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Where To Place Fuel Injectors?

Old 12-15-2004, 01:13 PM
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If you had a free choice of where to place your injectors what would be your priority and why.



It does mainly concern my secondaries. How far from the combustion chamber would you place them. What angel is preferable? I am building a custom intake and so far I think I like to place them at a 45 degree angle about 5 inches above the intakes in the block, close to where the Lim meets the Uim. Would you move the primaries while you at it.



Also does anyone know if all injector bungs mate up. So far I only found bungs from MSD for a reasonable price.



It is for a fd3, not sure if this matters.



Thanks

CW
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Old 12-15-2004, 03:13 PM
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a buddy of mine made a little more power by moving the secondary injectors to the upper intake. it might be that the 1600's need more time/runner length to atomise the volume over 550's?



mazda has an sae paper, its on the 787b and they found that placing the injectors close, like where the primaries are, gave better response and fuel mileage, however they weren't after peak power and they we'rent using giant injectors
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Old 12-15-2004, 03:52 PM
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Originally Posted by j9fd3s' date='Dec 15 2004, 02:13 PM
a buddy of mine made a little more power by moving the secondary injectors to the upper intake. it might be that the 1600's need more time/runner length to atomise the volume over 550's?



mazda has an sae paper, its on the 787b and they found that placing the injectors close, like where the primaries are, gave better response and fuel mileage, however they weren't after peak power and they we'rent using giant injectors



I seemed to remember someone on the forum mentioning keeping the primaries where they are for better driveability.
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Old 12-15-2004, 06:46 PM
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Originally Posted by j9fd3s' date='Dec 15 2004, 01:13 PM
a buddy of mine made a little more power by moving the secondary injectors to the upper intake. it might be that the 1600's need more time/runner length to atomise the volume over 550's?



mazda has an sae paper, its on the 787b and they found that placing the injectors close, like where the primaries are, gave better response and fuel mileage, however they weren't after peak power and they we'rent using giant injectors

Some of the people I know making big power have blocked off the holes in the housings. All of the injectors are in the manifold.
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Old 12-17-2004, 02:02 PM
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The fuel injectors should be placed as far away from the combustion chamber as possible, this allows for better atomization as the fuel is dispersed over a greater distance and greater time in the runners. The danger with this setup is if the injectors are placed too far from teh combustion chamber there could be a phenomenum callled fuel "drop out" as the mixture travels from the injector to the combustion chamber.



If you ever see a radical fuel injected setup where each runner has it's own throttle body and an injector that is placed just slightly above the trumpets that is what allows for max power gains. (note i haven't seen these setup on a rotary before)
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Old 12-17-2004, 03:30 PM
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Originally Posted by Cheers!' date='Dec 17 2004, 01:02 PM
The fuel injectors should be placed as far away from the combustion chamber as possible, this allows for better atomization as the fuel is dispersed over a greater distance and greater time in the runners. The danger with this setup is if the injectors are placed too far from teh combustion chamber there could be a phenomenum callled fuel "drop out" as the mixture travels from the injector to the combustion chamber.



If you ever see a radical fuel injected setup where each runner has it's own throttle body and an injector that is placed just slightly above the trumpets that is what allows for max power gains. (note i haven't seen these setup on a rotary before)



Thanks that is what I thought.



CW
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Old 12-17-2004, 08:29 PM
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Originally Posted by Cheers!' date='Dec 17 2004, 03:02 PM
The fuel injectors should be placed as far away from the combustion chamber as possible, this allows for better atomization as the fuel is dispersed over a greater distance and greater time in the runners. The danger with this setup is if the injectors are placed too far from teh combustion chamber there could be a phenomenum callled fuel "drop out" as the mixture travels from the injector to the combustion chamber.



If you ever see a radical fuel injected setup where each runner has it's own throttle body and an injector that is placed just slightly above the trumpets that is what allows for max power gains. (note i haven't seen these setup on a rotary before)



Agreed.
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Old 12-18-2004, 02:39 PM
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Old 12-18-2004, 04:07 PM
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Originally Posted by j9fd3s' date='Dec 18 2004, 01:38 PM


Ok,

so the paper doesn't mention a trade off. I guess then closer is better.



CW
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Old 12-23-2004, 02:20 PM
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Generally, the closer the injector, the better mileage and crisper throttle response. The further away from the cobustion chamber, the more overall power. The best way to run it (ironic MAZDA does it this way?) if its a stagged system is primaries close to the combustion chamber for good idle and low load performance and throttle response, then run the secondaries as far from the combustion chamber as possible for ultimate power. This system works well and gets you the best of both worlds without the problems of either. If you placed your primaries far from the port, you idle, throttle response, and gas mileage will suffer do to fuel drop out and "wetting" of your manifold runners. At high RPM theres enough velocity to keep the fuel suspended and keep fuel from pooling and sticking to runner walls, but who drives at redline all the time unless this is for a drag car only. If you placed your secondaries close to the port, you wont gain a thing.



~Mike..............
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