high flow exhaust = 3-5% mpg gain?

[Varn]

Any time your exhaust is free flowing beyond a certain point you are pushing more combusted and unburned gasses out of the exhaust. Manufacturers know this and add catalytic converters to make sure it doesn't get into the atmosphere.

I think an interesting experiment would be to block a bit of the exhaust and see if helps fuel efficiency at low amounts of throttle settings.

[Frank Lee]

Essentially, by adding power, the car would be able to cruise at a given speed under a lower load percentage.

It is well established that engines operating under lower load percentage are LESS fuel efficient.

[Ladogaboy]

Originally Posted by Frank Lee

It is well established that engines operating under lower load percentage are LESS fuel efficient.

That's where the tuning comes in. I can GUARANTEE that my car is less fuel efficient at 80% load than it is, properly tuned, at 40-50% load. The engine might be more efficient at 80% load, but being efficient and being fuel efficient aren't always the same thing.

[mwebb]

Originally Posted by Ladogaboy

That's where the tuning comes in. I can GUARANTEE that my car is less fuel efficient at 80% load than it is, properly tuned, at 40-50% load. The engine might be more efficient at 80% load, but being efficient and being fuel efficient aren't always the same thing.

and how would you document as in provide the proof that supports your ALLEGED claim ?
oh i know
you will provide the BSFE charts for your system .

remember
your are entitled to your own opinion ,
but
you may not provide facts by decree ,
(unless you are a politician)
you must provide VALID and REPEATABLE
test results .

ready
begin

absent documentation , your claims are bogus as in
false and this thread should be moved to the unicorn corral .
by definition

[Ladogaboy]

Originally Posted by mwebb

and how would you document as in provide the proof that supports your ALLEGED claim ?
oh i know
you will provide the BSFE charts for your system .

remember
your are entitled to your own opinion ,
but
you may not provide facts by decree ,
(unless you are a politician)
you must provide VALID and REPEATABLE
test results .

ready
begin

absent documentation , your claims are bogus as in
false and this thread should be moved to the unicorn corral .
by definition

Why would I need to provide Belgian Snowboard Federation Education charts?

Please define acronyms prior to using them, otherwise, people will find it more difficult to cogently argue their points.

As for what I was referring to, it's rather simple math. Also, keep in mind, I am referring specifically to a particular vehicle that isn't meant to represent the general population of cars. But that works both ways: What works for 1.6L naturally aspirated engine does not necessarily apply to a forced-induction engine, and vice versa. Speaking basically: While making 240 hp @ 80% load, it might be more efficiently producing power than it is when making 150 hp @ 50% load; however, why would I need to waste that extra energy in drive train loss and/or air resistance? 70 mph @ 50% load is fine for me. I don't need to drive at 100 mph or find ways to make my car run under 30% higher load just to maintain the speed limit.

So, in essence, the higher the load (regardless of overall engine efficiency), the more gas is burned. Since the increased power allows the car to cruise at specific speed under a lower load, the car uses less gas over all (fuel economy).

And this was my only point. It is the same reason why current engines are more efficient than their 20-year-old counter parts, but some of those 20-year-old vehicles are still getting better fuel economy. Other factors than just engine efficiency factor into fuel economy.

I am waiting on the interface that allows me to track my personal load range, fuel usage, and other factors (I hope that's what you meant by Belgian Snowboard Federation Education), but I have already seen the charted results from other people with similar cars. I guess I'll have to track them down if common sense and basic reasoning doesn't prevail.

[Frank Lee]

Acronyms can suck when you don't know what they are, but google is your friend.

[California98Civic]

My P&G ("LOG") routine has me accelerate with 70-80% load, then cut the injectors and glide. Repeat. When I accelerate my instant fuel efficiency numbers drop into the teens or twenties. But then with the engine off and gliding my overall average climbs up into the 60s, 70s, 80s, and sometimes higher. The higher load and heavier foot are meant to use the best engine efficiency for my car effectively by shortening the "pulse" duration, making the lower instant averages less important to the overall average calculated by my Ultra Gauge through the engine-off glide. High load is engine efficient without being fuel efficient. And high load engine efficiency followed by longer engine off glide makes for fuel efficiency. Works for me.

[Ladogaboy]

Originally Posted by Frank Lee

Acronyms can suck when you don't know what they are, but google is your friend.

I know. I Google searched BSFE, clicking "I'm Feeling Lucky." Phew... I was lucky to figure out what your acronym meant (still going with Belgian Snowboard Federation Education).

Seriously, though, I would like to make two points clear:

First, you are being hypocritical by stating (without references) that all engines are most fuel efficient at 80% load, but chastising me for not proving a negative. If you want me to prove that my engine is less fuel efficient at 80% load than it is at 50% load, I can do that, but it will take me a little time. At this point, all I have is that information from other people with similar engines/configurations.

Second, I'm not sure why I would need to provide math for the statement that: My car is less fuel efficient (regardless of load) when it requires more gas to go a given distance. That should be fairly self-proving. And by the by, I am NOT stating that the exhaust IS the cause of this mileage increase. I simply stated that it *could be* a *proximate cause* on vehicles that are tuned to take advantage of it.

[some_other_dave]

I think you're confusing two posts here--Frank is well-known here on the board, he likes to make his points in a manner that is both laconic and sarcastic. And sometimes his points are made simply to "stir the pot".

Mwebb is the one who challenged you to provide proof. I think he was confusing engine efficiency and fuel consumption, which is easy to do. Too bad he tried making his point in a very combative (and pretty obnoxious) way...

-soD

[Ladogaboy]

Yeah, really don't mean to be combative either, so I'm sorry if I came across that way. One thing I noticed before joining this forum is that most people are working with similar platforms (at least, primarily), and some problems that I am going to encounter either aren't an issue or are handled in a different way. California98Civic brought up a good point about pulsing and gliding, which I have seen is proven to be more efficient, but P&G isn't an option for me. I can't turn off AWD, and I can only fix so much of my ~.33 cd. Unless I can figure out a better way, cruising at constant speed at low loads seems to be my best bet for highway mileage. On the aside, targeted mpg on hills seems to garner fantastic gains in mpg.