not to add to what is becoming a ****-throwing thread, but i think you were a little too quick to make that comment Mark. i know what you were trying to say, but just to add i think you WILL get some gains with a properly tuned header. the thread starter also mentioned a non-stock port timing, so there are gains to be had with a proper exhaust.
moreover, a properly tuned (i.e custom) COLLECTED header should always make more power than a non-collected header...don't think there's ever been a comparison, but exhaust tuning theory seems to confirm.

 

Assuming the same AFR they'd be at 82%. And that's not a guess...

85% actually.

http://www.sdsefi.com/techffhp.htm

 

Yeah! Now you guys are starting to get to root of my question...

In a perfect world, I would rather run more, smaller injectors sequentially, but since there's only room for 4 total then I'd rather have larger injectors that run at a lower duty cycle. (granted I don't have an AFC yet, so it's kind of a gamble right now on how rich it'll make me) My question was whether I should put them in the primary or secondary position initially. After thinking about it, I think I'm gonna go forward and stick the 550's as the primaries. My reasoning is thus:
1. The primary runner is smaller thereby intake velocity will be higher - better atomization
2. From driving, I feel as tho the engine could use a little more fuel from 3k-3.8k
3. The injector pulse is halved(?) once the secondaries kick in - I won't run as rich as I could be up top.
^^^^^^^
correct me if I'm wrong but does the duty cycle DROP to ~50% after the secondaries kick in?

thanks guys, ~rich

 

And what are you going to use for fuel control? The stock ECU runs rich as is, and a larger primary injector flow will most likely cause flooding, as well as screwing with your low RPM power.

How do you know the engine needs more fuel from 3-3.8k RPM? I'm telling you, put a voltmeter on the O2 sensor, and unless there's something SERIOUSLY wrong with your fuel system, it will be pegged rich at that point. The stock ECU, in open loop mode, goes lean under decel fuel cut. That's it. If it's lean anywhere else, you need to figure out what the problem is and fix it.

Yes, the duty cycle halves as the secondaries kick in. But this doesn't change how rich the stock ECU is running up high. I'm pulling out 30% with my SAFC-II above 5k RPM, and I'm STILL running rich.

Go ahead. Swap them in. Do a few "butt dyno" runs to prove to yourself that it's running better. Then, put a wideband in and come back with the AFRs it's running. I'm betting turbo guys will laugh at how rich it's running.

-=Russ=-

 

I only upgraded my injectors AFTER I put it on the dyno and knew for sure what my AFR's were, and even then there's probably some other issue I need to get worked out eventually with my fuel system. To do this **** by the seat of your pants is rediculous, especially on an N/A. I bet you could get a baseline pull w/ wideband for between $60-80 at a local shop.

The other thing that a dyno can do for you is help you spot other little problems such as ignition breakup. If you really want to upgrade your injectors (and it should be in the secondaries) you better have a dyno sheet to prove that you need to, and to prove that you will actually make gains.

Now let's say you do need more fuel. You could easily get more by cranking up your stock injectors a little bit with an SAFC. Install an SAFC and get to a dyno, and only if you cannot get the car to richen up should you even think about getting new injectors.

 

Dyno tests have proved otherwise on non-turbos. But the fact is that the longer you can keep the exhaust pulses apart on a rotary, the better flow and HP you will get. You can call racing beat, you can call mazdatrix, you can call rotary raceing and reliability and they all will confirm this.

Now this is different from a piston motor (and since piston theory keeps getting pushed into this thread) On a piston motor you can time the exhaust pulses to actually increase the velocity by stacking up on exhaust event to another. But on a non-renisis rotary, the mixture is still expanding and burning as it is exiting the engine and has not been cooled by the travel through a head.

But back onto the rotary... if the exhaust is collected, it really does not matter with stock or near stock (as street ports are) porting. In fact there is little gain of a header over just a down pipe and stock exhaust manifold if the header joins together and (again) there are no major timing changes in the ports.

What can I say if you don't believe??? Not my problem.

 

You don't listen!

 

big deal I don't listen - it's 2 fuel injectors and I can swap em out in less than 20 mins. I was hoping to get some deep soulful answers both pro and cons which I got. thanks all!

Besides, I have something brewing in the back of my mind and this install will be a good test for things to come. However, If you really want me to do what you say you can tell me if I can run the primaries without the diffusers and if so do I have to remove the injector rail spacer. thanks again guys ~rich

 

It'll make you too rich.

True, but it doesn't matter how much you atomise it. Excess fuel won't burn, it'll just absorb combustion heat and cost you power. That's what overly-rich mixtures do.

The butt dyno is terribly unreliable at guessing power, and it's even worse at guessing mixtures. You're planning your mods based on very weak info. Lot's of people have tried bigger injectors in an NA and been disappointed.

It doesn't matter whether you upgrade the primaries or secondaries, it'll still be 10% richer than it would be with stock injectors, and that's a huge amount. Plus with no fuel control there'll be a step in power delivery as the mixtures abruptly change when the secondaries come on. People spend a lot of time trying to eliminate the 3800rpm hesitation, but you're deliberately introducing it...

If you insist on fitting bigger injectors, put them in the primary position. fit a fuel controller and have it properly dyno-tuned. A trip to the dyno beforehand will probably prove you don't need to do anything.

 

http://rx7.com/cgi-local/2ndgencalc.cgi


by their rotary fuel calculator:

i see, at 85% duty, a max of 225fwhp
at 100% duty, they say 460's will support 262 fwhp

 

Now that's what I'm talking bout! Thank you very much NZConvertible. However, I'm not getting a 3.8k hesitation, I'm getting a huge ~3.8k surge in power and I think I know what's going on... ~rich

 

Transitioning over 3800 RPM should be very, very smooth. I honestly can't tell at ALL that my injectors are transitioning to running 4. If it's not smooth, there's a problem that needs to be fixed first. Is there a chance your primary injectors are clogged and not flowing properly, and that getting them cleaned would fix it?

-=Russ=-

 

It is normal for a surge at 3800 on a S4 non turbo, or if porting has been done to the aux port inputs

 

And what's that based on? The SDS EFI calculator shows the basis for the numbers (BSFC), and they make perfect sense.

I'm not recommending pushing injectors to their limit, I was just pointing out that the power mentioned (172rwhp) is well within the abilites of the stock injectors. Same goes for the original poster n/a-luvr.

[QUOTE=n/a-luvr]...I'm getting a huge ~3.8k surge in power and I think I know what's going on... /QUOTE]And that's my point. You think you know what's going on, but you don't actauuly know for sure. For the price of a dyno run with logged AFR, you could save yourself the hassle of what is most likely going to be a disappointing result. If you do need a bit more fuel somewhere, you'd be much better off doing it with a fule controller and stock injectors. At least this will also enable to to pull fuel out from the known rich areas.