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We're assuming 87 octane.
For being a cheap back to basics roadster, we're expecting that for only running at 170HP it'll use regular fuel.
 

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interesting, I've heard that all miatas since 2000 (give or take) require premium. Just something to chew on :smile
 

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Brentil/Rodeo,
Remember someone in the forum posted the specs for the 2.4 VVT ECOTECH and although is 10:6:1 compression ration it said 87 regular octane.:smile
 

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RODEO said:
interesting, I've heard that all miatas since 2000 (give or take) require premium. Just something to chew on :smile
From the Mazda site
Recommended fuel Premium unleaded, 91 RON
Minimum fuel requirement Regular unleaded, 86 RON
Reading online that seems to be the consensus too. Supposedly the user manual says you can use octane below 91 at a performance hit.

However the 2.4L engine is only producing 19.7% more power (28HP), but has an increase of 42.9% in displacement (0.6L). There is the compression ration to take in account too though. The ECOTEC is 6% larger in the compression ratio aspect being 10.6:1 compared to 10:1 of the Miata. However it is understandable on the Miata insce it's only producing 19.7% less power on a massive 42.9% displacement drop with a lower compression ratio.

Also from the tech PDF TCL posted here...
http://www.solsticeforum.com/forum/showpost.php?p=10834&postcount=10
it says
Recommended Fuel: Unleaded regular
 

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LatinVenom said:
Brentil/Rodeo,
Remember someone in the forum posted the specs for the 2.4 VVT ECOTECH and although is 10:6:1 compression ration it said 87 regular octane.:smile
One of GM's online phamplets indicated that the 2.4L VVT would run on regular 87 pump gas. Hopefully that is true! :thumbs

edit: OOPS, Brentil mentioned that! :cool
 

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Brian said:
I am sure that it will run fine on 87, but with that compression ratio you may want to use midgrade.
If the ECU is specificaly designed for 87 octane gas, then running anyhting then that can actually cause power loss. The main benefit of higher octane gas is it can be compressed farther before detonating, and if your engine isn't designed to take that into account you'll end up causing issues.
 

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cant newer ECUs change timings to optimize for various gas grades? Under that assumption I would think that the high octane gas would allow for more aggressive timings and better performance.
 

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brentil said:
If the ECU is specificaly designed for 87 octane gas, then running anyhting then that can actually cause power loss. The main benefit of higher octane gas is it can be compressed farther before detonating, and if your engine isn't designed to take that into account you'll end up causing issues.
At the very least, running a higher octane than the car is specified to use is simply a waste of money. I always run into posts on forums from people who cannot believe how much more power they can feel by running 93 octane in their 87 rated engine. Its hogwash. The engine will burn the higher rated fuel, but the computer doesn’t know how to take advantage of it.
 

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Brian said:
cant newer ECUs change timings to optimize for various gas grades? Under that assumption I would think that the high octane gas would allow for more aggressive timings and better performance.
IF the ECU has been programmed to do that. My Ford ZX2 S/R has, but that's because I have the S/R package that added the performance ECU upgrade. And if you use anything but 91+ octane in my car it runs like poop, it can do it, it's just not designed for it anymore. Most cars are specifically designed for a certain gas type. It saves the manufacture a ton of money because they only have to design, program, and validate one fuel grade.
 

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Fformula88 said:
At the very least, running a higher octane than the car is specified to use is simply a waste of money. I always run into posts on forums from people who cannot believe how much more power they can feel by running 93 octane in their 87 rated engine. Its hogwash. The engine will burn the higher rated fuel, but the computer doesn’t know how to take advantage of it.
Exactly. And I've seen actual cases of power loss in some cars because the fuel isn't detonating when the system is expecting it too. It'll detonate past the peak of the piston ark causing the explosion on the downward thrust instead at the peak when compression is the greatest. Now keep in mind from what I've been told that's very rare, but like FF said in general you're throwing your money away.
 

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Fformula88 said:
At the very least, running a higher octane than the car is specified to use is simply a waste of money. I always run into posts on forums from people who cannot believe how much more power they can feel by running 93 octane in their 87 rated engine. Its hogwash. The engine will burn the higher rated fuel, but the computer doesn’t know how to take advantage of it.
I beg to differ... with one caveat. If the engine is equipped with knock sensors, and retards the timing accordingly it WILL run better on higher octane fuel provided that you're getting a fair amount of "knock retard" with the lower grade. If you can run more total timing (base + x degrees timing advance - y degrees knock retard) then you'll make more power.

If, on the other hand the PCM doesn't adjust timing based on knock sensors, then buying "better" gas is pretty much a waste of money.
 

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2KWK4U said:
If, on the other hand the PCM doesn't adjust timing based on knock sensors, then buying "better" gas is pretty much a waste of money.
Yeah, that's what I was trying to say. If your cars computer wasn't designed to adjust for these types of things you're not going to get anythign from it.
 

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Current GM engine management history should be a good indication. The series II 3800 Supercharged requires premium while the regular 3800 does not, 04 Impala and Monte SS. With the Series III, new in the 04 Grand Prix GTP, the engine was designed to use Premium for optimum performance, but will run on 87 grade gasoline. There is a slight performance hit.

My guess would be yes, the Solstice will be able to use 87. Another example: Look at the Cobalt specs. The 2.2L, uses 87 while the 2.0L SC prefered 91+, but will run on 87 with a performance hit. The Supercharged solstive due in 07 would prefer 91+, but will run on 87 also.
 

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GXP said:
Current GM engine management history should be a good indication. The series II 3800 Supercharged requires premium while the regular 3800 does not, 04 Impala and Monte SS. With the Series III, new in the 04 Grand Prix GTP, the engine was designed to use Premium for optimum performance, but will run on 87 grade gasoline. There is a slight performance hit.

My guess would be yes, the Solstice will be able to use 87. Another example: Look at the Cobalt specs. The 2.2L, uses 87 while the 2.0L SC prefered 91+, but will run on 87 with a performance hit. The Supercharged solstive due in 07 would prefer 91+, but will run on 87 also.
Welcome to the forums.

Actually pretty much any Supercharged or Turbocharged engine requires 91+ octane, and should in general never have anythign lower then what it's rated for run in it. The reason higher octane gas is required for force induction engines is because you're massively increasing the presure inside of the combustion chamber. If you use lower octane gas it'll pre-detonate causing knock. Which is the wave from the explosion hitting the intake valves while they're still open causing them to knock back into their housings. Higher octane gas permits it to be compressed to greater levels before it detonates. Helping to negate knocking. It can still happen though, and if it does if the car has knock sensors it'll alter engine characterisitcs. Even though cars can sense and change the settings it's still not a good idea because you're still initially causing knock for the car to be able to sense it and change.
 

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Fformula88 said:
At the very least, running a higher octane than the car is specified to use is simply a waste of money. I always run into posts on forums from people who cannot believe how much more power they can feel by running 93 octane in their 87 rated engine. Its hogwash. The engine will burn the higher rated fuel, but the computer doesn’t know how to take advantage of it.
One of those posts was probably me. I have run experiments on full tanks, 3- and 5-tank series, (that's over 400 and 1000 miles) of mileage checks. I used standard fill techniques, and the same station, and ran through three seasons (late summer, winter, spring).

Go ahead, call me a geek.

But, on a 1997 cavalier with the 2.4l twin-cam (revised Quad-4) with 35000 miles (at the time), I got about 6%-12% better (averaged around 9%, if memory served correctly) gas mileage using 92 vs 87 octane. At the time, I decided to run hi-octane in it.

I re-did it on a few tanks at around 100000 miles, and got similar if not slightly better results. Mind you, that's 2-3 mpg on average better. Figured the cost hi-octane was a wash, and a guy that worked in petroleum products that I talked to said there are some additives and detergents that are in many higher-test fuels that might help to keep parts cleaner (haven't been able to substantiate this). Sold the cavalier at 135,000 miles, still running like a champ.

I don't think there's any special fuel sensors or anything, I figured at the lower octane there must be incipient knock that the engine just takes care of by retarding timing, and higher octane reduces the changes of it.

I also have heard that the RL Vue is highly sensitive to octane - with significantly more torque on 92 octane vs 87.

Having blabbed on about all that, the ecotech is supposed to be able to determine fuel by engine burn characteristics (advance knock sensors? special mojo? ***SHRUG***) and adjust power and spark accordingly. You can run 87 and the engine will do ok, but you'll get better power and torque if you run on 92 or higher, and if you switch it may take a tank for the car to "adjust".

I think many european engines now do this, including (I think I heard this, anyways) the ford focus.
 

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There is more to gas than just octane. The cheaper gas generally does not have any detergents or deicers whic is important in our neck of the woods. BP's famous "you go or we pay the tow" winter deicing ad campaign is limited to 93 octane Super, I believe. I too have felt the difference in fuel. My GTP's both worked okay on moderate doses of 87-88 but really preferred 93. Kohler Engine (in your lawnmower) calls for at least 89 octane to reduce carbon deposits....hmm.
 

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I understand that this is a topic that will never be fully settled, but if and when I have an engine that is running a compression ration of 10.6 to 1 I will try to error on the safe side and at least use mid grade gas. I know that the BTUs produced by each grade are the same so theoretically the same amount of energy/mileage will be attained, but I would play on the safe side with this engine. If the compression ratio was 8 to 1, well then I would go right ahead and use 87, but it is not. This is just like the corvette, it can run on 87 but like 91/3 a whole lot more.
 

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Trivia...Don't know how current knock sensors work but the ones about ten years ago were just a simple microphone tuned to the frequency of metal clanging and stuck in the valve cover. With a timing light on the car you could bang on the side of the block with a wrench and watch the engine retard for several minutes. OK, it's just something to do to while drinking beer with friends in the garage. Guess it doesn't take much to entertain us simple minds! :cheers
 
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