injector size??

[CESCO]

I kind of switched gears and decided to build a 71 bronco rock crawler/racer. so here is what I have for a motor in it and would like some input on what injectors I should run.

302 bored .30 over
longer connecting rods with shorter pistons
very mild roller cam
165 afr heads
1.6 roller rockers
GT40 upper and lower intake ported to match heads
just running shorty headers by jbl
I am going to use a 93 wiring harness and computer
the guy who did the machine work for is estimating it to be around 350hp 400lbtq at the the flywheel. I had him build a 347 for my stang and after the dyno he was real close on his guess for hp/tq

this motor will prob not rev over 5500rpm.

so what do you guys think I should run for injector size? I am going after low end on this motor.

any input would be appreciated!!

[badstanglx]

i would go with 24s

[CESCO]

i would go with 24s

thats what i was kind of thinking but wanted to see what other people thought before I buy any.

[John4cam]

24's. No need for anything more

[Killercanary]

24's are more than adequate. That combo should be a stout lil' mill. I know the long rod setup increases piston dwell time and I know in theory this should help promote TQ production if the cam timing events are setup to maximize this. If you are going long rod make sure you get a cam with timing events that can capitalize on the increased piston dwell time offered by it. I was going to do a long rod setup many years ago, but I have to admit that to this day I haven't seen any real world example that seems to show a benefit going this route.

[CESCO]

Well the engine is already together but do remember the machine shop telling me that they called comp cams and told them what I was wanting and in return they told us what cam they were going to send. You brought up a good point, I am going to ask if they used a degree wheel to match it up. I to have mixed thoughts on this engine but am trusting the engine builder to tell me that this will be a more reliable and have more torque by doing this.

[Balaska347]

24's will work fine but wont do much more. I would do 30's which will work just as good and you have room to grow. You might think this is it but trust me its never enough. Why limit yourself when the price is very close.

I actually have a set of 30's forsale cheap. $100

[Killercanary]

24's will work fine but wont do much more. I would do 30's which will work just as good and you have room to grow. You might think this is it but trust me its never enough. Why limit yourself when the price is very close.

I actually have a set of 30's forsale cheap. $100

I made 380rwhp/380rwtq with 24's with 45lbs of base FP. For his combo the 24's will have a better atomization than the 30's with the power he will be making. When running NA I'd always go smaller injector with more base FP, but that is me.

[CESCO]

I have a set of 19lb that was in my car before I built it. I was thinking about trying them first to how they worked. what do you think? I have a afm that I can use it during the start up to watch and see what it is reading.

[phillysrt4]

Based on my understanding of the MAF computers in mustangs, if your computer knows what injectors you're using, it will be able to compensate at idle by changing the injector pulse width or the number of pulses per second it emits. You wouldn't notice any issues until you started running it either under load or near redline. In both instances, you may not notice you're out of fuel until its too late.

Probably better safe than sorry and get the 250cc (24 lb) injectors than take a chance with the smaller ones.

[map351]

http://www.rceng.com/technical.aspx

http://www.gtsparkplugs.com/InjectorSizeCalc.html

[CESCO]

http://www.rceng.com/technical.aspx

http://www.gtsparkplugs.com/InjectorSizeCalc.html

Thanks for the links!


ok, now I am really unsure of what I should do. When I did the motor in my car I used 36lb injectors and according to the injector calculator that is capable of 461hp. when I had it on the dyno we estimated my flywheel hp around 450-480hp. so here is what I am getting at, we had to turn the fuel down to 30% for it to run. They told me that I could have went to a smaller injector. I am going to send an email to the person who will do the dyno tune for me and see what he thinks. I will keep you guys updated

[Balaska347]

I made 380rwhp/380rwtq with 24's with 45lbs of base FP. For his combo the 24's will have a better atomization than the 30's with the power he will be making. When running NA I'd always go smaller injector with more base FP, but that is me.

Wow thats crazy. I never heard of anyone running those kind of numbers on 24's. your duty cycle must have been 100%. 30's are pretty much maxed out between 380 and 400 rwhp. What ET did you run in the 1/4?

[Killercanary]

Wow thats crazy. I never heard of anyone running those kind of numbers on 24's. your duty cycle must have been 100%. 30's are pretty much maxed out between 380 and 400 rwhp. What ET did you run in the 1/4?


I run an AEM EMS on my car and one of the beautiful things about it is that you can see duty cycle. I was at 80-84% duty cycle when I made those numbers. I didn't run the car in that form at the track. After I made those numbers I swapped in a set of 30's along with AFR 185 comp heads and probe shaft mount rockers. After that swap I ran a 11.5 at 121mph.

[Balaska347]

sounds like you where right there with the duty cycle. Im curious to see where Im at now because I just swapped my 30's for 36's because alot of big name tuners and engine builders told me my 30's would be pushing it with 400-420 rwhp. We'll see where the duty cycle is soon with the 36's. I still have the 30's if they are too big.

[CESCO]

I talked to the tuner and recommended that I go with 30's just to be on the safe side of things. So I am going to order the 30's and go with that. I'll let you guys know the what happens...