A friend and I are just trying to understand the differences between SFI and batch fire and how they work. Before SFI I thought all FI was SFI, but from what I’ve read here is SFI fire sequentially at low to mid rpm’s, and batch fires at higher rpms, ok. So TPI is said to be all batch fire. It fires left and right banks separately but at the same time. So that means each cylinder is not only getting a shot of fuel when the valve opens but also 7 more shots of fuel puddling up behind the valve until it opens, right? Or does the mists of fuel stay in suspension long enough? It just doesn’t sound very efficient, but granted it works. Did they do batch fire because the old slow computers were not fast enough to handle SFI? Has anyone tried to convert TPI to SFI or is it not worth the effort for just a little gain? Well are we on the right path or out in left field somewhere? A good explanation would be much appreciated. Thanks

 

The way I understand batch fire is it only fires twice for each cylinder. Yes the fuel stays in suspension long enough, you have to remember the speed at which this stuff happens. Even at idle your looking at betwen 8 and 16 (depending on idle speed) revolutions per second, which in a four cycle engine will give you 4 - 8 firing's on each cylinder per second. Also yes SFI is more efficient. You can convert TPI to SFI, but it'll call for an aftermarket computer, and new wiring. I think batch fire was more of a cost issue than a speed issue, but it was probably both. It's a small gain for a fair amount of work, but if your gonna go to an aftermarket computer anyway you might as well. It is more efficient as well as providing a bit more power, due to greater accuracy of fuel metering.

 

With the TPIs the injectors all fire once per crankshaft revolution. They use two wires to had some redundancy, and for the load on the traces on the printed circuit board, but they all fire off of on driver.

SEFI fires each injector independently. The fire the injector when the valve is closed so the heat in the port can vaporize the fuel so that it burns better in the chamber (real long story shortened).

Typically you see injector pulse widths of 2 msec at idle, please look at the enclosed photos for an idea of what's really going on. At 3 msec and less the fuel is just dribbling out of the injector and these photos are of tiny injectors that do give excellent atomization.

On the large injectors on my car (55#/hr) it actually runs much better in batch fire rather then SEFI. Because the injectors are pulsing 2x as often at low rpm and better thus better atomizing the fuel.

BUT
YOU"VE IGNORED THE IGNITION SYSTEM

If you add a cam posistion sensor then you can add the CNP (coil near plug) ignition system like the new LS1s have, and that my friend is worthwhile.

BTW, I've actually run my car in SEFI, and Batch fire, and DIS and CNP. So this info ain't fairy tale mag carp.