To 93 or not to 93

[SRG963]

That is the question.

I don't have a tune yet but I'm still running 93 octane.

Owner’s manual says to increase to 89 if you hear knock.

Running a performance V8 on regular just doesn't make sense to me, never has and never will.

What is everyone else running?

[Joe Weinstein]

Unless a motor is specifically tuned for 93 or 89,
it produces all the power it will, from 87 octane.
There is no difference in the quality, cleaners,
additives etc. between octane ratings. Before
we had fancy ECUs controlling fuel injection,
timing, and detecting knock, the only safe way
to get more power was upping compression and
timing, and hoping.
So, don't worry, be happy. Or get a 93-octane
tune, and gain 40 or so hp.
Joe

[-Ray-]

I used 87 up until the tank before my tune.
Then I got a 93 tune of course.

[G8Smitty]

I've run 92 in mine since the day that I bought it. I read where everyone stated that I was wasting my money so I switched to 87 for one tank. I noticed a fairly significant degradation in performance about 1/4 way through that tank of gas. I've run 92 ever since. I cannot get 93 where I live and have no tune currently.

[grt08g8]

theoretically speaking, this is correct but try it yourself. I get 2 to 3 more mpg from 93, and I can also tell a difference in throttle response.
Unless a motor is specifically tuned for 93 or 89,
it produces all the power it will, from 87 octane.
There is no difference in the quality, cleaners,
additives etc. between octane ratings. Before
we had fancy ECUs controlling fuel injection,
timing, and detecting knock, the only safe way
to get more power was upping compression and
timing, and hoping.
So, don't worry, be happy. Or get a 93-octane
tune, and gain 40 or so hp.
Joe

[Joe Weinstein]

You may be right.

However, I *know* my car handles better and is smoother,
just after I've changed the oil and checked all my tire pressures,
even if I didn't have to adjust them. ;)

I'm saying that just to be extra sure of a feeling or mileage difference,
I'd want to run an experiment where I didn't know which sort of gas
was in the car for a few tanks, and to write down what I thought was
in it, and if I was right after the few random tanks of both sorts, I'd
believe myself.

Joe

[wreckwriter]

89 until tune, then 93. Anything else is just porting your wallet.

[caretaker]

Got almost 10K on mine and have only used 87 so far
with no problems. No mods yet.

[SRG963]

Copied from another gas related thread I started, Thanks for the info Norm


Your timing also gets pulled more often with 87 because of the "Knock retard" function of the PCM. I noticed this when logging with HPT VCM Scanner. The Knock retard barely ever engages on 93, but it did frequently with 87.

Any thoughts on this?

[JoeSyko]

All the pumps I've seen out here in California have 87, 89 & 91 but no 93 octane. What's with that? I've seen 93 octane at specialty stations where racing fuel is sold but not any of the regulars like Chevron, Texaco, Shell etc...

Also, you all are saying to get it tuned to take advantage of 93 octane. Is there a 91 tune as well?

[wreckwriter]

All the pumps I've seen out here in California have 87, 89 & 91 but no 93 octane. What's with that? I've seen 93 octane at specialty stations where racing fuel is sold but not any of the regulars like Chevron, Texaco, Shell etc...

Also, you all are saying to get it tuned to take advantage of 93 octane. Is there a 91 tune as well?

Yes, there is a 91 tune available.

[G8GTlawride]

Got almost 10K on mine and have only used 87 so far
with no problems. No mods yet.

Try 93 and post your findings (other than the expense).

[Rusty]

Since I've had mine for only a month and live in FL, I'm curious if any FL G8 drivers have seen a noticeable difference with the <10% ethanol gas entering most pumps by now...

2 months or so ago, there were only a few stations in my town that sported this boondoggle... now I can't go anywhere without some sign declaring I'm dropping creamed corn into my tank... Has MPG or performance degraded for anyone out there since the switch?

[-Ray-]

Rusty, we get ethanol added to our gas in the winter. It does lower my mileage. I'm not driving my G8 this winter so it shouldn't be a problem for me. Which reminds me, I need to look for another vehicle.

[caretaker]

Try 93 and post your findings (other than the expense).

O.K. I took the challenge. Since that post I have put
about 1600 miles on the GT using 93 octane.

I have gone through 4 tanks (60+ gals.) of 93 octane
with the following results.
Started with less than a quarter tank of 87.

Very first thing I noticed with 93 was a rough idle.
I know a lot of you guys have said you experience this,
but with 87 I had a very smooth idle.

Next I started to feel a vibration in the accelerator pedal and
even the steering wheel at lower engine revs. I seem to remember
some of you saying that you had felt this also, and it was the DOD
kicking in. I never had this with 87 octane.

As far as mileage - on the highway about a 1.5 - 2.5 drop in mileage
over the same roads, same conditions, same driving technique.
On 87 I would get 26-27 M.P.G. highway and got about 24.5 - 25.5 with 93.
I don't do much real city driving but I did get my worst ever mileage
16.3 with the 93 octane.

So I went back to 87 last week and things are back the way they were.
Better mileage, smooth idle, no vibration.

So for now I am sticking with 87 octane. Without a tune or other mods
93 seems a waste of money. IMHO.

But in the spring I intend to start modding. I have been letting you guys
be the testers, and taking notes. I intend to get the CT Tiggeress to
400+ HP all at once. For sure then she will need 93.

Yep, that's right, my IOM GT is a female - sexy, beautiful, yet dangerous
and not to be ignored.

BTW - G8GTlawride - you owe me $19.52 :eek:
I won't hold my breath waiting. :bleh:

[-Ray-]

AFM will not engage at idle. It just doesn't happen. Putting 93 in a car tuned for 87 only nets you less spark knock. Adding 93 will not increase the timing past the stock calibrations.

[caretaker]

AFM will not engage at idle. It just doesn't happen. Putting 93 in a car tuned for 87 only nets you less spark knock. Adding 93 will not increase the timing past the stock calibrations.

So Ray, a don't want to differ but
I just went out and started her up in
engineering mode and the DIC says AFM is All Active
at idle in both park and drive. ???

[wreckwriter]

"All active" means all cylinders are active, AFM is not on.

[caretaker]

"All active" means all cylinders are active, AFM is not on.


My mistake. Thanks.

[g8_795]

"All active" means all cylinders are active, AFM is not on.

wreck is correct once again.

[Art708]

You may be right.

However, I *know* my car handles better and is smoother,
just after I've changed the oil and checked all my tire pressures,
even if I didn't have to adjust them. ;)

I'm saying that just to be extra sure of a feeling or mileage difference,
I'd want to run an experiment where I didn't know which sort of gas
was in the car for a few tanks, and to write down what I thought was
in it, and if I was right after the few random tanks of both sorts, I'd
believe myself.
Joe

Hell, mine runs better after I wash it.

[-Ray-]

wreck is correct once again.

Yep, wreck is the correct one. LOL

[wreckwriter]

Yep, wreck is the correct one. LOL

not very often lately.

[G8GTlawride]

O.K. I took the challenge. Since that post I have put
about 1600 miles on the GT using 93 octane.

I have gone through 4 tanks (60+ gals.) of 93 octane
with the following results.
Started with less than a quarter tank of 87.

Very first thing I noticed with 93 was a rough idle.
I know a lot of you guys have said you experience this,
but with 87 I had a very smooth idle.

Next I started to feel a vibration in the accelerator pedal and
even the steering wheel at lower engine revs. I seem to remember
some of you saying that you had felt this also, and it was the DOD
kicking in. I never had this with 87 octane.

As far as mileage - on the highway about a 1.5 - 2.5 drop in mileage
over the same roads, same conditions, same driving technique.
On 87 I would get 26-27 M.P.G. highway and got about 24.5 - 25.5 with 93.
I don't do much real city driving but I did get my worst ever mileage
16.3 with the 93 octane.

So I went back to 87 last week and things are back the way they were.
Better mileage, smooth idle, no vibration.

So for now I am sticking with 87 octane. Without a tune or other mods
93 seems a waste of money. IMHO.

But in the spring I intend to start modding. I have been letting you guys
be the testers, and taking notes. I intend to get the CT Tiggeress to
400+ HP all at once. For sure then she will need 93.

Yep, that's right, my IOM GT is a female - sexy, beautiful, yet dangerous
and not to be ignored.

BTW - G8GTlawride - you owe me $19.52 :eek:
I won't hold my breath waiting. :bleh:

Where else could you get such good advice for under twenty bucks?

[caretaker]

Where else could you get such good advice for under twenty bucks?

LMAO!!

Right on! Consider it paid in full. :cheers:

Even if Ray did jump my ass for something I didn't even say in the post,
but did question after he corrected it and was finally put to rest by Wreck.

If you can follow that last sentence, please explain it to me. :blink:

[-Ray-]

You need to point out where I jumped your ass. Because I'm missing it.

[Chewy]

Also, you all are saying to get it tuned to take advantage of 93 octane. Is there a 91 tune as well?

Yes the difference is some 8bhp or so I've heard...

[caretaker]

AFM will not engage at idle. It just doesn't happen. Putting 93 in a car tuned for 87 only nets you less spark knock. Adding 93 will not increase the timing past the stock calibrations.

Maybe you didn't jump my ass (kicked it softly maybe) but I didn't say anything about AFM at idle.
I was talking about AFM/DOD at lower rev's while driving.
With 87 I could not feel DOD going off/on, but I felt some kind
of vibration with 93. I had read in other posts about some guys
feeling this vibe and saying they thought it was from DOD.

Basically my test was just to see if there was any improvement
by using 93 without any kind of tune, and to me at appeared to
be a waste of money.

That I hope we agree on. Feel free to correct my ignorance whenever
it shows. I am BCE (before car electronics).
Give me a simple engine with a carburetor or two and
I'll find all sorts of H.P.
:cheers:

[-Ray-]

I certainly didn't mean too. I am too direct I guess. Posting even more so. I agree with good gas and cool air, 93 is a waste of money with a car tuned for 87. In warmer air, I can see where it would help you not lose performance.

[caretaker]

I certainly didn't mean too. I am too direct I guess. Posting even more so. I agree with good gas and cool air, 93 is a waste of money with a car tuned for 87. In warmer air, I can see where it would help you not lose performance.

Ray
Direct is GOOD.

Keep it up.

[SRG963]

Basically my test was just to see if there was any improvement
by using 93 without any kind of tune, and to me at appeared to
be a waste of money.

I had a very similar test. We ran out of gas and I was forced to use regular (87). My MPG average went down 1.5 due to the switch in octane.

My rough idle/throttle lag/hesitation was removed with the update I got 8/16/08 and now with the intake, she growls like a beast. The intake added a 2-3 MPG average also.

[SRG963]

So why does GM recommend Premium on the GXP and not the GT? Does the extra 55 HP make that much difference?
http://media.gm.com/servlet/GatewayServlet?target=http://image.emerald.gm.com/gmnews/viewmonthlyreleasedetail.do?domain=999&docid=45388