Discussion about BSFC

Is BSFC used for anything other than theoretical injector size calculation?

Can BSFC be a measure of awesome-ness? (Power?)

In reply to Swank Force One:

Yes, it's used more than sizing injectors. For that matter, I don't think that we use it for injector sizing.

But I don't think you use it to measure power. That's what power and torque curves are for- WOT testing. BSFC maps are for more than one throttle position.

Or wait.

Did i just discover the number that has a huge impact on MPG?

alfadriver wrote: In reply to Swank Force One: Yes, it's used more than sizing injectors. For that matter, I don't think that we use it for injector sizing. But I don't think you use it to measure power. That's what power and torque curves are for- WOT testing. BSFC maps are for more than one throttle position.

What's the other practical applications for it?

I was messing around looking at some dyno results and remembered reading about BSFC on RC Engineering's website.

Did some calculations, and found out that my favorite turbo motor regularly ends up with BSFC well under the 0.50 point, which from everything i'm reading, seems to be REALLY strange.

In reply to Swank Force One:

It is used to project fuel economy.

being that it's fuel flow/power, its easily converted to 1/thermal efficiency. Which can be used for fuel economy.

alfadriver wrote: In reply to Swank Force One: It is used to project fuel economy. being that it's fuel flow/power, its easily converted to 1/thermal efficiency. Which can be used for fuel economy.

Got it.

So... and i realise this is going to open up a huge can of worms, but:

What are some key factors in a motor that will sway BSFC one direction or the other?

Swank Force One wrote:

alfadriver wrote: In reply to Swank Force One: Yes, it's used more than sizing injectors. For that matter, I don't think that we use it for injector sizing. But I don't think you use it to measure power. That's what power and torque curves are for- WOT testing. BSFC maps are for more than one throttle position.

What's the other practical applications for it? I was messing around looking at some dyno results and remembered reading about BSFC on RC Engineering's website. Did some calculations, and found out that my favorite turbo motor regularly ends up with BSFC well under the 0.50 point, which from everything i'm reading, seems to be REALLY strange.

It's a big tool for powertrain matching. You know how much power a car needs to move certain speeds, you know what the gear ratios you have available, so you can see how applicable an engine will be for a car.

I don't think it's that odd that you'd have numbers lower than .5, if the units are right. Is that WOT? Or part throttle?

Swank Force One wrote:

alfadriver wrote: In reply to Swank Force One: It is used to project fuel economy. being that it's fuel flow/power, its easily converted to 1/thermal efficiency. Which can be used for fuel economy.

Got it. So... and i realise this is going to open up a huge can of worms, but: What are some key factors in a motor that will sway BSFC one direction or the other?

Compression ratio, cam timing, resulting effective compression ratio map, back pressure, EGR, friction, pumping losses, kind of fuel used, pretty much everything.

Some of those combine to pumping efficiency, some integrate into losses, some into the basic PV efficiency...

But it's all a ratio of fuel in compared to power out. The high level of system efficiency.

alfadriver wrote:

Swank Force One wrote:

alfadriver wrote: In reply to Swank Force One: Yes, it's used more than sizing injectors. For that matter, I don't think that we use it for injector sizing. But I don't think you use it to measure power. That's what power and torque curves are for- WOT testing. BSFC maps are for more than one throttle position.

What's the other practical applications for it? I was messing around looking at some dyno results and remembered reading about BSFC on RC Engineering's website. Did some calculations, and found out that my favorite turbo motor regularly ends up with BSFC well under the 0.50 point, which from everything i'm reading, seems to be REALLY strange.

It's a big tool for powertrain matching. You know how much power a car needs to move certain speeds, you know what the gear ratios you have available, so you can see how applicable an engine will be for a car. I don't think it's that odd that you'd have numbers lower than .5, if the units are right. Is that WOT? Or part throttle?

That's WOT under full boost. I'm seeing numbers like 0.42.

Typical calculators put that number at under what n/a motors tend to do, and turbo motors are generally thought to have a higher BSFC than n/a motors. RC says 0.60-0.65.

Might be one of those things that has been spread as misinformation for so long that it's become "true?"

In reply to Swank Force One:

Just remember that BSFC is NOT a dimensionless unit. 0.42 may also be 0.65, if the right unit is changed. g/hp-hr, g/kw-hr, lb/hp-hr etc- the same data point will be a different number.

I'm doing lb/hp-hr.

Swank Force One wrote: Or wait. Did i just discover the number that has a huge impact on MPG?

Swank Force One wrote: Typical calculators put that number at under what n/a motors tend to do, and turbo motors are generally thought to have a higher BSFC than n/a motors. RC says 0.60-0.65.

Note that BSFC is fuel consumption, not fuel efficiency. A lower number means less fuel consumed per unit of power produced.

Turbo motors generally have a higher BSFC at WOT than NA motors because they typically run richer in order to keep the engine from being damaged. In theory, a turbo at part throttle ought to have a lower BSFC than a naturally aspirated one because it's harnessing otherwise-wasted energy in the exhaust. That's kind of hard to measure, although the increasing prevalence of turbo engines to achieve higher CAFE ratings would tend to suggest it bears out in reality.

Right, but because BSFC is consumption per unit of power, it has a large bearing on efficiency. It's making more power, efficiently.

Where i'm finding this thing is on the outlier is that when i'm calculating this... we're talking AFRs under full bore at richer than 12.0:1, and still landing below 0.50 BSFC, which would be normally attributed to "efficient n/a motor" range.

Swank Force One wrote: Right, but because BSFC is consumption per unit of power, it has a large bearing on efficiency. It's making more power, efficiently. Where i'm finding this thing is on the outlier is that when i'm calculating this... we're talking AFRs under full bore at richer than 12.0:1, and still landing below 0.50 BSFC, which would be normally attributed to "efficient n/a motor" range.

12:1 is pretty lean. And with a decent compression plus the efficiency added by what the turbo brings- it's not all that far fetched to have good BSFC. Heck, our NA motors run about 11:1 at WOT (for component protection) and some of the turbos run 9.5:1 (same reason). So with those number you say, that's not bad. For sure, lowering the compression from 10 to 8.5:1 is WAY more than offset by using 20% less fuel.

Swank Force One wrote: Right, but because BSFC is consumption per unit of power, it has a large bearing on efficiency. It's making more power, efficiently. Where i'm finding this thing is on the outlier is that when i'm calculating this... we're talking AFRs under full bore at richer than 12.0:1, and still landing below 0.50 BSFC, which would be normally attributed to "efficient n/a motor" range.

How are you calculating it? What kind of dyno? Are you sure your dyno numbers are comparable to the inputs used for the rule-of-thumb calculations?

Thats a decent number. How big is the sweet spot?

The Saturn graph that was posted in the last thread has a BSFC sweet spot in the 250g/kw-hr range (0.41). Its alright (for peak #s on an OEM tune), but not spectacular. Its a motor designed 25 years ago. One thing I've noticed about newer tech motors is that their peak numbers aren't that different, but their sweet-spot gets a whole lot bigger.

The Prius 1NZ and 2ZR will stay around 230g (0.38) pretty much most of the time, unless at a high RPM WOT condition, or during warmup & not charging. Its inefficiencies come from electronics, (which are more predictable/consistent)

In reply to codrus:

Taking available fuel, which is different than what's actually being delivered. Using ballpark crank hp numbers based on whp numbers on a mustang dyno.

I realize my numbers are vaguely ballpark at best, and I only have wot figures, which aren't accurate for reasons above.

I just noticed that the motor is doing far more with less fuel than well... anything else i've seen.

Alfa, I should clarify that the dyno didn't see leaner than 11.8 with a sniffer, so probably richer than that in my experiences.

I'm just trying to figure out what this says about the design of the motor, and learn about bsfc in general. We don't have a way to get actual accurate numbers out of one of these.

Swank Force One wrote: In reply to codrus: Taking available fuel, which is different than what's actually being delivered. Using ballpark crank hp numbers based on whp numbers on a mustang dyno. ... I just noticed that the motor is doing far more with less fuel than well... anything else i've seen.

Perhaps that Mustang dyno is miscalibrated and the car is making less horsepower than it claims? Alternately, perhaps your injectors are larger than the nominal figure, or the fuel pressure is higher than you expect it to be? Any of those could throw off the calculations by a significant amount and make the motor appear more efficient than one would expect.

In reply to Swank Force One:

To follow up on what Cordus mentions, when BSFC maps are made, there are multiple measurment systems for pretty much everything but engine torque- since that's just the load cell.

There's air flow and fuel flow that are directly measured, which is compared to exhaust chemistry (which is somewhat backed up by the a/f via the WB sensor). Plus, the torque is of the engine, and not through the trans/wheels, etc.

I'm currently trying to have a live road "BSFC"- but know that I can't really compare it to dyno data, as the enigne works as it thinks it's working. But it's a good idea for relative calculation of itself.

(For sniffer, you mean an O2 sensor stuck up the tailpipe. I'd lower 1 a/f to the number based on mixing)

If your engine is really that efficient, then the results should show up quickly on the road and track events.

codrus wrote:

Swank Force One wrote: In reply to codrus: Taking available fuel, which is different than what's actually being delivered. Using ballpark crank hp numbers based on whp numbers on a mustang dyno. ... I just noticed that the motor is doing far more with less fuel than well... anything else i've seen.

Perhaps that Mustang dyno is miscalibrated and the car is making less horsepower than it claims? Alternately, perhaps your injectors are larger than the nominal figure, or the fuel pressure is higher than you expect it to be? Any of those could throw off the calculations by a significant amount and make the motor appear more efficient than one would expect.

We've verified fuel pressure, injector size, and power numbers were about what i would expect for the modifications given. (Aside from fuel injector size.)

This is a recurring theme on these motors. 350-400whp on 460cc injectors has happened more times than i can count.

alfadriver wrote: If your engine is really that efficient, then the results should show up quickly on the road and track events.

They do show up.

I think what i learned here is that BSFC for an existing motor based off a dyno result is pretty useless for anything other than getting a ballpark for injector size in the event you want more power.

alfadriver wrote: In reply to Swank Force One: It is used to project fuel economy. being that it's fuel flow/power, its easily converted to 1/thermal efficiency. Which can be used for fuel economy.

Winnar Winnar. BSFC shows how efficent an engine is.. Used extensively in the diesel industry.

Related BSFC question.

What would be the best way to measure BSFC & improvements before and after fuel tuning, without a dyno? 10%, 20%, 30% etc. pulls from idle-redline then graph, before and after, datalogging TPS, map, rpm, speed (to derive accel/estimate power), and fuel?

Should I ever do another LeMons team with a 1G Saturn, I'd like to tune the stock PCM to remove some of the richness at WOT to get better mileage in racing conditions.

In reply to ProDarwin:

Assuming you keep the injector calibration the exact same, the best you can do is some equivallents- for fuel flow, find the best conversion for your injectors from pulse width to fuel flow, and then use that and nothing else (make sure the injector calibration remains the same, and that the fuel pressure is the same)- then you can use fuel PW as a substitute.

Power is a little harder- if you can run it on a dyno, that's good. BUT- BSFC isn't well measured on a transient performance test. It's more a steady state thing. So for a test to test comparison, you need to make sure that the engine speed rise rate is exactly the same from test a to b.

From there- you can run a few throttle amounts, do your best time alignment of the data, and do the calculation.

But if all you are doing is reducing how rich the engine runs at WOT, the fuel economy improvement should be pretty linear. Assuming spark stays the same, that is. You don't lose much power from 12.5 down to 11.5, just like you don't lose much power going from 12.5 to 14.6.

Since you are using the stock PCM, I'm pretty sure the engine is going rich to protect the components- which would be the manifold, sensors, and catalyst. Which I bet would be different from a stock set up when you are racing.