3)Modern 3-way cat converters require the engine to run with a stoichiometric mixture (neither lean nor rich).
Fuel efficiency peaks with a slightly lean mixture.
So in that sense the cat converter causes lower MPG, but only a couple percent.
The slight restriction of the converter can be partly compensated by a less restrictive muffler.
I’ve read this thread. I owned 2 VW Rabbits ( a German bulit 78 and a US assembled 80). Both got me around 45mpg. Sure they were fast (LOL) but they were great basic transportation. It’s time for acting as if 25-35 mpg is acceptable.
Whatever happened to the USCar project (Al Gore’s other big project)? And the Automitive X-prize?
Your point is true, Circuitsmith, but that’s controlled by the MAF sensor, the MAP sensor, and finally the upstream O2 sensor. The cat converter has no entry into the ECU’s formula for fuel metering.
“The cat converter has no entry into the ECU’s formula for fuel metering.”
True, but the sensors and ECU set the mixture to stoichiometric (wavering around that value actually) in order to satisfy the converter’s needs.
If there were no converter the ECU could run things slightly lean most of the time and save a little fuel.
True.
Even under the previous EPA testing regime, most cars were capable of significantly better fuel economy than the EPA says.
Half of today’s bad fuel economy is bad drivers.
I disagree with fuel efficiency peaking at a slightly lean fuel mixture. The unburned carbon monoxide has a very low heating value and very little additional heat is released by burning that last bit of carbon monoxide into carbon dioxide.
The additional pumping losses due to pumping more air through the engine can easily offset the meager heat gain of the completely burned fuel.
The reason maximum power occurs with a approximately 12:1 air fuel ratio is because this rich mixture results in the most BTUs released per pound of air consumed by the engine.
@the same mountainbike
Try “mea maxima culpa”.
Pax tecum.
2.The Honda Civic VX (49 state) has “lean-burn” capability and has an EPA combined of 43 MPG; the CA version has no lean-burn and gets 40 combined.
Here’s a graph from a automotive engineering book (can’t recall the name, it’s at home) I have:
http://mysite.verizon.net/tbrown59/gif/AF_Ratio.gif
Specific fuel consumption (lower solid curve) varies as the inverse of efficiency.
How about looking at catalytic converters in another way. Sure you can answer “Yes cats. hurt mileage” even if the hit is 1/10 mpg less,the answer would technicaly be “yes”
We could ask “is the mileage reduction from using a cat. so great that the benifits come at too high of a cost”? Are there some that claim NO benifits from using catalytic converters?
I respectfully disgree that the ECU is programmed lean to satisfy the needs of the converter. Lean operation is to reduce CO and unburned HC output. It provides more oxygen per unit of fuel for more complete combustion. Lean is made possible by modern multiport fuel injection’s ability to more finely mist the fuel and more exactly meter it. This same ability makes possible more complete combustion of the fuel more rapidly and at a better point in the power stroke, enabling better use of the energy in the fuel, reaping more power per fuel unit with lower unwanted emissions.
Lean is done for reduced emissions and better mileage. It’s not done in order to provide optimum conditions for the converter.
Oldschool, the question is good, but it’s based on the assumption that cat comverters adversely affect fuel mileage or create a restriction, but no evidence exists that I’m aware of that this is the case.
I feel pretty safe in suggesting that the deigners of cat converters have published such data to the automotive design teams in their industrial catelogs, but unfortunately it’s not published to the general public. They’re not hiding anythiung, there’s simply no point in publishing the data…the general public would have no use for it or even understand it’s application.
I respectfully disgree that the ECU is programmed lean to satisfy the needs of the converter.
I respectfully disagree too, and that’s not what I said:
"the sensors and ECU set the mixture to stoichiometric…in order to satisfy the converter’s needs. "
Stoichiometric is neither lean nor rich.
Interesting statistic I read today (source USA Today). Average 0-60 time in the 80’s was 14sec,today it is 9 sec. with the same gas mileage.
What else does this stat. indicate? the demise of really underpowered cars? probably so.
MB I am from the school that cats. don’t hurt mileage at all, but for arguments sake I was willing to concede that 1/10mpg hit.
My point is that I respectfully disagree that the ECU in any way adjusts the fuel mix for the purpose of meeting any needs of the catalytic converter.
Further, I’d argue that the converter has no needs beyond being kept above 400F and not having its catalyst coated with byproducts of the combustion process. The gasses out the port easily keep the converter above 400F, especially since the ceramic is so good at retaining heat.
I have no aguement with a 12:1 ratio for maximum power. But the converter’s needs are not taken into acount for the metering of fuel.
Thanks.
To me the change in the average 0-60 time with the same mileage suggests that today’s technology uses the energy available in the gas much more effectively. It goes back to previous discussions on today’s sensor-based systems being much more accurate and responsive than the simple reaction-to-vacuum venturi system, the fuel being better vaporized as it enters the chambers, higher engine operating temps (I can remember when 165 degree T-stats were common), better cylinder and component design, and better materials and manufacturing technologies. More gears help too. 4-speeds used to be the things of hot rodders, now even family sedans are five speeds.
It’s still a suck-squeeze-bang-blow world, but we get far more out of the fuel in the process.