Quote:

how dependable would one be on a mild hemi in a street car?



But seriously. I have done quite a few of Hilborns using the FAST XFI. The systems work very well with a few caveats:

* To get a stable vacuum signal (map signal to the ECU) hoses are run to a vacuum accumulator box. This works fine but there is no provision for using an IAC (idle air control). ECUs use both an IAC and timing control to control idle RPM. Without an IAC idle speed is harder to control.

* With 8 butterflys as the engine gets hot, the spacing can change causing an increase in idle RPM. This is a generic characteristic of any system like this. Usually the ECU can compensate.

* The eight stacks must be synchronized to get a good idle.

* If the engine is high in HP, and the car is light, the "tip in" just off idle can be hard to control with your foot. Street cars are no problem, but big injected Hemis in light hot rods can be a hand full.

* Finally, you must run sequential injection using a dual-sync distributor or other method (at least that's all I would ever do). Since there is very little plenum space under each butterfly, bank-to-bank injection causes fuel to sit waiting for the valve to open. The cam overlap can cause a "pop back" through the stack. This happens only at idle. With sequential injection you inject just as the valve starts to open. The mixture goes directly into the chamber and no pop back occurs.

But the throttle response is great and the HP is as good as the normally aspirated engine can get.

My typical FAST XFI 2.0 system with all components, injectors, etc., and the Hilborn manifold runs about $6500.

BTW: You should seriously consider an electric EFI fuel pump. Once running, belt drive pumps work fine but they are usually reserved for high HP engines that require the extra RPM based flow. Starting a street car with a belt driven pump is tough. High HP guys, running belt driven fuel pumps on the street, add an separate electric fuel pump just for starting. But I wouldn't do it on a street car. There are plenty of EFI electric pumps that will handle well over 1000 HP.

Last edited by Mopar_Rich; 09/14/11 01:11 PM.