Basic Questions: How much exhaust flow? What is the temperature?
How much intake air flow?
Well let's look at the problem... first what goes in must come out. So there obviously are two parts to the exhaust, air intake flow and fuel flow. There just isn't any other place for the two to go. So if we know what the intake flow is and the fuel flow, we know the exhaust flow.
So let's try to put some simple equations together that you all can do your own calculations as you didn't really give me enough data to get the number for your particular setup. And it's better to know what you are doing yourself anyway.
(Caveat... we are going to ignore second order effects like the hat flow cooling the air, the supercharger compression heating the air before getting to the valve, and the volumetric efficiency (how good the valve system and combustion chamber are).) Anyway...
Number 1 Problem: What is the intake airflow?
The engine is 500 cubic inches and turns some particular rpm, let's guess its 7000 rpm for some simple calculations, and some boost pressure, let's guess 30psi. I'll show you how you can substitute and recalculate for yourself. Standard air density is .0765 pounds/cubic foot at standard day (59 degF and 29.92 "hg). We will assume no secondary effects and 100% volumetric efficiency for these calculations. That will give the maximum amount. Actual volumetric efficiency is probably at most about 80% but could be as low as 60%. We will also ignore the fuel flow for calculating the airflow. Even though it is there and a high mass flow, it is small in volume, as we will see.
I like units with pounds and seconds. But I'll also show some other units. You can convert to something else if you want.
The flow through a supercharged engine is actually controlled by the capability of the valve to allow the mixture to pass and, of course, the engine cubic inches. Mostly, however, it's the valve system that limits the flow. So let's start out and see what the airflow could be making the assumption that we can pack the cylinder full at each fill.
Airflow (pounds/second)
= (500 in3) / (1728 in3/ft3) * (.0765 lb/ft3) / 2 (revs/fill) * 7000 (revs/min) / (60 sec/min) * ((30psi+14.7psi)/14.7psi) = 3.93 lb/sec of airflow
(Simply stated at 30psi boost Airflow = .000561 * RPM )
(or Airflow = .000184 * ((Pboost+14.7)/14.7) * RPM )
Now, I'm sure you asking what is the CFM (cubic feet per minute). Well, it probably isn't what you think since we could find the CFM into the supercharger or CFM out of the supercharger, as they are quite different by the ratio of the pressure outlet to inlet and ratio of temperature outlet to inlet. We will assume that the temperatures are the same or close between the inlet and outlet of the supercharger. (They are in fact very close if you wish to measure them.) If the boost is 30psi the CFM going in is ((30psi+14.7psi)/14.7psi) or about 3 times that coming out because of the pressure change. Airflow is, of course, constant between the inlet and outlet of the supercharger. OK...
Intake CFM (ft3/min)
= (3.93 lb/sec) / (.0765 lb/ft3) * (60 sec/min) = 3082 CFM
(or Intake CFM = 784.3 * Airflow (in lb/sec) )
Number 2 Problem: What is the fuel flow?
I'll assume 80 gpm and you can redo with whatever fits in.
So what is the CFM of 80 gpm you ask.
Fuel CFM (ft3/min)
= (80 gal/min) * (231 in3/gal) / (1728 in3/ft3) = 10.7 CFM
Fuel CFM = .134 * GPM
Hardly anything compared to the 3082 CFM of air. Agreed some fuel will vaporize but not a whole lot. Nitromethane does not like to vaporize and there isn't much time for it to do so. Volumetrically, the fuel is about 0.4% of the total engine flow by volume. We need to know how much does 80 gpm of fuel make in fuel flow by weight.
Fuelflow (pounds/second)
= (80 gal/min) / (60 sec/min) * (231 in3/gal) / (1728 in3/ft3) * (62.4 pounds/ft3 density of water) * (1.137 100% nitro specific gravity) = 12.6 lb/sec fuel flow.
( or Fuelflow (lb/sec) = 0.158 * GPM )
By weight the fuel/air ratio is 12.6/3.93 = 3.2 . The stoichiometric mixture for burning nitro methane is about .59 . This is a pretty rich fuel mixture. Clearly there is something going on in the combustion chamber other that normal combustion like we take for granted in a normal automobile OR a lot of fuel is used for cooling and is just jettisoned out the exhaust pipe. Probably some of both are going on.
So we know that the exhaust flow is the sum of the air and the fuel. For this hypothetical probably best case with no secondary effects the exhaust flow is equal to the airflow of 3.93 lb/sec plus the fuel of 12.6 lb/sec or a total of 16.5 lb/sec. That is out of all eight pipes. One pipe, of course, would be 16.5/8 or about 2 lb/sec.
The temperature of the exhaust is better measured by your data system so you probably know what it is from your computer data. Depends how you run the engine what temperature that you get.
Now if the boost is different ( you probably measure that with your onboard computer too ) as I just guessed at 30psi, you can get an answer. If it is say 45psi instead replace the 30psi in the equation above with the 45psi number and recalculate.
A top fuel dragster engine rpm does not vary all that much from starting line to the finish line (after throttle down, of course) so the intake airflow is fairly constant from starting line to finish line.
Summary
So to sum up exhaust flow is the sum of the airflow and the fuel flow. If you know RPM you can get pretty close with the above estimate on the maximum possible airflow. If you know the FUELFLOW GPM you know that part too. The sum is what goes out the exhaust. You measure the temperature.
Actually, the airflow is probably less that the above calculations dependent on how good the cam profile, valve size/system, and heads are. I would guess that the best to be expected is probably 80% volumetric efficiency. If you want to refine your answer and think your engine flow is superb then use about 80% of the airflow number. If you think it is not so good use 60% of the airflow number. It's probably somewhere in between.
Good Calculating... Jim H.