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Idle quality with 1000cc injectors

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I have a project I need a little advice on. I have a Japanese V twin 1080cc engine. For all intents and purposes imagine a quad cam 4lt V8. Its turbo charged and injector calculators suggest 2 injectors somewhere between 750cc and 1000cc. I have a Bosch DBW throttle per cylinder. There are variations used in stock trim on this engine with 2 injectors per cylinder, one below the throttle blade and a shower style. Ducati also do this. As this is now forced induction and for the sake of simplicity could I get away a single 1000cc injector after the throttle spraying directly down the intake track at the back of the valve or would it be difficult to maintain a smooth idle and off idle response. I can do 2 injectors per cylinder but not sure how that works with pressure differential on injectors in different locations i.e. before and after throttle body.

Idle quality with big injectors will depend on many factors in your described setup. I've got customers with 1300cc, 4-cylinder engines running a lovely and stable idle on 1000cc injectors.

You'll need to look at the OE spray pattern as most modern large injectors will have a very narrow spray pattern and OE will likely have a wide one to make for better atomisation. Your injector angle and distance from the valves will also impact this, before you even take into consideration the cam profiles, is there a lot of overlap?

If you're running 2 sets of injectors per cylinder on a staged setup the second injectors should only really be coming online when you are entering boost and the throttle is open so differential pressure won't be an issue as the manifold and boost pipes should be under the same or very close to the same pressure

Thanks for the reply Chris. Thats more or less what I wanted to hear especially if you have one per 325cc cylinder on what I assume is a hayabusa.

This is a TL1000 engine. I have an Ecumaster Pro 8, PMU and dash. The stock TL1000S has a 440cc 2 hole injecter mounted in each throttle body. The TL1000R has smaller 260cc injectors in the same location and and additional pair of 260cc shower injecters. Not sure on the spray angle. The engine has around 32 degrees of overlap. Many have swapped the 440cc injectors for wrx injectors for a better spray pattern but I have no experience in this.

Without measuring, the injectors are around 100-120mm from the valves. New injectors will be in roughly same location and when I design the adapters and injectors bosses I'll duplicate the angle

In the past the stock bike has always run fine with just the 2 injectors and I never saw any real advantage to swapping ecu's, wiring, throttle bodies etc just to have the 4 injector setup off the R. However wasn't sure bumping the size up by double that they would perform ok at low rpm. I'm going to build the harness for 4 injectors just so they're there but try 2 for now I think

Good point re the differential pressure.

I'm not discounting the great discussion on design, placement, but pragmatically for what it's worth...I've not yet encountered a situation where ID1050x (1065cc/min at 3 bar) have not offered sufficient control for excellent start, idle, drivability. I have also achieved emissions lab success on them, with values near stock, and that requires strict fuel delivery control. In short, with the right injector, data, and an ECU which allows use of proper injector characterization data, a 1000ish CC injector can work really well.

Thanks Mike.

That's exactly the injector I had in mind. I'll still wire for a second set just in case. However if its not a general consensus that these injectors are difficult to tune for idle, off idle and general low rpm drive-ability I think I'll go this route. Lot less fabrication work for the shower injectors too.

With the correct hardware, you can get a lambda 1 idle on an EJ207 using ID1700's and E50 fuel.

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