87 octane fuel requirement

[Snakebitten]

I can assure you that I won't be holding you up in the fast lane, nor am I there to raise your property values. Just a tourist leaving rent money for the native landlords and restaurants. ?

By the way, 65 years in Texas. So welcoming new neighbors from elsewhere has been a lifelong necessity. Far beyond what any of the other 49 states have encountered. Not even close. And I'm not complaining! Nor can I blame them.

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[HammaMan]

I can assure you that I won't be holding you up in the fast lane, nor am I there to raise your property values. Just a tourist leaving rent money for the native landlords and restaurants. ?

By the way, 65 years in Texas. So welcoming new neighbors from elsewhere has been a lifelong necessity. Far beyond what any of the other 49 states have encountered. Not even close. And I'm not complaining! Nor can I blame them.

Not just TX seeing influxes, though the border could use a DMZ with automated turrets IMO. The branch covidians have driven many people south and east of their previous locations.

Based on current events I think we should given both israel and ukraine a 1' wide stretch of the US southern border so it could get some attention.

 

[Deleted member 17130]

This thread has definitely taken some turns and so my apologies if this has been addressed already but…

I live in CO where 85 octane (NOT E85 that is 85% ethanol and can handle higher compression but do not use unless vehicle designed for it) is “regular” - I have been advised by people who know more about these things not to use this in a turbocharged engine that requires higher.

85 as standard is more of a relic from most cars being naturally aspirated. Basically octane is a gauge of how stable a fuel is before it ignites under compression, which is what causes knock. Because of the lower air pressure at altitude in a naturally aspirated engine the engine can handle more compression at any given octane without causing knock. Basically the lower density of oxygen in the air means there is less to combust which allows for the lower octane.

Enter turbochargers: since turbos create extra power and efficiency by compressing the air entering the engine (giving it more oxygen so it naturally runs richer) this compensates for that difference already. Basically the turbo is already compensating for the lower oxygen density by compressing the air prior to putting it into the engine- so you don’t have that natural reduction that allows for 85 octane.

Personally I always put 91 (premium) in because in Denver 91 at Costco costs less than 87 (mid grade) at most other gas stations. I also always used it in my GTI before this. My wife has a CR-V with a 1 liter turbo that doesn’t have any min required so we put 85 in that and it runs fine but it’s a 1.5l 190 hp engine - vs my 3.5L 400 hp.

My understanding is engines generally can retard the timing enough to compensate for the knock so it might not matter. The fact that Ford is so explicit about their 87 requirement makes me think that ends up out of spec for how they engineer it and I’d rather just play it safe.

I’m sure someone who knows a lot more about engines will fix the things I said inaccurately here (I’m an economist not an engineer) but hopefully I got the general sentiment correct.

Either way I keep to 87+ personally though I would venture to guess there are 100s of thousands of vehicles on the road doing just fine running 85 with this requirement so you are probably safe. As someone mentioned earlier if you aren’t pushing it to its limits (flooring it or towing) I’m not sure you are bumping against those compression and timing issues anyway but again I don’t know the technical details.

I also take advantage of those extra ponies and torque when I have to pass people regularly on 285 which is a 65mph two lane road where Texas and Florida license plates are regularly driving 50 with a trailer. I need to get up to 90 to 100 quick to pass them even if I cruise at 70… those 400 ponies and 500 ft pound torque will still pull quite nice at speed or trying to catch a passing lane going up hill. Just gotta do something about the 4Runner from California trying to get by the trailers in those zones that take about 15 seconds to get from 50 to 60…

Utah was the same way, I had a 3.3 TT Stinger and it called for 87 octane but that 91 would perform better. In Washington DC, 85 would have screwed with that car when I had it there so they didn't sell it because you're at sea level. 85 in Utah or Colorado works just as well as 87 or 91 for a turbo at high altitude locations. Less dense air, less oxygen going into your intake and engine therefore the 85 octane makes for a more ideal air-fuel ratio. And it's OK to switch back and forth if traveling to and from high altitude-low altitude locations. The computer will adjust fuel tables to prevent knock via the knock sensors anyways. I just wouldn't play around with ethanol without a tune personally. My tune on the Stinger used to spray methanol in the cold pipe, pre-throttle body and doubled as a valve cleaner. I hate GDI-only engines except I love the power you can make. That car made 490 whp and about 460 tq.

 

[Los150]

In FL we have e85 and 87, but I have always seen both e85 & 85 octane in other states. Typically, we don't have 91, we have 93 as our premium unleaded.

"E85 is not the same as 85 octane. E85 is 85% ethanol and used in flex fuel vehicles, the ones with the green leaf in their logo. At elevation you may find 85 octane which is used to help counter the thinner air."

Here's a photo of pump in Colorado (top) Florida (bottom)

Any even then, it varies in state. In South FL you're more likely to see the bottom pumps and in Central FL (Orlando) I've seen pumps resembling the top one, offering 91 as an option. Central FL is only about 85ft elevation vs 5ft or less in South FL.

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