The engine was built by Rotary Performance for the previous owner so I have no way of knowing to what extent it was ported. To make matters worse, the old car's s4 harness / injectors was modded to a s5 setup but I didn't do the engine swap into my current s4 car so they not knowing, reverted it back to a s4 setup with 460cc injectors!

So now I have no idea how many total cc's I was pushing(I think they were red tops). That being said, I just bought 2x brand new 550cc injectors for my '87 n/a, street-ported ride cause I feel it needs more juice (plus i like the idea of using brand new injectors). Regardless, this upgrade is the precursor to a RB header install (does a rotary run leaner with better flowing exhaust?) I do remember the previous owner telling me the port-actuators have been discoed.

I'm wondering WHAT POSITION should I put these injectors in - primary or secondary? I know the majority here puts bigger injectors as secondaries (for higher rpm power?) but my thinking is primary is a better choice for me. The porting, the header and I'm not afraid to dump some cash into a fuel management system if need be - any suggestions?

Should I go bigger cc's when it's all said and done? I have to fix my leaky pulsation damper this weekend so I'd like to swap primaries while everything is apart. Thanks in advance ~rich

 

When I put 550cc on my secondaries, my car performed worse. It would flatten out in high RPM.

At the time it was mildly ported, RB header, without emissions.

 

AFAIK you do not need to 'upgrade' injectors on n/a's, they already run rich. Send the stock ones out to get cleaned/balanced, and use an SAFC to lean them out a bit

 

Ok


All stock FC N/A injectors are 460cc. Do you need to upgrade? Absolutely not, you would forget half the mods you have done to your N/A before you needed more fuel, N/A FC’s run dog **** rich from factory. The only mods to a NA that would require more fuel is a P port or forced induction.

No the S injectors come on at 3.8k RPMs and cut the duty cycle down on the P injectors. Hardly anyone pushes enough power below 3.8k to need more fuel. More fuel does not = more HP.

No just fix the PD.

 

That is TRUE providing you're not running lean... I think I may be because I get a surge of power when I get to my 3.8k secondary activation.

I'm thinking it's either cause my 5-6th ports are always open thus causing the a slow intake charge and causing the engine to run lean at lower rpm's OR it could just be I've got a huge peak in my powerband at that rpm.

btw, do headers cause a rotary to run lean?

~rich

 

no with the ports wired open its ike running a car with a hot/high rpm cam, doesnt make much low end power,...

the reasomn u feel a surge of power at 3800ish is ussually because the port timing is becoming more optimal so its making more power...

header wont make the na rotary run lean.

 

That's highly unlikely. The stock injectors can support ~250fwhp, and you'll be no where near than unless you have a bridgeport. NA's already run very rich under load, so you'd be better of taking some fuel out, not adding more.

Put them in your toolbox until you actually need them...

You always upgrade the secondaries first and you always put the smaller injectors in the primary position. At low load only the primaries are firing, and smaller injectors handle the small pulsewidths required for idling and cruising better than bigger ones.

If you really want to dump some cash get a Haltech or similar. Unless you plan to get pretty serious a piggyback fuel controller like an S-AFC is probably all you need. You'll be able to optimise the rich factory mixtures for better performance, i.e. lean it out. If you go ahead and install those bigger injectors you will definitely need to do this, otherwise the super-rich mixtures will cost you some power.

No.

 

When people here say "can support 250~fwhp" I always assumed it was under a theoretical 100% duty cycle, not the stock ecu duty cycles.( is it 80% then 50%@3.8k? I forget... )

Anyways, the reason I'm being obstinant about injector upgrading is because the engine has LOST performance since being transplanted. Granted the new car is heavier but I'm only comparing how the engine revved, responded and did donuts! lol Aren't red top, post '87.5 injectors 550cc?

thanks again ~rich

 

No the duty cycle changes as needed based on AFM postion and Pressure Sensor.

Then you have another issue or your butt lies.
No High IMP-(12-13ohm) 460cc

 

is this another dumb injector NA thread by someone used too tuning lean burn hondas and Toyotas???

The absolute last modification you want to do on a non turbo rotary that is remaining normally asperated is to put in bigger injectors.

If anything (as mentioned several times above) you want to get the system leaner over the stock maps at above 4k RPM. This is for all somehat stock N/A motors (and your motor N/A luver is considered basiclly stock with only a street port on it).

Get your aux ports working, port match and polish your intake runners, and get a stand alone (or at very least a SAFC).

But if you are considering just bigger injectors, you will make less power unless you find a way of leaning out the fuel. Mazda delibertly ran the motor RICH at upper rpms to increase the lubrication and cooling.

And a header will do nothing for leaning out a motor. It has nothing to do with mixture levels at all (and will not really make any more power over just a downpipe unless you go with true duals from the manifold back).

and even with a duty cycle of 80% the stock 460cc found on all non turbo FCs, there will be more fuel than a street port motor will be able to use making 200 HP, well alone start getting near the 225-250 mark (numbers you will not see even with the mods you have outlined out)

 

I suggest returning the injectors and getting a wideband O2 sensor to determine WTF your engine is doing before guessing and adding more fuel.

As stated numerous times, 2nd gen RX-7s run stupidly rich at high RPM. I've heard tell of the stock ECU pushing the AFR into the 9:1 range. That's significantly richer than the turbo guys tune, and totally unneeded on a NA - best power at high RPM is somewhere around 13.5:1 or a bit leaner.

I don't have a wideband, but with a SAFC-II, I'm pulling out 30-40% up high, and still running rich of stoich (based on the narrowband O2 sensor).

You don't need more fuel. You need to fix your setup, and more than likely subtract fuel.

-=Russ=-

 

Injector duty cycle seems to be universally misunderstood. The ECU does not work on duty cycle, it simply calculates an injector pulsewidth (the time the injector is open) based on rpm, airflow, manifold pressure, air temp, coolant temp and other factors. Duty cycle is just a calculated number representing the percentage of the engine's cycle that the injector is open for. The engine cycle duration varies from 80ms at 750rpm to 8.6ms at 7000rpm, so as revs increase so does duty cycle. IDC at idle is 3-4% (primaries only) and at full load and redline it'll get up to 60-70% (stock engine). Once mods have increased fuel requirements to the point where peak IDC exceeds ~85% then you need bigger injectors.

The 250fwhp I mentioned was at ~85% IDC.

This wouldn't be because of the injectors.

 

Leave it to NZ to leave you scratching your head. "Humor"

 

No, I used to run big dodge 8's but thanks for the flame. Ask a question and get a jerk. Is this how you guys encourage people to join this forum? or maybe promote rotary use? Sorry for crashing your private rotary party...

back to the subject of headers and lean engines - won't the small port overlap on turbos and very small overlap on 6 ports allow some intake velocity increase thereby increase in lean intake charge from exhaust scavenging? or does the inefficient nature of the rotary not make scavenging possible?

~rich

 

Much thanks to those who are a positive aspect to my thread.

NZConvertible; you 'da man. ~rich

 

You'll have to excuse the frustration. Sometimes as a moderator it can get a little annoying to have people re-ask questions that have been covered a million times and are indeed answered in the FAQ (that we have spent considerable effort developing).

Anyway to answer the question it's going to be very difficult for your to make your NA run lean by anything but radical (bridge, peripheral, J) porting. In general you'll gain a lot by simply leaning it out (using an S-AFC or other fuel controller). But if you want to confirm, all it takes is a few runs with a wideband O2 sensor and you'll know where you are.

 

Sorry for my redundancy - I wasn't aware that when I did a search it didn't search the FAQ's too. But I just checked the FAQ's section and it looks like it searches the forums? I did a search looking for the answer before I posted - did I do something wrong maybe?

Regardless, my question has been answered - thanks! ~rich

 

I think a bridgeport is a bit of an overstatement, but yes you are going to need significant mods in order to require MORE fuel for an N/A. I managed 172rwhp andI run about +6% on my SAFC. I still run a little bit lean after 7k, which I think could be a fuel pressure problem (haven't had time to mess with it). I do have 550 secondaries and an FD fuel pump. Some other people here run 550 secondaries in their N/A (I believe Kahren does) cars without extreme porting, but the average car needs less fuel, not more.

My mods are street port w/ T2 housing, RB header, straight midpipe, RB catback, ported manifold, Pineapple port sleeves etc.

 

Er, Kahren has STOCK ports on his car.

 

Some have managed to run out of fuel without super radical ports, but it's far from common.

 

No, we ask people to read the sticky threads and archives at the top of the 2nd gen tech section before posting, and before posting threads on subjects that have been covered countless times, and proven consistently.

And you are the only one to flame here... I did not call you personally any names, as one would if they were flaming... You did however. I simply asked if this was another dumb injector thread. However you did not appear to know that calling people names is flaming, or that calling a moderator names or attacking a moderator is a banning offense. Good start you are having here.

Please read these threads (which you appear not to have read before posting again):
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/all-members-new-old-must-read-before-posting%3B-rules-guidelines-456843/
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/frequently-asked-questions-2nd-generation-rx-7-faq-fc-494667/
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/specifications-what-did-2nd-generation-rx-7-come-w-options-standard-features-249616/

, hmm actually based on size and displacement the rotary is much more efficient than 98% of the automotive engines out there... You may wish to visit How Things Work and read up on the rotary engine.

 

Not really. Four 460cc/min injectors are enough for 240-250fwhp, and how are you going to get that without a bridgeport?

If you really are running lean then I think you definitely have a problem somewhere. With those fuel mods and tuning you should be running extremely rich. 172rwhp is well within the scope of the stock injectors.

 

dont just quote hp levels for injectors, rpm matters too. for example i have 4x550 on my na and they are at 69% at 8k rpm with 180 whp. guess where the 460s would be?

 

where to put them?

put them in the primaries!! then hate your life

 

at what, 99% duty?

i was running in the 90's IDC's with ~250whp in my 91 TII swap (read: 550's) BUT thats with higher fuel pressure and under 8k rpms -as kahren was saying with the higher rpms of the NA- you're still going to be pushing the duty cycle of 460's to get to 250 flywheel(?) horsepower