Well its been a few days. Been busy. Its actually busy at the work place. So its hard to get this article done. As for that other super secret jeep motor:grinpimp: I havn't started any calculations on that. Corey, I will start sending you PM's

So now class is in session:

This is where we start pluggin in the past equations and we see things coming together. The next one we calculate is the Mass Flow Rate (MFR) . This number is used in conjunction with PR to look at compressor maps to find the best turbo application for your engine. But we are not done yet. So here is EQ8:

MFR = VFR x Air Density OR:

MFR= [(2.703)(psia)(VFR)] / (Tin + 460)

= [(2.703)(14.7)(366.72)] / (85 + 460)

= 26.74 pounds per minute

This is the output of a 4.7 stroker with NO turbo. So the next one is very simple to figure the out put of a turbo running 10 psi of boost. All we do is multiply the above number by the DR.

MFRturbo = (MFRna)(DR)

= 26.74 x 1.51

= 40.38 pounds per minute

Now this calculation is based on running the engine at 5300 rpm. So, run the calculations for 1500 rpm (we want the turbo to start spooling), again at 3000 rpm (the range we want the turbo to be at its highest efficiency). These are numbers I wanted to work with. Use your own numbers for what you want. It is important you do this because we will use these numbers as a reference later in the article.

The reason I like to work with DR, is it gives you a more real world true effect of the out come. I feel that using PR will give a false outcome. This could lead to a bad decision on the design/build process. But other people/shops may work with PR even I may disagree with that process.

So lets punch some numbers at different RPMS assuming a max 10 lb/boost across the range.

MFR @ 1500 rpm = 11.43 lb/min

MRF @ 3000 rpm = 22.85 lb/min

To get your numbers first calculate VFR at the given RPM. Then take that number and plug into the MFR equation to get your flow at the given rpm. These numbers are guidelines that we must stay within to get the best possible results.

Now lets talk about possible horsepower output of this engine. Remember to plug your numbers in place of mine since they may be different. We will use the Brake Specific Fuel Consumption equation (BSFC). An average turbocharged gas engine will burn between 0.55 - 0.65 pounds of fuel every hour for each horsepower developed. We will use 0.6 pounds because this is a safe and fuel efficient area. We know our boosted MFR. We must come up with a Air/Fuel ratio now. We know that we never want to go above 14:1 to avoid to lean and burning up the motor. Under boost, a safe ratio is 12:1. This is all in the programming of the ECU fuel system. I have talked to some of the drag race crowd, and they tune as low as 10:1 under full boost. But these are full on race set ups. Some will even go with a lower ratio. But we are working with a daily driver. So lets just use 12:1 in the equation.(EQ9)

HP = [(MFR)(60)] / [(A/F ratio)(BSFC)]

= [(40.38)(60)] / [(12)(0.6)]

= 2422.8 / 7.2

= 336.5 horse power.

Using this equation, you can play with the numbers to see what is possible. This form of equation is your normal Bench top dynoing. This is only a tool. Real world outcome can have a drastic difference. But I have ran this exact same numbers for a buddy. He went and did a real world dyno and I was off maybe 2% of his actuall output number.:smokin:

This above result is also very conservative for a Daily Driven motor. I also stumbled onto a website that works with what needed injector size for horsepower output.

http://www.injector.com/injectorselection.php
This is just a guideline as well. We might dig deeper into fuel injectors later. Again, just use this as a guidline as well. There is much more to fuel injector set ups that must be understood.

Next class, looking at actual compressor maps and understanding how to read them with the tech info we have calculated.