Re-flash to run lower octane fuel?

[Mike Poore]

The lease is up on Barb's '05 Aviator in September, and we'd like to buy it and give it to the kids. Only thing is, it has the 4.6 DOHC motor, I think exactly the same one as the '04MM, and requires 91+ octane fuel. Can we buy a chip to re-flash the 'puter allowing it to run on 87?

It's a wonderful vehicle, and would be good, safe transportation for them and the three children; but sucking up 93 octane gas at 15MPG could be a deal breaking issue.

[Bradley G]

And take all the fun out of it?:D
Of course you can, you need the ECM code, and someone who can burn a chip or flash the ECM.
A newer hand held tuner would give some adjustibility as well.

[Mike Poore]

And take all the fun out of it?:D
Of course you can, you need the ECM code, and someone who can burn a chip or flash the ECM.
A newer hand held tuner would give some adjustibility as well.

I was hoping it was gonna be that easy. I guess a hand heald tuner would be the way to go, since John has a Mach 1 with the same motor. It would be a way cool birthday gift ....the Aviator and the tuner. :D

Thanks buddy. :high5:

[rayjay]

Will do better MPG wise with 87?

[CRUZTAKER]

Dennis tuned our Aviator. And just as with the Marauder, it isn't wise, nor is it any more efficient to de-tune the car for cheap gas.For what little saving one would get saving 10-15 cent a gallon over 25 gallons, it isn't worth the sheer amount of timing that would be pulled from the motor.

[Dennis Reinhart]

The lease is up on Barb's '05 Aviator in September, and we'd like to buy it and give it to the kids. Only thing is, it has the 4.6 DOHC motor, I think exactly the same one as the '04MM, and requires 91+ octane fuel. Can we buy a chip to re-flash the 'puter allowing it to run on 87?

It's a wonderful vehicle, and would be good, safe transportation for them and the three children; but sucking up 93 octane gas at 15MPG could be a deal breaking issue.


I could make a lower spark and adjust EGR and improve it some so you could run 87

[Mike Poore]

I could make a lower spark and adjust EGR and improve it some so you could run 87

Thanks, Dennis. I sent a PM.

[Mike Poore]

Dennis tuned our Aviator. And just as with the Marauder, it isn't wise, nor is it any more efficient to de-tune the car for cheap gas.For what little saving one would get saving 10-15 cent a gallon over 25 gallons, it isn't worth the sheer amount of timing that would be pulled from the motor.

Barry, it's 30 cents a gallon difference, here. John and Megan won't care how fast they get there, but need the room and safety the Aviator will provide my grandchildren.

I've gotten the answer I need, thank you Brad & Dennis, and think it might be useful and entertaining to discuss the fine points of changing the tune, for reasons others might consider. :)

[JACook]

Guess it's a matter of perspective. 30 cents per gallon on a 25 gallon fill is $7.50, but
weighed against a $100 fill-up, it's kinda chump change. Or, to look at it another way,
the cost savings would give you the equivalent of about 1.75 gallons per fill up. At 15MPG,
that's only an extra 26 miles per tank, -IF- the detuning doesn't cost you any efficiency.
And that's a very big 'IF'.

And, of course, you're not gonna get that tuner for free.

Out here, Chevron premium is usually 20 cents more than regular. I'm not willing to
accept the potential risk for <5% gain, but hey, if it turns out well for you, I'll be
happy to change my tune, so to speak... :)

[CRUZTAKER]

Guess it's a matter of perspective. 30 cents per gallon on a 25 gallon fill is $7.50, but
weighed against a $100 fill-up, it's kinda chump change. Or, to look at it another way,
the cost savings would give you the equivalent of about 1.75 gallons per fill up. At 15MPG,
that's only an extra 26 miles per tank, -IF- the detuning doesn't cost you any efficiency.
And that's a very big 'IF'.

And, of course, you're not gonna get that tuner for free.

Out here, Chevron premium is usually 20 cents more than regular. I'm not willing to
accept the potential risk for <5% gain, but hey, if it turns out well for you, I'll be
happy to change my tune, so to speak... :)

Bingo.

Jessica wants to bak it down as well...that why we are looking into a Suburu AWD waggon rather than detuning a big V8 SUV.

[Mike Poore]

Bingo.

Jessica wants to bak it down as well...that why we are looking into a Suburu AWD waggon rather than detuning a big V8 SUV.

Those questions make it an interesting discussion, Barry.

Bottom line: will de-tuning it negate any gains in cost per gallon of fuel. What is the break even point; and are we talking about genuine savings or just making us feel good. :dunno:

Charlie (bluerauder) is good at these cost analysis issues, and I think, Dennis has those data.

It may be an interesting exercise for all of us to consider, though. I can see, however, the wisdom of going with a hand-held device, as Brad suggests, rather than burning a chip, if the initial cost doesn't negate any savings over the long run.

[Krytin]

You have the perfect test.
Check you mileage before and after the de-tune and the question will be answered once and for all!!

[Mike Poore]

You have the perfect test.
Check you mileage before and after the de-tune and the question will be answered once and for all!!

Um, I was hoping someone else would try it, first. :D

[Stangracer89]

No. 10:1 compression. It is not a mileage or cost issue. It is a detonation issue.

[Stranger in the Black Sedan]

You can always pull timing and lose major HP, and it will run fine but why. The muscle car guys still find that you lose a lot more HP building an engine w/ too high compression, and having to back a ton of timing out to not detonate, than you would lose building the engine w/ appropriate compression ratio and running aggresive timing.

In this case it is reverse engineering of the wrong kind. I'm sure someone with a crown vic would love to trade engines with you.

[Bluerauder]

Charlie (bluerauder) is good at these cost analysis issues, and I think, Dennis has those data.
I ran some numbers for Mike and sent a PM. Here's a summary ---

Mike's proposed course of action results in a savings of only $200-$300 per year on a fuel bill that is about $4000. Not a big savings in my opinion. That's only $3.85 to $5.77 a week. Less than a typical lunch.

It would take 16-24 months to offset the cost of a typical tuner at this rate.

However, if the tune results in a drop of just 1 MPG to 14 MPG, that savings is nearly completely offset and the net savings is only $19.00 for the year.

The loss of any more MPGs than that (e.g. down to 13.9 MPG) would cost more than the savings and it would have been better to keep 15 MPG with 93 Octane.

On economics alone, this doesn't appear to be a reasonable solution. Factor in potential damage to the 4.6L DOHC and it is a "No Brainer" IMHO. I wouldn't do it.

[MitchB]

First, lets understand and all agree that you can run regular grade gas without engine damage - if you tune for it. No one here thinks of a Marauder as an economy car, but there are things you can do to boost fuel mileage a little. My father insisted on putting regular into his Marauder and it never detonated, but I looked at how active the knock sensor was in pulling timing, so I just retuned it for 89. The car is not as fast as it was and I do not know if he is really saving anything in the end, but still, you can do it. Aside from detuning to run on regular gas - which may or may not actually save you money, there are other things I have done and you can do to increase fuel mileage with minimal impact on performance.

Mitch

[MENINBLK]

With gasoline costing over $4.00 a gallon,
you think that the 20 cents in savings is worth wrecking the engine ???

You cannot tune the Marauder engine for 87 octane.
There are physics within the engine that require 91 octane
and they cannot be changed without some physical change
to the engnie itself.

Tuning for spark timing and EGR will only delay the inevitable **BOOM**.

[MENINBLK]

No. 10:1 compression. It is not a mileage or cost issue. It is a detonation issue.

The compression is not the problem.
There are plenty of high compression engines running 87 octane fuel.
The problem is the design of the combustion chamber.
The flat area where the piston just clears the head is called the quench area.
When an engine is deisgned using quench pistons, like ours,
they develop maximum compression and have very close tolerances to the head surface.
This design tends to produce detonation with lower octane fuels.
This is why there is a need to run 91 octane or higher.
Swap out your pistons for non-quench pistons and you lower the quench area,
lower the compression and can now run a lower octane fuel.

Now you will need to retune to get back all of the lost horsepower.

[Stranger in the Black Sedan]

With gasoline costing over $4.00 a gallon,
you think that the 20 cents in savings is worth wrecking the engine ???


If he's really intent on pinching pennies, there is no saving him. Let him do it.

[Aren Jay]

Bingo.

Jessica wants to bak it down as well...that why we are looking into a Suburu AWD waggon rather than detuning a big V8 SUV.


Subaru's are great as long as you are not BIG.

But Subaru's do not get great gas mileage, better for city worse for highway.

My Marauder gets better Highway Mileage than my NA Subaru ever did.

[JACook]

The compression is not the problem.
There are plenty of high compression engines running 87 octane fuel.
The problem is the design of the combustion chamber.
The flat area where the piston just clears the head is called the quench area.
When an engine is deisgned using quench pistons, like ours,
they develop maximum compression and have very close tolerances to the head surface.
This design tends to produce detonation with lower octane fuels.


The two biggest factors in determining octane requirements are compression ratio, and
cam timing. Or, more specifically, when the intake valve closes. A close third is combustion
chamber design. A large open chamber tends to be octane friendly only because it results
in such a low compression ratio, it's too lazy to detonate without serious provocation. Start
pushing the compression ratio with an open chamber head, and you very quickly use up
that octane tolerance. I've seen aluminum open-chamber heads that would detonate on
92 octane at anything over 9:1, while OTOH, I've built iron head 10:1 FEs with closed
chamber heads that would run on regular. The key is to use a tight chamber with multiple
quench pads, tight piston-to-head clearance, and the right cam timing.

Modern cylinder head design almost universally favors more compact chambers with
multiple quench pads. The 4.6L 3-valve runs 10:1 CR on 89 octane. That cylinder head
has 3 quench pads. (The variable cam timing is also a big factor.) The 4.6 4-valve has a
fairly open chamber, with 2 rather small quench pads, similar to the current "Hemi". The
Chevy LSx engines use a tight chamber that bears a striking resemblance to the Yates
Cleveland head. All of these engines use a tighter piston-to-head clearance than what
was common in older engine designs.

While it is indeed possible for quench pads to promote detonation, that's the exception
to the rule, when the quench clearance gets into the .060" to .080" range. Tighten that
clearance up, and good things happen. The best engine builders will actually flirt with
having the piston just kiss the cylinder head under high-rpm lift-throttle conditions.

Having built a few engines myself that danced on the edge of streetable compression ratios,
I can tell you that, done right, quench pads are one of the more important tools in combating
detonation. The turbulence caused by multiple tight quench zones allows for a much faster
burn rate. A faster burn, along with a physically compact chamber, greatly reduce the engine's
octane sensitivity. If anything, I'd say the MM's cylinder head and piston dish design have
too little quench, not too much.