PCM will add more timing and you’ll get more power and maybe better mileage depending on how you drive. Being our resident Ion guy and the only avid hyper miler here I figure I’m qualified to test...

the plan:

im gonna start filling the car with 91-93 octane fuel and after a couple tanks start collecting data... the reason to delay collecting data is for the entire tank of fuel to equalize out to 91-93 octane, and for the PCM to recognize that it’s getting different fuel (IF it even can)... then I’ll measure timing advance at cruise and while WOT from idle to redline and prob get a couple 20-50 pulls recorded to see what time...

then ill I’ll resume filling it with 87 (like normal) and after a couple tanks take all the measurements again and see what I’ve got, and all along the way I’ll note mileage averages and driving feel and whatever else I notice...

my hypothesis:

i dont think that premium fuel fuel will do jack diddly s**t in a car that isn’t built for it, which no stock-ish Saturn is...
running boost? Running elevated static compression ratios? Had the car reprogrammed for 93?

if you answered “NO” to these then chances are you’re wasting your cash running premium fuel (other than the additive package that usually comes with premium), or are you? Well find out soon...

 

Assuming this thread is aimed at me, get an elm327 and torque pro app. You'll see exactly what I was talking about. Or use a wideband/interceptor.

Now, I dont know long term affect of my stock pump or injector seals on e85. But I'm swapping all that out next week.

And the car has not logged any knock. Ive also got a nylon washer between my knock sensor and the block. Helped a hair with more timing.

 

Not aimed so much just at you, but also some guys on other sites (and in person) who claim the same for the S cars... I’m legitimately curious (but still skeptical) to see if there are any true benefits aside from the additives that are usually found in premium unleaded...

Sorry
as to data acquisition, I have a hard mounted UltraGauge which gives the same data as Torque (though my version doesn’t log acceleration tests), so I should be able to grab data such as timing advance and engine load and the gauge will extrapolate the data such as instant and average mpg for shorter trips...


im guessing the nylon washer is to de-sensitize the knock sensor? Maybe the issue is that with the factory tune it pulls timing very conservatively (slightest hint of knock) and thus gains can be had?


I figure that if the Redlines can run E85 with no long term issues with fuel pumps and seals, we can too, I don’t see any reason for GM to spec different parts in such a similar car, though I’m a little worried about testing high ethanol concentrations in my car... I did run E15 whenever I ran across it and it was fine though...


After filling with 93 for the first time (ouch, poor wallet lol), I’ve not noticed much yet, though to be fair I wasn’t expecting anything until possibly tank 3 or 4...

 

I have run premium in my 06 Navigator since new. It now has 190k miles on it, I did put one tank of mid grade in it in Denver many years ago on a cross country trip because of the altitude and have never heard the end of it! The car has a three valve 5.4L v-8 rated at 300 hp and a six speed ZF automatic. They went to an 87 octane tune for 2007 and newer, I think they rated the engines the same on hp. Good luck with your tests maybe the advance curve will be a little different and give some mileage boost.

 

It could be... the only way I see it making a big difference in mileage is if the PCM is pulling timing at WOT between 1500 and 2500 RPM(window in which I pulse and glide)... if the fuel change gives me a few degrees there then the engine is working more efficiently during each pulse, which would make it take less time which would help the pulse/glide length ratio...

 

Redlines have a higher flowing pump than we have. Not by much, but they are different.

I remember reading something on e85 effects on the pump, just don't remember what. Some companies offer an aem ethanol safe pump. I'm not to concerned about that though.

Just unplugging the iat sensor pulls up to 5° of timing.

I'm just aiming for a somewhat reliable route to get the turbo dialed in while I search for a good le5 bottom end. By that point though, ill also be going full standalone.

I found the low output saab 9-3 uses a 27.4# injectors. I'm planning on toying with those and an aem450 pump before I start with the fmu and afpr. Have a much better chance with those vs the lsj injectors. A return style will help out quite a bit also.

I modify cars. Mileage is never a concern to me. Although I do want a 3rd gen sw2 to daily for mad lowz and dad life. Ha

 

While I’ve not seen the actual fuel pump in either my Ion Redline nor my sedan, I figure it’s plausible that the LSJ cars have a better fuel pump, though nobody mentions the pump upgrade being a necessity until you get near 500 wheel...

I modify anything I can get my hands on lol, but this is my daily and mileage is the first priority. If I can gain a little power without sacrificing reliability or mileage I go for it...

So far, I’ve pumped approximately 20 gallons of 93 into the car (I do ridesharing so it goes fast when I’m working) and haven’t noticed much if any effect. It may run a little smoother at lower RPM, and possibly pull a little harder as it winds up, but not a huge difference...

i wish I had had the foresight to have grabbed the appropriate data while I was still on 87, before the switch. That would make the fuel change a true A-B-A test instead of just B-A...

My thought is that perhaps the PCM was de-tuning the engine to avoid ping on 87 octane, based on a few random occurrences. Switching to 93 may eliminate what knock there was and restore full timing, yielding a mild gain in power, but I fear the PCM will be slower to de-tune once I switch back than it was to add the timing back that had been previously lost... in other words, I’m fearing the data won’t be 100% representative of what was actually going on...

still excited to actually have the data though...

 

So I’m coming up on having gone 500mi on 93 octane, think that sounds like enough for the PCM to have learned the difference?

im anxious to begin instrumented testing lol

 

So I’ve finally begun testing on this, after having gone 540mi on 93 octane...

at cruising conditions I have 24.5 degrees of advance at 1000 RPM (27mph) and 31.5 degrees at 1500 RPM (40mph), and 35.5 to 36 degrees at 2000 RPM (54mph), and I’ve measured the timing curve as best as I could, at full throttle, from 1000 to 6000 RPM



i also made a point to graph it (roughly) to visualize the timing curve... next I’ll try and get a couple times acceleration runs in 2nd gear... I figure a 20-50 pull should eliminate the variables of launching and any gear changes...

then the the car will resume its normal diet of cheap 87 octane fuel lol

 

Nice.

How many samples does each point on the plot represent?