Hi All,
I've been researching upgrading the engine side fueling on my build. I currently have a 8374 single turbo with stock 550 primaries and used 1660 secondary's. The general consensus seem to be to build the fuel system around what your system could be capable of and not your immediate plans. I haven't dived too deep into the math but it seems for a high power build a 8374 could probably use in the territory of 6000CC's of gross injector to be well into the safety zone with my build plans (Howard Coleman Fuel Injector Sizing). I plan to run a lower boost to keep reliability up but its good to have the headroom. alongside increasing my total fuel capacity I also have probably original primaries and secondary's with unknown history. Additionally I've seen it regularly touted that injector technology has advanced a lot and that even larger primaries now should be able to more accurately be tuned for idle. I will be using my existing PFC for the meantime and I'll get the new PFC master for tuning. I know the PFC is a little dated, not sure how much this plays into injector options and control, I know newer/ more modern ECU's allow the option for increased crank resolution through thing like FFE FD Hall Trigger Kit but this isn't an option with the PWC. Does this effect injectors?

In researching options I've come across the JP# Engine Side Fuel System as a potential option for a complete kit. In their primary injector options they list they comment that the DeatschWerks 700cc is recommended for power FC users. I've read that with the accuracy of the injector dynamic accuracy that tuning idle is not a problem so I'm not sure what the reason for the recommendation is. The 700CC"s vs the ID 1050's are also a 125$ price increase. Similarly the DW 2200CC's are also 280$ cheaper than the ID 2600CC's. even with all DW injectors I would be at 5940 gross CC's which should be plenty of fuel.

This leads to my questions:

1. Why would the DW 700's be recommended for power FC users. is this just due to the logic that smaller primaries are easier to tune idle with or is there some other limitation of the power FC that I haven't found yet?
2. How do DeatschWerks injectors compare to injector dynamic's? I tried searching but couldn't really find much info online.

 

There are a couple of things. you should double check me too, i'm going off the top.
First any injector has non linear areas, both at high duty and low duty.
The FC Tweak/Master will actually look for cells where the injector duty is too low, or too high, and will want to adjust accordingly, which is good, no other ECU setup will do this.
The other thing is that the Power FC has a minimum duty cycle at idle.

so the long and the short of it, is that at some point the car will be too rich at the minimum injector duty, and the options are to live with it, raise the idle speed, or run smaller injectors.
the only PFC specific thing is really that it polices low duty cycles

 

Will quote John Renna on this - For primary injectors, use the smallest injector you can get away with. The smaller the injector, the longer the pulse width at idle. The longer the pulse width = smother running engine.

The DW injectors are quality injectors like ID and a fair pricepoint. We've sold many of them (they are popular on other platforms) and no issues reported.

 

I've never had a problem with ID1050s and PFCs at idle outside of the fact that PFCs are pretty lame duck in and of themselves by todays standards. ID and T1 also have (in my opinion) a reputation more rooted in motorsports which is a plus given that it behooves them to put out product without trying to cut corners - that isn't to say that DeatschWerks puts out a bad product necessarily just that there is a very different standard the two organizations are held to.

 

1. no real answer but theres no reason to run anything smaller than a 1000 for the primary. whether ID or otherwise. the power fc has no issue running an injector of that size.

2. for street driven cars, there will be no difference. at "our" levels, some of the things that separate brands and/or products is not a factor. for longevity, reliability and consistency, i would pick the ID but that is based on nothing besides my feelings. we have done a few cars with DW injectors and they are out in the world living their best lives. if the budget is there, we default to ID.

the ID2600 is a MASSIVE injector and not something that would advised for use with an 8374. 1000/1700 or thereabout will be more than enough fuel for the 8374 with a proper pump at standard pressure. the issue you run into with large injectors like that is controlling the ramp in and getting them to spray a "small" amount of fuel. basically they are hard to control at reasonable power levels. injector sizing isn't just about math, at certain sizes they have different characteristics and traits. this needs to be factored as well when making a decision.

 

Makes sense. I had mentioned 2600's because that was the only other secondary injector that JP3 lists as an option in their Mazda RX7 FD3S 13B-REW Fuel System (engine side) (OEM LIM) system. seems like other suppliers have 1750's as an option.
so if using injector dynamic injectors then the best combo would be 1050's with 1750's.

 

Yes. Or you can use 1300 primary. For your set up, the 1000 will be plenty though. If the difference in cost between the 1000 and the 1300 is negligible for you then in this case I would go bigger. So 1050/1750 or 1300/1750.

That will take you far so long as you have at least a 340lph wired correctly and even then a 340 is more than adequate. You can CAN go too big for pump as well. That combination will easily and comfortably support up to ~450whp.

 

I had started with the thought that a bit too big a fuel pump wouldn't hurt, but I'm starting to question that. My thought is that if the bump is too big then its just an increased electrical load on the car for no reason. Is there any other downsides of too big a fuel pump? I was originally planning on using a 525 because of a post by Turblown on a 8374 build running out of fuel with E85. That being said I don't plan on running E85 due to lack of availability and my fuel injectors wouldn't have enough capacity for that power on E85 anyways.
I need to do more digging again now, I want the pump to be a bit overkill so I never run out of fuel but I also don't want to be ridiculously overkill like the 525.

Something like a Walbro 450 would still be overkill maybe a little less so.

 

Two reasons come to mind with oversizing a pump

1. Too much volume at low fuel usage (idle, low fuel demand) can overwhelm your fuel setup. If your return lines are undersized for that volume, you'll overload the fuel pressure regulator.
2. You'll overheat the fuel. Circulating the fuel with the increase flow rate will transfer a ton of heat into the fuel in the tank.

 

That all makes sense. I'll do a bit more digging/reading before I make a decision.