Fuel injectors & fuel pressure for best atomization, MPG and low to mid RPM power?

[NewbVetteGuy]

I've been reading too much so now I need to come back here to get my head screwed back on straight again...

I'm trying to find an "ideal" fuel injector for my combo and my goals; I'm definitely interested in taking advantage of any modern injector tech or fuel pressure changes from stock to give me what gains are possible. I'm VERY interested in maximizing fuel economy, having lightning-fast throttle response, and improving low through mid rpm power.

My intake is a long-runner SBC intake that's a GIANT version of the old long-runner GM TPI intakes (A "First Fuel Injection" intake https://www.firstfuelinjection.com/) and I'll be using the Holley Terminator EFI, to do sequential injection; I can flash it to the Holley HP software if necesssary / advantageous.


I finished reading the epic 2011 "If EFI is so great how come race engines use carbs" thread, so some topics brought up there are still dancing through my head.


A lot of people with these TPi intakes swear by the Bosch III injectors and I've read that the atomization just gets better and better with them with more pressure. My thought was at a minimum to use the Bosch III injectors at 4 Bar -like the LS1s or even up to 5 bar -as Porsche apparently used the Bosch IIIs @ 5 bar for a while. -Although I also read that higher pressures and increasing the orfice size for more flow can reduce the injector response times fairly significantly....

Are there better injector options available today that can get me better atomization and that will work well with this intake's stock injector placement and angles? Note: 5 bar is the max pressure I can run at.


Has anyone looked at the Nostrum Energy Kinetic Intake Track Injection (K-ITITM) injectors? http://nostrumenergy.com/PDF/Sam_Barros ... 0Final.pdf
They were touting huge increases in atomization (up to 80%) early on and fuel economy improvement in some sort of single cylinder engineering engine of up to 20% early on. They don't have an injector purpose-built for TPI intakes yet, but they do have a generic port injector for sale.


Adam

[Belgian1979]

There is obviously a trade off to be made :
- more pressure means more flow, but this might put your injectors at an opening time at idle that is in the non-linear area and thus hard to control.
- more pressure means that injector opening times will increase (injector dead time)

At a certain point, your injectors won't be able to handle the higher pressure.

More pressure is usually a bandaid for a problem in another area.

[Circlotron]

If you're not primarily interested in maximum power then it might be interesting to play with different fuel rail temperatures. Also load dependent inlet air temp.

[NewbVetteGuy]

More pressure is usually a bandaid for a problem in another area.

My understanding is that the Bosch IIIs were run on different engines at 3, 4, & 5 Bar from the OEMs, no?

If the LS1 ran Bosch IIIs @ 58 PSI / 4 bar is it a bandaid?

If Porsche ran Bosch IIIs @ 5 bar, is it a bandaid?



My goal is simply to find the injectors that have the best atomization and work for my application and power level (440 hp). I'm not looking to up the fuel pressure to support more power; simply to get better atomization.

My understanding is that going with a slightly undersized injector and increasing the pressure can accomplish that goal, no?



Adam

[englertracing]

How about Dual injectors?

Has anyone ever run efi down nozzles?

[peejay]

How about Dual injectors?

Has anyone ever run efi down nozzles?

Mazda was doing aspirated nozzles in 1983 and staged injection in 1986.

Alternatively, Chevy's original Vortec engines with the "spider" injection have the injectors pretty far away from the port and they all have plastic tubes that spray down further into the port than they could have got with a regular injector in the 1990s. I don't think they're aspirated, but I do remember that if you don't have 65psi fuel pressure then the engine WILL not start. 62psi isn't enough...

[user-23911]

I haven't read that other thread yet.


For reading you can't go too far wrong reading up from the megasquirt manuals, a lot of the old errors have been corrected now.
Can't go too far wrong with a megasquirt computer either, got to be better than a "name brand".


Standard EFI pressure is usually either 3 bar or 3.5 bar. The LS1 might be the only one using 4 bar?
3 bar is usually used for turbo, 3.5 more commonly used for N/A.
Most injectors are rated at 3 bar.
More pressure means more flow but longer dead time (slower to open).
Less pressure is better as you can make use of a smaller PW for a better idle.
A pump will flow more at less pressure and less at higher pressure.

As far as the spray pattern and atomisation goes.........that varies with pulse width.
A short PW will give better atomisation than a longer PW ....so it's just a decoy. No need to worry about it unless you're going stupidly big.

[Belgian1979]

More pressure is usually a bandaid for a problem in another area.

My understanding is that the Bosch IIIs were run on different engines at 3, 4, & 5 Bar from the OEMs, no?

If the LS1 ran Bosch IIIs @ 58 PSI / 4 bar is it a bandaid?

If Porsche ran Bosch IIIs @ 5 bar, is it a bandaid?



My goal is simply to find the injectors that have the best atomization and work for my application and power level (440 hp). I'm not looking to up the fuel pressure to support more power; simply to get better atomization.

My understanding is that going with a slightly undersized injector and increasing the pressure can accomplish that goal, no?



Adam

The OEM's may run different pressures and have tuned their ecu's accordingly. There is no secret in changing parameters when you use a higher pressure. If it atomizes fuel better, depends on the injector type I guess. I think you're better off leaving more time for the fuel to atomize in the intact tract due to the presence of intake heat.

If the problem is to solve an injector being undersized we're talking a different subject all together.
Let's assume that Porsche wants to use a small injector because of the advantages that it gives to keep injector linearity at idle. But that same engine has a very high power band, requiring a lot of fuel flow at higher rpms (assume turbo). The best way to solve the problem would be to install a secondary injector, but a bandaid could be (!) to use a slightly higher fuel pressure so the injector would just about flow enough at high rpm while still staying within linearity at idle. Not sure that is what they did, but it could be.
On the other hand if you use an injector with high fuel flow, it speaks for itself that atomizing the fuel is compromized since you will have to move more fuel in the same time frame.

Like I said, the best way to deal with a problem of high fuel flow is a double stage, but things get complex from that moment on.

[digger]

BMW ran them at 5b on s50b32 and s54b32 late 90's time frame.

i remember reading a paper a while back that injection pressure changes the cone angle of the injector spray, at some rpm and load it helped at others it didn't.....

[NewbVetteGuy]

How about Dual injectors?

Has anyone ever run efi down nozzles?

This is a 98% street only build and I'm definitely not looking to hack up the intake for dual injectors, although I think I get the theory.
(Traditionally placed, close-to-the-valve injectors for idle and low to mid RPM, then 2nd set of injectors placed up high / further away from the intake valve comes on at WOT and provides higher levels of atomization and increased O2 via cooling effect from fuel vaporization.) -Right?


Adam

[NewbVetteGuy]

If the problem is to solve an injector being undersized we're talking a different subject all together.

No worries there, I don't own any injectors currently. I just want to maximize fuel economy and low to mid RPM power -I say that, not because I want to lose high RPM and WOT power or don't care about it, I say that because it seems like at WOT and high RPM the fuel is pretty much going to atomize well and be fine no matter what. That's not really difficult.

Let's assume that Porsche wants to use a small injector because of the advantages that it gives to keep injector linearity at idle. But that same engine has a very high power band, requiring a lot of fuel flow at higher rpms (assume turbo). The best way to solve the problem would be to install a secondary injector, but a bandaid could be (!) to use a slightly higher fuel pressure so the injector would just about flow enough at high rpm while still staying within linearity at idle. Not sure that is what they did, but it could be.

That was my thinking, too.

On the other hand if you use an injector with high fuel flow, it speaks for itself that atomizing the fuel is compromized since you will have to move more fuel in the same time frame.

Like I said, the best way to deal with a problem of high fuel flow is a double stage, but things get complex from that moment on.

Appreciate the input. Definitely not interested in double stage or dual injectors per cylinder; just getting a good single injector.



David Redszus had some really great insights and quotable moments in a few of the EFI vs. Carb posts and made some statements that particularly with port injection and with injectors fairly close to the valve that improvements in atomization ala high fuel pressure really helps and that traditional low pressure (assumption 3 bar) fuel injection really doesn't provide appropriate levels of atomization.

I think I remember a direct quote with him stating that evaporation of fuel droplets is based upon 3 factors: "time, temperature and turbulence". Well with the point-of-injection being set in my application and being close to the valve, I don't have the benefit of time. I'm going to be using a cold air intake and a coated intake, so I don't have much of a temperature advantage in the intake tract, anyway. And although I should have good turbulence with very fast moving air through the TPI-style intake and profiler heads and then the turns required to navigate a 23 deg SBC head; that's about all I have.

If I understand correctly, David's statement left out the 4th major factor which is the starting droplet size (although he spoke to it later); surface area to volume ratios are much higher with smaller droplets, hence my desire to focus on an injector that flows enough fuel with the smallest possible starting droplet size.

There was a lot of great insight and recommendations shared on that thread, but I'm having difficulty trying to figure out how to apply it to my actual build / engine. I'm way too new at this to do it on my own.

Adam

[NewbVetteGuy]

BMW ran them at 5b on s50b32 and s54b32 late 90's time frame.

i remember reading a paper a while back that injection pressure changes the cone angle of the injector spray, at some rpm and load it helped at others it didn't.....

I remember reading that some injectors respond well to more pressure (maintains a good spray pattern with smaller droplets) and some respond poorly. From what I've seen and heard both from FIC and on here, the Bosch IIIs seem to be injectors that "like" more pressure. I am mildly concerned that their response times / latencies aren't great to start with and increase the pressure from 3 bar to 5 bar is only going to make that worse, though...

Adam

[Belgian1979]

Timed injection might be a subject to study if that's what you're after.

[chimpvalet]

Anybody have experience with Denso UC type?

[turbo2256b]

Without EGR fuel economy will never be all that great.