cougar motor in a stang

Unit 5302 · 06-17-2001, 03:04 PM

As far as the way MAF would help, it can actually read the amount of air coming in.

Speed Density injection systems have no way of measuring air, or fuel for that matter. They go off a baseline of stored information in the database. They use a BAP sensor to determine air charge density, a temp sensor to determine coolant and air temps, and a TPS to determine throttle position. Based on that information, it changes the injector cycle based on parameters it has stored.

So, when you change a cam (which makes a big difference in airflow), the computer is trying to inject fuel at the rate for the stock roller cam, not the new smaller cam, and you run rich. If you get an adjustable FPR, you can turn down the fuel pressure so it will be injecting less fuel, and get the engine back within the adjustment tolerences of the SD computer. Even though SD is pretty damn good at adjusting, it can't cope with cams and heads without a little tuning help.

MAF uses an actual MAF sensor, which measures intake charge temp, density, and actual airflow so the computer can adjust the injector cycle accordingly. It's not very good at making adjustments though. There isn't a whole lot of ability to compensate if something isn't jivving.

An example of MAF's limitations would be adding 24lb injectors to a 5.0. With MAF, there's a damn good chance the car won't even run. SD will run, albeit rich at startup, and it'll have a bit of idle surge. So SD has more ability to compensate internally, but MAF is far better at actually measuring data.

Of course that pertains to keeping the stock MAF. MAF sensors can be recalibrated to show data for larger injectors as well.

[This message has been edited by Unit 5302 (edited 06-17-2001).]

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06-17-2001, 03:04 PM	#5
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	As far as the way MAF would help, it can actually read the amount of air coming in. Speed Density injection systems have no way of measuring air, or fuel for that matter. They go off a baseline of stored information in the database. They use a BAP sensor to determine air charge density, a temp sensor to determine coolant and air temps, and a TPS to determine throttle position. Based on that information, it changes the injector cycle based on parameters it has stored. So, when you change a cam (which makes a big difference in airflow), the computer is trying to inject fuel at the rate for the stock roller cam, not the new smaller cam, and you run rich. If you get an adjustable FPR, you can turn down the fuel pressure so it will be injecting less fuel, and get the engine back within the adjustment tolerences of the SD computer. Even though SD is pretty damn good at adjusting, it can't cope with cams and heads without a little tuning help. MAF uses an actual MAF sensor, which measures intake charge temp, density, and actual airflow so the computer can adjust the injector cycle accordingly. It's not very good at making adjustments though. There isn't a whole lot of ability to compensate if something isn't jivving. An example of MAF's limitations would be adding 24lb injectors to a 5.0. With MAF, there's a damn good chance the car won't even run. SD will run, albeit rich at startup, and it'll have a bit of idle surge. So SD has more ability to compensate internally, but MAF is far better at actually measuring data. Of course that pertains to keeping the stock MAF. MAF sensors can be recalibrated to show data for larger injectors as well. [This message has been edited by Unit 5302 (edited 06-17-2001).]