MILD THUNDER

iTrader: (3)

Maybe this will help explain it

SB

iTrader: (1)

BSFC is how much fuel is used per HP. It does not necessarily tell you if motor is rich or lean.

BSFC is figured by two measurement only: fuel (lbs/hr) and HP.

BSFC was invented to see how efficient a motor is at converting fuel into hp, and thus is only accurate if fuel flow and hp measuring is accurate.

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So yes, BSFC can be influenced by being rich or lean, but it is not a rich or lean indicator.

What effects BSFC ?
Air fuel ratio
Carburetor sizing (restriction)
Intake manifold (all aspects)
Cylinder heads (all aspects - runner sizing,shape, combustion chamber design, etc,etc)
compression
piston design (dome can interfere with flame propagation, can interfere with air movement during overlap, etc,etc)
piston ring placement (lower it is, more are for fuel to hide from combustion)
piston ring thickness (friction)
piston ring tension (friction)
crankshaft design (aerodynamics, fluid dynamics, etc)
oil pan design (windage, crankcase volume, wet sump vs dry, vaccum pump, etc,etc)
camshaft - oh boy !
exhaust - oh boy !
This is just a few things, so the list of what effects bsfc goes on and on

It all effects bsfc because, again, bsfc is just about how much fuel is used per hp is made ! As you can see, many things effect hp even iof the same amt of fuel is used.

MILD THUNDER

iTrader: (3)

How long since the fuel turbine was calibrated? Was the fuels specific gravity checked before the pulls?

I hate to say it, but if you ended up making less power, with afrs in the 10s shooting for brake specific numbers, your tune prob isnt so good.

Its proven a gasoline engine will make its best power around 12.5 air fuel ratio. Most shops dont use an 8 pack wideband, so you are seeing the average for each bank. Its imperative to play a little with fuel to see how the engine responds once you get in that ballpark afr range.

Timing can and does alter egts as well. The engine will stop responding with power increases, well before it goes into detonation from too much timing. In other words, lets say you have an afr reading of 12.4, and you have 34 deg of timing in it. You bump timing to 35. You see a 8hp gain. You then bump to 36, and see another 8hp. Again, you bump it to 37. Bu, You see no gain, or maybe 1-2hp. Thats where you stop. Theres a lot of variables on what timing the engine requires. Chamber design, piston design, stroke, bore size, afr, spark plug style, etc. Not every big block wants 34 degrees, from a 454 to a 632.

I think there is some mental blockage that guys think they are helping the engine by retarding the timing to what THEY think is safe. Well fuk, why even dyno then? Forget the science behind it, just slap the distributor in at 32 and call it good lol.

Throwing extra fuel at it will show lower egts usually, but that doesnt necessarily mean thats a good thing. We all strive for the best , most efficient power making combo, will argue about alum vs iron head chamber heat, etc. Then when dyno time comes, the crutches are pulled out.

What kind of timing did you guys have in the engine bck?

sutphen 30

I'd say his afr meter is off by a little.

bck

Engine made the best power @ 34 iirc. Jetting was changed based on a combination of egt, plug readings and bsfc. I noticed O2 did not change much when jetting was changed. I could however see changes in power and bsfc when jetting was changed. I'll take a closer look at the sheets later today.

MILD THUNDER

iTrader: (3)

What fuel were you using on the dyno ?

bck

93. Didn't ask if it was non ethanol

MILD THUNDER

iTrader: (3)

It be intersting to see the dyno sheets , with the various jetting combos , timing, bsfcs, etc .

Sounds like the combo is making good power though

bck

remember these are the same engines I posted all the dyno sheets from a few months ago. This time around it was strictly jetting changes. I just printed the first and last pull this time around. There were 2 extra pulls in the middle that I didn't print.

getrdunn

iTrader: (7)

Brake Specific Fuel Consumption BSFC simply refers to how efficient fuel is turned into horsepower. Although important it will not tell you if the engine is rich or lean, it will however let you know how efficient or less than efficient the fuel consumption is as it relates to targets set for type of fuel and output power of the engine. I've seen BSFC all over the board on more than one engine. (Valvetrain issues). Hydraulic lifter failure, incorrect springs, broken springs, valve lash settings, agressive cam lobes with incorrect lifters/springs and on and on. So with your builder paying close attention to BSFC just know he's looking for any inconsistencies that wil make tuning nearly impossible along with potentially damaging your engine.