That is very true. There are so many different Q-jets around and you need to get one as close to OEM as possible. This site has a lot of GM carb spec sheets. You can look up what number carb came on your engine. You can also use it to select which jets and metering rods belong in your car's carb. I have taken many swap meet carbs and re-configured them to OEM specs for my particular engine. GM carb sheets