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The Monte Carlo SS and Hurst Olds Cutlass were my grail cars in high school. I've always kind of preferred the q-ship kind of car over the Z28 or T/A.

180 sounds about right. Z28s were about the same, using the same or a similar engine. But they were an upgrade over the earlier 80s versions for sure.

I recently learned that the much maligned 5L Turbo T/A from the early 80s was severely underrated at 200+hp and put the 6.6L 1979 T/A actually to shame. Kind of like no one knew what the 3.8L V6 Buick Regal GS/Grand National was really putting out, either. Until later. It wasn't easy to find hp numbers in those days. Probably out of shame.

Those were some sad days for horsepower out of formerly good engines. They put emission controls on them cuz they had to, upped the rear end ratio for CAFE, and otherwise didn't change a thing.
 

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The Hurst Cutlass production was sold out for the year when I placed my Monte Carlo order or I probably would have ordered it instead. The base Monte Carlo had the then new 4.3L V6 which was derived from the classic 5.7L / 350 CID V8 small block. That V6 was a new engine for that year and since I was getting ready to start the PhD program I wasn't interested in dealing with a maybe problematic new design while also immersed in grad school. In retrospect, like the 3.8L /231 CID, the 4.3L ultimately turned out to be a very good design for GM. I bought an Olds Toronado with the 3800 in 1989 after finishing grad school and later had a 1997 Pontiac Gran Prix with that same engine which was up into the 200HP range by then.

Rodger
 

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This has seemed to be a good topic of discussion. I brought a used CPO Cadillac for a great price. And I was going by what I was currently driving. And as I stated, living in Cook county Illinois, the previous car cost $25 - 30 to fill on 87 octane(Shell). This car has cost $43 - $46 to fill on 93 octane(Shell). So $60 - $65 more a month to waste in traffic may not be much to some but it is others. And I didn't state I wouldn't us 93 octane. Just not possibly every fill-up. And don't get started on the summer/winter blends that make matters worse in this state. I feel like I kicked a hornet's nest.
I don't think you can blame the $60-$65 extra per month on the octane unless you are driving a massive amount of miles. 15,000 miles a year at 25 mpg = 600 gallons a year x 60 cents extra per gallon for Premium and it would be $360 a year or $30 a month. If you are driving 15k miles a year and it is almost all in traffic seems like a real pain in the neck.
 

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2016 ATS 2.0T AWD Sedan
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Discussion Starter #44
I don't think you can blame the $60-$65 extra per month on the octane unless you are driving a massive amount of miles. 15,000 miles a year at 25 mpg = 600 gallons a year x 60 cents extra per gallon for Premium and it would be $360 a year or $30 a month. If you are driving 15k miles a year and it is almost all in traffic seems like a real pain in the neck.
That's about right. I'm about 60 miles a day and about 2.5 hrs roundtrip. So I go use gas. And wintertime, a real pain. I'll run this car for 4 yrs and about 100,000 hopefully.
 

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This is kind of OT, but a fun discussion. Rodger, you'll probably appreciate this. My Dad liked Oldsmobiles, going back quite a ways. If I recall correctly, the "Rocket Engine" was an OHV engine that only Olds and Cadillac offered for a while and Dad was favorably disposed.

Anyhow, in 1977, my Mom and Dad bought a new Delta 88. Well, that was one of the first years that GM offered "corporate" engines, which meant the 350 in that Delta 88 was a Chevy. That provoked a class-action and entitled Mom and Dad to a new Oldsmobile with a "Rocket Engine." Of course that Olds 350 wasn't as good as the Chevy when choked out with emission controls (I think because it was designed to be larger displacement). Also, they got a silver one that the paint came off of in about five years.

Bad Times at The El Royale for GM and Big Three.
 

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That's about right. I'm about 60 miles a day and about 2.5 hrs roundtrip. So I go use gas. And wintertime, a real pain. I'll run this car for 4 yrs and about 100,000 hopefully.
25k a year is a ton of miles, if you want to save money on fuel I would forget about the 87/91 octane question and buy an Accord hybrid or similar and get 48 mpg using 87 octane. Your model ATS - $2950 per year in fuel, Accord Hybrid $1150 ($1800 savings per year / $150 per month).
MPG LINK

My current job/lifestyle has me driving less than 5k miles a year and I may never keep my 2013 long enough to get to 100k miles. Also part of the reason I would go with whatever octane is recommended. I actually use Premium most of the time in my V6, The cost to me is minimal because of how little fuel I use.
 

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Discussion Starter #47
25k a year is a ton of miles, if you want to save money on fuel I would forget about the 87/91 octane question and buy an Accord hybrid or similar and get 48 mpg using 87 octane. Your model ATS - $2950 per year in fuel, Accord Hybrid $1150 ($1800 savings per year / $150 per month).
MPG LINK

My current job/lifestyle has me driving less than 5k miles a year and I may never keep my 2013 long enough to get to 100k miles. Also part of the reason I would go with whatever octane is recommended. I actually use Premium most of the time in my V6, The cost to me is minimal because of how little fuel I use.
Actually the brought the car with 32,000 miles on it. So I'm more at like 15,000 miles per year. I thought about a Hybrid, possibly the New Insight. But the way the dealer treated my mom when she was looking for a vehicle, I couldn't give them the time. But the American dream, A Wife, Kids, House, and a Cadillac in the driveway. even if it is the baby one.(y)
 

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Higher octane helps prevent knocking/detonation. ...
Just so we're clear: "Octane" is a characteristic; it is not an additive so it can't do anything.
 

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Fuel choice seem to be increasing in most areas. My 2014 ATS has the 3.6 designed to run on 87 on which it does well although factory programming puts it into too high of a gear for low to moderate speed steep grades creating a light knock and I use the paddles to drop down one gear to avoid this; I found 89 octane also is sufficient to prevent the issue. My 2008 CTS with the first gen 3.6L direct injection behaved the same say. My 2016 Z06 has a supercharged 6.2L and it drinks the recommended 93 octane except that it gets a couple of tanks of 91 octane just before winter storage because 91 is the highest octane available here that is ethanol free; I drive conservatively once it has 91 in the tank. The Z06 revised factory tune does take advantage of 100 octane fuel which reduces the propensity to pull timing under track heat and its setup is a little different than the typical high/low octane map in most vehicles with 93 octane as both the normally recommended and also minimum octane fuel for normal use.

For the pickup, I have to pick and choose because most of the year I like running diesel/soy blend for the added lubricity which keeps the injection pump and injectors happy. In winter I patronize the two area stations that have soy free because even with anti-gel additives and the larger fuel filter heater in the 2018 soy blend still gels far too easily in very cold weather. The most convenient source of soy free can't be used in the pickup because it is "red dye" diesel which is road tax free, I use that in the generator and tractor but using that in a highway vehicle is an invitation for a very large fine for tax evasion.

One of the Japanese manufacturers sold an export version of their small pickups in part of the world that had a switch to select either low octane or normal. In the normal position, it acted like other vehicles with the ECM advancing timing to normal levels unless the audible knock sensor called for timing retard and this results in operation that often creates at least minor knocking until it becomes sufficient to trigger the sensor and even then the ECM will continue to try advancing the timing repetitively to the point of knocking. In the low position, the ECM ran only the low octane map but could still retard timing further if needed. This setup likely would run afoul of some obscure EPA regulations in the U.S. but it would be a nice setup for people who would like to be able to run their vehicle on a lower octane with far less potential damage from frequently having enough knock to trigger the knock sensor.

In short, think of the recommended octane and knock sensor setup as being much like the engine overheat protection built into the ECM. The system is designed to protect the engine from immediate destruction when operated outside of typical operating conditions but it doesn't mean that it is good for the engine to frequently hit the conditions that trigger these protective measures.

Rodger
I enjoy saying, 'lubricity.' LOL
 

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Just so we're clear: "Octane" is a characteristic; it is not an additive so it can't do anything.
I should have said higher octane fuel, or gasoline.

Would have been more lubricious that way.

Also I have had two vehicles previously that recommended "premium" fuel, but the recommendation was for 91. Both normally aspirated, but higher compression ratio engines. Apparently, there are 91 octane gasolines available some places. Here in Texas 93 is standard.

I found it interesting that the ATS recommended 93.
 

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Large percentage of the country has something less than 93 as Premium.

See below, interesting that Cadillac doesn't have faith that their knock sensors will stop knock. Next question would be if you can really hear slight knock. Manufacturers do whatever possible to increase performance and fuel economy, many buy cars with these features in mind but then immediately try to save some money by buying lower octane fuel which does the opposite.

From the 2013 ATS Owners manual -
Recommended Fuel If the vehicle has a 2.5L L4 engine or a 3.6L V6 engine, use regular unleaded gasoline with a posted octane rating of 87 or higher. If the octane rating is less than 87, an audible knocking noise, commonly referred to as spark knock, might be heard when driving. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. If heavy knocking is heard when using gasoline rated at 87 octane or higher, the engine needs service. If the vehicle has the 2.0L L4 engine, use premium unleaded gasoline with a posted octane rating of 91 or higher. You can also use regular unleaded gasoline rated at 87 octane or higher, but the vehicle's acceleration could be slightly reduced, and a slight audible knocking noise, commonly referred to as spark knock, might be heard.

From the 2018 Owner's Manual -
Interesting that they changed the recommendation from 91 to 93 but we are still debating if 87 is ok. They also say using the lower octane will reduce fuel economy so the savings to go to 87 looks better than it really is.

For the 2.0L L4 turbo engine (LTG), premium unleaded gasoline meeting ASTM specification D4814 with a posted octane rating of 93 is highly recommended for best performance and fuel economy. Unleaded gasoline with an octane rated as low as 87 can be used. Using unleaded gasoline rated below 93 octane, however, will lead to reduced acceleration and fuel economy. If knocking occurs, use a gasoline rated at 93 octane as soon as possible, otherwise, the engine could be damaged.
 

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Discussion Starter #52
The wording is what gets me. If the manual or the gas cap stated Premium "required", instead of "recommended", there wouldn't be a conversation. So on that, I'm going to be the guinea pig. Since I brought the car, I've run 3 full tanks of 93 and I'm getting 26 mpg. I filled the car with 87 yesterday ($28) and the next couple of tanks and see where my mpg's stand and if there's any knocking.
 

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The knock sensor will moderate knock within the range of the ECM available timing parameters but knock moderation only occurs once knock has started so every time you trigger the sensor you have already exposed the combustion chamber and reciprocating parts to the shock loading of explosion rather than controlled burn and doing this over and over increases the odds of increased wear followed by catastrophic failure at an earlier than normal operating hour interval. Knock sensing hasn't changed much since it first became common decades ago and is still based upon reading the vibration signature associated with detonation and if the system is made too sensitive it will false detect on normal operating behavior of the engine. The manufacturers could further refine this detection using DSP technology to better discriminate between sources of stimuli to the sensor but the expense and complication to do this make it undesirable. Measuring octane is a fairly involved process, there is no direct fuel spectral decomposition result that will directly indicate octane because there are many methods of modifying the achieved octane so it can't be sensed like the automatic differentiation that occurs in a flex fuel system that will run anything from regular through e85 ethanol blend.

In short, if you use the preferred fuel grade for the engine then the knock sensing system will operate as intended to protect against unusual conditions and on rare occasion it will have to slightly retard timing to prevent excessive knock. If you use the minimum allowable grade, which is high enough octane that the knock control system can prevent rapid destruction under typical operating conditions, then you are constantly leaning heavily upon this protective system to continuously control knock and every time it has to further retard timing and/or command power reduction realize that this is a reaction to heavy knock that wasn't previously controlled. In order to meet the all important CAFE requirement, the ECM is trying to run as much timing as possible so once knock occurs it doesn't decide to wait a week before trying to return timing to nominal but instead is constantly running as much timing as possible which means frequently having to retard further after knock occurs when running a less than desired fuel grade.

Areas that have 91 and 93 available often achieve this with 91 as "pure gas" (no ethanol) and 93 is an ethanol blend with the ethanol providing further resistance to detonation. Pure ethanol (also propane) can provide an extremely high octane rating but has less energy by volume so fuel mileage drops and some fuel systems can't deliver enough fuel running e85 to provide the pure gas or e10 power rating, this is common in direct injection systems where the cam driven high pressure pump is being run near its delivery/pressure capability.

Rodger
 

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The wording is what gets me. If the manual or the gas cap stated Premium "required", instead of "recommended", there wouldn't be a conversation. So on that, I'm going to be the guinea pig. Since I brought the car, I've run 3 full tanks of 93 and I'm getting 26 mpg. I filled the car with 87 yesterday ($28) and the next couple of tanks and see where my mpg's stand and if there's any knocking.
They said 93 is "highly recommended" and "If knocking occurs.... it could damage the engine". They told you what they recommend, anything past that is whatever you want to do, it's your car. Impossible for them to require 93 as it isn't available in many states, then if Premium was "required" it would put people in a panic whenever it wasn't available or someone filled it up with the wrong grade. It's not that severe of an issue.

On the other hand it's an engine that has a history of damaged pistons and Premium likely adds about $350 a year if you are driving 15k miles a year. My guess is all car costs combined are roughly $5000-$6000 per year? I highly doubt you will ever have engine damage from using 87 I just wouldn't see the gain being worth the risk and the expected reduced performance and mpg.

I don't think you can control the variables enough to get exact mpg to octane data. If they could have gotten the same mpg and hp using 87 they would have tuned if for this fuel. I don't think you can hear slight or occasional knock. If I understand correctly, if things go as planned with low octane, it might knock, if it does the engine will pull timing, then at some point it will try to go back to normal and repeat the process. How much it knocks will depend on how often it tries to go back to normal as well as the conditions it is driven in.
 

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I agree that the added cost of 93 is nothing to try to shy away from. Not even a tank of 87 once in awhile. It's just not wise and what you save is minimal, unless you run 87 quite often....which isn't good for the LTG.

I also agree that if the added cost is that big of a deal, then you should be or should have been looking at super efficient cars...trying to offset the cost after the purchase is like trying to find the most budget parts to replace the m series parts on a BMW because you're unhappy with the costs of the replacement OEM parts.

You could also tune it and get an E85 sensor so you can run 50/50 E85/93. That would be safer than 87 and give you power benefits while offsetting the 93 cost.

Chicago driving requires being ready to go full throttle across 3+ lanes....87 at full throttle will likely generate KR....enough knock will blow the engine.
 
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