Deleting the Primary fuel rail
02-19-17, 06:00 PM
#1
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Deleting the Primary fuel rail
Sorry if this has been discussed, I searched but maybe I'm not using the right terms. I'm considering an aftermarket LIM, both the excessive and cxracing manifolds use a 4 injector setup. Most people block off the the centre two injecter holes as the primary ports are getting fuel from the primary injectors. The only time these extra holes get used are when using a 6 injector setup for e85. But why not just use the secondary rail and run both primary and secondary injectors off of it and eliminate the primary rail all together? Not only would it be cheaper if upgrading from stock (fuel rail and fittings), but also less cluttered, and fewer connections to leak. In theory (at least in my head), the primary rail would be far more prone to heat soak being on the iron, so wouldn't cooler fuel temps also be a benifit?
What do you guys think? Has this been a thing and I'm reinventing the wheel? Or am I out to lunch?
What do you guys think? Has this been a thing and I'm reinventing the wheel? Or am I out to lunch?
02-19-17, 07:58 PM
#2
I believe primaries is technically a more optimal spot to inject.
But I think you don't see it more often due to a hangover from older injector capabilities. With the new style ID/EV14 injectors, larger sizes can still be controlled really well when you want lower volume. You no longer need to worry about 1600cc injectors killing your idle, which originally drove the need for 750 or 850 primary upgrades.
But I think you don't see it more often due to a hangover from older injector capabilities. With the new style ID/EV14 injectors, larger sizes can still be controlled really well when you want lower volume. You no longer need to worry about 1600cc injectors killing your idle, which originally drove the need for 750 or 850 primary upgrades.
02-19-17, 10:54 PM
#3
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the reason the primaries are in the place they are is because its a pretty optimal place to put them. Mazda even calls it something like semi direct injection.
response, and efficiency are both better with the primaries, but no loss in power. its enough that even the race cars moved injectors from the trumpets to lower down on the intake.
other than that, all the other stuff is true, it would be easier and cheaper just to have 4 normal injectors on 1 rail, like every other car, fewer places to leak. temps are probably about the same though.
oh so, i guess you could do it, but ecu needs a full retune and the low rpm/load load drivability will be the hard part
response, and efficiency are both better with the primaries, but no loss in power. its enough that even the race cars moved injectors from the trumpets to lower down on the intake.
other than that, all the other stuff is true, it would be easier and cheaper just to have 4 normal injectors on 1 rail, like every other car, fewer places to leak. temps are probably about the same though.
oh so, i guess you could do it, but ecu needs a full retune and the low rpm/load load drivability will be the hard part
02-20-17, 12:31 PM
#4
As everyone has said good dispersal and a more optimal injection location. I don't have any evidence but I'd also think that having fuel entering the chamber from either side rather than a single side would reduce any 'wetting' in the manifold (even though this is mainly a carb issue) when using both primary and secondaries.
Last edited by dguy; 02-20-17 at 12:31 PM. Reason: Words.
02-21-17, 11:59 AM
#6
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I never thought of the primaries as almost direct injection, that's a very good point. I guess I'm reinventing the wheel, not exactly a new platform, it was probably tried and failed 20 years ago. Thanks for the input everyone, I'll scrap the idea, it is a street car after all.
02-21-17, 10:32 PM
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I never thought of the primaries as almost direct injection, that's a very good point. I guess I'm reinventing the wheel, not exactly a new platform, it was probably tried and failed 20 years ago. Thanks for the input everyone, I'll scrap the idea, it is a street car after all.