Advantage of Sequential-Fire vs. Batch Fire on a FAST system

[carbuff]

I have a question. Reading another post made me think of this...

As I understand it, the advantage of a sequential fire FAST (or any EFI system) vs. a Batch fire system is the injector being fired timed to the cam timing. However, as was pointed out earlier in the other post, it's very typical for an injector Duty Cycle to be over 75-80% at WOT.

Given that, the injector is going to be firing most of the time regardless of cam timing at WOT (at least in the upper rpms).

I suppose I could see a small advantage at lower RPMs where the Duty Cycle is much smaller. So, the injector timing would be closer to the cam timing...

Anyway, just wondering what people think the advantages of the SFI are. I'm not really considering it at the moment, but rather thinking out loud...

Thanx!
Bryan

 

[89 coupe]

When you step up to big injector's then the sequential becomes necessary or you will most likely have some low speed problems. You also have individual cylinder tuning capabilities you do not have with batch fire.

 

[KTamez]

Originally posted by 89 coupe
When you step up to big injector's then the sequential becomes necessary or you will most likely have some low speed problems. You also have individual cylinder tuning capabilities you do not have with batch fire.

I think for most applications a B2B system will be more then sufficient. One thing misunderstod about the FAST systems, is that although you get a sequential box, it does not run in sequential until >2000rpms.

IMO the biggest gains come from the ability to have Individual Cylinder corrections, which can come in handy in any application.

Many very hiogh HP cars run w/ B2B systems w/o a hitch, so it really just depends on your budget.

Good luck!

Kurtis Tamez
94 Firehawk (Modified)
97 Z28 (Off the Deep End)

 

[Craig Smith]

Originally posted by KTamez
One thing misunderstod about the FAST systems, is that although you get a sequential box, it does not run in sequential until >2000rpms.

Actually, a sequential system fires the injectors sequentially at ANY RPM, no matter what. But, as per some of the older documentation, cylinder sychronization isn't enforced until you go above 2000 RPM. What that means is that before you cross 2000 RPM, the injectors are probably firing at a different time relative to the intake valve event, and individual cylinder ignition control will probably work on the wrong cylinders. Once the 2000 RPM threshold is crossed, everything gets synchronized and as long as your crank sensor doesn't skip a pulse anywhere, it will stay synchronized, even when you go back under 2000 RPM.