Is it better to run 4 equal sized injectors (850s) or 2 550s and 2 1300s? Does it really matter? Is there an advantage to either setup?

I am shooting for 325 rwhp. Based upon calculations either setup would work, with the 1300s having a little safety margin about 350rwhp.

 

I think there are two ways go. Either go 850's all around to save money, or go 550 1600. The reasons +/- are if you go all 850's it will be a little cheaper , but harder to tune for idle due to the larger primaries. 550/1600 cost more cuz the fuel rail etc but you will keep the good idle. IMO, just do 850/1600 unless you are sure you won't go single. 1300's have been known for crappin out.

 

550/1200 injectiors with a rewired fuel pump is good for over 350whp.
550/1600 is good for over 400whp.

It is not worth the tuning problem and mod problems to run 850 primaries unless you are going realy big power.

 

What about a 550x2 primary and 720x4 secondary combo? I always thought the smaller injectors would be more precise, and having more of them would give you the safety "head room" you needed.

 

It all depends what your power goals are. If you can support the power that you want with 2x550's and 2x720's, then that is just fine. I dont know what you mean by "precise", to me it's just about getting enough fuel for the application. I cant remember what the formula is for figuring it out, but that combo wouldn't put you very high.

Back to the original question, I would suggest getting 2x550's and 2x1600's. It's a common setup and it will easily meet your power goals plus give you some room should you want to go higher.

 

I'll be running 550's as primaries and 4x1000's on my GZ lim. Twin gt30's though.

 

My goals are about 320, 350 to the wheels with a GT30R. http://www.deatschwerks.com/catalog/
has the calculation, and they say 6 550s will be enough, but I don't want to run over say 70% duty cycle, thats why I was thinking 550 primary, 720 Secondary. By precise, I meant less of a fuel "dump" and more of a fuel spray. To me 1600s are way too much fuel even on low cycle. If I'm way off the mark let me know.

 

And where are you going to put 6 injectors on a 13b? Unless there's some mod I haven't heard of yet, stick to 4 injectors . A better calculator is here, http://rx7.com/cgi-local/3rdgencalc.cgi

 

550/1300 should be fine. that's what my friend runs on his sequential FD with street port, FMIC, and 1 bar boost. it drives just fine and has enough fuel up top. just make sure your EMS is set up to scale those injectors properly.

 

Xcessive UIM with Xcessive fuel rail. Thanks for the calc.
The EMS should be able to handle it, my question is do have to huge secondaries even though I wont get even close to needing half of their potential, or can I run four smaller injectors near the mid range of their duty cycle and the same/better efficiency? I don't mean to step on any toes, I just want to beat this into my head.

EDIT: Using that calculator with 2x550 primary and 4x720 secondary at 62% duty full load and 80% max duty its rated for 411 FWHP, which is way more than I'm shooting for. The 2x550 and 2x1300 only allows for 346 FWHP with the duty remaining the same. Am I wrong for thinking this or is this the better way to go?

 

Anyone?

 

Just go with the 550/1600's, it works fine. Do it right the first time, you may want more power later.

 

The nice thing about 4 injectors is you don't need to install additional fuel plumbing. Each joint you add is another potential leak or point of failure.

Regarding injector sizing, I'm not claiming to be an expert but I would try to size my injectors to match the amount of air in each runner. The primary intake runners are completely separate from the secondary intake runners after the throttle body, so I don't see the point of sending 75% of the fuel through the secondary runners unless your secondary intake ports are three times as large as your primary intake ports. (I realize the size of the port doesn't directly correlate to the actual amout of airflow, but I hope you get the idea).


PS, have you got any links to 13B/ GT30R dyno plots? From what I hear, that turbo is "too small" for a rotary, but I'd love to see results that say otherwise. I imagine it would be a very responsive setup.