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Injector size requirements

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Im trying to work out the injector size I need for my power goal yet still be able to idle at lambda 1 on both 98 and E85 fuel. I've used several calculators and most average around the 1400cc for 600hp @ flywheel on E85. Since this is my first attempt on tuning im unsure what the idle pulse width would be on 98 pump as below about 1.2ms the injector flow not linear. Ive been looking at ASNU 1500cc injectors with diffuser plate but not 100% if these are too big. I had Bosch 2200cc injectors but found guys had issues with stable idle on 98. I don't want to buy another set of injectors and have issues. Any help would be much appreciated.

Engine is a sr20VET 4 cylinder with link ECU

If your running E85 you need to look into compatibility of the injector with your fuels, if I'm running anything other than pump gas I always advise ID1300's, you could get away with these on a slightly higher base fuel pressure or the new ID1700's and keep a stock base fuel pressure. The reason I recommend them is because of their all stainless internals, there's no chance of degradation.

Another important thing is your choice of fuel line, don't just go for normal rubber or braided rubber lines, they will perish and you'll always have the smell of fuel, PTFE lines will hold up best and not leak vapors

These ASNU injectors injectors are a base Bosch motor sport injector like the ID's and have stainless steel internals. I'm using Teflon braid hose in dash 8 for feed and dash 6 return with all full flow fittings. Also have a fuel temp sensor just before the fuel rail and a twin pass fuel cooler with fan between the fuel regulator and surge tank on the return side. Both lift pump and supply pump are wired through separate solid state relays. A little overkill on a Gti-r but meh.

Just injector size is bugging me.

Injector Dynamics online calculator is a pretty accurate representation of fuel injector requirements in my experience. Even if you're not specifically using an ID injector it is still a useful resource. A very quick and dirty rule of thumb that I often refer to for a quick sanity check when sizing fuel systems is that you need approximately 1 litre/min of fuel flow for every 200 hp you want to make. This will give you a reasonable ballpark for pump gas but you need to multiply the result by 1.4 if you're running on E85.

I would be picking the ID1300 and be happy in the knowledge that these will be able to deliver a stable idle quality and consistent AFR on pump gas while still supporting your power aims on E85.

I ended getting a set of ASNU 1300cc injectors with the spray plate. Also now have the full Motec data sheets and ASNU short pulse width adder info for 3 bar pressure. Just waiting on the 4 bar short pulse width info. Car isn't running yet as I'm still wiring in the Link G4 Thunder so can comment about idle quality.

What people forget with injector sizing is the RPM, having tuned a ve engine they like the revs and at 10000 plus RPM you don't get a lot of time to get the fuel in. You may be light on with 1300 cc injectors.

I forgot to say, the link G4+ platform has no trouble controlling 2200cc injectors on pump fuel, unlike other ECU's

Rpm limit I've set is 8500 as its just a weekend street car. 4 Bar base pressure the flow rate goes up to 1512cc, would that be closer to my power goals on E85 Grant?

This will be the first and most likely the only car ill tune so its a bit of a learning experience.

Will depend on lots of things, what size turbo you are running, how much boost, cams you are using, head work etc. Just a basic look on the ID site you will be up around 90% duty cycle on 25PSI boost at 8500rpm. Once you start driving your VE you will get addicted the the revy nature of these engines, they just keep making power. The one I tuned the power line was still going vertical at 9000RPM. It has Kelford cams though. Way different to the SR.

Grant's point is valid - you do need to consider engine rpm as this dictates cycle time and hence the available time to get the fuel into the engine. This is why rpm is accounted for in the ID online calculator too.

I haven't personally used the ASNU injectors however there seems to be a lot of people achieving good results with them. I have no doubt you'll be able to achieve a quality idle at stoic on pump gas with these.One other advantage with the modern EV14-based injectors is that they can comfortably run at very high base fuel pressure so if you're a little marginal on flow, you can run 60 or even 80 psi base fuel pressure. Obviously this affects the characterisation data and also will put more strain on your fuel pump too however.

Like Andre said, you can raise the fuel pressure but this just creates another set of problems. Most if not all electric fuel pumps struggle to provide much flow at higher pressures and if your base pressure starts at say 70psi and you run 30psi boost the 460 Walbro e85 pump will draw well over 25 amps and pump a cup full of fuel per minute. It is best to run the correct size injectors or you need a serious pump. The Bosch 044 is one of the few pumps that has ok flow at 100psi but you would need two or three of them to run that pressure with the flow you would need.

Is there any disadvantages running a higher base pressure at idle? If not i may just start start with 4 Bar base pressure. Im using a SX 18302 fuel pump with a Solid State Relay powering it so it should have enough flow for what i'm after. Specs of pump below


Motor wise its a VET head no port work with a Hypertune intake. Using the (SR20VE (20V) cams and a stronger set of springs, turbo is a GTX3076 .82

Attached Files

That pump looks good, you should be fine fine at 4 bar base pressure.

Here is a Gasoline Injector Calculator I put together that accounts for RPM and injector rest time. It gives a fixed 3ms for the injector to rest between spray events. Notice that is gives the "standard 85%" at 6000 rpm. Twist the motor up to say 10000 and you get a way different answer.


Hope this helps and have fun tuning.


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