MPFI with 16 injectors

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ChargerST
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MPFI with 16 injectors

Post by ChargerST »

I've been thinking about converting my car (500ci BBM) to multi point fuel injection and having a custom intake built. The concept of having 16 injectors (2 per runner) seems quite interesting. When having 1 injector at runner end (close to valve)and the 2nd injector at runner entry what setup is the best (easiest to set up, best power, etc.)?

Rpm based bias: low rpm - fuel only (mostly) from lower injector. High rpm - fuel only (mostly) from upper injector. Crossover from injector 1 to 2 inbetween.

Injector 1 constantly supplying fuel with (like the old mechanical injection systems such as Bosch K-Jetronic) - could be set up in a way that no controls are needed. Fuel supply would be just enough for idle. As soon as the throttle is opened second injector would supply additional fuel.

What are your thoughts?
Thanks,
Stefan
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Rick!
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Re: MPFI with 16 injectors

Post by Rick! »

K-Jetronic injectors still need "controls".
My brother's 598BBM uses single BA3 160pph injectors on methanol with a 300 shot and still is under 80% duty cycle.
Using gasoline, your two sets of injectors would be tiny so they might handle very low pulsewidths properly.
Sounds like you are mulling over a science experiment that could get costly with additional parts to support "mechanical" and EFI injectors.
There are several aftermarket engine management systems that have the ability to run two or more sets of injectors.
Maybe look into them to simplify overall system control.
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Re: MPFI with 16 injectors

Post by Orr89rocz »

Yeah, why not do it right and run a complete efi system like holley dominator. It will control and phase in the secondary injectors just fine
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Re: MPFI with 16 injectors

Post by rebelrouser »

as mentioned it is all about injector flow, fuel pressure, and pulse width. The only reason I would see to use two injectors per cylinder would be if the fuel demands of the engine were so great that at idle you could not control the idle fuel quality of the engine with one big injector, usually like in a turbo, or supercharged application. The other issue is fuel pressure and amperage draw on the drivers in the computer. The higher the fuel pressure the higher the amperage spike when the injector opens. Some engine programs will tell what the size of injectors is needed if you plug in your engine, and then you can see what is available. I helped a couple guys that tried to set up a turbo setup, by just using what injectors they could buy cheap, and not sizing them properly, they really struggled until we did the math and figured out what was really needed.
Now the other issue is do you need the dual injector setup for performance, or do you just want the look of a trick setup? Nothing wrong with that, I have built a lot of stuff just because I wanted it to look neat. I am sure if you want the neat look, your engine is big enough, a dual injector setup could be done, I just don't see a performance advantage.
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Re: MPFI with 16 injectors

Post by Circlotron »

I can imagine there would be some advantage to using a combination of a very small and a much larger injector. The small one, apart from being probably generic and cheap, when it is operating will need a much greater "on" time and so it will be much more controllable than a large one with short pulse width where the opening and closing times form a greater percentage of the total time.
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Re: MPFI with 16 injectors

Post by ptuomov »

ChargerST wrote: Fri Sep 18, 2020 6:30 am I've been thinking about converting my car (500ci BBM) to multi point fuel injection and having a custom intake built. The concept of having 16 injectors (2 per runner) seems quite interesting. When having 1 injector at runner end (close to valve)and the 2nd injector at runner entry what setup is the best (easiest to set up, best power, etc.)?

Rpm based bias: low rpm - fuel only (mostly) from lower injector. High rpm - fuel only (mostly) from upper injector. Crossover from injector 1 to 2 inbetween.

Injector 1 constantly supplying fuel with (like the old mechanical injection systems such as Bosch K-Jetronic) - could be set up in a way that no controls are needed. Fuel supply would be just enough for idle. As soon as the throttle is opened second injector would supply additional fuel.

What are your thoughts?
Thanks,
Stefan
My thought is that THIS IS AN AWESOME IDEA!

Here's how I would do it. Get high quality independent throttle bodies (8) that bolt on close to the intake port. Do cross ram trumpets into an airbox with a transparent plexiglass cover. Have the small injectors spray at the intake valve (downstream of the throttle) and the large injectors spray into the trumpet inlets. That setup has the potential of driving great at all rpms and loads and looking $money$.
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Re: MPFI with 16 injectors

Post by ptuomov »

rebelrouser wrote: Fri Sep 18, 2020 8:31 am as mentioned it is all about injector flow, fuel pressure, and pulse width. The only reason I would see to use two injectors per cylinder would be if the fuel demands of the engine were so great that at idle you could not control the idle fuel quality of the engine with one big injector, usually like in a turbo, or supercharged application. The other issue is fuel pressure and amperage draw on the drivers in the computer. The higher the fuel pressure the higher the amperage spike when the injector opens. Some engine programs will tell what the size of injectors is needed if you plug in your engine, and then you can see what is available. I helped a couple guys that tried to set up a turbo setup, by just using what injectors they could buy cheap, and not sizing them properly, they really struggled until we did the math and figured out what was really needed.
Now the other issue is do you need the dual injector setup for performance, or do you just want the look of a trick setup? Nothing wrong with that, I have built a lot of stuff just because I wanted it to look neat. I am sure if you want the neat look, your engine is big enough, a dual injector setup could be done, I just don't see a performance advantage.
I agree with a lot of these sentiments.

My (turbo conversion) car has single set of 80 lbs injectors and it idles steady at 700 rpm with 8000 rpm redline. The car has 100x dynamic range in terms air and fuel flow at idle being about 1% of that at the peak power. JDS in UK hacked the computers to get the original '87 Bosch LH fuel injection computer to do that, they did something that I thought was impossible. Still batch fire, too. (They _didn't_ say there would be no math...)

Another thing with cars that have a large dynamic range is fuel pump sizing. I've got two Bosch 044s, the second one turning on with load. In a bypass regulator system, little things like fuel heating and consequent fuel thermal expansions screw with the AFRs. In my opinion, the selected aftermarket ECU should really have a fuel temperature sensor and compensation (unless flatheading the pump, which is harder to set up).
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Re: MPFI with 16 injectors

Post by Racer71 »

On the bike based engines we use in dirt track cars we use individual runners with one smaller injector after the throttle blade then at 8k rpm we turn on the larger “shower” injectors which are above the blades housed in the top of the air filter assembly. Keep in mind these are on methanol so the fuel demands and cooling abilities of the fuel are in high demand as they turn close to 17k rpm for extended periods of time.
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Re: MPFI with 16 injectors

Post by Bill Chase »

Small primary close to valve for drivability, and larger further away from the head ramped in based on boost and rpm.. surprised someone hasn't mentioned one of the biggest benefits of doing this.... air fuel charge cooling.


It is one of the biggest reasons blow through carb guys can get away with higher pressures before needing an intercooler.
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Re: MPFI with 16 injectors

Post by englertracing »

Counter popular implementation.
If the setup is port restricted it might loose top end with nozzles far up stream.
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Re: MPFI with 16 injectors

Post by Belgian1979 »

IMO: 2 injectors are usefull if you produce so much power that you need very large injectors. These have the disadvantage that the are very erratic in how much they deliver at very small pulse widths like at idle. This is where a dual injector system excells. It allows you to have super good idle control while at the same time being able to deliver huge amounts of fuel to your engine at the top end of the range.

The second consideration is how much rpm you use. Since a dual injector system necessarily means putting one injector way up in the inlet tract, it will have to run a decent amount of rpm in order to get it to work well.

Another advantage as mentioned is that the intake charge is cooled, but I don't know how much that is worth.

Disadvantages are the complexity and cost.
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Re: MPFI with 16 injectors

Post by David Redszus »

Two injectors per cylinder have been used quite successfully for many years. They were used on the Mercedes DTM engines and are currently being used on turbo Yamaha drag snowmobile engines. Ditto for Formula One engines as well.

If high fuel flow is required, twin injectors solve several problems. To accommodate high fuel delivery, an excessive duty cycle is needed, typically up to 85%. Beyond that, larger injectors are used but large fuel flow injectors usually deliver very large fuel droplets, which is not desirable. Raising fuel pressure has the side effect of altering the spray cone and droplet formation. Large capacity injectors do a poor job at idle and low partial throttle fuel requirements.

Fitting twin injectors properly sized, can produce the needed volume, maintain proper spray pattern, and provide a smooth idle. One injector is placed near the inlet valve and is used for low speeds when more time is available, to provide a quick throttle response. The second injector is placed closer to the open end of the trumpet, to allow more time for fuel evaporation. The fuel flow is phased from the low to high injector as a function of rpm and throttle position.

Modern engine management systems, like MoTec, can handle the fuel control function very easily.
Fuel control meaning not just fuel mass but also mixture preparation for maximum power and throttle response.
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