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3 injector stages for rotary engine (turblown cast rotary intake manifold)


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I am evaluating Link and Haltech ECU solutions for a journey I am on with an FC3S Rx7.

I am considering an after market manifold setup like that coming from Turblown Engineering. It has 2 primary injections and up to 6 secondary injectors. If I go down that path, I am expecting to have primary, secondary and tertiary injector stages.

The Haltech supports > 3 stages, but it looks like Link supports two only. Is this correct?

What other options might I have with Link to achieve the same?

Proposed setup:

2 x 1000cc ID injectors at stock primary position (or 2 x 1300cc)

2 x 2600cc ID injectors in new lower manifold outer runners (equivalent to stock secondary position)

2 x 2600cc ID injectors in new lower manifold inner runners (adds to primary port)

The Turblown lower inlet manifold in question also supports side port injection so that adds the option for another two injectors, resulting in 8 in total.

Manifold link: Turblown Cast Rotary Intake Manifold

Other options/suggestions will be taken on board

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G4X currently only supports 2 stages.  If you need 6500cc/min per rotor this thing must be pretty wild and is going to idle at something like 3000RPM, so drivability or economy is not a consideration - what is the need for the small primaries?  I would expect you could do 2 x 2600 primary and 2 x 2600 + 2 x 1000 paired as secondary without drama.

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  • 3 months later...

Thanks for the reply, and apologies for acknowledging your reply earlier. I must have missed the push notification.

My project is a journey of research and fun not just top end power, it needs to be drivable on the street, emissions friendly as best as practical. So small primaries are needed. That makes it harder to manage fuel flow capacity given my second requirement: Max injector duty cycle < port opening time for optimal fuel injection, hopefully cleaner burn again potentially better for emissions and torque. These are factors the manufacturers aim for. Shorter pulse widths also allows for some adjustment to port open time and injection start/finish potentially assisting in the positioning of fuel in the chamber. Again, probably not measurable except via emissions, but its the fun of trying for me.


1. Manageable at low rpm (900-100rpm)

2. By design max 25% injection duty cycle

based on those two criteria I worked through various capacity, flow calculations and concluded that the Injector Dynamics injector selection tool was actually a sound place to confirm. I produced a mud map of various boost, rpm, AFR, fuel pressure combinations et al and a little bit of sensitivity analysis on the piston engine parameters provided in the tool (not useful for a rotary). I then made adjustments for the rotary engine cycle and calculated fuel flow and confirmed opening times from there. I extrapolated that and compared against some very old telemetry data from the car 15+ years ago and found the results were reasonably consistent. Having numbers come up and say, put 4 x 2600cc injectors in did cause me to take a step back.

No for the journey, I would expect 1st stage (2 x 1050) and 2nd stage (2 x 2600) will get me to my first goal (more power than my brother's Aston Martin for bragging rights over a beer :) ). The 3rd stage (2 x 2600) injectors is because the new manifold will take them, and all things considered, the car build might be able to use some of it.

I understand what I am attempting is not the norm, but have got confirmation of the approach from two sources that would be regarded as very reliable: Good control of fuel injection is part of "the secret sauce" to a top grade solution.

So, I would be kicking myself, if I found after doing all the work needed for a major car uplift, that I could not engage the stage 3 injectors.

I've spent quite a lot of time comparing my options for the ECU and the Link is nice. Not having a 3rd stage is the only significant drawback I find in comparing it to Haltech. As an Aussie, both are designed in Australasia so a plus either way.

I've attached my injector duty cycle "heat" map that shows a subset of the results determined using various calculations and the ID web tool: Fuel Flow Calculator | Injector Dynamics where I picked off the flow and duty cycle based on RPM for each injector. Each column in the spreadsheet represents a different combination of calculations.

Injection and Flow Calcs 13B Injector Dynamics solution.png

Injection and Flow Calcs 13B Injector Dynamics sample calcs.png

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Hypothetically: Third stage via setting the injector outputs to GP PWM Outputs with a frequency table and DC table.  You could make the frequency table match RPM (i.e. Frequency = to 120/RPM), and then you can create a duty cycle table as your third stage fuel table.  This would obviously have no corrections for varying fuel pressure and the other fuel model equation inputs and thus might be quite crude.  There are math channels that could be used to implement more logic, however.  That said, I think it could theoretically be possible.

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An interesting idea thanks.

Preference would be to have full control over fuel and timing maps. If say a DO is used to turn power on to the stage 3 injector supply, control them in parallel with stage 2 injectors then use the same enable condition to select a different map or equivalent for the combined injector set?

Having Stage 3 support sound much simpler.

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Since our biggest ecu at present only has 8 injector drives, the engines that could actually run 3 stages is very limited - 1 and 2cyl only, so there are no plans for 3 injection stages in the near future.  It will likely be a consideration for G5 in the future, but still a fair while off I would say.





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One does need to concentrate on market needs, and rotary engines remain niche. I had hoped the G5 would support 3 stages, but alas no.

The 2 rotor engines with an aftermarket manifold setup supports 6 injectors for side port only and 8 injectors when peripheral ported. Power range from 400RWHP to 1000+ RWHP.

For the rotary there are only two rotors but effectively 6 cylinders & 360 degree cycle, so the demands on the injectors are double to tripple that of an equivalent piston engine. My 6 injector setup is effectively 3 injectors shared across 3 chambers with half the port opening time of a piston engine. Hence the high flow rate requirement of the injectors. The primaries need to be small enough to idle stably and not at a ridiculous rpm, that makes the setup for secondary and optionally tertiary that much more important as compared to a piston engine.

Piston engines normally only need two stages as one can supply two injectors per piston.

Thank you very much for the feedback and interaction. All the best. It is a credit to Australia and New Zealand for our market leading ECUs in a tough international market.

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