tookwik

How high is the need for higher cc injectors when upgrading to a single turbo? Is it possible to run a smaller single turbo on the stock injectors with a pfs pms, fuel pump, fmic and all the other typical mods?

IRPerformance

iTrader: (41)

You probably won't be able to run more than 12-13psi boost.

spoolin93r1

i've got stock primaries and 1680cc secondaries. i hit 97% with 16psi and a t78. you're gonna need some bigger ones if you want any kind of power. typically the stock ones max out around 380-400whp

Wargasm

stock injectors + single = kaboom

Wargasm

Seriously though, even with a small single ... those stock injectors are probably going to hold you back at about 10 psi.... It's not really worth going to all the trouble to go single to end up with a ~300 rwhp car with no room to grow (due to small turbo, small injectors, and crappy PFS PMS)

My T04S turbo makes around 415 rwhp at 15 psi and I run about 90-95% injector duty on a 550/1600 setup.

Brian

apneablue

would you consider that a bit on the unsafe side? Really, I am asking a legit question and not trying to be a smart ***...

I am going with a similar setup 750 / 1600 and just want to know where I'm gonna end up IDC wise.

Wargasm

Yeah 90-95% are my -peaks- that hit sometimes if the weather is cold (a bit more fuel goes in there)....

A typical 3rd gear redline pull with my car at 14-15 PSI will result in a peak around 90%.... Then again, maybe only 87 or could be 93 another time. I was just throwing out 90-95% to give my "worst case".

I am planning to move to a 850/1600 setup when I get around to it to give myself more safety room because I am pushing it a little I think.

Your base fuel pressure plays a part too... I run pretty low fuel pressure of 36 PSI at 0 PSI manifold pressure and I use a 1:1 boost compensating regulator. So that means that compared to some other people that jack their pressure way up, I have to open my injectors more length of time to get the gas I need.... if you run a little higher pressure, your duty cycle will drop.

Brian

teeter

with a T04s, I'm at ~90% duty cycle at 9psi with stock injectors at about 11:1 AF ratio

can't run any more boost till I get the 1600s in.

john

Wargasm

Your base fuel pressure plays a part too... I run pretty low fuel pressure of 36 PSI at 0 PSI manifold pressure and I use a 1:1 boost compensating regulator. So that means that compared to some other people that jack their pressure way up, I have to open my injectors more length of time to get the gas I need.... if you run a little higher pressure, your duty cycle will drop.

Wargasm

Your base fuel pressure plays a part too... I run pretty low fuel pressure of 36 PSI at 0 PSI manifold pressure and I use a 1:1 boost compensating regulator. So that means that compared to some other people that jack their pressure way up, I have to open my injectors more length of time to get the gas I need.... if you run a little higher pressure, your duty cycle will drop.

apneablue

x-cuse me for asking questions which I feel are dumb, but why don't you increase your fuel pressure?

Wargasm

This crazy forum and double posting!!!

Well, there are a couple of factors involved with changing your fuel pressure....

If your pressure is too low (very low) then you might not get a good atomization of the fuel droplets and you will have poorer driveability and maybe less power too. The gas will kinda dribble out, not spray out in a fine mist. Less fuel comes out in the same time, so you also need to open them longer to get the needed amount.

If your pressure is too high this can make it hard for the injector to open or make it open more slowly because there is a real, physical pressure (the fuel pressure) against the injector pintle (the little pin in the middle that pulls back to let fuel squirt out). Your fuel pump will have to be working a little harder too to maintain that high pressure all the time too. The good part is that your fuel is well-atomized and you get more gas for a certain "open time".

So let's say you have a kick *** fuel pump, super strong lines... a high voltage "super injector" that can open even against 200 PSI of pressure... why not just jack that pressure way up and enjoy driving on stock injectors!?

Well, at idle speed, you only need a tiny amount of fuel... and the injectors have to open for a small amount of time in order to only put in a small amount of gas... but there is a minimum amount of time that they really work well at. Most injectors aren't going to be happy if you try to open them for 0.001 ms! So you see, even if you could somehow run 100 PSI of pressure, it might not work well at IDLE! Compromises, compromises.....

The "open time" issue is very important. If you think about it, as the engine RPM increases, the amount of time that you have to squirt in fuel goes down. This is because each rotor chamber is only in position to take in air/fuel for a certain amount of time. At 8000 RPM, each rotor chamber is only in the right position to accept fuel for 7.5 milliseconds! So in that 7.5 milliseconds, the injector must OPEN, SQUIRT, CLOSE. The typical amount of time a large 1600 cc/min injector takes to open might be around 1.2 ms... and it may take another .5 ms to close. So for the sake of argument, let's say that the injector takes 1 ms to open, 0.5 ms to close. Now out of your 7.5 ms, you really only have 6 ms in which to actually get gas going into the engine.

Sorry for rambling... but as you can see there are many factors you must balance...

Snook

iTrader: (12)

ok I just got 850s and 1300s for my new setup which is equivalent to having stock primaries and 1600s like you. I dont understand how you are at such dangerously high injector cycles with only 415rwhp. previously I had stock primaries and 1200s and was running ~400rwhp on cold nights at 16.5psi and the highest I ever saw was 87% I believe and it was usually 84% on those cold nights and 81% the other times. So I had 800cc less injectors than you and 15rwhp less yet 6-11% less duty cycles it doesnt make sense. I have the stock fpr and large m2 boshe fuel pump if this makes a difference to you. Are you running considerably less pressure than stock or something?? Ill be very dissapointed if I cant make 415rwhp safely lol. I was originally shooting for 525rwhp but then we calculated my injectors would do around 475MAX until I read this I was going to be almost satisfied with that #.

XSTransAm

maybe he was running 8-1 afr

$150FC

hey wargasm, nice post.

apneablue

Wargasm! thanks man...wish more people would break stuff down like that for idiots like me...This should go in the archive in the fuel management section or something.

spoolin93r1

my base fuel pressure is now set at 42psi. i put down 439whp and my injector duty is still pretty high with the 1680's. i guess it doesn't help that i've got a/f's under 10:1. i guess it depends on how safe of a tune you have. if you're comfortable with 11.5:1 a/f, then you'll have a much lower duty cycle, but it's a little on the risky side

XSTransAm

10:1 is way beyond safe, its just plain bogging the car down and washing your walls with gas... you should be at 10.8-1 at the richest.

im suprised your spark plugs still fire that rich.

Snook

iTrader: (12)

10.8 is about the stock AF and he is running exactly 2 times the hp of the motor from stock. You really want to reduce the chances of something going wrong at that hp and rich is the way...although thats really rich lol

Wargasm

To give you some ideas... I run pretty rich for safety at 1 bar - 10.8:1. My fuel pump (Supra pump) also has trouble keeping up under those conditions, so my fuel pressure is DROPPING slightly up around 6500 RPM or so... This means that I have to compensate by opening them longer than you might guess... leading to some high duty%.

My next "to do" is to run thicker wires to the pump to see if that will help it keep up under high demand. If that doesn't work I need to do another fuel pump setup.

Snook

iTrader: (12)

thats strange I think supra guys tune for 11.5 and its good for 500rwhp for them. Any way yeah that really scared me. Its time for you to get another fuel pump. I dont think ill have that problem with mine since its huge. only problem is that the fuel gauge doenst go past 3/4 full because of it.

teeter

see
http://www.roadraceengineering.com/f...pflowrates.htm
for flow rates on the supra pump at 12v and 14v.

its good to have people who know stuff across "car groups"

john aka mitsubishi fanatic

apneablue

You making me worry a little...My fuel setup is 750/1600 with the supra pump...Steve had asked me what I expect from the Gt35r setup. I just told him I want as much as possible. Rich/Steve said at 1bar I should be around 430rwhp...(is this where you are at?) You think this pump will be at its limits? I guess if anything I could just strap a stoc pump to it and run them together.

Wargasm

Well I will say this... time and time again, people find that the factory RX-7 wiring is a bit crappy and it doesn't support high current flows and good voltages either....

I plan to run wires straight off the battery (with a switch) for testing purposes to the fuel pump and see if that cures my fuel pressure dropping problem. If it does, I'll wire up something more permanent using the factory relays and control circuits but just with beefed-up wires. If it doesn't help out, it means my pump is just too girly and I need a bigger one!

Beast From The East

Hey, 'gasm - Chris just wired up my Walbro direct from the battery. Don't have my fp gauge installed yet so I'm unsure of my pressures, but I know it is doing well at 15 psi with my 550/1300 setup. I'm running afrs of 10 to 10.8 at that area with high 80s duty, and at 16 lbs I'm running too rich (9.2 and stumbling) and hit 97%. Using your dyno map as a base, btw. Took out another two degrees of timing across the top to compensate for our crappy gas in CA, and modded p17, 18, and 19 to get better granularity between 12 and 16 psi.

I definately need to add in 850 primaries if I want to go any higher (I have my lovely can of VP 103 unleaded sitting in the garage right now.....). 18 to 20 on that should work nice.

Beast