The BSFC chart thread (post 'em if you got 'em)

[slowmover]

[some_other_dave]

I'm guessing that those numbers are all obtained with WOT (Wide-Open Throttle). It would be lovely to see a full map made using different throttle settings... Which I'm guessing may not be available.

-soD

[slowmover]

It's hard to find much info. This is the first time I've seen any BSFC numbers (outside of a few comments posted elsewhere).

But the '03 chart on the CTD



pretty closely follows my experience for under 60 mph (24-26 mpg, empty or loaded). I don't think 24 at 70 is do-able due to aero resistance.

Original article is a decent read, but without links to other articles cited, not worth much in and of itself.

[UFO]

That map was not done figuring in wind resistance?

[RH77]

It's odd to see what you can stuff a Cummins Diesel into. So far this month, I came across a Jeep Wrangler and Ford Ranger, both of which looked otherwise stock (with the exception of the "C" badge on the fender and the exhaust note).

With the Jeep appearing to have the advantage for off-roading, the Ranger looked to be a working farm truck -- I wonder if the combo offers better FE in addition to the obvious torque -- and what exactly was in it? I'm sure there are a variety of compact, 4-cylinder Diesels to choose from, outside of the average consumer market...

RH77

[slowmover]

Originally Posted by UFO

That map was not done figuring in wind resistance?

So far as I can tell.

OTOH I average 24 mpg, empty or loaded (up to 2k payload) across Gulf Coast Texas with some fairly stiff winds depending on the time of year. My motor has a slightly higher rating than that one, but is an otherwise similar truck. The times I have chosen to run 68 mph show about 22 mpg with no adverse winds. I have not come across anyone getting 24 at 70 in a CTD. At 60, yes, numerous instances.

The purpose of this graph was in discussion of timing advance changes to improve FE. (Mine is stock).Maybe my truck would do better with a timing change, but I'm loathe to add a tuner at this point.

[abell75]

Originally Posted by MetroMPG

If that line does show torque at WOT, that may make it incredibly useful: could you not essentially use it to extrapolate what throttle/pedal position to use to get the engine closest to the sweet spot at a given RPM?

EG. in the Saturn chart, 7/9 throttle @ 2000 RPM looks like it would put you squarely in the 250 g/kWh island.

Of course it doesn't work quite that simply, because the engine doesn't "idle" at 2000 RPM ("0/9ths"), so you'd likely have to factor in the amount of pedal required to get there with no load on the engine.

I think our group is close to nailing this down, but since I just got an Ultra-Gauge I thought I'd ask for some clarification. (I get to apply the science, yay!)

1. Have we concluded that torque on the chart correlates to load and/or throttle position on the SGII or the UG?
2. If we have, which is the preferred gauge to monitor (load or TP)?

It would seem to me that load correlates to torque, and the %load we should target during the Pulse part of P&G is defined as that which puts us in the middle of the most efficient island. Others have mentioned TP though; is there a reason it would correlate better?

It's difficult for my brain to believe that accelerating at 80% load/throttle is the most efficient use of the fuel - I've always been told that slow/steady acceleration is better. I have faith in science though (oxymoron alert!), and will certainly give the high load rapid acceleration approach a shot.

If we do reach this conclusion, perhaps it should be added to the BSFC wiki page.

[superchow]

Originally Posted by abell75

It's difficult for my brain to believe that accelerating at 80% load/throttle is the most efficient use of the fuel - I've always been told that slow/steady acceleration is better.

The way I understand this is when you optimize the following:

1. High load to reduce pumping losses through restriction in the intake manifold.
2. Tall gearing to maximize the speed gained per engine speed increase.

The combination should be reduced pumping losses in the engine and slow and steady acceleration due to "long gears".

[some_other_dave]

Originally Posted by abell75

It would seem to me that load correlates to torque, and the %load we should target during the Pulse part of P&G is defined as that which puts us in the middle of the most efficient island. Others have mentioned TP though; is there a reason it would correlate better?

Load would take into account how much air is actually going into the engine, or the air pressure in the manifold which more or less correlates with how much air is going in.

Throttle position is related to load (and manifold pressure), as the air has to go through the throttle body. But engine RPM, air temperature, and other factors affect the actual amount of air going in as well.

The throttle position is very useful for telling when the driver goes to Wide-Open Throttle (WOT) or when the throttle is closed, and also when the throttle is being opened which indicates the driver wants to accelerate. But it is less useful than load for showing what is going on in the engine IMHO.

-soD

[fjasper]

forums.vwvortex.com/showthread.php?547541-bsfc
Sorry about the partial link, I don't have enough posts to put up a link yet.
(poster put up a BSFC graph at WOT, calculated from OBDII data)