Mechanical Fuel Injection
FIE offers online Tuneup Calculators for registered users. Please read the information here! This is meant to help you get the most from the calculators and to keep you out of trouble...
The tuneup calculators are NOT meant to give you a final, definitive tuneup for going down the track! They are intended to help you with component selection. Before you risk your hardware on an actual pass, you should be willing to invest a few hundred bucks to have your system flow tested. We hope you'll have US do that for you. From the calculators, you'll be able to see how much nitro you could run with your system before you run out of pump or nozzle area. You could find out what nozzles are optimal for your setup by getting your system pressure up around 130 psi. You'll be able to see the effects of changing components and what that will do to your main jet and pressure. You'll also be able to see the effects of weather on your main jet selection. There are many factors involved in a system that the calculators here do NOT consider. These things are only revealed on a fuel flow bench while measuring what is actually expelled into the engine.
In order to use the calculator and get anything useful from it, you must have accurate numbers to put in! You will have to know your pump flow and RPM most importantly. If you just use the numbers advertised for your model of pump, don't expect things to be very close. For example, an Enderle 80A-1 pump DOES NOT flow 7 GPM as they advertise. If you use 7 GPM in the calculator, it will give bogus (lean) information. You need real flow tag information.
Different manufacturer's nozzles and jets flow differently. In fact, all of your nozzles probably flow a bit differently. Our calculator cannot take that into consideration, so take what it tells you as a guide or "rule of thumb". When it comes to knowing all the facts and figures, there is no substitute for having your system flowed by a professional. This is one reason why high-speed bypass sizes and pressures are not dealt with in the calculator. You need REAL numbers to figure that accurately and having your pump, nozzles and bypasses flowed together on the test bench is the best way to do that.
You will have to guess on your volumetric efficiency (VE). Guess high! If you guess high and you are wrong, it will be rich and safe. A mechanically injected motor with stock heads and small cam might have a VE as low as 90%. Maybe worse! A motor with trick heads, monster cam, pulse tuned stacks, etc. might actually achieve 110% VE or more through a specific and narrow RPM range.
While using the Supercharged calculator, the big variable is blower output. There's a chart at the bottom of the Supercharged calculator page to give you a number for this. These numbers reflect a standard bore case with freshly stripped rotors. If your case has been reconditioned and overbored slightly, it will create more output and using the standard number will give you a LEAN tuneup. As the teflon strips on your rotors wear, output will drop off and your tuenup will be rich. Unstripped blowers can have anywhere from 15-25% less output than the same blower with rotor tip seals. Just like the VE for the normally aspirated folks, the blower output is the big variable that you'll have to play with. If your blower is freshly stripped or has very few passes on it, you can be assured of achieving very close to the posted output numbers.
What other stuff can you do with the Tuneup calculators? Here are some ideas...
- Find your optimal nozzles - Input the parameters for the equipment you have now. What does the calculator say your pressure will be? Go back and put some smaller nozzles into the calculator and play with it until you get a pressure of 100 psi or so at 8000 RPM. The higher the pressure, the better atomization you will get from your nozzles. Amazingly, a lot of injected folks are running pressures of 40-60 psi at the finish line. Their nozzles are too big!
- Find your actual VE or blower output - If you've been running your car for a while and know exactly what main jet works best, put your info in the calculator. Hit the "back" button and adjust the VE (or blower output) up or down until it reports your favorite main jet. Now you know what your volumetric efficiency (or blower output) is. Now you can use this to accurately predict how a nozzle change, a pump change, weather change or re-strip, would effect your setup.
- Changing hardware - If you've got a proven setup and want to change pumps or nozzles for whatever reason, you can enter your current hardware into the calculator. Check what it reports and adjust VE until it reports your situation. Now, change the pump flow to the new pump output and see exactly how your tuneup will change. This also works for changing nozzles, changing percentages of nitro, etc.
- Changing weather - You might have a sweet setup now, but if you go to a track whose altitude and weather conditions make a drastically different situation, what do you do? Get out your notebook and input the facts from a day at your home track into the calculator. Go back and adjust the VE in the calculator to get a main jet answer that is what you used. Now, enter the predicted weather conditions for the new track and it will tell you exactly how you need to change your tuneup. You may wish to do this for all your favorite tracks and get some guidelines for how to change things to get the most from your setup everywhere you go during the season.
- Use the calculator to help mix your nitro if you don't have a hydrometer. It converts nitro percentage "by weight" to nitro "by volume". They aren't the same! If you are mixing with measuring cups instead of a hydrometer, this could be very useful.
- You've been running alcohol and want to try a little nitro. The calculator will help you find a main jet/nozzle combination to use.
- You're running a belt driven fuel pump and it is a little on the small side (or big). How much should you speed it up (or slow it down) with a pulley change to get it in the sweet spot? The calculator will let you adjust the drive ratio to suit your needs.
- You've got weather information and want to convert it into an actual "corrected altitude".
- How much does fuel temperature effect your tuneup? Play with it in the calculator and find out. It can be significant!
- How much horsepower am I making? Well, the calculator doesn't figure horsepower exactly, but if you run straight alcohol, the "pounds per hour" figure that the calculator spits out is pretty much a horsepower figure. If the calculator says your optimal setup is burning 784 pounds per hour of methanol, you are making about 780 horsepower. Now, you need to be burning all that fuel! If you are running things way rich, then you'll be flattering yourself. Fuel going out the exhaust pipes does not contribute to generating power.
Ok, you've read all this and now you want to play...proceed to the Tuneup Calculators:
* Normally Aspirated Tuneup Calculator
* Supercharged Tuneup Calculator
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