Inliners International Forums General Discussion Blown and Injected How many injectors??? Why 6?

Okay, I'm about to start cutting holes for the injector bungs on my clifford intake for my injected/turbocharged 250 project and a couple friends and myself got to thinking.......with the siamese ports on these motors, why can't I run ONE injecter per intake runner since only one of the cylinders that are sharing that particular intake runner is on an intake stroke at a time? Why do I have to have 2 injectors per intake runner if both cylinders aren't asking for fuel at the same time?
In theory, I wouldn't have to get larger injectors either if I am able to supply 2 cylinders with one injector since only one of the cylinders is wanting fuel at a given time.
Is it all happening too fast for one injector to keep up? Would the duty cycle be too high?
Any/all thoughts and ideas would be greatly appreciated!

The 1-2 and 5-6 paired cylinders have an early event and a late event. Which one is it? Is it going to fire twice?

Excuse my ignorance, but what do you mean when you say they have an early event and a late event? Are they 'sister' cylinders where one is firing at TDC and the other at BDC?
Even if that were the case, with the firing order being 153624, there would be at least one other cylinder firing between a set of 'paired' cylinders. I would think an injector could squirt again that quickly.
I'm only talking injectors, not spark.

Small injectors will be easier to control when the fuel demand is small (ie: idle).

Don't forget about the fuel charge robbing issue when doing port fuel injection. You may have better luck putting the injectors further upstream in the intake. Tom

Tom,
I'm aware that a smaller injector will be easier to tune when fuel demand is small, but what do you think about my idea of using one injector per runner instead of two per runner?
I don't know what you mean 'fuel charge robbing issue' either. Care to elaborate for me? If I move farther upstream i will have to increase the angle of the injector vs the runner....
Thanks for the insight!
Jason

Say I have a tuned port V8 engine, there is one injector per intake port not two. If I mount one injector in each of the runners on my clifford intake for my 250, that seems to be more true to mimicking the set up of the tuned port. Why do I need to put two injectors in a place that is only feeding one intake port at a time? I know it's the way it's been done, but is it necessary? I have three runners, at the end of each runner are two cylinders that need fuel, but not simultaneously, why can't i feed them both with the same injector.....they aren't trying to eat at the same time.
I'm real tempted to try it unless someone can think of a real good reason why it wouldn't work.

I think you will have to use higher flow injectors to deliver enough flow at high rpms without having pulsewidth overlap problems. Of course larger injectors leads to idle flow instability issues. That is the main reason I think two would be better, in addition to being able to target the spray cone at the backside of the intake valve.

Why do you think one for two cylinders would be better?

Here is a topic started a while back.
https://www.inliners.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=64928&fpart=1

Copo Rat,

You need to look at the valve events in each port, not the firing order, to figure out the fuel robbing issue. When #2 intake valve is closing #1 is just starting to open so you need to inject fuel at the right time to each valve.

With a carb you have a manifold full of fuel to help crutch it by until you reach a critical point ( about 400 to 500 HP ) then you have a problem because the supply can't keep up with the demand unless you run it very rich and kill the power. This is a simple explanation.

I use carbs, so my fix was to divide the ports, if you don't 1&6 will run lean.

Maybe if you put the injectors up stream it will fill more of the runner and help?

Harry

French,
I don't necessarily think that one injector per runner will be better, just curious as to why it couldn't work 'as good' as 2 injectors per runner.
I have a much better understanding of this after the info that has been given via this thread, and I'm sticking with two injectors per runner. I was unaware of the valve events between certain shared cylinders that cause a 'fuel robbing issue'.
I still believe it can be done, but I'm not willing to try it and it's a street motor that I can't have huge injectors in, causing idle and low speed problems.
Thanks a ton for your info, it is greatly appreciated!

Thank you to everyone that has contributed to this thread as it was hugely helpful to me in making my decision (2 injectors per runner), as well as teaching me more about certain valve events that occur that cause 'fuel robbing issues'. This is my first inline motor and I'm still learning.
Thanks all!

Good luck - post pics. We love pics.

French, here are some pics for ya.....got a little done at work today, bung holes (ha) are in, and we mocked up the bungs, injector, rail and throttle body to check for clearance. Have to cut bungs to length and weld in....hopefully by the end of the week they will be in!

Nice! That looks so much like mine, but cleaner and nicer.

What Throttle body you using?

Thanks Tom, much appreciated. There are several on here that I highly value the opinions of, and you are one (my signature is a quote from another). I used yours as a guide and you have helped along the way.
The throttle body is from an '08 Trailblazer (4200). I'm going to use ALL the electronics from that vehicle. Working on the cam and crank reluctors now. Once that is figured out it should be 'game on'!

Does anyone have any opinions on whether or not I should 'smooth' the ribs in the floor of the intake or not? Injected, turbocharged 250. Will the fact that it is under boost negate any ill effects the ribs would have? Thoughts?

I believe the ribs are there to add heat to the fuel that would puddle in the intake with a carb. A turbocharged engine has plenty of intake heat will under boost. If it is easy, smooth them.

Thanks again for the info......they will be removed. I couldn't find a good reason for them to be there on a boosted application, (though I'm obviously no expert). They are perpendicular to the 3-4 runner and I thought they could possibly impede the flow to those cylinders. But, if they don't impede the flow on a N/A motor, I guess it wouldn't on a boosted motor.......anywho, they gone!

It's nice to have a mill at your disposal when needed.

copo-rat,
I think the ribs are to direct fuel from a carb to the end ports, not needed for your EFI.

Harry

So how big of a deal is it if the injectors are slightly 'shrouded' by the end of the bung/ceiling of the runner? The tip of the injector is NOT sticking into the runner. If that makes any sense.

It should not matter because the spray pattern will not hit the injector bung wall.

MBHD

Reach in and take out the first 3rows from side to side,The ribs were there to help channle the fuel to the end runners and they worked a little to well and would lean out the center two cyl.I have done this to many of those intakes.

I agree with Hank on that (shouldn't be an issue, unless it's way further up there than it looks in the pics).

If I read it right you are going to cut the bungs shorter than they appear in the picture (the one with the injector and fuel rail).

Are you going to match those to the ceiling of the runner, or are you planning to leave some of the bung hanging below into the airstream (attempt at airflow direction, or turbulence generation for better atomization perhaps?)?

Hank, Larry - thanks for the info! I will most likey remove all the ribs from the bottom of the intake.

Nexx, The bungs are trimmed and are tacked in flush with the ceiling of the runner. I just don't have any pics of that yet. I'm not leaving them protrude into the runner at all. I'm actually having them welded in (by a good friend/co-worker) on the inside and then I will clean up the welds and smooth it all out. We decided to not weld the bungs on the outside just to keep it cleaner looking. I'll post more pics hopefully early next week when we have more progress.
We have a tiny interference issue with the fuel rail and TB and TB adapter. Not tiny enough to be ignored. I'm contemplating my options:
Mill the 'carb' mounting flange flat (as it is on an angle currently) and gain some clearance, mill the bungs a little shorter to get the rail farther away from the TB and adapter, mill the TB, TB adapter and back of the rail to gain the clearance needed. I originally wanted to remove the angle from the mounting face of the intake and gain the clearance that way, but I don't want to try to drill deeper and tap the holes afterward as two of them would be left too short to use. Don't want to use heli-coils either. Just have to weigh the options. Quickest option would be nice, but I don't want to be hasty and make a decision I'll regret!

I would mill the injector bungs more.

It would not hurt if the injector is protruding into the port.

Not a big deal IMO.

MBHD

Copo, thanks.

Finally made more progress. Milled a little off the front of the TB adapter and bought a new -6 fuel rail instead of the -8 that I had before. I also bought a tool for making the injector holes in the fuel rail all in one step instead of using multiple tools like we did with the -8 rail. Enjoy a few pics!






Still have to deburr the holes in the fuel rail and make some mounts to bolt it to the intake once it's assembled.

Looking good!

Are the bungs welded from the inside of the intake runner?
What TB is that, a Trailblazer or ??

Are you going to use throttle by wire?


MBHD

Hank,
The bungs were welded on the inside and then ground smooth. The TB is from an 08 Trailblazer and yes, I will be running the throttle by wire set-up that the Trailblazer uses. I'm actually using ALL the electronics, sensors, ecm and harness etc from a 2008 Trailblazer (and adding a Buick GN turbo as well! ).

nice

Copo, nice progress.

I learned something from your pics: The 2008 throttle body is completely different from the 2002-2007 throttle bodies. This could solve a hood clearance issue for me, thanks!

Copo,

One item to check is the injector spray cone angle, you want the fuel to hit as far in the runner as possible. If the injectors are too far back e.g. injector bungs too long the fuel may impinge on the bung wall and puddle off with poor atomization. The injector tip should be very close the inside of the runner.

A good rule of thumb is to use injectors that have a spray cone pattern that contacts the outside edge of the intake valve on a closed valve.

Are you using pintle-type injectors or multiple orifice ceramic disc type?

Lime,
Glad I could indirectly help! Doesn't the '08 and up use a different ECM? Won't you have to change gas pedals if you go to an '08+ throttle body?

Efi & French,
I can't seem to find what the spray cone angle is or if they are pintel type of multiple ceramic disc type. I found that the 'long' version of the injector I have has a spray cone pattern of 30 degrees, but I don't know if the 'short' injectors that I have are the same. I would guess they were. Looking at the end of the injector, there are four holes, does that designate a 'multiple orifice ceramic disc type'?

Here are the specs of the injector I have:

Siemens Deka 60lb SHORT EV1 High Impedance Fuel Injector
Static Flow Rate (GAS): 62.7 lb/hr = 646 cc/min = 474 g/min
Dynamic Flow Rate 2.5ms PW @ 100Hz (GAS): 20.2mg/pulse
Coil Resistance: 12 Ohms (This high-impedance injector will work with all factory ECM/PCM injector drivers)
Gain: 0.11ms/mg
Offset: 0.055ms
Turn on time @ 14VDC: 1.14ms
Turn off time: 0.85ms @ 600KPa
Factory Tollerance: +/-6 %
Spray Pattern: Cone (4-Hole)
Connector: Minitimer (Bosch EV1)

Four holes would indicate a ceramic disc type - also called SMM (silicon micro-machined). They have good control characteristics and an evenly distributed spray pattern. I think it is a good choice.
I can't help identify spray pattern but generally speaking the farther upstream you place it the narrower you want it to avoid wetting down the port walls. That leads to hesitation issues.

Lacking any hard data, try hard to put the injector tip flush or slightly protruding from the bung.

Have you looked to see where the injector CL is going to point at inside the runner?

What ever happened to this? I was enjoying the read

Riveted1
WOW, that was a quick 5 months wasn't it!? Unfortunately I have no progress to report. New house and a 3yr old daughter is where I'm spending my time. That and driving......we live pretty far out.
I was just thinking about what's left to do. I need to clone myself......then find a job for my clone so I have more project money.
Sorry for the stalled project!