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Old 10-13-2015, 06:51 PM   #21
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I noticed the high difference when visiting DS in Maryland. I really doubt the gas costs that much more. I assume the regular price is being subsidized by premium users. So far we have at least a few reasonable stations here.
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Old 10-13-2015, 08:10 PM   #22
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Originally Posted by Car-Guy View Post
I guess I'm desensitized to paying a higher prices for premium. I've been driving a number of higher performance (typically higher compression) cars for years and they all recommend premium, (although most seem to run okay on regular in a pinch.) Not sure I'd want to run a steady diet of regular in those cars.

I've actually seen (measured) the difference between regular and premium gas in competitive driving conditions in higher compression engines. 0 to 60 and 1/4 mile ET's. I've also read claims that you get more mileage out of premium but I've never actually measured it myself since there are to many variables and to be honest, I don't really care if I get a mile per gallon more or less.

BTW, the price difference in my area is between 30 and 40 cent per gallon depending on the station.
When I first got my Acura TL, I used premium for awhile and would switch back and forth between it and regular.... since I had a good number of takes on each I think the variables would even out.... and guess what... no difference in mileage....

I have also read in a different forum that there is no difference in the amount of energy per gallon, so there cannot be any difference...

Now, I do believe that a modern high performance engine would produce different HP and torque numbers since they have to retard it so it would not blow up... my TL was a nice engine, but not a high performance one...
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Old 10-13-2015, 08:14 PM   #23
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let's see - the injectors were about $500 and the fuel pump was about $200, then I had it tuned so I could switch maps back and forth from 91

so maybe a grand? it puts down 420 awd ft pounds of torque on e85
You've measured it? Can you show us before and after dyno graphs? I 'd love to see them.
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Old 10-13-2015, 09:37 PM   #24
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My car "requires" premium. It has an anti-knock sensor, and the forums say that using a lower octane gas will retard the ignition, and reduce the gas mileage. So you won't save money. I've tried regular and mid-grade, and I can't really tell much of a difference in performance. YMMV

Agree on the many comments that many/most cars do not require premium, though they may recommend it for maximum performance.

But it also seems to me the only time the system is going to do something like retard the spark to prevent knocking, would be if you were really pushing it. So I would think that if you drive conservatively, you would only very rarely see these conditions that might lower the mpg.

If your daily commute involves flooring it to go up an on- ramp to merge into 75 mph traffic, then maybe premium would help.

To the OP - are you sure premium is required?

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Old 10-13-2015, 10:09 PM   #25
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To the OP - are you sure premium is required?

-ERD50
Here's what the owners manual says. It's an Acura.

"Your vehicle is designed to operate on premium unleaded gasoline with a
pump octane of 91 or higher. If this octane grade is unavailable, regular
unleaded gasoline with a pump octane of 87 or higher may be used
temporarily. The use of regular unleaded gasoline can cause metallic knocking noises in the engine and will result in decreased engine performance. The long-term use of regular-grade gasoline can lead to engine damage."
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Old 10-13-2015, 10:27 PM   #26
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Acura CSX Type S which also says 'Premium Unleaded Fuel Only' on the filler door and 'Premium Unleaded Required' in the owner's manual. 9 years old and 140,000 miles almost all of which has been with regular unleaded. No noticeable difference in mileage between the two fuel types and no engine issues. I'm not a racer but highway speed is not infrequently 85 mph and I have 'fun' driving it.
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Old 10-13-2015, 11:18 PM   #27
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My cars have all required regular, but I wish they had an optional diesel engine available.

I'm too cheap to buy a car that requires premium.
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Old 10-14-2015, 08:58 AM   #28
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looked at the pump last night, high test is only 25 cents more than 87 octane
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Old 10-14-2015, 09:19 AM   #29
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looked at the pump last night, high test is only 25 cents more than 87 octane
I picked the wrong state to own a car that requires premium. Premium costs $.55-$.60 more per gallon that regular. According to GasBuddy most states have closer to half that difference.
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Old 10-14-2015, 09:28 AM   #30
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Our car was purchased new in '06. Back then the difference between regular and premium gasoline was $.20 per gallon. I did the numbers, expected the additional fuel cost would be around $75 per year, so we went for it - a car that requires premium fuel.

The additional cost for premium gas then rose to $.25. 2 years ago it rose to $.50. late spring this year is went to $0.60, and yesterday at Costco it was at $0.70. We put 15k miles per year, get around 23mpg, so the additional cost is now over $400. It won't break the bank, but over 5 or 6 years it is a sizable amount of money.

Premium gasoline - first and last time for us.
We've got an '06 ES330, and there is no reason that vehicle should have a motor which runs high compression. DW complains about the premium, but we've averaged 7k-8k miles per year since we bought the car in late '08. Lexus has actually stopped putting high compression motors in their vehicles I believe, at least in the "granny" cars.

One other consideration is one's atmospheric pressure. Here in Denver, the highest octane we can get is 91. My other vehicles take 85. But, the higher the altitude, the lower the Patm and the less like likely hood of pre-detonation. There is play within the ECU to adjust for small changes in timing, but if it senses a knock it will go into "safe mode" and it limp around.

With that said, how little we drive the vehicle and we are looking to sell in the next 6 months (DW wants a bigger vehicle and we're expecting a 3rd child), we are just going to run premium until we can sell it. And yes, the new vehicle will take the gasoline commoners use.
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Old 10-14-2015, 09:28 AM   #31
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The only somewhat modern vehicle I've ever owned that requires premium is a 2000 Park Avenue Ultra, which is supercharged. I'll admit I've put 87 octane in it on occasion, and never noticed a difference. But, I never did that back-to-back, so there was always some 93 octane in the tank for it to mix.

My understanding with modern cars is that they're "smart" enough to adjust the spark timing and other functions when you put a lower octane fuel in, and in most day to day driving, you won't notice much of a difference. But, if you tend to drive hard (high speed, fast acceleration, etc) you might notice. And, fuel economy might suffer a bit as well, but again, if you're an aggressive driver you're going to be guzzling a bit, anyway.

I've heard that Chevy/GMC pickups with the old 4.3 V-6 could actually get messed up if you put premium in them! They were designed to run on 87 octane, and normally, when you put premium in a vehicle that only needs regular, you're just wasting money but doing no harm. However, with the 4.3, it would actually mess up the engine if you did it too much.
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Old 10-14-2015, 09:33 AM   #32
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You've measured it? Can you show us before and after dyno graphs? I 'd love to see them.
this is the e85 and 91 octane tune
Attached Images
File Type: jpg dyno fxt.jpg (88.1 KB, 17 views)
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Old 10-14-2015, 09:55 AM   #33
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My understanding with modern cars is that they're "smart" enough to adjust the spark timing and other functions when you put a lower octane fuel in, and in most day to day driving, you won't notice much of a difference.
The concern of pre detonation is on the compression stroke, not the ignition/combustion stroke. A vehicle's ability to adjust for this via timing is case by case and depending on when the detonation is happening on the compression stroke. The ECU may be able to compensate by adjusting air/fuel ratios, but it only goes so far.

What one notices and doesn't notice, may or may not be helpful. YMMV. Surely, the safe thing to do is to run the mfg recommendation. One could most likely have their vehicle tuned or sell it. But trading cars is almost always a losing endeavor for finances.
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Old 10-14-2015, 10:19 AM   #34
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My Audi Q5 "requires" Premium. The manual says the car will operate with Regular, but to replace with Premium as soon as practical, or something to that effect. In my area, Premium is 93 Octane, and my car requires 91 Octane. So, when I remember I will alternate fill-ups, when car is half-full, with mid-grade. However, I don't keep religious track of this; life is too short and I bought the car knowing it requires Premium.
On a sort of related note, before buying the Q5 I considered the Volvo. It called for Regular, but got less MPG. I did a gross calculation of the relative costs, and the Q5 with Premium came out much cheaper -- i.e., the gas usage costs.
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Old 10-14-2015, 10:55 AM   #35
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The only somewhat modern vehicle I've ever owned that requires premium is a 2000 Park Avenue Ultra, which is supercharged. I'll admit I've put 87 octane in it on occasion, and never noticed a difference. But, I never did that back-to-back, so there was always some 93 octane in the tank for it to mix.

My understanding with modern cars is that they're "smart" enough to adjust the spark timing and other functions when you put a lower octane fuel in, and in most day to day driving, you won't notice much of a difference. But, if you tend to drive hard (high speed, fast acceleration, etc) you might notice. And, fuel economy might suffer a bit as well, but again, if you're an aggressive driver you're going to be guzzling a bit, anyway.

I've heard that Chevy/GMC pickups with the old 4.3 V-6 could actually get messed up if you put premium in them! They were designed to run on 87 octane, and normally, when you put premium in a vehicle that only needs regular, you're just wasting money but doing no harm. However, with the 4.3, it would actually mess up the engine if you did it too much.

Can you give some real backup for that stmt on the 4.3 engine? With my limited knowledge I cannot see how having higher octane could mess up an engine at all... there is nothing that the higher octane can do to mess it up.
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Old 10-14-2015, 11:03 AM   #36
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this is the e85 and 91 octane tune
So the lower trace is the 91 octane torque and HP, and the higher one is the E85?

Were there other mods to the car besides the injectors and the fuel pump?

Thanks!
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Old 10-14-2015, 11:32 AM   #37
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So the lower trace is the 91 octane torque and HP, and the higher one is the E85?

Were there other mods to the car besides the injectors and the fuel pump?

Thanks!
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Cobb AP protune, Cobb CAI, Crawford AOS, VF52 turbo, Perrin catback, CNT downpipe, SRTI gauges, bulletproof TMIC mod, 2" lift

I think that's about it


I used to take my car to enginelogics in Stafford for performance work/tuning when I lived in Houston.
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Old 10-14-2015, 12:26 PM   #38
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Both of our vehicles have high compression engines that require 91 octane or better. The engine computers will compensate for lower octane fuel but there will be a performance and mileage penalty.

The price differential between the two grades of fuel is not something that I'm currently concerned with, nor would that drive the selection of a new vehicle.

Driving around town or locally the savings would be negligible. Any longer distance trips that we take usually involves a rental car for reliability concerns, and the fuel selection is out of our hands.

If cost per mile is a major concern, why not consider a diesel, such as the TDI? I hear they get fantastic mileage, and low emissions too.

_B
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Old 10-14-2015, 12:45 PM   #39
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Can you give some real backup for that stmt on the 4.3 engine? With my limited knowledge I cannot see how having higher octane could mess up an engine at all... there is nothing that the higher octane can do to mess it up.
I tried Googling but can't find anything. And you'd think that if it was a common problem, it would come up pretty easily. The way I found out about it was that I had a friend who had an '05 Silverado with the 4.3, and we had gotten into a discussion about octanes. He said that too high of an octane could hurt an engine. I said that was BS...that if an engine wasn't designed for it you're just wasting money, but it wasn't harmful.

This guy was one of those "I always have to be right" types and we got into an argument about it. Like you, I just couldn't understand how a higher octane could hurt an engine. But, he was adamant about it. At the time, I was able to find some corroboration that actually backed him up online, but that was about 6 years ago, and I can't remember what it was, or how "official" it was.

So, what I heard could just be an old wives' tale. Another one of those anecdotes I heard was the 2.7 V6 my old 2000 Intrepid had was similar enough with the programming, intake, fuel injection, or whatever to the 3.5 used in the Intrepid R/T and Chrysler 300M, that if you put 93 octane in it, you'd get better performance up to about 90% of wide-open-throttle.

I don't know if it was true or not, though. One thing I did discover though, is that if you floored it, as soon as the car hit the rpm where the horsepower peaked, around 6000 rpm, it would upshift immediately, even though redline was around 6500 I think. However, the torque peaked at around 4900 rpm, and I discovered that if you floored it, but then let off a bit once it hit 4900 rpm, it seemed like it helped with acceleration. I don't know if it really did, or if it was just in my mind.
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Old 10-14-2015, 12:57 PM   #40
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I'm no expert, but a pretty decent back yard mechanic and here's my take. Regardless of Octane in the tank, you can get almost any engine to knock by feeding it the wrong mixture for a given engine RPM. For instance, drive your vehicle up a descent size hill without pressing on the gas pedal to increase the RPM and it will eventually bog down (RPM will decay). Then press the gas pedal slightly and it will more than likely start to knock on you. And yes, knocking, or pre-ignition, is not good for your engine. However, an occasional knock is not going to lead to engine replacement for most.

Now, 50 years ago, before modern ignition systems, engine problems cause by excessive knocking was more common. In today's engine not so much. That issue really went away with the 15K mile tune-up from the 60s. Hell, I still have the original spark plugs in my 100K mile Camry engine. Runs like a top.

The only time I consider premium gas if I'm driving in the mountains where there will be a considerable amount of hill climbing. That when I risk the excessive knocking.
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