REW Stock ports
Bnr Stage 3 non sequential
Power fc
Meth
Intake. full Exhaust. Intercooler
Supra pump
Air pump delete

I'm increasing boost from 7psi to 13-15psi with a tune and installing an rx7store ultimate fuel system with 1680s and 850s.
I would like to utilize the stock ports for mpg's as much as possible when cruising and I think the 1680s are overkill for 15 pounds.
What are best injector sizes for this setup with an emphasis on mpg's and should I use the pressure regulator?

 

I'm trying to understand your thought process on fuel economy a little better. Could you elaborate? Remember that the secondary injectors don't activate at low loads.

 

I didn't realize that about the secondaries. Should I keep stock primaries or use the 850s?
I'm thinking this whole fuel kit is overkill for my application but if it won't effect gas mileage then I'll just use it.

 

Something to consider: The RX-7 is a sports car. Its sole mission is to go fast and look good. Everything else is secondary.

If you are worried about MPG, buy a Prius or a TDI.

With that being said, you can expect 20-25 MPG on the highway if you have a good tune and keep your foot out of it.

Vince

 

What 850s are they? Stock or aftermarket the stock ones are a bit harder to tune aftermarket topfeed will have a better spray pattern and with a good tune you should get decent mpgs for a rotary but thats mostly in the tune ive noticed with the stock850as primary it gets to a point where even if you reduce it it wont flow any less fuel specially at idle which where fuel economy is really murderous

 

Fuel economy in an FD is a strange topic because they don't really go hand in hand. If you're driving long distances and want to make the most out of it then with a good tune and the right tires you should do relatively well if you find the right speed. Otherwise just driving around town will be awful. It's part of the price we pay to drive what we do. Thankfully we have huge fuel tanks.

 

All bosch injectors and kg rails and regulator. I just want to keep the gas mileage I have with the stock fuel system under light load with the extreme fuel kit.
I could get 550cc top feed primaries instead of 850s if it would matter.

 

850s and 1680s are fine. I think you're a little confused about how injectors run. You can tune those aftermarket injectors to run on a completely stock system and get the same mileage as you would with stock setup. The larger the injector the more room you have to play with in terms of power upgrades. So if you decide in the future to run 17-19 psi you will have the fuel to do so. Where as of you were on stock fuel system you would most likely run 80%+ injector duty cycle (meaning your injectors wouldn't be able to inject enough fuel fast enough, run lean, and then pop goes the rotary.

 

The size of injectors wont affect fuel economy if they're small enough to get you the resolution you need. The issue is how many Ms your injectors are running at light load. EV14s or ID1000s from what I've been reading have a pintle that is light enough and a great spray pattern.

 

FD stock ports are capable of 26MPG highway with 550cc primary injectors. Under cruising conditions, the engine is in a vacuum state so turbos are doing nothing but just free spinning with the incoming air flow. The key with the larger injectors is trying to get close to the atomization capabilities of the smaller injectors. Sometimes that's harder than it sounds.

 

For your application I would recommend you keep the stock primaries.

 

Stock 850s used at primaries are the worst thing you can do.

550/1200 is good for over 350 whp.
550/1680 is good for over 400 whp.

Engine type, with tuning, and driver style affect mileage, not injector sizes.

Since your question is invalid, you are invalid!

 

Bosch EV14 (or ID) in 725/2000cc. These have a much better spray pattern and are easier to tune tune than the old-style Bosch 850/1680s you are talking about. I honestly never recommend using the old injectors anymore. There is just much better stuff out there. You will never get a good idle or cruising AFR with those. The stock primaries may be sufficient for your goals, but they are old and you will have better results with the new stuff. If you need help or want me to build you a fuel system just ask.

Ihor @ IRP

 

i was running old-style 1000cc primaries and still got 25-28 mpg highway, 18-20 in town

 

What engine and setup? Also what speed on the highway?"

 

To add to the afore questions; what is your idle AFR like?

 

stockport 13REW single turbo, now im running 9.4CR rotors, i always set my idle afr to around 13.0. both setups had 1000cc pri, 1600cc sec RC engineering injectors. honestly the only problem i had with 1000cc primaries was during very light throttle (basically decelerating) it would start to buck a little in closed loop (14.7 afr). but it was hardly noticable and other than that it ran perfect. it usually gets about 25mpg at 70-75mph. ive done some economy trips keeping it at 60mph and once pulled 30mpg!

Ive been looking at trying to eliminate the need for secondary injectors. Ive tried 1600's in the primares, and even ID2000's. 1600's do not work too well, those injectors dont like pulsewidths under about 1.4ms, which results in idle and cruise in 11-12 AFR range and lots of bucking and rough idle. The ID2000's work a better, but im still testing

 

The main problems with the old-style injectors are the spray pattern and the staging. I'd also be curious what the cruising AFRs were. It is nearly impossible to get good crusing AFRs and still have a good transition when you tip into the throttle. I'm betting your EGTs were sky high to get it lean enough for those kind of gas mileage numbers.

 

I'm currently running 850/1200cc injectors. That is stock secondary injectors for primaries and secondary bored out to 1200cc. With some running, advance timing and running around 15AFR I was able to get 27MPG on the highway. The problem I'm having is my idle sits at 10.4 AFR. I'm thinking of changing my primaries back to 550cc stock unless I can find something new. Still running stock fuel rails etc. I am however running a Walbro 400lph fuel pump.

Are there any recommendations as to which side feed injectors?

 

15.0 is too lean in my opinion. I would ditch the side feeds all together. They are old technology. If you are running a power fc you will not be able to lean the AFRs out enough at idle, as you are finding. The bored out injectors are also problem prone. I had 3 sets fair last year along so I will not install them anymore. Best bet is the 725/2000 ev14 combo I mentioned but it is definitely more involved as you need to change rails. How much power are you trying to make?

 

I'm definitely getting ID725s for primaries and I'll most likely keep my bosch 1680s for secondaries. With a good tune I should get slightly better gas mileage than I do now under light loads.
I've decided to go back to sequential 15-13-13psi and with that and meth it won't be the easiest tune so the newer injectors should help. My afr's are 14.7-15 while cruising and 13.2 at idle and full boost. I get great gas mileage if I try but I usually forget I'm trying at some point.

 

I'm trying to avoid going to top feed since that's going to be an expensive undertaking. I'm currently looking for a bandaid not the cure. There are other things I need to replace first (all new bushings, rebuild twins) that are higher priority.
I haven't had any problems with my bored out injectors but yea; I can't lean out my idle at all. And yes I'm running a PFC.

 

Your options are to either deal with it, or go back to the stock 550cc primaries.

 

That's what I was afraid of. :-/
Was hoping for newer tech side feed injectors. :-/