Ever had any of these questions:
I had the same fuel injection questions myself. After several years of research and trial and errors I’ve figured out these and other answers to your fuel injection needs. I’ll try and share them with you below.
First, let us go over some details about fuel injector sizing.
If you are an older mechanic, I am sure you have swapped many carburetors’. You know what happens when you put too big of a carburetor on a small block Chevy; it runs like crap until the rpms get up. Same thing will happen with too big fuel injectors. So you have two options, try some different ones until you find the size that works (I would not recommend this, but will work.) The best method is to do a little planning and calculating to determine the best-sized fuel injector for your specific engines fuel requirements.
It is as simple as having a good idea of your estimated horsepower and entering the data into a calculator like below:
Link to Fuel Injector Calculators:
Your injector size and flow rate is not static; your injectors will have an operating range for their given size. This operating range for any given fuel injector, can be expanded by adjusting the input fuel pressure.
However, there is a limit and the closer you run your injectors to that limit the performance of the injector will be compromised. For example, if you have a 60lb an hour injector and run it on a stock engine, you might be able to reduce the pulse rates (how fast it operates, more on that later) or drop the fuel pressure to make them work. However, they are going to be operating at the very bottom of their capabilities and way away from their optimal designed operating sweet spot.
The injector manufacturer rates injectors for the optimal fuel pressure but you can generally deviate from that up to 20%. The more pressure on the back of the injector when it opens the more fuel will go through it. Think of it like changing the jets in a carburetor the bigger the whole the more fuel will go through it. However, fuel injectors are very pressure sensitive, so they are easy to adjust in that sense.
A fuel injector’s measurements come in one of two units, lbs (pounds) or cc (cubic centimeters) per hour.
To determine lbs per hour or cc’s or other fuel related conversions try these simple calculators:
It is very important to have enough injector capacity when you are running your engine hard. I like to double check my calculations in a couple ways.
First, use a wideband o2 sensor, it is necessary these days and the price will pay for itself in fuel millage and cut down trial and error. Make sure your not running lean on the high end and data log for analysis after runs.
Secondly, if you have data logging capabilities view and monitor your pulse widths. The pulse widths should not exceed 20 for most injectors. With a margin for error, I like to stay under 18.