Gas. 87, 91, 93 Octane?

[Beege]

Picked up a 3.3 rwd today. Dealership is insisting it runs on 87. I'm used to 91 coming from a turbo 4cyl.

If you're using 91, please explain why

 

[Never thought]

Picked up a 3.3 rwd today. Dealership is insisting it runs on 87. I'm used to 91 coming from a turbo 4cyl.

If you're using 91, please explain why

Premium is recommended. But the manual says to run 87 or higher. Haven’t tried 87

 

[PA_RN]

Actually running 93 octane as thats what premium grade is in my area. From what I understand higher compression engines like most turbocharged ones traditionally run better/more efficiently on higher octane. It can run fine on 87 but the engines timing is changed to prevent engine knocking. I know there's a few new turbocharged engines designed specifically for 87 octane but I don't believe the Stinger is one of them. So yes, you can run 87 octane and be okay, just with a performance drop. Don't think anyone has done a dyno to compare yet though so I couldn't tell you by how much. It's more important to get top tier gas than anything else to help prevent build-up Licensed Brands | Top Tier Gas. Also to maximize engine performance and longevity keep and eye out for an oil catch can kit when one is released.

 

[DaJackson]

Dealership is insisting it runs on 87.

It will run on 81 too (if thats even a thing) the difference is how well it will run and the performance of the engine. You should be running 91 or 93, whichever is in your area. The cost difference between that and 87 isn't worth it, a couple bucks a tank at best.

 

[Never thought]

It will run on 81 too (if thats even a thing) the difference is how well it will run and the performance of the engine. You should be running 91 or 93, whichever is in your area. The cost difference between that and 87 isn't worth it, a couple bucks a tank at best.

Not true. The manual says anything below 87 octane can cause serious damage to the car.

 

[EchoesMyron]

The ECM will retard the timing if detonation is sensed by running a lower octane fuel than required. This will cause a pretty big drop off in performance. Like others have mentioned, it can compensate for 87 with reduced performance but lower than that it may not be able to compensate for and it will cause detonation which can cause serious engine damage.

I live at 5000' of altitude so the highest we have available here is 91 and that's what I run. Octane requirements drop slightly with increases in altitude because...well, it would take a lot to explain it but just take my word for it.

The way I look at it is that I spent $50k on a car, I'm not going to cheap out on the fuel. You don't get any real benefit to running a higher octane than recommended but there can be serious consequences to running lower.

Also interesting to note is that my '13 Optima SXL Turbo only required 87. It was either running less boost or a lower compression ratio than the Stinger. (there are other possible factors as well).

 

[mldavis2]

I don't have my Stinger yet (ordered - none with my specs anywhere) but I do remember my '00 Pontiac GrandPrix GTP (supercharged) had a 8.5:1 compression ratio. It was tuned to run on regular octane fuel and worked very nicely. 3.8L V6 and 30mpg highway, but the boost was not all that much -- until you got into the mountains. Loved blowing past struggling econoboxes climbing those twisting mountain roads up Big Thompson canyon headed for Estes Park. My new Stinger will get a chance this summer to duplicate that.

 

[Beege]

Someone please correct me if I'm wrong but doesn't the lower the octane mean it will combust earlier?

 

[EchoesMyron]

Someone please correct me if I'm wrong but doesn't the lower the octane mean it will combust earlier?

Yes, pretty much.

Octane rating is essentially a measure of the fuel's resistance to self-combustion. When the air/fuel mixture is compressed during the compression stroke of the engine, it heats up. If it gets too hot, the fuel can ignite by itself before the spark occurs which would try to push the piston down while it's still coming up. This is called detonation, pre-ignition, or spark knock. Obviously trying to force the piston down while coming up can cause damage.

Higher octane ratings mean that the fuel can reach a higher temperature in the engine during compression before it's in danger of detonating. An engine with a higher compression ratio will squeeze the mixture more on the compression stroke therefore increasing its temperature more which will increase the octane requirements of the engine. There are also other factors involved such as ignition timing (when the spark occurs)

Forced induction engines (turbo and supercharged) typically use lower overall compression ratios because the air is being compressed to a degree before it enters the engine and then compressed again inside the engine. The resulting temperature increase can be pretty high so a lower compression ratio is used to compensate and decrease the possibility of detonation. Intercooler systems also help lower intake charge temperature.

Modern engine management systems use knock sensors to identify whether the engine is experiencing detonation and then will retard ignition timing to stop the detonation. Retarding the timing results in a measurable power loss. This is why if an octane of 91 or 93 is recommended, you could still run a lower number like 87 with reduced power output. The system can only compensate so much which is why going very low, say 85, could cause detonation that the system can't adjust out and engine damage could result.

 

[EchoesMyron]

Loved blowing past struggling econoboxes climbing those twisting mountain roads up Big Thompson canyon headed for Estes Park. My new Stinger will get a chance this summer to duplicate that.

@mldavis2 That's in my backyard! Big Thompson canyon is a fun drive although it is closed right now because there was a huge flood that wiped out a lot of the road a few years ago. It was open with some temporary repairs after the flood but they are currently working on permanent repairs. I don't know whether it will be open by this summer or not. There is an alternate route available (highway 36) but it's not as fun. You cold always take Lyons canyon up and then take a jog south to Estes. That one's a little more twisty.

If 34 is open and you're up for an adventure, try turning off at Drake and taking the back way up. It's a lot tighter than 34...slower speeds but higher G's. In addition, the Peak to Peak highway between Estes Park and Nederland is a blast. The drive through Rocky Mountain National Park is also amazing but it's usually clogged with bumper to bumper traffic. I once had a clean drive all the way through the park at around 2am...I don't think I saw one other car. It was a lot of fun.

 

[mldavis2]

I've been going to Estes Park for decades and we hike all over that part of the hills and drive the roads all the time. Love it. Good to see someone else appreciates the value of turbocharging in thin air.

 

[Powerpuff Mookie]

98 for me

 

[corradoMR2]

Modern engine management systems use knock sensors to identify whether the engine is experiencing detonation and then will retard ignition timing to stop the detonation. Retarding the timing results in a measurable power loss. This is why if an octane of 91 or 93 is recommended, you could still run a lower number like 87 with reduced power output. The system can only compensate so much which is why going very low, say 85, could cause detonation that the system can't adjust out and engine damage could result.

Yep, I filled my last tank with 87 just to try it out. I noticed the difference in responsiveness and overall thrust. Not putting 87 anymore.

 

[Never thought]

Yep, I filled my last tank with 87 just to try it out. I noticed the difference in responsiveness and overall thrust. Not putting 87 anymore.

Good to know. Thx for sharing!

 

[Dick Dastardly]

98 for me

I think we need to avoid confusion. In Europe 98 = 93 in USA
In UK we have Shell and Tesco Momentum that offer 99 RON - which I always use - I have convinced myself it is good for at least 20bhp!

 

[davebo]

The cost difference between that and 87 isn't worth it, a couple bucks a tank at best.

Man you're lucky. Around me the difference between regular and premium can get up to 60 cents a gallon so you're looking around 9 bucks for a fill-up. I'll definitely try out 87 once I've got a Stinger, then likely end up switching back and forth based on if I'm doing any boring highway road trips or if the weather will be bad that week.

 

[Plainolmoo]

Yep, I filled my last tank with 87 just to try it out. I noticed the difference in responsiveness and overall thrust. Not putting 87 anymore.

And the Guinea Pig Award goes to....

 

[FireArmTom]

What about octane boosters? Any benefit or just a waste?

 

[EchoesMyron]

What about octane boosters? Any benefit or just a waste?

In theory, they would boost the octane to whatever number they claim. In practice...who knows. They are not really 'octane in a can' as octane is a type of hydrocarbon molecule with 8 carbon atoms (C8H18). Instead they use other chemicals that would increase the fuel's resistance to self combustion in the same way that octane would. Think of it as more of an 'octane equivalent' than anything else.

I personally have never used them and from what I've seen/ read, when tested some deliver the claimed numbers and some don't. I just buy the actual gasoline recommended for my car rather than take the risk.

If you were traveling somewhere where high quality, high octane fuel weren't available then I could see using an octane booster as a temporary solution but I wouldn't rely on it as a replacement for the correct octane of fuel.

 

[mldavis2]

As a chemist and former service manager, I agree with @EchoesMyron. The old tetraethyl lead was also an octane booster but any time you introduce something into fuel, other than fuel, to retard combustion, you risk deposit buildup which might be difficult to remove even with the products like Chevron designed to do so. Injector cleaners are formulated for fuel buildup, not additive buildup. I would avoid them.