Injectors: Go Big or Go Moderate?

[Cringer]

I am wondering if there are any downsides to buying too big of an injector. I would think it would be good in terms of EOIT, meaning you could spray later and not have it sitting on the intake valve...what else am I missing?

[GHuggins]

Depends on the mods you have planned. Target something around a 60 to 70 percent DC with those mods.

[04silverado6.0]

Definitely size to achieve 60-80% duty cycle. I generally recommend shooting for 70%. Too big will be giving up power without dialing in the eoit on a dyno, i hear driveability suffers after max power is achieved via eoit on way oversized injectors.

[TheMechanic]

Good question. My first thought was if you could just pick a very large injector then why didn't the factory do that so that they could use one injector for almost every single make and model they have and save on production, supply, and cost. I can only guess good accurate atomization, spray pattern and direction etc. must be the issue. Software can control dwell time, total time of spray, and SOIT/EOIT.

[Alvin]

Quality over all else.

[Bill@HPTuners]

Quality over all else.

Yup. I have id1050x's in my 600hp mustang and can take the belt off the blower and run 400hp and the driveability is identical.

[etxd]

Higher quality injectors will have the higher flow rates with better control at lower injector duty cycles. +1 to the recommendations above.

[pannetron]

Letting the fuel hit the intake valve while it's closed might give you better fuel atomization than spraying only late with the valve open. Also, spraying fuel too late can wash oil off the cylinder wall. Late EOIT may help avoid knock and give some extra power but depends on your intended use.

[07GTS]

i tried the big rout thinking it will be the last injectors i get that will also suit future mods, aside from the issue i had with them they were too big 210lb, dumping all the fuel in in a very short time is different to dumping the same fuel in over a longer PW, i found it better with the smaller injectors around the 75% then the larger ones at 43% if u have fuel pressure control u can go bigger and run lower base pressure like im doing 1500cc now at 40psi so they should be about the same as my last 1000cc ran at 70psi base but this time i have more head room to increase the pressure if i have to

[Alvin]

Lower pressure is OK but be mindful of the pressure difference while in boost. Seems like better power is made with the pressure is higher in almost all cases..


for example. Car can maintain a good WOT AFR but with higher DC and weak pump. Say it's down 15 psi.

Fix pump, adjust tune, same AFR.. its not uncommon to see 15-20 rwhp.

[Turbo6TA]

I am no injector expert, but I think that with the stock ECM, you can only go so big on the injector flow rating without having idle problems.

In my case, I have a supercharged LS3 Corvette running a very moderate max boost of 7 PSI (575 RWHP). My injectors are rated at 72 Lb/Hr @ 58 PSI.

At the top of the my engines WOT power (6,400 RPM / 7 PSI Boost) my injector duty cycle is 70%. However, at idle, the duty cycle is just 1%.

I don't know how low of a duty cycle these injectors can efficiently operate at, but my 1% sure is low ... I certainly would not want larger injectors than what I already am using.

Too big of injectors ... Idle quality may suffer.

[nicks1031]

Sizing appropriately for your power goals is the way to go. Idle quality can suffer greatly from an injector that is too large. Here is a visual example.

Take this 52lb injector. Black horizontal line represents a relative idle flow rate. Nicely into the linear range.

52lb.PNG

Now take this VERY large injector for example. Horizontal line is below where Minimum Inj PW should be set.

Big Injector.PNG

[pannetron]

Make sure you have the short pulse adder data entered correctly!

[07GTS]

yea mine is full aftermarket fuel system with manifold referenced regulator, the 1500cc will be about the limit of idle on petrol, 210lb can idle on ethanol just fine, if the injectors are good and data is right idling in the 0.5ms PW is fine for them, always get quality injectors with data

[blindsquirrel]

Bosch 210s were intended to be CNG injectors, not sure that's a good example to use as why big injectors are not good. They're just not good injectors for liquid fuels, period.

I don't think flow rate is the one single thing that determines how an injector behaves at small PWs, the characteristics at the bottom are what's important. Rules of thumb that applied 25 years ago may no longer apply. I mean, there was a time when a 36lb injector was 'too big' to give a clean, controllable idle. Things have changed.

[07GTS]

Bosch 210s were intended to be CNG injectors, not sure that's a good example to use as why big injectors are not good. They're just not good injectors for liquid fuels, period.

i wish that was mentioned about the bosch 210's before people purchase them from performance shops, they dont like ethanol over time as i found out when they go sticky and flood the engine, thats when i looked up and found they are CNG injectors so that was wasted money

[blindsquirrel]

A referenced regulator can help increase the PW at idle/low load. Gives the same result as lowering fuel pressure on a non-referenced system, but doesn't lower the max flow rate at WOT because the pressure comes right back up as vacuum decays (or boost builds).

[blindsquirrel]

i wish that was mentioned about the bosch 210's before people purchase them from performance shops, they dont like ethanol over time as i found out when they go sticky and flood the engine, thats when i looked up and found they are CNG injectors so that was wasted money

I've heard of the 210s locking up with normal underhood heat, even without ethanol.

[MeshaalMMT]

buy quality injectors and bigger than you think you need. you will never have issues if tuned right.