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To: ColoradoSpringsPrius

I noticed you have an open mind.
I have thesis I would like to share with you.

Here it goes:

"The Prius Mpg's inconsistency readings are because we do not identify the variable that makes it change".

Why? We have tried to relate the mpg even to our grandmothers and grandfathers state of mind, and it does not work. We can not get consistent mathematic relation.

There is a variable that we have not try yet.

Since the moment the Prius have a different polution output thru the muffler, maybe the variable is located just outside the muffler. THE AIR. Yes, the air. Just the air.

Did we ever consider the oposition of the air outside vs the output of the muffler? Which are the factors that realy affects that kind of oposition?
Maybe, some of the variables that we have before could consider respect to the air instead to the bladder.

If we could put caps with different output orifices to the muffler as a way to manipulate the counterpressure output. Or just reduce or increase muffler diameter. Or none of that. Maybe the different air densities are the one that are hiding the constant number that we are looking for to manipulate. Air density, barometric factors, etc.
 

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Rmarchena said:
To: ColoradoSpringsPrius

I noticed you have an open mind.
I have thesis I would like to share with you.

Here it goes:

"The Prius Mpg's inconsistency readings are because we do not identify the variable that makes it change".

Why? We have tried to relate the mpg even to our grandmothers and grandfathers state of mind, and it does not work. We can not get consistent mathematic relation.

There is a variable that we have not try yet.

Since the moment the Prius have a different polution output thru the muffler, maybe the variable is located just outside the muffler. THE AIR. Yes, the air. Just the air.

Did we ever consider the oposition of the air outside vs the output of the muffler? Which are the factors that realy affects that kind of oposition?
Maybe, some of the variables that we have before could consider respect to the air instead to the bladder.

If we could put caps with different output orifices to the muffler as a way to manipulate the counterpressure output. Or just reduce or increase muffler diameter. Or none of that. Maybe the different air densities are the one that are hiding the constant number that we are looking for to manipulate. Air density, barometric factors, etc.
I don't know enough about physics or engineering to reply intelligently - in fact, I basically know nothing about physics or engineering! - but I have little doubt that air is one of several factors that we're not used to considering when thinking about mpg. For instance, my wife and I seem to get consistently better mileage at 60 mph than DanMan - and the major difference in our situations seems to be Colorado's thin, dry air versus that thick, humid stuff they make people breath in Florida.

And it's not just wind resistance: That extra humidity probably makes roads a little stickier. I suspect that road surface has more effect on mpg than we're used to thinking it does.

So to find the CAUSES of variability in Prius mileage we must, as you say, look beyond our grandparents' state of mind. But (please correct me if I'm wrong) you think Priuses are not just variable but actually inconsistent with regard to mpg - i.e., two Priuses, driven in the same conditions, may get dramatically different mileage. I'd bet cash money that Prius drivers with very similar driving styles and situations - length of drive, speed, number of stops and starts, hills, ambient temperature, amount of wind, size of load, etc. - have very similar mpg. Unfortunately such comparisons are extremely difficult to make. The only practical test would be to have different cars drive the same course at the same time in the same way. So if Priuses actually are inconsistent, it's going to be hard to prove.
 

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Backpressure on the exhaust is certainly a factor in engine power output (and thus a factor in fuel economy). I recall a couple people describing replacement mufflers they used that allow better flow (less pressure at the exhaust headers). I was somewhat suspicious though, because I think they may have defeated the emission reduction properties of the catalytic converters in the process. But I don't recall them describing the replacement in enough detail to understand whether emissions were compromised. Anyway, due to the nature of the Prius transmission and the computer controls on it, additional engine power tends to show up as better fuel economy, not as better 0-60 times.

The problem with trying to find one single answer to Prius fuel economy is that so many factors had to be finely tuned to get the Prius where it is. So exhaust back pressure may be a factor for some, alignment for others, etc.
 

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Wheel Rpm at any given time is a known constant thus giving accurate velocity numbers. Unless the wheels are slipping on the pavement this will always be one known variable in the equation giving us known distances traveled through simple equations. (I don't see alot of Prius burnouts!)

The other being the fuel itself, the only way to accurately measure the fuel consumed is at a single point in the fuel "feed" system (hence fuel line). A "differentially compensated" inline vane type fuel flow meter applied as close to the tank as possible would generate accurate flow rates out of the tank and that data sent to the ECU or other computer. Diagnostics would show "live ROF" (rate of flow) and computational data output such as fuel "passed" through the flow meter over a given time. This leaves the simple equation of (total Miles traveled / (total sum of the calculated flow rate / whatever time sampling rate you choose)=MPG.

The definition of the Fuel meter is a differentially compenseted mass flow meter that takes into account atmospheric pressure as well as differential pressure at the input and the output. An example of input pressure would be the fuel tank fill level as the fuel is consumed. Output pressure (or lack of) example would be rapid acceleration causing the fuel pump to pull hard on the meter.

Fuel is pumped into the tank and extracted by the engines fuel pump. Speed is determined by how much fuel is being consumed in a "rate" formula per set velocity or acceleration curve. If you want the final answer on fuel consumption this is the only way it can be done. At the two vaiables that directly effect the outcome.

Trying to measure anything else in my opinion (even the fuel in the tank with a float system is not accurate due to things that marchena mentions such as barometric conditions , temperture and what not. Ask any Twin turbo 300Z guy, he'll tell you air desity advantages that are directly proportional to rate of fuel flow.

A system such as this would also "fix" the fuel gauge errors. We would fill the tank til a certain sensor (electro or electro-mechanical) would send a "full indication" as a beep or whatnot which the car would automatically know that it has X gallons of fuel (Car would then be filled to the same amount everytime, yes, you could possibly put in more but would defeat the purpose of the fuel gauge accuracy. If the tank filler was designed to elliminate any chance of overfill then this would be moot.). Fuel flow would then be deducted mathmatically from the total in the tank "bank" and would give you a constant linear consumption curve. Only drawback I see to this is that you would need to fill the car to that point of "full" everytime you have a fillup. Only other option is to have "fillup" flow meter!!!
 

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I suspect what can skew a fuel flow meter is the evaporative emissions system sucking fuel vapors out of the fuel tank and putting them into the intake manifold to be burned, bypassing the injectors (and any added fuel flow meter). I believe this is why higher MPG is often seen after a fill, and when the tank gets low.
 
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