What octane can I run in a stock 2.9l v6?

[Subarute]

I read on another forum that I can run 93 octane as it's " a cleaner burn, better mileage and slightly more power. " Is this true? or maybe 88 octane is better? im currently running 87 octane, 10% ethonol.

 

[Subarute]

this is in a 91 ranger btw

 

[Dirtman]

None of that is true. The 2.9 only has a 9.0:1 compression ratio. Using anything over 87 octane is just wasting money. Higher octane fuel just means it resists igniting under high compression, there's no benefit whatsoever in a low compression engine.

 

[Subarute]

None of that is true. The 2.9 has a 9.0:1 compression ratio. Using anything over 87 octane is just wasting money.

Where im at 88 octane, 15% ethonol is cheaper

 

[Subarute]

thats why i ask though. thanks

 

[Dirtman]

That engine is made to run on no more than 10% ethanol. The more ethanol in the fuel the worse your fuel mileage will be. Ethanol is not as efficient as gasoline. I'd stick with 87 octane e-10

 

[RonD]

Yes, +1 to Dirtman's posts

As said Octane is a HEAT rating, well to be more accurate "Oct" is 8 and "tane" is a carbon chain, so 87 'octane' is a percentage of 8 chain carbon molecules, very simplified.
8 chain are more stable, less likely to self ignite when heated, so the more "octane" molecules the more stable

A gallon of 87 octane gasoline has EXACTLY same energy as a gallon of 93 octane, but read on

Ethanol can bond to the 6 and 7 chain carbons to make them more stable, so ethanol increases Octane rating
But ethanol has less energy per gallon than gasoline

So 10% added ethanol would lower MPG a bit, not 10%, maybe 2%
15% even lower MPG

Ethanol can also bond with WATER, gasoline can not, all gasoline will have some water in it, in the winter this water can freeze in the fuel lines or filter and cause issues
So winter gasoline will have ethanol added which prevents the water from freezing

 

[decipha]

The only time you need higher octane fuel is if you cannot reach mbt without detonation. This is usually always due to cylinder pressure. In order to reach those kinds of pressure you need either a higher compression engine or some type of power adder that increases cylinder pressure. Otherwise, for the most efficiency a lower octane fuel is better.

Perfect example is my 03 marauder daily driver. Its a bone stock high compression (10:1) 4v modular engine which requires premium fuel from ford as do all ford 4v 4.6 engines. I have it de-tuned for 87 octane and although it makes slightly less power at WOT ~10rwhp, it does get slightly better fuel economy.

 

[adsm08]

Where im at 88 octane, 15% ethonol is cheaper

Where you are at it isn't legal to put that stuff in your Ranger.

If you actually stop to read the signage that is supposed to be posted around the E-15 88 Octane pump handle, it is illegal to run that stuff in non-flex fuel vehicles older than 2001.

 

[PetroleumJunkie412]

None of that is true. The 2.9 only has a 9.0:1 compression ratio. Using anything over 87 octane is just wasting money. Higher octane fuel just means it resists igniting under high compression, there's no benefit whatsoever in a low compression engine.

There IS a high compression 12v 2.9 with a 9.5:1 compression ratio. There's a VERY small chance his Ranger has that block.

I read on another forum that I can run 93 octane as it's " a cleaner burn, better mileage and slightly more power. " Is this true? or maybe 88 octane is better? im currently running 87 octane, 10% ethonol.

Run 87 with as little ethanol as possible.

Turn your phone sideways, and click on the link to my build thread if you want to get more GOFASTS out of your Ranger ??

 

[sgtsandman]

Running higher than 10% ethanol fuel is going to cause issues with your fuel system. Degraded seals and hoses. Possibly internal corrosion problems. This is on top of the already mentioned legality issues. Unless you are have engine problems that running a higher octane can help remedy, I would stick with what is recommended by Ford.

 

[4.0blue98]

High octane will contribute to carbon buildup due to incomplete combustion if your engine isn't designed for it... Like my 4.0 ohv.

 

[PetroleumJunkie412]

There is one loophole here. And I hate to say it because it'll probably cause someone to **** something up.

But, if you adjust your distributor to 12 degrees (up from base timing at 10 degrees) and run 89 octane you will see a bump in power.

Octane is a measure of detonation resistant properties.

Significant timing advances causes detonation

Adjusting timing massively increases the performance in the 2.9.

If you **** it up, you will **** up your engine.

 

[Dirtman]

This is why EDIS + knock sensors are far superior to distributor systems. The computer can push the timing to the very edge. Also allows higher compression engines to run on lower octane fuel since the computer just retards the timing when neccessary to prevent knocking.

My engine couldn't run to well on 87 octane without the knock sensor. And in my case using 93 octane can give a boost in power since it allows the computer to advance the timing more, but it can run happily on either.

 

[PetroleumJunkie412]

And those are the exact reasons I'm converting from TFI to EDIS, and adding a SOHC knock sensor