DTA Fast E48 injector question

[ONEBADBUG]

So I'm finally wiring up my Subaru Buggy project, and all 4 injectors go to one terminal. I don't understand how that can work. Wasted spark I can get, but how can the injector fire on the "off" cycle?
This is my first venture into aftermarket engine management, so please go easy on me. I"m old and old school!

[blue thunder]

It is quite simple: The 48EXP can only handle batch injection. This means all the injectors open and close at the same time. Sequential can have some benefits in fuel consumption and maybe throttle response (especially when using large injectors), but other than that batch injection is just fine (max power and torque do not differ).

Hope that helps,

Cheers,

Robin

[ONEBADBUG]

Thanks. Still not clear in my brain, though. I guess at TDC one revolution from ignition, the exhaust valve is open,but the intake is not. The injector sprays into the manifold, and the fuel just sits there waiting for the intake valve to open.
So wouldn't the injector pulse time have to be 1/2 the amount of a stock system?
For sure the Subaru system has a separate circuit for each injector.

[andy198712]

its all happening stupidly fast in the engine....

[blue thunder]

Yes, most of the time the injector will spray against a closed valve. This isn't always a bad thing: the valve is warmer than the intake manifold and can help atomise the fuel better. At full load, even with fully sequential injection this happens (as there is no way to provide enough fuel when intake valve is opened). Just like andy said: everything happens really fast in an engine and the fuel which is sprayed onto the closed valve will be sucked inside the engine a fraction of a second later.

Cheers, Robin

[Jadewombat]

Sequential injector timing only helps mostly at low revs. At higher revs when things get going it doesn't matter much about timing because things are moving so fast and the injector pulse becomes longer anyway to where the injector is spraying open most of the time.

If timing were critical and gas got 'backed up' or collected on the intake valve, then engines wouldn't run on carbs. at all.

[ONEBADBUG]

Thanks guys. I know I am overthinking it, but that's part of why I'm doing this project. When I'm done, I will know this stuff inside and out!

[raygreenwood]

Sequential injector timing only helps mostly at low revs. At higher revs when things get going it doesn't matter much about timing because things are moving so fast and the injector pulse becomes longer anyway to where the injector is spraying open most of the time.

If timing were critical and gas got 'backed up' or collected on the intake valve, then engines wouldn't run on carbs. at all.

Yes.....sequential can make a significant issue off the line with throttle response.....and in keeping carbon out of the ports. That being said....if you are tuned properly you will not notice.With batch fire you will set the system generally to run very slightly leaner at idle.

Also...no...the fuel hitting the back of a hot closed valve does not help atomization. There is not enough time for flash evaporation of the fuel to happen in the few milliseconds it takes for the valve then to open. Also...that is not atomization anyway. The problem with injection (as compared to carbs) is that the injectors produce micro droplets....not atomization like a venturi does. What complete atomization is a high speed higher density air column slamming the droplets in the ass while they are still in mid-air in the port. Anything the droplets touch...port walls...valves etc....they wet onto instantly. It requires about 5x the airflow to remove these droplets and get them into the air stream. Thats time the droplets don't have before the next cycle...so fuel gets either sucked in poorly atomized (like from the back of a valve)....or takes about 2-3 valve cycles to scavenge off a port wall.

Of course this is all at idle and up to about 1500 rpm. After that....the time interval is so quick...in milliseconds....the droplets do not have the time to wet onto anything. You will be fine. Ray

[ONEBADBUG]

Thanks, like I said, I'm doing this to learn. I started thinking about it because the stock Subaru system has 4 individual circuits, as do most cars, I think.