The Fuel system is perhaps the most critical part of any high performance system. Without the proper Air/Fuel Ratio you can't make full power, or even worse - you can destroy a perfectly good motor really quick! The first thing to consider is that it's the fuel that makes the power. For every amount of air you can squeeze into the cylinder, you must also have the proper amount of fuel to go with it. Too much fuel and you drown, too little and you start burning things up. It's that fine line that you're after, if only it was that easy.

All too often I see cars with huge fuel systems, for no apparent reason other than to jump on the band wagon. Don't get me wrong. If you're planning ahead that's one thing, and it is better to be too big than to be too small. The sad thing is when people are pushed into theoretical ideas of what they need. While with the proper Regulator or FMU (Fuel Management Unit) you can run a huge Fuel Pump, it is the injector size that is most critical. This is the one piece that should definitely be matched to the motor. While I have fallen prey to what size injector I should be using, I quickly learned that doesn't always work in the real world. For every Mustang running 11's and 12's with 42 lb. injectors, there is another running 10's with 24 or 30 lb. injectors.

Sure a 42 lb. injector will work with the right amount of fuel pressure, and the correct tuning device, but at what cost? Typically, idle quality and mileage are what suffer, as they can be tough to tune correctly. With many combinations a 24 lb. injector will work great by running a higher fuel pressure under load. This will allow your car to run properly, especially when not being pushed hard, which is very critical for a street driven motor. Huge injectors can be great on race only cars, but will be hard to tune around on a daily driver. Don't get me wrong, there is a point of no return, too.

As an example, my five liter Mustang has a reasonable motor and Vortech supercharger. I originally started out running about 8 lbs of boost and using 30 lb injectors. While the car didn't run too bad, it didn't idle all that great, my fuel mileage was pretty bad, and it would often times load up at low speeds. After trying a few tricks with the Mass-Air Meter and not having very good results, I switched to 24 lb injectors.

Even though everone said it wouldn't be enough injector, I knew the numbers said they would. To keep up with the horsepower I was making, I did what every magazine said not to do - run a lot of fuel pressure. Under full boost, I ran about 80-90 lbs of fuel pressure. Unfortunately, at this pressure, it's not as easy for the computer to properly control the injector. Actually, this is only one of the problems with running an injector at its limits. Another is that you are at the limit and are running a huge risk of motor damage due to lack of fuel. As if this wasn't enough, remember that you are completely limited by your injector size. If there isn't enough fuel, you'll never make more power. A little time on a DynoJet was more than proof of this.

With the boost at about 8 lbs. and while running with 24 lb. injectors, my car did just fine at it's limit of 437 rwhp (Rear Wheel Horsepower). It was obvious that the car was making good power (just over 500 hp at the flywheel), but it was limited by my choice in injector size. When comparing my results to another car with a similar set-up (big Dart heads, Vortech S-Trim @ 12 lbs boost, etc...), my car was about 50 hp higher at 4800 rpm, but then hit the wall of my limited fuel system. As one would expect, both of our cars (his also had 24 lb. injectors) had very similar peak HP numbers - about 437 hp (mine) and 423 hp (his). I'd like to think that this is a perfect example of what kind of limit the wrong fuel system can have on an otherwise good set-up.

While it is important to understand the limit of certain injector sizes, it's still important not to go overboard. I knew that I had better street results using 24 lb. injectors, but I also know that I can't make full power using them. For this reason, I was somewhat forced into going back to using my 30 lb. injectors, which proved to be what I needed. Because a properly calibrated Mass-Air Meter is crucial to getting a set of injectors to work properly, I switched to a Pro-M 77mm unit to help solve my slight drivability problems. Not only did this work out great with the new Meter, but it also allowed me to safely up my boost to 14 lbs without fear of running out of fuel.

While I have shown what works for me, to each his own. My biggest recommendation is to make your changes gradually. Remember to do the math - a 24 lb. is 25% bigger than a 19 lb, a 30 lb is 25% bigger than a 24 lb. , etc... I'm not saying to always try and run small injectors, but suggesting that huge injectors aren't always an improvement, as my results proved. To help find the right injector size for your application, use the following formula: