DODGE RAM FORUM banner

93 octane worth my money?

12K views 51 replies 25 participants last post by  jmr 
#1 ·
so since its my brand new truck and all, i was thinking of spoiling it rotten with 93 octane gas every fill up. any pentastar mechanic super techs out there know if its a good idea? the manual says 87
 
#30 · (Edited)
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"...
 
#31 ·
snrusnak- I see we're on the same page.
but you have a slight wrong thinking...

Fact is, that the knock- sensor set the ignition point on the ping boarder, which means, it recognizes, when the gas mix ignites by it self through pressure and heat and not from the spark plug.
87 octane gas has a lower self- ignite point then 91 or 97 octane.
the thinking issue what the most people have is, that they think higher octane = more power. this is partially wrong.
in a normal engine like the dinosaur engines in the ram's, where the base goes centuries back, you will not see nothing. not in power increas and not in mpg.
the ram engines are pimped constructions from a forgotten time...technically.
A modern engine has a variable intake (the hemi has it since 2008 to get a better filling, similar to a 4V engine-which increases the compression in the cylinder and comes close to the critical point, where the variable ignition point can not go back far enough to prevent the gas from self- ignition, which makes higher octane necessary), double overhead camshaft, variable cam shaft, direct injection...just to name some of the most significan differences. These engines having a high grade of filling. they having compression from up to 14:1. these engines need premium gas.
and here is the point.
it is also fact- the higher the octane, the better the combustion because it is more controlled and the timing can be set more exact.
high compression makes the engines more efficient and also improve the emissions. and this is what it is all about. CO.
In europe for example you will not get the low octane gas anymore, because even with the old engines, with higher octane you will have better CO. In europe the cars getting taxed by kg CO/kilometer. the boarders are not reachable with regular gas.
the minimum Octane in europe is 95 octane. you do not get regular no more there.
the engine sizes there are very much smaller and every manufacturer has ~1.4l 3 cyl. turbo engines with 180 hp in the program. ford started this way with the new fusion, where such a small engine- ok-its a 4-cylinder- but with high efficiency- is built in. Eco boost they call it...
the ethanol is part of this emission reduction and how you said, the ethanol does not effect the octane.
but it does effect the burning temperature which can damage the older engines.
Technically is high octane on a low compressed engine not effective- except in CO emissions. just try it out- test the after a gas tank full 97 octane and after a tank full 87 octane.
generally I would recommend the octane the manufacturer says it has to be. It has reasons.
The most people having trouble with their engines because they think they have to crank up a monster truck for a 2 mile ride to the dollar general or moving with the monster from the tj maxx parking lot 300 feet over to the marshall's parking lot.
This is what kills the engines because the engine stays cold, the gas washes in this condition the oil film from the cylinder, the gas is very rich and burns bad with high CO and soot built up and the ethanol in the gas creates with the soot a greasy, gluey film which sits as residue in EGR valves and other exhaust gas touching components. especially the oxygen sensors and catalytic converter are getting killed this way. and this happens no matter what octane the gas has.

but I agree with you when you say that if 87 octane would be the most expensive, the people would think it would be better.

The problem is, that nobody is really interested in explaining why we even have different gas octane assortement.

Btw- I was talking about normal, modern engines- not the high powered sport car engines, where the high octane is even more important, because of high rpm, high pressure and max hp output.
 
#32 ·
No offense but I didn't read everything you wrote LOL. I'm pretty sure you're saying the same thing I was just in more depth.

More compression and more ignition advance = need for higher octane(more resistance to detonation).

The stock pcm will retard timing if too low an octane is used(knock sensor will detect it).

That's basically all I was saying.

Higher octane has the potential to produce more power(if used in an engine that will take advantage of the higher octane).
 
#33 ·
I believe the 5.7 C/R is 10.75, top choice of compression for this engine is 11.00 to one. In my experience with high performance engines you should always run premium gas with anything above 10.00 to one compression ratio. The only reason why you can get away with 89 oct is the computer and the sensors feeding it info to make the proper changes in timing and air/fuel mix. If our truck had a mechanical electrical system without a computer you would def get ping/ clanking while racing, towing or uphill. You 4.7 guys are only at about 10.00 to one compression so you can run 87 oct. Rule of thumb, higher oct is for higher compression and higher pressure from forced induction. If you have a forged lower end that can take 20 lbs of boost at some point over 14 lbs of boost or so you would have to use fuel higher than 93 oct (race) because of the pressure. If you don't believe me go to Indy Cylinder and check out the 605 street with and without a blower. With a blower you must use race gas because of the pressure. The superstreet 572 you can run 93 or race gas. If you dispute this you can argue with their builders. And btw, these gen 111 hemis can run 93 oct on "almost" 12.00 to one compression because of the quench pad on the heads where as the gen 11's couldn't get much past 11.00 to one. The quench pad sort of directs the flame to ignite in the proper place at the proper time. Less un-spent fuel is wasted as is in the gen 11 hemi heads but correct me if you have a better explanation of it. And then you have your dual plugs to help fire as well. I'm currently on a 91 tune and I run 93 oct, nothing less. There was similar designs like this on the 67 440 and 426 max wedge heads (quench pads). If I was on an 89 tune I would run nothing less than 91 oct because I've seen what could happen at 7000 rpms with not enough oct. Lman is the only one here who's got it right. If you think you know better and your engine can always depend on your sensers to prevent catastrophic failure then go for it, it's your truck. Not saying it will happen, just saying it could. You da man Lman. :smileup:
 
#38 ·
My bad Cris65...sry. This talk about premium fuel being a waste of money is nonsense anyway. It's not a waste of money, it's a waste of time talking about it. People are going to do what they want to do with their money because it's theirs to spend...right or wrong. :smileup:
 
#44 ·
I haven't and won't since the Pentastar isn't made for it; the manual says to run nothing more than 10 percent ethanol blended unleaded fuel, and if you run E85 you risk damaging the engine and voiding the warranty, as well as risking a bunch of performance issues. E85 is 85 percent ethanol and 100-105 octane. The high ethanol content can quickly corrode standard gasoline fuel systems if they're not made for it.

Vehicles built for E85 also typically get 25-30% less gas mileage than running basic 87 octane unleaded. The main benefit of E85 is when it's price is significantly lower per gallon than unleaded gas thus offsetting the reduced mileage.

From the owner's manual:
CAUTION!
DO NOT use gasoline containing Methanol or gaso- line containing more than 10% Ethanol. Use of these blends may result in starting and drivability prob- lems, damage critical fuel system components, cause emissions to exceed the applicable standard, and/or cause the “Malfunction Indicator Light” to illumi- nate. Pump labels should clearly communicate if a fuel contains greater than 10% Ethanol.
Problems that result from using gasoline containing Methanol or gasoline containing more than 10% Ethanol are not the responsibility of the manufacturer and may not be covered under New Vehicle Limited Warranty.
E-85 Usage In Non-Flex Fuel Vehicles
Non-Flex Fuel Vehicles (FFV) are compatible with gaso- line containing 10% ethanol (E10). Gasoline with higher ethanol content may void the New Vehicle Limited Warranty. If a Non-FFV vehicle is inadvertently fueled with E-85 fuel, the engine will have some or all of these symptoms: • Operate in a lean mode. • OBD II “Malfunction Indicator Light” on. • Poor engine performance. • Poor cold start and cold drivability. • Increased risk for fuel system component corrosion. To fix a Non-FFV vehicle inadvertently fueled once with E-85 perform the following: • Drain the fuel tank (see your authorized dealer).• Change the engine oil and oil filter. • Disconnect and reconnect the battery to reset the engine controller memory. More extensive repairs will be required for prolonged exposure to E-85 fuel.
 
#43 ·
Its all about the performance you want. The supper is a cleaner fuel with more cleaning agents. If you can afford the extra cost up front it will pay for its self in time. The longer you drive your truck the closer you come to braking even or getting ahead.
Try a tank see for your self. You want go back . you might not notice a big difference in preformance on first fill up. But you will notice the downgrade when you try to go back. It will run fine again with reg. But not as good.
 
#50 ·
I play with Chevy engines a bit

I do know that if i have a 350 cu in 210 hp engine, it will have right at 9 to 1 compression & i can easily run 87 octane, if it is stock. If it has a Street & Strip camshaft & a real performance carburetor, you would have to step up the octane rating

If the engine is a 350 cu in 350 hp, it will have at least 10 to 1 compression & it would need at a minimum of 89 octane

a 700 cu inch engine would likely use 101 to 116 octane racing fuel, it would likely be called a Alcohol Blend
 
#51 · (Edited)
In a general sense, one might be able to translate a comp ratio number directly to an Octane requirement, but there are some variables involved,,,

The 5th Gen small blocks in the GM trucks run an impressive 11.0 to 1 on 87:

The ability to more precisely control combustion also enables the new engines to run with a higher compression ratio – 11.0:1 for the versions with regular fuel recommended

http://media.gm.com/media/us/en/che...May/Silverado-May-5/0505-silv-powertrain.html

(If memory serves, the 'versions with regular fuel recommended' are the 4.3 and 5.3, with the 6.2 running 11.5 to 1 compression and assumedly recommending a higher octane. The following deals with compression ratios,,,)

There’s the 355-hp L83 5.3L V-8, which will be the highest-volume variant in the pickups and SUVs, and the 285-hp LV3 4.3L V-6, also slotted into the trucks as a base engine. These engines share an 11.0:1 compression ratio.

The 420-hp L86 V-8 caps the range on the truck side, appearing in the premium GMC Sierra Denali and Chevrolet Silverado High Country. All the truck engines are branded EcoTec3.

The L86 has a lot in common with the LT1: displacement, block, bore and stroke, 11.5:1 compression ratio, cylinder heads, crankshafts, continuously variable valve timing and other hardware.


http://wardsauto.com/ward039s-10-best-engines/2014-winner-general-motors-62l-lt1-ohv-di-v-8

(Comp ratio on the RAM Hemi's is 10.5 to 1, I believe the Penta is 10.2, and we are familiar with the octane recommendations)

I do admire the ability of many modern manufacturers to utilize higher and higher compression ratio's on lower octane fuels. (Beats the heck out of the 70's, eh? ) :smileup:
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top