What you're thinking of already exists in many different forms.
Is your goal here simply for additional fuel for a turbo application? What is your power goal? And this is for a D series correct?
If so, having two sets of injectors and fuel rails for low/OOB and high/IB operation is a lot of unnecessary complexity for an engine already controlled by a standalone ECU, on a platform/architecture that cant take much power as it is.
Just get some 1200cc saturated injectors on a single rail and call it a day. Modern high volume saturated injectors have come a LONG way, and will have almost no discernable idle quality issues. Running 1000's over here, and no issues.
What you are talking about wanting to do is typical for large shot wet nitrous setups, and is very common for piggyback style boost applications.
-Advanced nitrous systems change the entire intake manifold and have two (or more) fuel rails and injector sets, one for normal operation, and others that engage when the button is pressed to supply the needed fuel volume.
-Piggyback turbo/supercharger systems also did this, like the D series Edelbrock turbo kit.
- The Edelbrock kit worked with the stock ECU, adding a piggyback ECU which managed things when the intake manifold was seeing boost/positive pressures.
- The intake manifold they built for this kit had provisions for 8 fuel injectors, and 2 fuel rails. The stock injectors mounted up top in the normal spot, while a second rail and injector set was mounted below the plenum. You can barely make out the second rail in this picture on my green car:
- I don't use the second rail, because the car already has 600cc saturated injectors on the primary rail, plus Demon2 and Neptune RTP engine management.
- The piggyback stuff simply got pulled off, but the injectors and rail were left there to plug the holes in the manifold!
- Here's a google search result for the Edelbrock kit manifold, showing the fuel system line loop for the second rail:
The only other necessary applications where two (or more) fuel rails/injectors are used/needed are:
1) an OEM application using a stock GDI injection system, with a second or 3rd set of injectors and rails to support power adders like turbos, superchargers, nitrous, or all 3 at the same time lol.
- Examples of GDI with aftermarket piggyback port injection added on for larger power goals, are solutions created for C7/C8 vette or newer Camaros with LT4 V8's, newer MK7 and up VW GTI's, R's, etc. Audi A4, A6, etc. or Porsche Cayman, etc.
- A video of such a system:
- Skip to near the end of the video to learn more about the setup.
Or 2) you have an application where you require so much BSFC due to your power target, that a single set of injectors and rail do not exist to support the desired power level.
- This is incredibly common in drag racing engines, especially where 4 bangers and I6's are trying for 1600+ whp, on E85, methanol or nitromethane, all requiring an insane amount of fuel to inject.
- For example, BoostedBoiz uses a ProJay manifold for their K swapped MR2, this manifold has 2 separate sets of injectors and rails. The Fueltech system manages everything.
In other words, on a D series, drop in technology exists today that far exceeds what "normal" needs are for a typical boosted/nitrous D build.
Grab some 2150cc saturated injectors from Fuel Injector Clinic:
2150cc Honda (B, H, D) FIC's Data Matched high performance fuel injectors featuring high impedance Bosch core, E85 compatible, with a lifetime warranty.
fuelinjectorclinic.com
,drop em in, install a Walbro 525 fuel pump, larger fuel lines, a 1:1 rising rate regulator with base pressure set to 60psi, and you have enough fuel to support 1000whp on E85:
Short of concreting the block, going copper head gasket with cylinder rings and head receiver grooves, massive head studs (i.e. very serious drag racing), the average D build cannot survive this power level, therefore a need for more fuel beyond this drop in ready technology is unnecessary for our world.