93 Octane In Mojave

[dcmdon]

The 3.6 is tuned to run on regular.

If it was tuned to run on premium, it might make a bit more power and actually get a bit better fuel efficiency , but that is the trade off.

Higher octane (which is a measure of resistance to detonation) allows a higher combustion ratio and more ignition advance, two things that increase engine thermodynamic efficiency. So they help both power and fuel economy. But it's a small bump. Small enough that manufacturers need to weigh it against the increased fuel cost.

When you have a turbocharged engine, things can really change. My wife's car has a 3.0L turbo 6 in it and it officially makes about 10% more horsepower on premium than it does on regular. It matters more for turbos because it allows them to run more boost at mid RPM which can bump power and torque noticeably.

But all modern cars designed to run on premium will run fine on regular. They will just have less power. Prior to the Covid/Biden fuel price insanity, premium was 30 cents more per gallon. So we ran only premium in her car.

Now, locally, premium is 1.20 more than regular. So we're running regular. The car adapts. There is less boost and less power, noticeably so. If I was going to tow with it, I'd run premium, but now that I have the Jeep, we tow with my truck.

So in summary, in a normally aspirated engine designed to run on regular, like our 3.6, there is absolutely ZERO benefit to running premium.

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[ShadowsPapa]

I wonder how many times this will get repeated since it was all said originally here (and elsewhere)

But all modern cars designed to run on premium will run fine on regular.

Not necessarily.........
Toyota says not to do it. Other true experts agree. Short term, a tank if you can't find premium won't be a killer, but not all can adjust down to prevent the ping of detonation if there's enough heat and pressure. Timing being backed off isn't enough. I proved that with a car I had - backed the distributor off until timing was actually ATDC, not BTDC and it still pinged. The compression and heat were a problem.
A high compression engine that can't let off the pressure by adjusting cam timing and valve lift may be damaged. Knock sensors typically cause timing to be backed off. But with high heat and high compression, that won't cut it.
There's a big difference in the language in the book -
"recommended" means they strongly suggest you do, but it's not absolutely necessary as you'll just lose power and performance.
"Required" is a different animal - required means that the compression is high, and combustion pressures high enough it's going to cause damage if you don't (especially long term)
Even modern engines can only do so much.

 

[dcmdon]

I should have said. Most.

But also. ALL turbo engines should be able to run on regular. Because their compression ratio is low and boost can be reduced to zero if necessary.

 

[Jeeperjamie]

I should have said. Most.

But also. ALL turbo engines should be able to run on regular. Because their compression ratio is low and boost can be reduced to zero if necessary.

I don't think that's accurate. My son borrowed our BMW 435I and drove it for about 2 months while he was deciding on what vehicle he was going to buy after his mustang was totalled. He didn't realize the recommended fuel was 93 octane. One day he calls and said the think is idling rough and has poor acceleration. I came over hooked the scanner up and I was showing a misfire in cylinders 2 3 and 5. I asked how he has been driving it, was running 160 on the interstate or something all the time and he said no. Then I asked about the gas and he said he had been running 87 regular in it. Had to be what caused it. The car only had 28,000 miles on it. Twin turbo Straight 6, never had the coil packs and spark plugs go out before 100,000 miles ever and never more than one failure on at time on the 7 BMW's we have on other than this one.

 

[FloridaMan655321]

I've added 20hp by running 93 and added racing stripes. I say go for it!

Jokes (maybe?) aside, I will use higher octane if I have to fill up at a less than reputable gas station. I started doing this after owning European cars as they are really sensitive to our 'Murican gas. I also throw in 91 about every 4-5 fillups.

Oh, and after owning a BMW, I found that Mobile, Chevron, and Marathon seemed to be the best. I have easy access where I live to these, but just if I'm traveling and fill up somewhere else like Shell, that is when I'll put in 93 (I'm sure Shell is fine, just saying).

 

[ShadowsPapa]

I should have said. Most.

But also. ALL turbo engines should be able to run on regular. Because their compression ratio is low and boost can be reduced to zero if necessary.

Yeah, you lose boost - thus power.
So really, if the engine is made for it, why would you reduce it to limp mode?
Go buy an old Honda Prelude that's half rusted to gone and run whatever you like it in.

So what happens if you SC a 3.6 with 11.3:1?

I also throw in 91 about every 4-5 fillups.

Why? I never saw the logic in that since it's only octane - not magic refurbish your engine stuff.
Why would a person think that running high octane "every few fills" would matter or help anything? The octane difference doesn't remove carbon from valves or piston heads, it doesn't seal rings, in fact, it won't do a thing other than - get this - confuse your trim tables.
I discussed this with a tuner a while back (forum member) and since you can't see instant results in a tank, going back and forth does more harm than good on modern engines.
People that say "I put the good stuff in and could feel the results" are imagining the placebo effect. The butt dyno is as real as an honest politician.

If you run top tier gas anyway, there's literally no difference that the engine would seer.
And if you run higher octane of the cheap non TT gas, you are seeing the same crap they sell at the 87 level. Their 91 is the same as their 87 in "quality". It's only the octane level that's different (and even that can vary a bit based on how they achieve that octane level)

87 Octane from a top tier station is better than 91 from a cheap station.

I will use higher octane if I have to fill up at a less than reputable gas station.

Why? It's still gas from a less than reputable station.
Just as dirty.

 

[FloridaMan655321]

I don't think that's accurate.....

Yes, I was going to say, German cars are very finicky with lower octane. Hell, my old BMW didn't like 93 from certain gas stations (as mentioned in my post above).

 

[FloridaMan655321]

Why? It's still gas from a less than reputable station.
Just as dirty.

Well it doesn't happen often, but I'm just hoping to get some decent gas from a non top tier place. I'd much rather get 87 from Chevron or Mobile than 93 from Bob's gas in the middle of nowhere.

 

[Mojave Nunzio]

I use the banks throttle monster instead.

I use Banks also and love it

 

[dcmdon]

Yeah, you lose boost - thus power.
So really, if the engine is made for it, why would you reduce it to limp mode?
Go buy an old Honda Prelude that's half rusted to gone and run whatever you like it in.

So what happens if you SC a 3.6 with 11.3:1?

My wife's car is 95% as quick on regular as it is on premium. And at a price difference of $20 per tank, I'll run it on regular. It's very much not "limp mode". It's still wonderfully torquey and quick.

Back when the difference was 30 cents/gal, I ran premium. But now with the delta in the $1.10 range between premium and regular (In MA), it's not really worth it.

If you supercharge a 3.6, well it's going to be a low boost engine no matter what because the compression is higher than optimal for forced induction. Like you said before, you can only pull so much advance. As you know, it's a balancing act between octane, boost, ignition advance and A:F ratio when it comes making power while avoiding detonation.

Fitted with a big intercooler, a small pulley, and running on ethanol, you could probably make big horsepower. ha. Until a rod lets go. Or you burn a piston.

Back in the bad old days, I had an improvised water/alcohol injection system on my 1982 Saab 900 Turbo that used a windshield washer pump spraying "anti detonation fluid" (ADF) in BEFORE the turbo compressor. This was used in early cars to help atomize the ADF. It also eroded the compressor vanes. But it worked. I rigged it up in combination with a bleeder valve on the waste gate. By bleeding off air from the control hose, I could make the watstegate "see" less than actual boost pressure, which delayed it opening.

The turbo wasn't big enough to make full boost above 5000 rpm, so this all boosted power in the mid RPM ranges.

 

[MarylandMojave]

So what happens if you SC a 3.6 with 11.3:1?

At that point you have to use 93, but it’s worth it. My kit came with a new sticker for the gas cap that says 93 only.

 

[HappyGladiator]

87 vs 91 is 30 cents here so i always run 91. No misfire issues. I beat a Wrangler 392 yesterday,,,LOL.

 

[sharpsicle]

87 vs 91 is 30 cents here so i always run 91. No misfire issues. I beat a Wrangler 392 yesterday,,,LOL.

 

[JW Jeep]

Heck out here in Colorado I run 85 octane regular. I’ve ran it in 2 3.6s and even a couple v8s. However we are in higher elevation then most which makes a world of difference !!

 

[Chestnut]

Any one get knock below 2,000 rpm with their gladiators? I run 89 in mine because i get a knock below 2,000. I got sick of hearing it and feeling the computer pull timing.

But also. ALL turbo engines should be able to run on regular. Because their compression ratio is low and boost can be reduced to zero if necessary.

My WRX states multiple places 91 minimum, I was warned at purchase running lower would void any engine warranty claims. Forester XT is 89 minimum. 3 port controllers have limits to how low they can pull turbo pressures. I'm about 99% sure they can't go lower than what ever the spring pressure is set to in the waste gate.
Additionally in order for the controller to pull timing and pressure you have to experience knock and there is a lag time before that happens. We're talking miliseconds but that's still enough time for a couple ignitions. Every time it knocks on lower octane fuel there is still the possibility of some damage happening.

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