First of all I did a search, but all I could come up with were numbers for turboed 13b's. It would be greatly appreciated if anyone could share what has worked for their fuel injected full bridge ported 13b N/A engine. It is a 4 port frankenstien (GSLSE with 12a irons) and will be controlled by a Megasquirt. Throttle bodies used are two TWM 2930(IDF style) 48mm throttle bodies with capability of using up to 8 injectors. Yes I do intend to drive on street. It is part of my project build 82 rx626, which I will be starting a thread soon showing progress.

 

2x1000 or 4x550 should be more than fine for pump gas.

 

This should be plenty of fuel to maximize your performance. W/o boost, there is only so much fuel the engine can handle. The power is going to come w/ intake and exhaust tuning.

 

It's a solid "it depends".

My exhaust is quiet enough that I'm still good with two 680s.

But then, I'm kind of running a far different intake setup, too. Quad 48s will allow a ton of airflow, to say the least.

How close to static do you plan on running? Four 550s should be enough. Smaller injectors are better IMO because they allow much finer low-load tuning, if you care about that sort of thing.

 

i think since he's running 2 TB's, that you'd want 2 injectors of each one....

 

With 4 injectors you can stage them with the MS so your low rpm tuning will be much easier.

 

I had thought of installing 8x22lbs(~230) using four in one bank (primary) and then the other four in the second bank (secondary) it comes to like 2x960. Which is what you all are pretty much telling me. Will that work?

 

I don't know how quiet it is going to be it will have a custom rb header collected to a 3" to a large rb 3" ss presilencer to a rb 3" rotor shape muffler of course all this yet to be installed.

How close to static do you plan on running? What did you mean by this? And yes I would like finer low-load tuning.

 

He meant how close to that 85% duty cycle do you want to be close to.

 

Right... at peak fuel flow, I hit 90-95% duty cycle depending on air conditions. But, I'm only there for a very short period of time and I almost never run the engine up into that range anyway, so I don't particularly care.

 

Ok, I was not planning to be running close to 85%, I see what you meant.

 

I run 4-550's on my bridgeport. My duty cycle only gets to 50-51% with 42psi of fuel pressure. More fuel pressure should bring down your duty cycle if it gets to high.

 

Thank you guy's for your inputs!

 

So its safe to say that large street port s4 (6 port engine) would only need to upgrade the secondaries to 550's?

 

You should not need to upgrade at all. The stock fuel injectors are more than large enough.

I have heard that the FC computer simply will not allow more than 70% duty cycle. That still should be good for roughly 220hp.

 

a stock S4 is only running mid 12's between 4500-6500, @145hp it just doesn't need much duty cycle.

 

I would personally run only 2 injectors. Keep it simple. I'd use Injector Dynamics ID 725's. These may sound small but the story doesn't end there as that rating is at 43.5 psi. RX-7's run around 38 psi so whatever their injectors are sized at, they produce less in use due to the lower pressure. ID injectors are 30 years more modern in technology than most others out there. Their atomization is fantastic and on par with much smaller conventional injectors. They are very fast. They are also very linear with higher pressures. It is the pressure that will be the key. Run them at least at 60 psi. This makes them closer to a 900 cc injector at 43.5 psi. Go higher than this if you pump can handle it and if you can still tune for a good idle. Don't worry about numbers on paper. Worry about performance in the real world. These will top the other options. Keep in mind these injectors are still linear even over 100 psi!!! It's the 21st century. Good fuel systems need to run fast injectors at high pressure.

 

SO factory 4 x460 cc's on a LARGE street 6 port engine is sufficient fuel?

 

I thought RX-7s were standard 42psi base pressure systems.

Sure enough, I went and checked... spec is 35-36psi for GSL-SE and FC.

Huh. So the peripheral port was making a lot more power than I thought, since it was running with a Chrysler 55psi regulator.

 

A standard 460 cc 2nd gen injector when run at 60 psi is the equivalent of a 550 cc injector at stock pressures but with better atomization. Of course the fuel system has to be able to do it and I am making the assumption that the injector is still fairly linear.

Factory 460's are completely fine on even the largest street port engines. There is no need to upgrade them to a larger size. Too many people get into this habit when what they should be doing is upgrading the fuel pump and regulator. Then they should raise fuel pressure and retune. Even running only 2 stock GSL-SE injectors, if run at 60 psi, are good for 220 hp. Having 4-460's is more injector that than.

 

Thinking about it a bit more, the ID 1000's would probably be a better fit for a bridgeport. The 725's would be good for a streetport.

 

I'm making quite close to that, at stock fuel pressure.

My main concern is that at lower RPM, the pulsewidths are too short for decent tunability. There's a huge gap between 1.2 and 1.3ms when 1.0 of that is injector opening/closing time. Part of the problem is the granularity of the MS1 unit, but still, making the injectors even larger would make that worse.

 

You do need a good ecu with fine control and MS1 isn't going to cut it. The ID injectors are extremely good when it comes to spray pattern and atomization. Their 1000 cc units are almost as good at fuel atomization as a stock 460 cc injector and they can maintain it at extremely short pulsewidths. Far lower than stock injectors or others of their type. The limitation then comes from the ecu controlling them. It has to be capable which the MS1 isn't.

 

I should point out that I AM still using the factory injector cups with the aspiration hoses. IMO this is critical, and all too often I see people eliminate these and then wonder why it runs like crap.

 

Keep on going guys I'm still feeding off this thread! And I really do appreciate it!