im just trying to see what kind of injectors go with what fuel setup... im hopefully going to be doing a full bottom end rebuild and was hoping to run 15-20 psi....but if not, i might just get new pistons and only run like 10-15...so i just wanted to see the options of injectors i would be looking for...when do each ones max out, i currently only have a warlbro 255 intake pump...thanks
doug

I have the Accel 39# Injectors currently in my car with a vortech SFMU only. I am running the largest ring and the second largest disk (2.72"). I also used a pocketlogger to set idle fuel pressure as well as a pressure gauge.

For 39# Injectors, you should set idle in the range of 13-15 psi. This setup gives me STFT of +2/-2 and LTFT of -13 to -15. I haven't fully broken my built motor in yet but this should allow me to run 15 psi of boost easily. When boosting at 15 psi, I am shooting for a fuel pressure of about 85 psi. If you attempt to run 20 psi on these injectors, you will probably be looking at a fuel pressure in the neighborhood of 110 psi which will bring you close to the fuel pressure of running 8psi on stock injectors.

Keep in mind that max fuel pressure is not the only concern when upgrading injectors. The larger you go in injector size the rougher the cars idle will be during warmup (If you are running with an SFMU only. I do not like to mess with a SAFC due to the advance in timing they could cause). In my car with 39 lb injectors and extremely cold days, the car struggles a bit to idle smoothly until it is warmed up. Once warmed up, the car runs perfect. The idle problem is easily fixed by slightly pressing down on the gas during warmup to bring the rpms up a tad. Once the temperature needle begins to move, the car will idle perfect.


Hope this helps,
Kurt

that helps alot....i forgot to add i would be running a sfmu...im not too worried about lumpy idle... with 39# injectors, whats the lowest psi you could run? would these be a good all around injectors....you say you can run 15 easily, and 20 would be fine also....what about 10-15? thanks
doug

Originally posted by lickscissors
that helps alot....i forgot to add i would be running a sfmu...im not too worried about lumpy idle... with 39# injectors, whats the lowest psi you could run? would these be a good all around injectors....you say you can run 15 easily, and 20 would be fine also....what about 10-15? thanks doug

The amount of boost pressure you can run with a specific size injector is best determined by your planned maximum boost and the maximum fuel pressure that you feel comfortable running.

For the 39# injectors, I would say 20 psi is the maximum you would want to run. I will only be running about 16 - 18 psi on these injectors so I should stay under 100 psi of fuel pressure. I feel the most safe with staying under 100 psi of fuel pressure. To answer your question, you could run any boost pressure under 20 psi with the 39# injectors.

To be honest, I think it would be quite hard to get the 440cc injectors to idle correctly with just an SFMU. To achieve this, I think you would have to run somewhere in the neighborhood of 7-10 psi of fuel pressure at idle. I'm also not sure how smooth the idle would be after the car warms up. Probably with proper tuning they would work fine. I know I have thrown a check engine light in the past for being too rich and I'm sure it would be easy to produce a CEL with the even larger injectors.

With large injectors, I believe it is also an absolute must to have some type of device, pocketlogger, etc., to be able to read the STFT and LTFT from the ECU. Tuning by gauges simply does not give you an accurrate readout of how the car is really performing. For example, your air/fuel gauge may show rich but that is only under boost. What about idle conditions or cruising conditions? Save yourself hours of frustration by getting a logging device. It may even save your motor in the long run.


P.S. I also read that you are only running the walbro intank fuel pump. I wouldn't recommend pushing 100 psi of fuel pressure on only the walbro as I believe it begins to run out of steam at these pressures and you could risk leaning your motor out. I would recommend installing an inline pump if you plan on pushing high fuel pressures. I run two pumps - the walbro HP pump and the Accel inline pump.


Hope this helps,
Kurt

so i should be good with my range of 10-18psi with the 39# with the warlbro? sounds good...i guess ill start looking for a set of these then....thanks
doug

If you're running a standard SFMU/FPR setup on large injectors, the MINimum pressure might be the more important number. To idle correctly and have off-boost drivability, you need extremely low fuel pressures with large injectors. For instance, the Ford 42# will idle at about 20psi(fp), while Accell 42# will go all the way down to 15psi(fp). The Accels will be much more drivable, and still deliver just as much fuel under boost.

As far as max fuel pressure, that's not really important IMO. Max duty cycle (100% duty) is easy to figure out. The stock 235cc injectors max out (ie. lock up) around 130psi(fp). You can always add race gas if you wanna up the boost, rather than run higher fuel pressures.

30-39# injectors and a sfmu is a great setup for 15psi boost.
42#, sfmu, and optionally a safc are good for at least 18psi boost.

so you're saying 30# will work with 15psi? when do the 30#'s max out? also, whats the price differences with these....i like the idea of 30#'s because they're pretty cheap and easy to come by...thanks
doug

I think there are alot of options to consider with running larger injectors.

A quick list when choosing an injector size:

- Are you running only a rising rate regulator with the stock ECU (no standalone fuel system)?
- Will the injectors work correctly on low fuel pressures (daily driveability, dependent on injector make - the Accels seem to work well at low pressures)?
- How much boost do you plan on running?

I don't think it is very safe to run fuel injectors at extremely low pressures as I would assume they would need some pressure to operate correctly. I believe with the 30# injectors your idle fuel pressure should be around 20 psi and the 39# injectors should be around 15 psi (give or take a couple of psi).

As far as maximum boost, I disagree that you could run only run 15 psi on 30# injectors and 39# injectors. I believe XtremeRS is running the 30# injectors at 13 psi and they are almost maxed out so 15 psi would probably apply to the 30#. However, I would think you could run 18-20 psi on the 39# injectors. Of course with the 20 psi of boost on 39# injectors, the fuel pressure would be over 100 psi (near fuel pressures of the HRC kit on stock injectors at 8 psi). Time will tell as once my motor is broken in, I will be able to provide a maximum boost/fuel pressure for these injectors.



--Kurt

ok, so depending on my rebuild route (just pistons, or pistons and rods) ill be running 10-12 psi, or 15-18....so for 10-12 30# will work fine, and give me a little room to boost up to 15 every now and then.... this car is my daily driver, so i do want it to idle somewhat good.... i will be using the sfmu, no stand alone....so will i be able to use 30# and have a good daily driver? how about 39#? once your engine is broke in, can you pm me and keep me updated on how everything is working out? thanks
doug

i know this is old....but KTECLIPSE, have you broken everything in yet? how much boost are you running now, how have those injectors worked out? thanks
doug

^ also curious.....



14.5 @ 95mph / 7psi 185hp/180tq :thumbsdown

Yes, I have broken in the motor (about 1300 miles of city traffic) but haven't upped the boost to the max level yet. It has only been around 15 degrees here in New Jersey and that is way too cold for me to go out and adjust the Boost Controller and fuel settings. Also, at these cold temperatures I don't think it is good for any of the parts to be put under load/stress.

I have upped the boost to 10 psi and the car is running great. At 10 psi using 94 octane, I have an o2 voltage of approximately 1.0 on my data logger (slightly rich but hoping it will drop a few points down to .96 once I turn up the boost), and EGTs never rise above 1325 degrees under WOT. I was pleasantly surprised with the EGTs.

I also haven't checked my exact fuel pressures at 10 psi but doing the fuel calculation based on the vortech rise rates the max pressure I should be seeing at 10 psi is about 63 psi.

Idle ~ 13 psi
Vorteck 2.72 disk ~ 5:1 ratio

Idle + (Ratio * Boost Level)
13 + (5 * 10) = 63 psi

Doing the same calculation for 16 psi, yields about 93 psi. Not bad. 18 psi would put you at about 103 psi. Of course, these are all estimates.

The only small problem I have with the larger injectors is startup on cold days. The engine starts right up but will idle rough until the car is fully warmed up. The transition from open loop to closed loop during startup causes rough idle. It is only for a few minutes and is simply fixed by slightly stepping on the gas (bringing the rpms up to 1,200) until the temperature needle moves.


--Kurt

ok....im guessing youre running both fuel pumps? whats the max fuel pressure that the warbro and accel inline can push? how about the warbro alone?....i currently have 30# injectors and i thought id be comfortable with 15psi and be able to boost up to 18psi....but now i have my doubts...especially with only the warbro....how much did you get your 29# and where....thanks
doug

NEVER run more than 100 psi through an injector. At that high pressure your not going to be getting any more fuel through.

Oh I love my 8 injector setup! ;)

Yes, I am running both fuel pumps (Accel Inline and Intank Walbro HP).

When I had a return fuel line clog which was my fault (I had trouble getting the rubber fuel line onto the aluminum return that is run under the car. During my struggle, a piece of rubber hose ripped off from inside the fuel line. Once I started the car, the piece of rubber became wedged in the hard return line in the gas tank sending unit causing fuel pressure to build.) I saw extremely high fuel pressures. Fuel pressure was so high that it pegged the HRC fuel pressure gauge. This gauge went up to 160 psi. It was a good test of the fuel setup as during the high pressure I had zero leaks. This just shows that these pumps can build insane pressure.


I bought my 39# injectors straight from HRC @ $54.00. It probably wasn't the cheapest but I support the company as I like their turbo kit and service.


--Kurt

use the mathematical equation as a base and work your way from there. I tune to egt and digital a/f readings.