I bought a holley commander 950 tbi . I only bought the Tbi itself , no ecm or wiring. What Hp can it support? The website says 450-600 hp but I dont Think it would support that much. It has 4 85 pph injectors. (Delphi) Any Thoughts on the best way to set This Tbi up?. It will go on a zz430 . I have not yet choosen a ecm but will probably go with a 7749 for boost capabilites. Any Thoughts would be great

 

Low speed drivability is going to be tricky with a 4 barrel. Its going to be hard to get those four fuel injectors to fuel properly at low loads.

 

I dont know if The tbi is has progressive throttle I have not recieved it yet, Do you know of an ecm that can turn off 2 injectors during low speeds?

 

No, you would need to use an external injector driver. I was messing with the outputs on an ecm in hopes of being able to turn on an external injector driver when needed and coordinate the fueling entirely with the ecm but it seems like the outputs are a bit slow. There was a small ammount of delay in turning them off and on. Not real long but long enough to cause some problems if the throttle is suddenly snapped open or closed. I also wonder what would happen at the transition point when either the extra injectors have to be turned off and on. What the ecm commands might not be what it gets when the injectors are in transition. I heard there where also problems with sync and async fueling with the injector drivers. I sort of gave up on the idea. I think its doable but using a bored the hell out 2 barrel with the biggest injectors available and a VAFPR would be easier.

 

The only system that I know of with this ability is the Commander 950.

RBob.

 

Check which software loop was used to switch the output. The fuel & spark minor loops run every 12.5 msec. The major loops run every 100 msec. With some being broken down further to every 200 msec.

For a TBI setup to enable/disable injectors I would put the control code into the fuel minor loop. Still need to take care not to overrun the loop time. Removing extraneous code will help in this regard.

RBob.

edit: there is also a loop that runs every 6.25 msec. This is run at the beginning of every fuel & spark loop.

 

Goes off on a tangent....

I tried running the outputs outside of the loop for the AIR stuff/egr/CCP loop but there still seemed to be a strict upper limit as to how fast they would go. Hmmm... MAybe Ill try them again.

About overruning the loops, is there any sort of predetermined way to know how much code can be squeezed in before it pukes? Ive taken care to keep everything ive put in on a 1:1 basis but it would be nice to have some idea of how far I can push it.

 

Each clock cycle takes about 945 nsec, or round it to 1 usec for a rough guess. There is a maximum of 6.25 msec of time available between loops. In this case a loop is a minor loop, a major loop, then the 160 Hz code loop. This gives 6,250 instruction cycles (not instructions) within that time frame. Can count the cycles but unless done by machine that gets crazy.

What I did was to turn an output on at the begining of a minor loop then back off at the beginning of the 'waste time and wait for next interrupt loop'. Then hung a scope on that output.

RBob.