[Plus6g]

We need some clarity here. For example, 3 injectors would actually be firing 3 times each per-cycle, on 9 cylinders. Using injectors small enough but enough of them to total the required fuel, means each injection only has 80° to inject the entire cylinder's-worth of fuel. To inject less than 3x3 per-cycle would be less than optimal for fuel distribution. You can see I'm looking for best-case first, and compromise later if necessary. I would think altering the code to allow for 9 cylinders on any divisible number of injectors (1, 3, or 9) would be preferable to these gymnastics, though it is theoretically possible.

Disregarding redundancy for a moment, that's 3 injectors, each one on one of 3 channels, with 3 squirts each (every 80° repeating every 240°), on 9 cylinders, in 720°. To use fewer injectors may be attractive for simplicity, but then you have one injector opening 9 times per-cycle, and just the latency will suck-up much of the available cycle time. A single injector capable of that is possible, but then (again) raises concern that control of a humongous injector like that at cruise and lower loads. This would be like trying to perfectly fill a drinking glass with a fire hose.

A single injector firing 3 times per-cycle is an option, if fuel distribution is adequate and does not compromise reliability. I hope you can see why I'm hedging towards multiple injectors, as being "simpler" and more effective from a different perspective. Ultimate from that perspective would be 9 port injectors at 133cc each for optimum control, but will be compromised by other factors in balancing the system goals.

I also have concerns about raising BSFC to 0.65 for two reasons. First is if the heat-shedding ability of the engine could be insufficientl to support 200hp of cooling. That is unreliable, unless aux cooling is added, and any addition to allow for a shortage is teasing unreliability. If it can shed 200hp of heat, then enriching when you don't need it is wasteful and invites unreliability. Second, a BSFC of 0.65 for aux cooling, assuming peak torque at (example) 12.7:1 AFR, would mean running at 9.77:1 AFR. That is borderline on misfire, can quickly foul plugs, hurts power, and again invites unreliability. Just sayin', and using a lot of "ifs", but hoping to make the points. Fill me in if I'm short of info or assuming too much.

I think altering the code to allow for 9 cylinders is the way to go but I'm well out of my depth on that one.
At the moment the engine is still in its original packaging! Once the new workshop is completed I'll get it it mounted on a test stand and ponder some more. Its a Rotec R3600 supplied with a Rotec TBI as well. If I could find a supercharger that would allow a 'pass through' setup using the TBI, that would be the simplest of all. But its a bit of a blunt tool and doesn't allow for the data logging / protection systems of an electronic system.

[AlexE]

I like this project!

[PSIG]

Consider, that as the inputs on the Speeduino and its Mega are high-impedance, you can view and log most of the activity on the OE system and extra channels you choose to add. CLT, IAT, TPS, RPM, O2, etc. Whether this is to aid tuning the OE "electronic carburetor" system, or for baselines in a Speeduino conversion is up to you. Have fun with your Rotec!

[Plus6g]

Consider, that as the inputs on the Speeduino and its Mega are high-impedance, you can view and log most of the activity on the OE system and extra channels you choose to add. CLT, IAT, TPS, RPM, O2, etc. Whether this is to aid tuning the OE "electronic carburetor" system, or for baselines in a Speeduino conversion is up to you. Have fun with your Rotec!

Sadly, although its called a TBi, it isn't electronic. Its clever, just not clever enough to work under positive pressure.
https://www.rotecaerosport.com/_files/u ... 4974fd.pdf

[PSIG]

Indeed, and why it is misleading to be termed TBI, as it neither "injects" nor uses a controller, both being a typical component of TBI. Semantics aside, if it is capable of tuning the areas required for your fueling to be acceptable, you can use it. If not, a different fuel control is needed, and true TBI or MPFI are possible options. Let us know what you find as you proceed.