before/after 383 dyno results

[GARY C]

Because it uses fuel flow in its calculation, we tend to think that BSFC numbers are driven by fuel factors like jetting, atomization, etc., but in reality it's just a measuring stick for overall engine efficiency and it can't be directly 'adjusted'. Rather everything you tune or change in the engine can affect it for better or worse, but unless fuel economy is a factor*, its real value is as a clue to how well the combination is working. E.g. if it's relatively high, there may be something holding it back; if it's good, your combo is likely well-optimized. *(ask any customer if he'd rather have 40 more HP or 0.05 lower BSFC!)

B.S.A.C. is a little different, in that it's influencers are a bit more limited. For example if you changed the headers and it made almost no difference to power but the BSAC went up at high RPM you could conclude that the cam/header combination is over-scavenging, so rather than writing off the headers as duds, you might instead try a cam with less overlap.

There should be lots of guys here that could weigh in on the subject of how your BSFC and BSAC numbers look compared to similar engines that they are familiar with.

I don't know if this helps your BSAC example but in the prior sheets I posted we split the fuel system so half of it was reading the nitrous system, here is test 17 on nitrous reading the complete system.

[randy331]

...
I mean take the example of the engine I posted before and after on,...with the same carb and the same jets in the carb as the first dyno session, (the jets that produced best et in the car) the engine is producing 80 more hp on the same amount of fuel.

The question isn't how did that happen. We know how that happened. But, how do we get it to make 100 more out of that same fuel ???
...

I am not trying to be obtuse -- when you say the same fuel, do you mean it came from the exact same container and that container was not transported in the intervening days, weeks? What is the protocol for using a fuel source, start to finish? * Did the cap get replaced on the bung immediately or was it left open for minutes, hours ... ?

One of the ways that gases get dissolved is by the head space gas/vapor volume being replaced by environmental air which is mostly inert nitrogen. I am just pointing out that this is an area that gets assumed as identical and then you can possibly proceed down an alternate rabbit hole. When you are running an experiment your task is to identify potential confounds and this is one.

* When I was receiving hyperbaric treatments the lead tech was retired Air Force. He trained fighter pilots for high G flights (how to not black out, etc.). I was extremely impressed because over the months that I was there daily, EVERY TIME SOMEONE ENTERED A CHAMBER he ran down a checklist verbally and confirmed EACH ITEM. He did that regardless of whether anyone else was in the room. The other techs didn't. Your life literally depends on someone like this being anally methodical when you are trapped in a pressurized oxygen-rich atmosphere.

I mean the same amount of fuel burn rate.
In the testing I've done, there hasn't been any power difference in fuels unless one is oxygenated vs non.

I'm sure there are expamples there is, but most of us don't have the access to the equipment to validate that type situation.

Most of us work on what would be considered "not cutting edge" engines with limited data acquisition.

Randy

[Kevin Johnson]

I think you would be able to detect significant problems with careful use of a hydrometer (which is apparently included with some dynos).

4. Fuel Specific Gravity

A hydrometer is included with every SuperFlow dyno. Knowing the fuel’s specific gravity is important because it affects the accuracy of the BSFC readings, not to mention optimum carburetor calibration. Gasoline specific gravity typically ranges between 0.695 and 0.750. Today’s lighter oxygenated pump-gas would be at the low end of the scale.

To give a feel for the general topic:

Chemistry and Technology of Fuels and Oils

May 1970, Volume 6, Issue 5, pp 353–355:

Solubility of gases in petroleum products
Authors
V. P. Logvinyuk, V. V. Makarenkov, V. V. Malyshev, G. M. Panchenkov

gas solubility.jpg

Shell had a nice jet fuel brochure online but the link is now dead. You can download it with the Wayback Machine:

https://web.archive.org/web/20170329084 ... 2fuels.pdf


Good luck with your further investigations.

[MadBill]

...
Power comes from 2 things. fuel flow and BSFC.

How do we make more power using those 2 things ???

Randy

I think I'm still not being clear, so some examples:

o Heads with better flow and or optimized velocity can increase air consumption and produce more power but the brake specifics might go up, down or stay the same.

o Bumping the CR from say 9 to 11 on an NA engine will virtually always increase power, but in this case with probably little or no more fuel or airflow, thus lower brake specifics.

o With a stout engine built for it, pan vacuum can add 50 HP with no change in air or fuel flow, thus lower specific consumptions.

o Years ago I read of an A-B test on a stock BBM. 'A' was with the factory piston clearance, only ~ 0.001" AIR. 'B' was honed to 0.004". Due to friction reduction, it picked up over 20 HP; again there would have been no change in air or fuel consumption at a given RPM.

[Stan Weiss]

Here is the fuel lbs/hr. from PHR's dynos sheet in order of posting green, brown, blue lines. Top line is from one of Randy's before runs posted earlier.

Stan

Fuel_lbs_hr.gif

[Arthur]

Because it uses fuel flow in its calculation, we tend to think that BSFC numbers are driven by fuel factors like jetting, atomization, etc.,

BSFC is driven by jetting, atomization,.... but by many other things too.

What other things???

I've seen taking jet away improve BSFC at less power.
I've seen the dyno fuel tank running out of fuel during a pull and BSFC got stellar,... but at less power.
Q16 generally adds a power improvement, but sometimes at a loss of BSFC.
I've seen a vacuum pump add fuel flow and power, but at a little worse BSFC.

And Bill, your right , it's just a measure of efficiency,.... but good engines are efficient from what I've seen.

Power comes from 2 things. fuel flow and BSFC.

How do we make more power using those 2 things ???

Randy

You only make efficient combustion when air mass and fuel mass are conjoined as one past the seat
Every thing is subject to numbers that are open to subjective interpretation on variable parameters
That means when you aim for a number you don’t see the result
Cherio

[randy331]

...
Power comes from 2 things. fuel flow and BSFC.

How do we make more power using those 2 things ???

Randy

I think I'm still not being clear, so some examples:

o Heads with better flow and or optimized velocity can increase air consumption and produce more power but the brake specifics might go up, down or stay the same.

o Bumping the CR from say 9 to 11 on an NA engine will virtually always increase power, but in this case with probably little or no more fuel or airflow, thus lower brake specifics.

o With a stout engine built for it, pan vacuum can add 50 HP with no change in air or fuel flow, thus lower specific consumptions.

o Years ago I read of an A-B test on a stock BBM. 'A' was with the factory piston clearance, only ~ 0.001" AIR. 'B' was honed to 0.004". Due to friction reduction, it picked up over 20 HP; again there would have been no change in air or fuel consumption at a given RPM.

Those changes still changed fuel flow and/or BSFC or the power didn't change.

Lookin at the data on this 383, adding vacuum increased fuel flow a small amount. I found that interesting.
Guess that would be due to better ring seal with vacuum .

Randy

[CGT]

adding vacuum increased fuel flow a small amount

So would adding a 2 four barrel to 1 single four barrel adapter.

[PRH]

.

[PRH]

Those changes still changed fuel flow and/or BSFC or the power didn't change.

Any parasitic losses with show up in the bsfc.

Add a few qts of oil to the pan, create a bunch of windage, bsfc will go way up.

Put a big ass alternator on the motor, and connect it to a few batteries in a low state of charge, bsfc will go up.

Attach some sort of pump and make it do work, and it will affect the bsfc.

Any power you waste that doesn’t get applied to the load cell will impact the bsfc....... and many times they will have no bearing on the air or fuel consumed.



The power being produced from the amount of fuel and air consumed may not change with the addition parasitic losses, but any portion of that power that’s used for something other than loading the strain gauge will negatively impact the bsfc numbers.

Imagine a steady state test, where the motor has an additional water brake attached to the front of the crank.
You’re running the motor at 5000rpm, we’ll say it’s making 450hp.
You’re reading a fuel flow and seeing a bsfc result.
Now, add 100hp load to the front mounted brake........ the motor starts to slow down, so you release 100hp worth of load from the absorber so you can remain at 5000rpm.
The motor is still making 450hp....... and still using the same amount of air and fuel....... but the absorber is only seeing 350hp worth of load, and the observed bsfc numbers are now a lot worse, since it’s being calculated from the same fuel flow, but 100hp less observed power output.

[zums]

Besides obvious frictional losses and the fact that there is only so much you can do to improve a 23* chamber, anything you can do to reduce negative tq, i notice all the runs were made with relatively low water temp, be interesting to see a few pulls with 200-220 water temp
Tom

[Walter R. Malik]

BSFC can move all over the place and not make any difference at all, sometimes.

Getting the most power is done by burning whatever amount of fuel will effectively use-up all the oxygen in the cylinder.

Best economy will come from using whatever amount of air it will take to burn all the fuel.

Most people aim for that compromise which will accomplish both but, not the best of either.

[randy331]

Looking at the data the vast majority of the power improvement came from improved BSFC.
The average fuel flow in the 5000-7000 rpm range isn't really up from the first dyno session to the second one, but average power is.
The average power from 5000-7000 rpm (the first 4 pulls on second dyno session were 5-7k) is 20 HP better than the peak HP made on the first session, and doing it on the same amount of fuel.

So why?
Compression is the same so that didn't help.
Same oil pan and carb.
What changes were responsible for the BSFC and power improvement ?

Randy

Because shape and size are both important. IIRC this got your valve job (don't remember if you used a 50 on this or just a way better 45) and...damn I'll have to go back to the first couple of pages to see what you did. My memory sucks on stuff like this. So many pages with bull rap in them I get caught up in the weeds and forget the important stuff.

Yes, it has 50* intake and ex seats.

Is that part of improved BSFC ?

Randy