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Custom Dodge Ram Performance Mods - Engine - 3.6 Liter Pentastar V6 Discuss modifying your Dodge Ram with Performance Parts and Accessories!
Factory Spec: 3.6-liter V6 engine - 305 horsepower, 265 lb-ft of torque.


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  #21  
Old 05-16-2013, 09:12 AM
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snrusnak snrusnak is offline
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This explains why a hemi needs higher octane then the 4.7l.
Can you explain this? Both are 2 valve and both have similar shaped combustion chambers from what I understand.
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Old 05-16-2013, 11:06 AM
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Is the hemi not a 4 valve?
The hemi is definately higher compressed.
Has something to do wit the filling of the cylinder -higher filling-higher pressure
It is really a very coplex topic and to explain that would take pages.
I was years in school for that.
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  #23  
Old 05-16-2013, 11:19 AM
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I'm pretty damn sure the hemi is 2valve. And pretty sure compression ratios are comparable, both around 9.5-10:1.
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  #24  
Old 05-16-2013, 11:59 AM
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Engine Octane values for an engine are based on the Compression ratio, the 4.7 has a Compression Ratio 9.8:1, this engine can run on 87 Octane, the 5.7 engine has a compression ration of 10.5:1, its recommended Octane is 89. but can also run 87 without knocking.

And Yes snrusnak is correct, 2 valves per cyl

Last edited by Asur; 05-16-2013 at 12:18 PM.
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  #25  
Old 05-16-2013, 12:04 PM
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Here's a little Octane Information for those who would like to do some reading.

Unless your engine is knocking, buying higher octane gasoline is a waste of money. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.
It may seem like buying higher octane “premium” gas is like giving your car a treat, or boosting its performance. But take note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage, or run cleaner. Your best bet: listen to your owner's manual.
The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars.
About Octane Ratings

What are octane ratings?

Octane ratings measure a gasoline's ability to resist engine knock — a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane), and premium (usually 92 or 93). The ratings are posted on bright yellow stickers on each gas pump.

What's the right octane level for your car?


Check your owner's manual. Regular octane is recommended for most cars. However, some cars with high compression engines, like sports cars and certain luxury cars, need mid-grade or premium gasoline to prevent knocking.
How can you tell if you're using the right octane level? Listen to your car's engine. If it doesn't knock when you use the recommended octane, you're using the right grade of gasoline.

Will higher octane gasoline clean your engine better?


No, as a rule, high octane gasoline doesn’t outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.

Should you ever switch to a higher octane gasoline?


A few car engines may knock or ping even if you use the recommended octane. If this happens, try switching to the next highest octane grade. In many cases, switching to the mid-grade or premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.

Will knocking harm my engine?


Occasional light knocking or pinging won't harm your engine, and doesn't mean you need a higher octane. But a heavy or persistent knock can lead to engine damage.

Is all "premium" or "regular" gasoline the same?


The octane rating of gas labeled "premium" or "regular" isn’t the same across the country. One state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium. To make sure you know what you're buying, check the octane rating on the yellow sticker on the gas pump.

Oh by the way: Higher octane fuels burn slower so unless you can increase your initial advance (tuner) you will not see any difference. Also when a vehicle is tuned to use lower octane fuel a higher octane will create carbon deposits and over time will cause engine ware, overheating, and poorer fuel economy. Today's ignitions are computer controlled many are distributor-less so we shade tree mechanics can't mess with them. Many of today's vehicles recommend 91 octane but can use 89 or 87 if you don't hot rod them or over load them. Food for thought.

and all this information is taken from "American Petroleum Institute website"

http://www.api.org/ <---------- lots of good reading

http://www.consumer.ftc.gov/articles...ctane-gasoline

http://www.examiner.com/article/does...-improve-mpg-s

http://mechanics.stackexchange.com/q...ve-gas-mileage

http://www.nicoclub.com/archives/gas...ane-myths.html

http://www.carsdirect.com/car-buying...s-fuel-mileage

http://www.wanderings.net/notebook/M...sWorthTheMoney

http://www.whatcouldbegreener.com/14...will-cost-you/
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  #26  
Old 05-16-2013, 12:22 PM
Chris65 Chris65 is offline
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Thanks asur!
That's lots of reading and safes space on this server.
And explains better than I can do...
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  #27  
Old 05-16-2013, 10:04 PM
Lman Lman is offline
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Give it up dude. Your obviuosly not an engine guy. Lets end this now. Enjoy your Mopar
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  #28  
Old 05-16-2013, 10:36 PM
Lman Lman is offline
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Lets remember the ethenal thats in the fuel. My trucks an 04. Thats pre ethenal. If you want Cheap gas, buy Cheap gas. But dont try to dispute reasons for us non Cheap guys to by good, productive fuel. And you dont need a tuner to run high octane. Its not race fuel. You have a truck that costs $30 to $50k and you probably speed on the highway but when it comes to fuel it has to be the cheapest. Thats like eating fast food daily to save money but your body suffers. Well do as you will. Mopar to ya. Good luck!
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  #29  
Old 05-17-2013, 07:16 AM
Chris65 Chris65 is offline
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No, I'm absolutely not an engine guy...
Have no idea how that thing even works...
I will enjoy my mopar and for very long with the cheapest gas and oil I can find.

Btw- eating everyday in a five star restaurant is like spending twice as much for half of the food, thimk you done something good and the whallet suffers.
The truth, Lman, is in the middle. Safe where you can and spend where it makes sense.
The problem is to know, what is what.
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  #30  
Old 05-17-2013, 09:27 AM
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snrusnak snrusnak is offline
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Safe where you can and spend where it makes sense.
The problem is to know, what is what.
^^^

ethanol has no effect on octane rating. If it's 87 octane 100% gas or 87 octane 10% ethanol blend, they are both still 87 octane and have the same resistance to detonation.

You should always run the lowest octane possible that won't cause detonation/pinging. This will give the most power and cleanest engine. It is not unsafe to use higher octane than required, however, it gains you no power(technically loses some, actually, as it's essentially the same thing as retarding ignition advance), and it promotes carbon buildup in the intake/combustion chamber. And of course it's a waste of money.

There is not just one thing that determines the octane needed, there are several. The two most prominent factors are compression ratio and ignition timing. The stock pcm will NOT "adjust" for different octanes. What it will do is retard timing if you use too low of an octane, to prevent engine damage from detonation/pinging. It will not advance timing.

People always want to think more expensive is better, but it's not always the case. I can damn near guarantee that if they flipped gas prices nation wide (make 87 the most expensive and 93 the cheapest) that everyone would think 87 was "cleaner, better, and gave more hp"...
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Last edited by snrusnak; 05-17-2013 at 09:32 AM.
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