I've been looking for fuel injectors for my KA high rev buildup. I've been looking at the MSD 50LB.s high resistance injectors, and some fabbed RC 50lb.s low resistance injectors.
My question is which ones do you guy's think are better? Or should I just install the sr20det low resistance injectors?
I'm looking for high HP with reduced torque, and don't wan't my fuel to air ratio to rich. Looking to change my cams to PDM, so which injectors are better for that lift and duration. I will be using an SAFC and JWT ecu. Using the SAFC for a gas guzzling feature for 1/4mile time's, and using the JWT ecu for streetable smog application. Plan on NOS injection in the future.
I would like it if wikd240, devious KA, Darren, or Artic Dragon could help me with my problem. Looking for people with answers that are interested in these build up's. I know that fireplug know's a bit also with SR buildups so I would like input from any of you guy's........Thank's

VincentAngelo
AKA BigV

 

well vinnie, im no expert on injectors but i read thru what MSD had about injector ratings. according to them, high resistance is what is most commonly used in production cars, and they only require a low amperage. low resistance injectors are the opposite, high amps, and are generally used in race applications. (i bet you already read it but for anyone else who doesnt know, its a crash course.)

i think the high resistance would be ok if they were set to a longer duration to match hotter cams (not sure about the heat on the PDM cams you mentioned). if you plan on going to an aftermarket ECU then the low resistance would be better suited for you. just make sure you can run the current needs. they said one low resistance injectors need 6 amps of current headroom. the choice low vs high seems to depend on that, from the information i gathered. MSD also reccomended using higher flow injectors at lower operating cycles for hi-rev engines. i have NO clue on stock injector ratings, but yeah, 50lb injectors sound like they would handle just fine.

whichever you choose, i say two things that are a must: an EGT and an air/fuel meter. that way you can make sure you dont richen it up, and check to make sure your setup runs stoic. good luck with the build.

 

I'll defenitely look into the EGT and air fuel meters, probably install them next to my driver side door. If the PDM isn't hot enough for the duration and lift I might go with the JWT cams, but that is a shame because it is more expensive, unless I get my hands on a non ground cam and have it machined for my own specs.
Will a JWT ecu handle a low resistance injector? It is after all only a reprogrammed stock ecu, can it get chipped out for low resistance???????

 

thats a question you're going to have to ask JWT... the low resistance injectors will work, though theyre not normally used with stock ECUs on non performance cars. considering its a reprogrammed stock ECU, the only ones that can answer that is JWT, cuz i have no idea what kind of programming they throw at their mod ECUs. MSD has two hi flow quick response HiRes injectors, (the PN 2013 -- 50 lb/hr, 12 ohm is the one you're probably already looking at) that can probably get the job done quite well if the JWT ECU won't nicely run LoRes injectors.

 

i used the msd 72lb injectors with the 6ohm resistor pack from jwt... but that was based on talking to the people at jwt... mainly i went with them because of the longer duration... i went with the 72 injectors so that there was no chance of them running too close to peak output... it was suggested that i use the next step up from 50 to 72 because injectors have a hard time giving a proper spray patern with higher fuel pressure and close to max duty cycle... they also suggested that any injector that is used not to be pushed past 75% duty and flow cycles due to the poor atomization... they can actually produce drops of fuel instead of a fine fan patern due to the higher pressure... my injectors might be over kill with this motor but if i ever need em they are there already...
the jwt ecu and the resistors along with the cobra mafs cams and gears are pretty much their top of the line set up... and what they suggested for a high rev set up... then you have plans for nos on top of the equation... and you already know that the motor running lean is the biggest killer for nos motors... and you have some ideas of the system i want to put together on my ka... with the low res inkectors and the higher flow rate there is no chance of running lean... the only other thing i am thinking of getting is a 2 step timing retard set up so that i can retard the timing when nos is being used and do it all automatically... just my set up tho...

 

Well after reading several articles on high and low resistance, I guess I will be using the high resistance 50LB injectors. Basically low resistance injectors are used more for NA applications with EXTREMELY aggressive cam lobe and duration's, and does have a bit to do with how high rev the car is also. Low resistance respond's to dumping "more fuel" sooner than later. Another example of using low resistant fuel injectors would be on fast spooling, high boosting turbo applications to accomidate the larger volume of fuel to air...........
So since I live in Cali and am always concernd about smog I will be keeping modifications as far as ecu and electrical to the OEM recomended spec. After all I need these injectors to regulate my fuel much more efficiently, rather than gas guzzling..... Even though I am increasing the injectors and the entire fuel system I will be able to tune the car much easier to the cali smog requirements, not only that I will be using the stock fuel rail, which I ways told was fine to use until you get up to 70+LB injectors, or need applications over 250CHP in NA or FI trim.
Thanks for the help fellas it really helped me out, R&D on my KA high rev is almost done..........Then it is time for the Streetable high rev, high HP internal build up........... I will be using the JWT cams after all they are the most aggresive cam I can find for the KA......................
Do you guy's think I should drop my displacement to 2.2 for more high rev, or get the 90mm 2.4 bore forged internals with a little less high rev? I'm looking to make my car compete in a few rally's next year.........

 

hey, this is your build, how much of a screamer do you want?
if i were looking to make a screamer, sure with the 2.2 cuz what you lose in torque and displacement is obviously gained back in spin and peak horse (if the engine is completely set up for that). if you're sticking with hi resistance 50LB injectors, then the 90mm internals would probably be a safer bet, at least this time around. as wikd said, you dont wanna push the injectors too hard, or you lose efficiency.

 

Well what I am looking for is higher top speeds. Yeah 2.4litre's is the shiat for lowend power in 1/4mile times, but at the same time I would rather use more high end power to top out the redline at about 8600RPM and top out higher speed's using the original stock tranny........ Destroking the displacement is the only rule I can use to achieving that goal. Unless I keep the 2.4 displacement and install the NISMO 5th gear and change out the syncos.... It will be harder to achieve more CHPj at 2.2 since the displacement has been reduced for aspiration.

 

my only arguement against the 2.2 kit is the injectors you're gonna invest in might not be able to handle the upper range of a de-stroked KA. im not even sure what that range is to be honest, but no matter if its speculation or fact, it is something to consider.

 

Darren337 hypothetically you are correct....... Have you ever used an APEXI SAFC before? The throttle correction will prevent the fuel from running to "rich or lean" especially at higher RPM......
It does wonders that even the stock or reprogrammed ecu can't do.......... Not only can you raise throttle correction value's you can also lower throttle correction values for every 1 increment "500 RPM" you can use a throttle correction value of up to 50% fuel delivery.............
I think a stroker 2.2 would be pretty sick. with a compression between 10.5 or 11.2 for streetability...........

 

hmmm... never used an apexi SAFC so if you're quite confident with the equipment's capability, im sure you can pull this off without too much effort. good luck and i would love to see the results.

 

The SAFC is also a great tuner to use on a progressive NOS injection system, with a little dyno tuning and 3" exhaust it womps turbo's.........
Just so you get a better understandin of the APEXI SAFC I have taken pictures of the throttle correction pages if you need more info let me know..........

 

Page 1 SAFC thottle correction.............................

 

Page 2 SAFC throttle correction....................

 

Page 3...............