special tool

That is because you were at the true limit of the AFM.
The DME tosses in a bunch of fuel when it is maxed out.

HOWEVER, weighing air mass is NOT everything!
There are SIGNIFICANT (HUGE) differences to be made in these engines with more efficient rotating assemblies. I am NOT talking VE!!!
In other words:
Engine A - has stock shortblock. It takes in 30 pounds of air and makes 190
RWHP

Engine 2 - has dry sump, lightened crank, modern pistons (not from a
Cummins), light rods, etc. It takes in 30 pounds of air and
makes 225 RWHP.

The AFM/MAF sees the same thing, so does the DME.
This is the reason some unfortunate souls think I am full of **** when I tell them that APE MAF runs out at 400 wheel. Not seeing the big picture.

will951

Interesting discussion

Auto_Werks 3.6

hmm.. its all physics, so yes to an extent. So from a trap speed you could establish a MINIMUM avg horsepower to accelerate a car to a given speed over a know distance, but there could be more there...thats on the driver. HP lost to wheel spin would not show up in a trap speed. Time lost shifting and starting would though. More repeatable to go to a dyno... What else am i not concidering.

special tool

I agree %100 percent.
Well said - minimum.

fast951

The stock 951 AFM is rated at 800-1000 kg/hr. This will give you a idea of how much HP it will make before it maxes out.

When the AFM exceeds it's rated flow, it will max out and generates a max signal (~= 5Vdc). Once the max voltage is reached, the DME is no longer getting accurate data and fueling is out of control. The engine may continue to make HP, but it's uncontrollable.

The same thing could happen to a MAF that is not calibrated correctly for the application. Two identical looking MAF will generate a different signals (0-5Vdc) for the same flow.

Check out this FAQ it might be of some help..
FAQ

blown 944

I made 410 with some porting done to it.

Pretty sure it would have easily made 350 w/o the porting

gt37vgt

could you calibrate the AFM or chips so the AFM is only measureing say 70% of the air going into the engine and have an AFM bypass supplying the other 30%???

TurboTommy

ST;

perhaps you could tell us how 2 engines drawing in the same amount of air could have a difference in output of 35 horse, unless engine A was way out of tune. (Actually, 30 lbs of air is worth about 280 crank hp, give or take; so maybe, they're both out of tune)
You mentioned more efficient rotating assemblies. Generally, that would allow the engine to spin higher, but that would also mean it will be drawing in more air.

Auto_Werks 3.6

TurboTommy,
I'm no special tool, but I would imagine the answer is that there is energy stored in the mass of the rotating components. So engine A & B atomize and burn the same amount of fuel and air thus releasing the same amount of energy. The question is where that energy goes... in this case, we are looking for power not getting to the wheels.

Force = Mass x Acceleration, so speaking in terms of ONLY the rotating assembly, to keep the acceleration of the rotating assembly the same as mass increases, it will require more force. This force is the cylinder pressure during the power stroke. So by burning more air and fuel, the energy released in the combustion chamber increases, allowing the more massive engine to accelerate at the same rate as the one with a lightened rotating mass. The result is similar rwhp, but increased fuel and air mass consumption.

Auto_Werks 3.6

Its probably too late in the day for physics...If I remember correctly F=MA actually would only apply to the piston (linear motion), I have tried to over simplify. The basic principle is still similar, and it still relates back to the force in the combustion chamber. The behavior of the crankshaft (transmits power to the wheels), is bound by "Torque (force x distance) = moment of Inertia X Angular acceleration". The torque, or force x distance, is still supplied by the connecting rod, which is set in motion by the piston / combustion chamber forces.

I am really intrigued by the mechanics of internal combustion, and im not alway correct with my ramblings (I may delete both my posts tomorrow when I see them with while I'm a little more alert).
It is also interesting to note that not only is it important to remove mass from the rotating assembly, but concideration of where that mass came from needs to be taken into account. That is the "moment of inertia" part of the angular acceleration equation. For example based on T=IA, if you took 10lbs out of the theoretical center of mass of a flywheel, it would make no practical difference (other than wear on the last main bearing). However, if you took that same 10lbs from the very outside ring of the flywheel you then make a noticable change in the "I" value.

gt37vgt

fuel type and altitude can add up to the 8% or 35 hp difference along with different drive chain loss and dyno calibration . how often does a dyno operator do a full rolll down to calculate power chain loss ??

TurboTommy

gt37vgt;

a change altitude would then change the 30 lbs of air in the orginal example;
and, unless you're running nitromethane, no fuel will make up that power difference.

smokintr6;
?????????
to make a long story short, the mass in the rotating assembly will not change the power you can get from 30 lbs/min of air. It might change low load crispness (like reving for down shifting).
Reducing internal friction (I guess, dry-sumping might do that) will free up some ponies, but, still not the power difference that's being said.

toddk911

"practically" = kind of LOL

There are a lot of factors with any drag race. A car on a dyno, or for what I am getting at more so an engine dyno, there are no added variables. The engine makes X amount of hp or it doesn't. Track conditions, tires, suspension, clutch, style of launch etc. etc. etc. all effect an ET and trap.

I would think after you drag race you did you would be the first to realize that.

Yea, your traps show your car is alot faster than the ET you put up, but those traps you put up were not a true indication of your 600hp were they it?????

How many times have we seen a high hp car run a drag and loose traction or something and coast across the finish line with a 95mph trap but 9 sec ET?????

See my point????

toddk911

Your not considering that ST is never wrong. lol

special tool

You need a minimum amount of HP to accelerate a given mass a given speed in a given distance.
It can be more, but not less.