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Re: Re: Mdx engine design

EXCALIBUR said:


Thanks for the warning. It is not worth the risk of damage to the engine to save a few pennies at the gas pump. Just curious, with the MDX tipping the scales at $40,000+, why are we taliking about running lower grades of fuel to save money?
You hit the nail right on the head. At a difference of, say, $.20/gal (I don't think its that much), and 20 mph for 15K miles/year, that's only a difference of $150.

I think this is a conservative estimate.
 

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First off, as mystic pointed out.......

........the additional 20 cents (you can find some places where the difference is as little as 16 cents) does not make that much of a difference in cost.

That said, another important point should be noted:
Acura claims reduced performance using lower octane fuel. However, they do not define "reduced performance". It could be reduced power & torque or reduced fuel economy or both. I'm inclined to believe the latter. So, if you're going to get lower gas mileage by using regular, then it comes down to the same thing and doesn't make any sense to use the lower octane fuel

.............Just some food for thought! :)
 

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Re: First off, as mystic pointed out.......

vicpai said:
........the additional 20 cents (you can find some places where the difference is as little as 16 cents) does not make that much of a difference in cost.

That said, another important point should be noted:
Acura claims reduced performance using lower octane fuel. However, they do not define "reduced performance". It could be reduced power & torque or reduced fuel economy or both. I'm inclined to believe the latter. So, if you're going to get lower gas mileage by using regular, then it comes down to the same thing and doesn't make any sense to use the lower octane fuel

.............Just some food for thought! :)

Actually, regular burns slightly more efficiently than premium fuel.
So a couple of octanes numbers,
91 down to 89 is not significant.
I seriously doubt you will see a change in mpg unless you constantly run 87 octane or run with regular under high loads. Only then will the engine begin to ping causing the timing to retard and efficiency to drop. Of course no one knows exactly where the 'ping' point is for a given grade of gas. Most pinging is not heard.
But running 91 octane all the time is not a bad idea if in doubt.
 

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93 Octane~~~ All the time....

Local Costco Gas station is $1.419/gallon for 93 octane as my last filled up.

But local exxon/mobil/shell is running $1.679/gallon for 93 octane or $1.479/gallon for 87 octane.

So... what did I do? Go to Costco for 93 octane gas with $1.419/gallon. :2: :D :p
 

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Hi All:

___Worm posted some real good info about the difference between the 240 HP 03 Pilot and the 240 HP 02 X about two months ago. There is a 3 profile cam in the 02 X and a 2 profile cam in the 03 Pilot. They both produce the same max HP and have within 1% maximum Torque using the exact same bore/stroke/compression ratio … They do have different intake manifolds, exhaust setups, and KS’s although I am still not sure why you would need a different KS in the X vs. The Pilot? From my reads, cam profiles would not cause a change in octane but the pre-programmed timing plot from the onboard computer will. That being said, if you advance the timing just to the point of detonation and back off a small amount to allow for varying RPM’s, loads, and ambient air temps using a particular Octane fuel, the engine for all intents and purposes will not knock if its engine management HW does not degrade. If you advance the timing for maximum output in a particular area and install a KS to retard as soon as it senses knock, you can maximize performance in that particular area (range of RPM’s) and allow the KS to pull back timing upon detonation thus saving the engine from long term damage. The reason for higher Octane fuel is that it actually burns slower (slower flame front) thus allowing a more aggressive timing plot. It does not ignite the fuel as early as a lower Octane fuel before the Piston hits its most efficient height (degrees before Top Dead Center – TDC). It’s when the ignition comes far enough ahead of the piston hitting that sweet spot (a few degrees before TDC) when Knock occurs.

___The one item I always wondered about is why the Pilot with the same engine using different intake/exhaust manifolds/KS’s and supposedly outputs almost the same amount of maximum Torque and HP receives an 87 Octane recommendation? Only when towing loads does the Pilot get the Premium recommendation. With that, the Pilots timing may not be as advanced vs. the X to avoid the KS from retarding at a particular load on a particular warmer day. The real question than is does it hurt an engine when the KS backs off the X’s timing advance under very short duration high load conditions? I would say not. You could time the X with a less aggressive timing profile from the start to avoid knock at all RPM’s/ambient air temps/and only lose an almost un-measurable amount of HP/Torque in the process (ie. Honda Pilot). If there is no timing retard, you will probably not see a difference in performance since the engine did not change anything. The other wild card is emissions. Unburned fuel by backing off advance can be a problem if driven to far. The 03 Pilot appears to be in the same league as the 02 X in regards to its emissions (ULEV rating) using a possibly less aggressive timing plot so I don’t believe this to be a problem either? When entering the 03 X’s 260 HP motor however, there was a change in emissions and some amount of this could possibly be explained from a more aggressive timing plot but more than likely, the all new free flowing exhaust system gave both the HP increase and emission decrease. As for the highway mileage differences (17/22 vs. 17/23) between the Pilot and X, the Pilot not only has what appears to be a higher coefficient of drag (boxier look) but has a larger frontal area with a significantly taller profile.

___On the cost side of things … How many of you drive to your local gas station and throw $3.00 or $4.00 on the ground? Not buy anything but just throw it on the ground? Do you go to the local Grocery or Hardware store and do the same? In my locale, Premium (91 Octane) is almost always $0.20 more than Regular (87 Octane). Over a 10 year life span, you can purchase a lot of accessories/groceries/hand tools with that $1200 - $1500 … I don’t care if the X cost $10,000 or $50,000, throwing money away is throwing it away in my book. Since this has been discussed in great detail previously, could someone please hook up a portable Analyzer and look at the timing plot at various RPM’s using the two different fuels. You might as well look at the fuel trims for an idea about gas mileage as well which I highly doubt will change given the timing is only retarded at sense of knock and probably only occurs when the motor is close to its maximums. Gas mileage is thrown completely out the window with your foot in the floor as anyone will attest.

___To summarize, will the retard of maybe 1 to 3 degrees when you have floored your X cause long terms problems? IMO, no. As long as the KS pulls that timing back from knock, the engine is going to be fine even over a 10 – 15 year engine lifespan. This engine was designed for this. If there is not timing retard at the RPM ranges you drive in, there is probably not going to be a loss of performance or mileage … The real problems IMHO come from achieving maximum HP and Torque on a frequent basis over your X’s life span. Having an engine produce a particular amount of HP and Torque at WOT is great for the drag races but an almost un-measurable loss of maybe 5% max at WOT (reduced performance) is not going to effect an X owner one way or the other. In other words, anyone pushing any engine to its max on a frequent basis will achieve a much shorter vehicle life span and much lower fuel economy irregardless of what fuel they use.

___Anyone have an OBD-II Laptop Analyzer yet?

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
 

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Just wanted to clarify...

Some readers may get the wrong idea. Octane DOES NOT control the speed at which the gas burns, it is simply a measure of how resistant it is to any given temperature before combustion. Looking at the extreme, take a highly modified turbocharged engine. When you floor it, the air allowed into the engine increases DRAMATICALLY. The airflow sensor tells the ECU to get DRAMATICALLY more fuel into the engine PRONTO. Obviously, you must retain an appropriate ratio of gas to air, so you can't go overboard, nor can you skimp. Regardless, the temperature increase inside the piston chambers increases DRAMATICALLY too. Guess what. Your fuel needs to be able to behave itself until the pistons are in the correct position (as described briefly in the above post), that is, not combust due to high temperature prematurely.

Your MDX is no different of course, except it's not this extreme, and that is why most of you cannot tell of any power or fuel efficiency losses. Now, I dare any of you to take such a race-bred car like the Acura NSX to a racetrack on 87 grade gas and tell me that you feel no power loss at any RPMs !!! That's crazy VTEC going on there.

See it all depends. I am sure that even the Honda S2000, even with such a small engine, 2L, won't be working exactly as optimally designed at 8000 RPM with 87 grade gas.

MDX...I bet the engine computer is compensating at some degree for the 87 grade gas (especially for those of you in extreme ranges of the temperature scale found in North America). From basic physics we know that there is no free lunch. This compensation must have an equal and opposite reaction. That is, slightly reduced torque output at high RPM and perhaps 1-2 mpg drop depending on how hard you drive her. Very casual and "good citizen" driving is expected to show near zero difference, explaining what most of you are confessing to.
 

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My $.02 - - -

Run 91 octane if it makes you happy and you aren't worried about the cost. I will run regular unleaded unless I hear noticeable knocking under heavy load / hard acceleration which can damage the engine. Since I am not hearing knocking, either the fuel is fine for the programmed ignition curve or it is being retarded automatically by the computer before it is audible - either way it is not hurting the engine. I may be loosing a few horse power but it has been several years since I spent my spare time racing at the drag strip, and if I decide to do it again it won't be in the X.

I have never heard anything about premium fuel increasing the gas mileage as suggested here. I would think if it were true, the gas companies marketing departments would be all over it. The higher octane does not help when you are cruising, only when you are accelerating or under a heavy load.

I feel better now.
 

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True, but...

A couple of points of clarification:

1. Higher octane gas certainly does not improve gas mileage, as you stated. But it is required for maximum output and efficiency. So it's backwards...that is to say, if you compare it to an engine designed to optimally run with 91 grade and you use less, then yes, it DOES improve it, especially when high RPMs are involved.

2. Regarding racing the MDX, of course! :D But ECUs, even those back from the 1980s and perhaps 1970s, when they detect premature detonation (DONT read this as a "bad" thing! Remember, the computer adjusts as fast as necessary as so that no damage whatsoever is done), they adjust the timing of the spark plug firing, valve timimg mgmt, etc. and they KEEP this alternate mode of operation for XXX miles, REGARDLESS of whether or not you fill her back up with the best stuff on Earth or not at your next refill. For example my Mitsubishi had a 300 mile interval between "checks". As soon as the ECU senses premature det., it goes into alternate mode, and stays in it regardless of what you do, for 300 miles. Then at 300 mark, it goes back to default (optimal).

So yes your MDX may be experiencing maybe I dunno, .5, 1, 1.5, or 2 mpg drop in efficiency over its life since you are using regular gas. Don't worry, the engineers aren't going to make the difference like night and day, it's just over-engineering. That is to say, they make the "alternate mode" sufficiently different just in case you decide to floor the car with redline shiftpoints and towing a house on wheels. They just make sure it's plenty safe enough with the gas you are feeding her that is not as resistant to detonation before the optimal time to do so during the compression/decompression cycle(s). Lastly, don't worry, the engine is designed NOT to allow so much sensitivity in when the gas ignites, so that's why the different ECU mode is only slightly different from default, it's only 1-2 (at most) mpg loss, and only a coupla horses lost in power (high rpm almost exclusively).

You may indeed be saving I dunno, 50, 100 bucks a years overall by sticking to regular gas, so it may be sensible in an economist's viewpoint! :2:
 

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I find it interesting that your Mitsubishi only checks every 300 miles.

All of the GM cars I have owned back to my 1985 Trans Am were programmed to run max advance whenever the throttle was above 70% until it detected a knock. This was done to verify that the knock sensor was working among other things. It continually adjusted the timing from the base curve to keep the engine at the verge of knocking when at full throttle which is where the best performance is.

I am surprised that the computer in the Mitsubishi is so much less flexible. I sure hope the computer in the MDX is at least as good as what GM was building 17 years ago. Every other part of the MDX is better than what GM is building today! I guess I will need to order one of those expensive service manuals for the MDX to find out.
 

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Another factor, albeit not a major one in today's cleaner burning vehicles is 'age'.
Typically vehicles have a greater need for higher octane with old age due to the accumulation of deposits with a greater propensity for hot spots and pre-ignition.
Although I can't remember the last time I started using premium fuel in an older car not requiring it.
Of course, they always got regular maintenance, and the pistons and valves were usually moving too fast for any deposits to settle on them. :D
 

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Wow, tough crowd!!! Way too sophisticated for me...
By the way I just opened a fuel door on both of my cars:

2000 Mitsu Diamante: "Premium Fuel Recomended".
2003 Acura MDX: "Premium Fuel Only".

I use premium on both and try to save money on soda.
:)
 

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miro said:
Wow, tough crowd!!! Way too sophisticated for me...
By the way I just opened a fuel door on both of my cars:

2000 Mitsu Diamante: "Premium Fuel Recomended".
2003 Acura MDX: "Premium Fuel Only".

I use premium on both and try to save money on soda.
:)
When all else fails, common sense prevails! :6:
 

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The Simple Approach....

miro said:
Wow, tough crowd!!! Way too sophisticated for me...
By the way I just opened a fuel door on both of my cars:

2000 Mitsu Diamante: "Premium Fuel Recomended".
2003 Acura MDX: "Premium Fuel Only".

I use premium on both and try to save money on soda.
:)
Once again is the better approach! Why is everyone spending so much time 2nd guessing the engineers on this issue anyway. Our TL gets mostly premium, and if I get the MDX, it will as well.
 

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Re: Question...

ndahbar said:
Has ANYONE heard knock with their own ears on a late model car these days?! I highly highly doubt it. That's stuff from the Michael Jackson and Reagan era!
Haven't tried regular in my X yet, but the 2002 T-Bird will knock on 87 Octane when under load.
 

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Hi TopDog:
Why is everyone spending so much time 2nd guessing the engineers on this issue anyway.
___I don’t believe anyone is second guessing anyone else IMO. The X Manuals all state Premium unleaded is only a recommendation and that is the way most should read it … As for more threads on the subject, this one was a doozy.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
 

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We have been using regular for a while now with a tank of premium every 5 regular gas tanks 'cause we use it mostly to commute to office and back and haven't noticed any big reduction in mileage (22mpg :D with 70%hwy 30% city) or performance but mind you that there is no load other than me or my wife. I would definitely use premium when going to mountains this weekend with all the cargo.
 

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Yes, but....

xcel said:
Hi TopDog:___I don?t believe anyone is second guessing anyone else IMO. The X Manuals all state Premium unleaded is only a recommendation and that is the way most should read it ? As for more threads on the subject, this one was a doozy.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
Instead of saying that it is ONLY a recommendation, I think it would be more fair to say that it is STRONGLY recommended. It's apparently the same wording of that in the TL owners manual. FWIW, I think if I get an MDX, I'll keep it on mostly super unleaded as we do our TL. Thanks for the comments.
 

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Hi TopDog:

___No, the manual, online information, and even the X’s gas cap doesn’t say anything like what you suggested. If the X’s engine runs fine on Regular Unleaded, why would you “Strongly Recommend” anything else? I have seen posts regarding Premium use when driving in the mountains. It is in higher elevation areas with lower air densities when higher Octane fuel to prevent knock is needed even less …

___Fortunately, we all have the choice of fuel we decide to use when we fill up. Given all I have read, Regular Unleaded is more than just fine, it is a savings that many X owners can enjoy without loss of longevity and with only the possibility of losing maximum performance.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
 

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Thanks, but it is different on the TL then.

xcel said:
Hi TopDog:

___No, the manual, online information, and even the X?s gas cap doesn?t say anything like what you suggested. If the X?s engine runs fine on Regular Unleaded, why would you ?Strongly Recommend? anything else? I have seen posts regarding Premium use when driving in the mountains. It is in higher elevation areas with lower air densities when higher Octane fuel to prevent knock is needed even less ?
___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
The TL says premium unleaded only on the fuel cap. From the owners manual: "your Acura is designed to operate on premium unleaded gasoline with a pump octane of 91 or higher."
"Use of a lower octane gasoline can cause occasional, mettalic knocking noises in the engine which will result in decreased engine performance."
"we recommend gasolines containing detergent additives that help prevent fuel system and engine deposits."

So, I guess this is different wording from the MDX owners manual.... Or everyone ahs a different interpretation of it..... (And the argument goes on..
:2: )
 
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