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I'm closing in on dressing my short block and after mulling over some injector discussion from previous threads am curious as to what folks with more experience would consider the best avenue for me to take would be. A few years back I purchased an Xcessive LIM and commissioned a custom LMS-EFI engine loom that included paralleled secondary injector connections so I could run 4 injectors with the LIM. My non-engineer thinking was that it had 4 ports and I might as well run 4 reduced size injectors instead of 2 larger ones, seeing a discussion recently about adding fuel to the small primary intake runners not being beneficial is making me second guess that plan.
Prior to removal I was running Bosch EV series 725 primaries and 2000 secondaries with the stock LIM, EMS was a PFC and the turbo was an 8374 IWG unit. I made a little over 400WHP with no AI and was happy. I removed the engine for paint and when I comp tested it I found it was about 20 PSI lower on one face indicated a possible stuck side seal or corner seal issue.
I plan to put a freshly rebuilt half bridge engine in (I got it with a parts car, done by Rotorsports with paperwork) which I understand will make less low range and more top end power due to the larger porting. The new EMS is a Haltech Elite 1500 and reusing the turbo kit and my power goals haven't changed, right now I have no plans for AI but provisions exist in the harness for a mapped AI setup. As such I was planning on running ID 1050x primaries and 4x ID 1300x secondaries with the Xcessive LIM and a 450lph pump; I may also run a new fuel feed line but if I remain at the 400hp mark it doesn't seem like I need to. I tried to plan with provisions to make about +-530whp with the addition of AI and turning up the boost.
So, with the background and proposed plan being provided does my way forward make sense or is it superfluous? Would I be better off moving to ID 1050x primaries and 2x ID 2600 secondaries in the Xcessive with plugs in the extra injector ports or sticking with the plan to run 4x 1300 secondaries? Will I see a benefit from the Xcessive LIM at the 400hp level or sub 550 if I want to add AI and turn up the boost?
The topic of balancing the fuel distribution was discussed recently in the Adaptronic section, it got me thinking about this too..
Based on what I had on hand I decided to run:
1000cc in the block (stage 1)
2600cc in the secondary runner (stage 2)
1000cc in the primary runner (stage 3)
I don't know about the flow/velocity of an OEM UIM, but based on the stock throttle body I would expect good results with a primary:secondary injector ratio of 1:1.5 or 1:2.
My old setup was 725cc primaries in the block and 4 x 1000cc secondaries in the runners. This put a lot more fuel through the primary ports but provided what I thought was a good result. Wish I could go back and change the injectors to see.
The topic of balancing the fuel distribution was discussed recently in the Adaptronic section, it got me thinking about this too..
That may have been where I saw the discussion, I'll go back and take a look.
Based on what I had on hand I decided to run:
1000cc in the block (stage 1)
2600cc in the secondary runner (stage 2)
1000cc in the primary runner (stage 3)
I don't know about the flow/velocity of an OEM UIM, but based on the stock throttle body I would expect good results with a primary:secondary injector ratio of 1:1.5 or 1:2.
I don't have the outputs or infrastructure built into my harness for 3 stages of injection, only paralleled connections for sec inj 1 and sec inj 2. Thanks for bringing the TB back up, I remember that being a primary driver for the discussion.
I also had the same “situation” and the same train of thought but instead i opted for 2x1050x and 4x1700s . I wanted to decrease the gap between primaries and secondaries to make a smooth transition. Car makes over 650whp with 25% methanol and a pretty conservative tune and pretty rich AFR. I am not maxing the injectors duty cycle but i dont recall what my duty cycle was.
transition is very smooth
RGHTBrainDesign has tuned a lot of rotary engines now, and I think he claimed somewhere in this video that getting the primary/secondary ratio correct is helpful. I don't think he shared numbers, but it's pretty common for tuners to keep some data to themselves.
My car has an Xcessive LIM and 6 injectors, so this is something I've meant to test on my car, but it's a backburner project compared to other things like suspension bushings and maybe chasing down boost leaks. I did go as far as building complex math channels to calculate the fuel flow (cc/min) delivered by each of the six fuel injectors (basically flow rate multiplied by fuel pulse, with some math to handle injector dead time). I'm planning to make some changes based on what I found, I think my existing settings are sending too much fuel to the primary ports and not enough to the secondary ports. I'll be pleasantly surprised if my butt dyno or wideband O2 sensor will detect any difference.
Your plan to use ID 1050x primaries and 4x ID 1300x secondaries with provisions for AI is well-suited for your power goals and future flexibility. Proper tuning is key.
10-04-23, 07:59 AM
