How would a car that is batch fire react to having its injectors spray at different angles in the runners.

Or since the car is batch fire is there a disadvantage to just getting the injectors to spray in the manifold? Engine Vaccum should distribute air and fuel evenly correct?

 

Been playing with an injector flow bench lately and I can tell you for sure that with your design (I’m assuming you’re talking about the funny angle to get around the M112) you’d probably be better off something like the bosch/ford/SVO injectors then GM and a few others. They have significantly different spray patterns and characteristics (the GM injectors spray in a thin stream rather then fan pattern that you expect).

Real world, what will this do to how it runs? I’m not sure (till the last few weeks I was pretty much a believer in an injector is an injector is an injector… just pick the right flow rate… after hooking up my o-scope to the driver circuit that I’m using and using a strobe light to watch the spray pattern I’m really starting to change my mind)

 

Just thinking out loud here.....

I never really thought about the implications of batch fire injection until I installed the Electromotive Opti-Eliminator. With only the crank wheel, it could synch the sequential injectors to the wrong crank rotation. As a result, when the engine was cold, it would stumble off idle. It dawned on me that this was because the SVO injectors were spraying fuel on closed, cold intake valves. Hence, no atomization or vaporization when the valve opened and air started to flow... just a big blob of fuel. As soon as the valves warmed up, the symptoms went away. I assume that was because the fuel was now spraying on a hot intake valve, vaporizing, and sitting there waiting for the air to start moving. Is this a reasonable assumption?

I guess in a batch fire setup, where the injectors fire once for each crank revolution, the cold stumble problem might only be 1/2 as bad. Do 93 owners ever experience this problem?

When you think about it, a small spray of fuel droplets vaporizes, and produces a huge volume of vaporized fuel as it hits the closed, hot intake valve. Where does that huge volume of fuel go? Is it enough to actually expand back into the plenum? Is it enough to affect the A/F ratio distribution on adjacent cylinders?

Again, just thinking out loud....

Someone suggested this thread isn't "Advanced Tech" and should be moved..... I don't think so..... .

 

I'll go ahead and state my purpose for this thread,

We are machineing the injector bosses for my Eaton/LT1 project and there is no possible way the injectors can be angled to shoot the back of the intake valve (actually i think they more or less shoot the bottom of the runner just before the valve or possibly where the IAC port is)

So for my project I must decide (with the idea of my car being batch fire) wether I should angle my injectors

1. less than 90 degrees to intake runner (moderate clearance)
2. 90 degrees to runner (would be suficiant clearance)
3. just completely horizonal (great clearance but what about fuel distribution with BATCH FIRE, the purpose of the thread)

Okay having said that and put that thought on your mind

I don't think the 90-93 systems have any problem what so ever with fuel distribution with batch fire and stock cams.

I've tuned 42# SVO's on a hotcammed car before and had no problems with driveablity at all. We tuned those injectors in by the way because they where free and we needed something more.

I think the problem comes with the situation you have discribed and a cam with heavy overlap. Maybe on these "looser" cams the possiblity of multiple valves open at the same time even very briefly increases sooo....maybe more than 1 valve can be fighting for FUEL/AIR at the same time. I think this is a big cause of the BLM split problems some of us have.



Oh anthor thing is I don't really know wether batch fire means 1 fire per crank rev, 1 fire per cam rev, or maybe 4 small fires per crank rev. I'm thinking it might be 4 small pulses per crank rev cause fuel pressure holds rock steady while motor is idleing.

I think if the injectors fired at once per crank rev it would put a heavy instant draw on the fuel system. One you would see with a guage.



SO back to the orginal post. Do you guys think it matters where the injector fires on a batch fire car?

 

This has always struck me as interesting since I happen to be a much bigger 3rd gen fan then 4th gen but do own a ’97 and know what when you mess up the firing order of the injectors they do run rough, but for the life of me I can’t explain why. Your explanation is sensible, but if that was the case why do older batch fire cars idle well pretty much all the time (I’ve got an ’87 L98 car that I can tell the cold idle from the hot idle, but the reason is that it has another problem and once it gets warm the nice cold idle goes to a surge about every 5 seconds).

The thing is that swapping 2 injector plugs on an LT1 shouldn’t be as bad as the batch fire should be (since there you’ve basically got 8 cylinders getting fuel at the wrong time, rather then two), but it’s much worse. I’m not sure what the difference is…

Well, most people that do FI conversions tell you to never have the injector pointing so that it hits a runner/port wall. The idea is that if it does it’s always going to puddle out some.

OTOH, I can think of one perfect example that is doing just the opposite and works well, TBI setups. If you’ve ever taken a good look at them, the injector is spraying on the walls of the throttle bore and then even pudding on top of the throttle plate. They idle fine as long as they’re tuned right.

You say that like you’ve seen problems with non stock cams? Greater then an SFI setup would have?

Now I find that very interesting since I don’t know that I’ve ever seen an older GM ECM (165, 730…) run, V8 car that ran 36# or larger injectors that was idling right. What ECM was this and what fuel pressure were the 42’s running at?

I’m pretty sure that you’re talking about 2 different things since like I mentioned, you can get a rough idle on the later LT1’s by just swapping an injector connector with a stock cam.

Once per revolution. If you went with more then that the crappy gm injector drivers and slow high Z injectors wouldn’t be able to open/close fast enough to idle well.

The instant draw thing is pretty much a non issue, if you don’t get a drop at WOT, where in some cases all the injectors are effectively open all the time, then it’s not going to be an issue at idle

Well if it was me I’d try hard to keep them as close to aimed at the valves as possible. If you take a note from GM’s book, on the eaton blown V6’s they uses special heads that have injector bosses in the intake port rather then in the intake at all. I don’t think they would have wasted their time coming up with a new head design if they didn’t think it was necessary.

 

Hey Alvin, I've been watching your Eaton-LT1 project from afar, I'm a big fan of LT1 ghetto power mods :^)

Sequential injection gives better low engine speed operation. At speeds of 3000 rpm and above batch fire and sequential systems give the same performance. This supports the view that at higher engine speeds there is a common air/ fuel mass in plenum which is being pushed and pulled upon by the intake valve events.

I always remember "batch fire" as "bank fire" because the injectors are fired in banks of 4.

The trick to remember is that since batch fires injectors twice per cycle (similar to wasted spark) they fire the injectors with only half the pulsewidth.

The reason GM went to sequential fuel injection was mostly emissions.

FWIW, Holley made a N2O setup that raised the injectors out of the bosses and were pleasantly surpised that performance wasn't degraded noticalby. Jessie Coulter at Holley has that setup, pics here:

http://www.carprogrammer.com/Z28/NOSzels/


Hope this helps Alvin, keep us posted,
-Christian

 

This isn't Bryan this is Alvin I dont' think this is quite as cheap as people might think either

Update:

We had new injector bosses drilled and tapped 45 degrees from horizonal. Which means the injector will still be shot in the runner. Probally not as optimal as I would like but there is positively no other way.

I think the idea of fuel puddling in the intake probally won't be an issue. If it was an issue the TBI would be extremely ineffective because you can actually watch fuel puddle on the throttle body blades.

Our injector bosses look slick man, overly simple yet highly effective. We machined little pieces of aluminum to plug the stock injector bosses and redecked the upper surface.

Right now I'm trying to locate a piece of 6061 aluminum or stronger 10 x 16 inches.

 

The car with 42lbs injectors was a 93 F car and fuel pressure was stock.

I've got a 93 Vortec supercharged Z with 42lbs in Alabama the 93's don't seem to have any issue with the larger injectors.

I agree the 730's and 165's seem to have a problem with cutting the PW of a large injector to make a good idle.



Again, I don't see fuel puddling being a issue. Could anyone note back on a EFI swap or something where it did turn out to be an issue?

 

BTW

I'm really impressed with the way the older FORD computers handle larger injectors.

We installed some 36lbs injectors in a A9L 91 supercharged Fox last week and I just multiplied the injector constants by the factor of the (new flowrating/old flow rating) and it came out PERFECT

Don't know if it was a fluke or what, needless to say I was impressed. Most of you tuners know that it should never come out that easy

 

Man I was just thinking about something like that. Is there a point on the LT1 heads that it would be feasable or possible to put a boss in without running into a water jacket? If not, would it be possible to put one completely through the water jacket yet get enough cooling?

 

When my car was a stock 350 it would idle at 800 rpm when very cold in gear and then settle into 550rpm in gear. I never noticed any funny idling.

But with the stroker in it idles at 950rpm in gear when very cold and then settles into 750rpm when its warm in gear. I do notice a choppier idle for about 5 mins until the engine warms up.

But I always attributed this to my SRP forged pistons. I thought they just needed time to warm up and that they would expand slightly and seal better when hot and therefore idle better.

Now I'm not sure. I still kind of think its just the pistons.

 

I'm no FI expert but I'd like to share some experiences that might give you some hope:

My expereince has been that if the injector is moving the right amout of fuel, everything else is trivia. THat's kind of a bold statement but I've seen injectors that I thought were "good" but 1-2 in a set were shooting PINPOINT STREAMS of fuel. Like a little tiny "super soakers". You coulda put your eye out with the pulse of fuel they put out. Engine ran fine.

I've seen Buick Grand National motors with crank trigger sensor problems drop back into batch fire mode to run the motor and it runs EXACTLY the same as when it's in sequential mode. NADA difference.

Lastly, I've used carbs for YEARS. They use pretty low tech ways of metering fuel (how high tech is a choke plate to richen up cold air mixture???) and they do just fine, thank you.

MY THEORY WHY IT HAPPENS:

1. At idle and light throttle you are injecting a very small amount of fuel into a relatively large intake runner volume. Also, the intake is under vacuum which I'm sure helps the fuel flash into vapor more quickly as it exists the injector. It's got all kinds of room, time and help to expand, float around, atomize. Basically, like having a party in a high school gym with 8 of your best friends. No need to get elbow-to-elbow at the keg.

2. At heavy throttle stuff gets more crowded in there but you've got a LOT of air pulsing through the runner, stirring the fuel up and mixing it thoroughly as it is swept past the intake valve.

In short, I think it is somewhat a self-regulating situation.

 

How is the progress on this? Any new news?

 

http://www.thirdgen.org/techbb2/show...45#post1231645

 

Is anyone using a disc type injector, like Lucas etc?