I'm wondering what octane you people are running in your LS3??? Premium is recommended but not required according to GM. Have any of you tried both and what difference did you find?

Thanks....

 

I've used regular, premium and 10% ethanol blend and have not noticed any difference. The care runs fine on everything,

 

Premium only for me please, gas....is not gas, contrary to somes beliefs.

 

The car will run OK on regular, but power will be down somewhat. The computer retards and advances spark timing as needed to accommodate different octane ratings. Low octane = retarded spark = less power = lower fuel mileage. If you drive like a sane person, you probably not notice any difference in performance. Personally, I would use what the factory recommends and get the performance I paid for.

 

Shell V-Power only for my LS3!

 

Thanks for the responses guys.
I know that the ECM will alter timing to account for octane but is the difference in performance really noticeable on the street? I'm sure it would show up on the drag strip.
Also how much diiference in mileage do you get with premium?

 

There are two timing tables in the V8 ECU. The problem is if you START with 87 or 89, and then try the 91/93 octane you will see NO benefit. This is not because the gas isn't different. It is because the ECU does NOT switch back to the high octane tables on its own.

However, if you start at 91 octane and then run 87, you will see a HUGE decrease in the performance. The other issue is what your dealer ran in your tank. If they filled it with 87, and you've been runnign nothing but 91/93, you have NEVER gotten the full benefit.

Here is a simple process to reset the timing tables. This is not my process, but was developed by multiple people with both LS3 and L99 engines. Thsi applies to ALL V8 engines.

1. Make sure the engine and ignition are turned off.
2. Locate Fuse Panel in front of the passenger's side front strut tower and pull the cover.
3. Remove #5 and #20 (15A fuses).
4. Let the car sit for at least several hours (overnight is preferable)
5. Install #5 and #20 (15A) fuses
6. Install Fuse Panel cover
7. Restart vehicle and enjoy

Note: Do not unplug the battery. It has no effect if the fuses remain in the fusebox.
After you try this, post your results! I'm 100% positive you will be thrilled with the change.

(As a side note, the LLT V6 has a single timing table that uses a knock sensor to adjust for differing octane. There is no benefit to the fuse pull for the V6. There has been some inconsistent results doing this pull after MODS.)

 

Thanks for the response.Who knows what the factory and then the dealer puts in these cars. I can't try your process yet as my car hasn't come in yet. In fact I'm having trouble getting a build date from the dealer. I ordered the car 3 weeks ago and they tell me no build date yet. I don't believe it as it should be scheduled within a couple of days of order receipt. I suspect a lazy salesman.

Anyway, if anyone try's the process to reset the ECU I'd appreciate knowing the outcome.

 

Nice input on the reset

 

Glad to help. I'm still surprised GM didn't put some reset control in the ECU. I wonder how many people total are driving an SS around and have never felt the full power of the car.

As a V6 driver, I don't have anything like that. Ours is even weirder, but simpler. The ECU uses a knock sensor. Basically the engine tries to reach a maximum of 50* plus or minus. Timing is increased constantly until the knock sensor kicks in (long before our wimpy hearing would notice) and retards the timing. So, 87 octane runs just fine, but you're looking at timing advance in the teens. 93 (highest i've ever tried) sees 50*, but not constantly even at a steady RPM on the highway.

The first time I ever tried this, with a datalog running, my timing advance looked like a seismograph, ups and downs all over. Then I ran it almost empty, filled up with 91, ran it low, filled again with 91 and datalogged again. much smoother timing ramps, but would ramp up to 50*, drop to 40+, ramp to 50, drop to 40+, etc. Then I tried it with 93. same timing, but only dropped to mid 40s. So any gas will work in the V6, but just like the big brother, Premium is the best to run.