MPG premium vs regular at same HP level - ModernCamaro.com - 5th Generation Camaro Enthusiasts
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post #1 of 5 Old 11-21-2007, 11:24 AM Thread Starter
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MPG premium vs regular at same HP level

OK you have 2 cars making the same hp.

Lets say you have a higher compression engine that uses premium fuel that makes 400Hp.

Now you want it to run on regular fuel. So now you have to lower the compression.

Now you don't have 400HP

Now you need to do something to the engine to make it get back to 400HP while using regular fuel which is going to lower your fuel economy.

You will now probley get less MPG than the original engine that uses premium fuel just to make the same power.

If that was not true then why would there be any reason to make it use premium fuel.

My guess is it would get better MPG at 400HP using premium fuel which is better than getting worse MPG while making 400HP on regular fuel. This should make the cost between regular and premium null if 400HP is what you want. In fact I think you could come out better making 400HP using premium fuel, because I think the better MPG would more than make up the 20 cents per gallon price difference.

15 gallons of regular $49.50 @ 3.30 a gallon 375
15 gallons of premium $52.50 @ 3.50 a gallon 405

Lets say the regular gas car gets 25mpg 15g tank would be 375 miles
and the Premium car gets 27mpg 15g tank would be 405 miles

the difference is 30 miles a tank which means the first car would have to use 1.2 gallons more to go the same miles as the second. which would cost $3.96 extra

So for both cars to go 405 miles with 400 HP
the first one would take $53.46 on regular
the second car would take $52.50 on premium

Are there any tests like this?
Which do you think would get better MPG while still making 400HP?

I have heard of test of using premium in a car that does not require it, but never heard of a test like this.

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post #2 of 5 Old 11-21-2007, 11:54 AM
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The lower octane car could be tuned, lower thermostat installed, and a couple more old timer tricks. A better and maintained air induction unit, better exhaust, coolant bypass. A better camshaft with hp and fuel economy in mind. You will probably be thinking about increasing torque in the low rpm areas. You could actually increase acceleration performance and MPG while not getting back up to the 400hp range.

Edit: I found this on a site.

Higher octane fuel has only one beneficial feature - it allows an engine to run at higher temperatures with more advanced ignition timing under higher levels of compression witout detonating / knocking. Higher octane fuel does NOT have more potential energy and will not make an engine perform better unless that engine is knocking. On modern engines with knock sensors, higher octane fuel may make the engine run better if the knock sensors are retarding the ignition timing, which hinders performance. High octane fuel does not burn cleaner, it does not clean your engine, it does not increase horsepower or torque (unless you are experiencing knock), it does not smell better, it does not increase fuel economy (unless you are experiencing knock) and is not better for the environment. If you buy higher octane fuels for any of the above reasons, STOP!

Last edited by USA1Camaro; 11-21-2007 at 12:35 PM.
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post #3 of 5 Old 11-21-2007, 11:58 AM
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Never seen it quite like that. But I always sort of assumed this was the case. Your logic definitely makes sense to me.

Except I want to bring to the front one more thing that people like to argue over.

"If you put regular gas in a premium-use engine...you'll get less power, and less fuel economy."

I argue that. All you get by doing that is engine knock if your compression is high enough. In which case, you eventually destroy your engine. So less horsepower is a given, the knock sensors will try and adjust to the detonation which inhibits power a bit...but mpg? Does the ECU know what kind(octane) of fuel your using? No. So how can it pump more fuel (which I would assume is what would lead to the lower mpg.)

:shrug: This topic is debated almost as much as supercharger v Turbo Will be interesting to see what people have to say.

"Horsepower is how fast you hit the Wall, Torque is how far you take it with you."
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post #4 of 5 Old 11-21-2007, 05:10 PM
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every engine is different. and yes in SOME engines, higher octane fuel will produce more power, while in SOME engines lower octane will actually produce more power. to say it is ONLY to avoid knock is wrong. there is alot more to the power stroke of an engine involved. the octane rating determines how long the fuel will burn. (slow and long, or fast and short) the key to getting the most power out of ANY engine, is to get the burn to last from TDC to BDC without going out of that range, as well as 546878 other factors.

for example, if it takes your piston 2 seconds to go from top to bottom, you want to get a hot flame that lasts slightly under 2 seconds, timed perfectly. if your fuel does not completely burn within 2 seconds you get a knock. on the other hand... if your octane is so high that it all burns in less then one second then you are wasting 'time in stroke' ...in theory... im no scientist and i dont claim to know all, but it seems obvious that to find the perfect octane for ANY vehicle, (if you are meticulous and its high enough priority to know if there is a small difference in power and/or efficiency) you would have to test different octanes on a dyno, with every other factor the same. the only people this would be practical for is someone that has access to a dyno and alot of time on they're hands. thats why vehicle manufacturers do it for you, and reccomend a specific octane when you buy a NEW car.

if they say it runs good on 87, theres probably a reason they said it. im done rambling. just using too many words to try to explain a detailed theory i have bouncing around in my head.... in short, use what works best in YOUR vehicle, suiting YOUR needs.

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1992 Camaro RS - pretty much stock (only to keep its 25th anniversary edition book value)

all the other Camaros were sold
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post #5 of 5 Old 11-22-2007, 07:00 AM
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On 2 Identical motors one would have to add something to the one tuned for 87 to make identical power and depending on whether or not it made the efficiency better whether it would use the same. IE my GTO. Tuned for premium makes 400 hp. If i had it retuned for 87 HP would drop so I'd have to add headers and some more to bring it back up to 400. I would increase engine efficiency but since it is tuned for lower octane they should theoretically be identical when it comes to fuel useage. So using the same amount of fuel but at a lower cost in fuel I'd save, but the cost of what i needed to add to acheive the same HP level would equal out.

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