I have a 88 rx7 non turbo with original fuel injectors.

Will i gain anything by switching to the latest 12 hole or other newer fuel injectors.
I want to see if any will increase mpg and low rpm torque.
Also since i am not mechanically savy i would like any recommendations on plug n play type.

​​​​​​​Thanks

 

you could try the RX8 automatic injectors, which are close to the same flow as the high impedence later model RX7 n/a injectors.

it's probably what i would do if my stockers went kaput, though you'd need new clip ends, since they would only really be nearly direct replacements for the S5 n/a with the newer style denso clips.

 

You mean the 410cc yellows ones i see on web. If tthey work that wud be nice. Set of new 4 for 50 bucks on ebay ! Wonder if too good to be true.

 

the blues iirc were 450cc, or maybe i was thinking those were for the turbo cars and the yellows for n/a, i haven't flow tested any of them to verify, the info seems inconsistent.

 

I think the ones on my car are 460cc. Will it make a huge difference if replacement ones are 430cc or 500cc.
​​​​​​​I am tempted to order both and compare them side by side.

 

the stock n/a injectors are 440cc/min, the yellow RX8 injectors from what i double checked are 420cc/min at 3bar. this shouldn't cause any noticable running concerns, the S4 runs slightly rich as it is.

so if it were me, i'd opt for better fuel atomization and change over. course you will need to play with the seals to get the injector to fit the rails to block/LIM.

 

Stock N/A injectors are 460cc.

 

If i do get the rx8 injectors 425cc. or any other injector around 460cc would i need to have the ecu reprogrammed ?

 

if you ran a walbro it would probably offset the pressure and raise it up enough to flow the same as the stock injectors.

this is just hypothetical, but i would say it probably should work.

 

Whats a walbro? Sorry for the all the Q's

 

its a 255lph fuel pump, it tends to overwhelm the stock fuel pressure regulator and increase the rail pressures to the injectors and cause the injectors to flow more(often times unintentionally). with fuel injectors, the more pressure there is the injectors will also flow more, as an aside they will also atomize the fuel better with higher pressures however too much pressure can cause potential other problems like prematurely failing hoses/regulator/dampener.

we're only talking about maybe a 5-10psi increase though, so it's not a dramatic change and often times doesn't harm anything.

 

Thanks insightful. Since fuel injector technology has come long way since 1988, i was wondering if one can have aux port open all the time and have all four injectors on all the time. I mean how would one do it today with the same engine but todays electonics and fuel injectors.

 

the idle will become lumpy if you do that, even with newer injector technology. also isn't possible without ditching the stock engine management system and spending a bunch of money for very moderate gains.

 

You can wire your aux ports open all the time, but it doesn't really make sense. The aux ports are closed in the low end and open later because the engine wants high velocity air at low RPM, not lots of air.

Wiring them open is possible, and you won't suffer in the high end, but it makes more sense to just keep them functional. And as Insightful brought up, idle can be lumpy with the aux ports wired open.

As for the injectors, I'm not sure what you hope to achieve by having all four firing at once and cycling them lower to compensate. The stock system works perfectly and except the 3800 hesitation (which only happens if you have a bad ground or something) there is no downside. The secondary injectors only come online when needed, so it isn't like they are wasting fuel. The extra fuel is only really needed once the aux ports come online.

It seems like radical alterations like this would be very expensive and have little (if any) return.

If your goal is to save fuel the easiest way to do this is to do a full tune-up, and check all your plugs and wires. Change your fluids and filters. Then just drive it more gently. If you do this, you should be able to achieve the sticker value of 24MPG.

 

I see. Okay so is there any benefit to upgrade from the 1988 fuel injectors to current ones like ev, black ops etc etc. which i still plan on keeping around 460cc.

 

Well fitting new injectors could be done, but the more important ramification is cost vs. gains.

Our ECU is dumb. It has no learning functions, and it only has a narrowband O2 setup. So tuning on it is basically impossible beyond idle settings.

Assuming you buy four new injectors today and install them, you still can't really tune them on the stock ECU. With the four new injectors, you would have to buy (at the very least) an air/fuel computer and a wideband. Most likely, you would only see any real benefit with a full standalone, because you can alter the whole fuel and timing map with greater accuracy.

Even if the new injectors are the exact same flow rating (460cc), if you are hoping to take advantage of the superior atomization and spray pattern you would need to be able to tune them. And not just at idle, over the whole map.

I mean, you could drop in some injectors. But at the end, you would probably gain almost no power or fuel efficiency. And the biggest gain would be the S-AFC you would need to support the injectors, not the injectors themselves.

So after spending say $500 on injectors, S-AFC, and wideband, you would see almost no gains. And the gains you did see would be mostly due to the S-AFC, not the injectors.

 

That info helps a lot. I will keep my working original injectors