Spyder style manifolds and injector choice

[grtskydog]

Hello all. I couldn't find anything about this in searching, but I had a question about doing an EFI conversion (MPFI) using a carb-style intake and fuel rails...aka the "spyder" intakes like Edelbrock's Super Vic EFI. Will the injector spray pattern affect how well it runs? The reason for my inquiry is with most of these setups, the injector is pointing at the runner floor, and I've read some theories that fuel doesn't have time to atomize before it hits the floor of the runner. In the case of most, the injector is mounted vertically, so it's pointing at the floor at a good angle, but not at the valve directly. I would think a wider injector pattern that atomizes sooner would be better than a narrower "shot" at the floor. Anyone know of any recommendations for injector type for these manifolds, or should it not even make a difference? I'd be interested to hear anyone's experience/knowledge on this.

Reason I ask is I converted a Torker II intake with bungs for MPFI. This is on my Ford 351W. It runs fine, except for a rough spot between 1600-1700 RPM...regardless of engine load. My theory is that there is an airflow issue in the runners of that intake, but I also wondered if injector spray pattern would affect it. I tried some Venom injectors and it idled rougher, but the engine didn't "wobble" at 1600 rpm (I probably could have tuned the idle, but that wasn't the mission). Hence my spray pattern theory. I currently run Ford Racing 30# EV-1 style on it. The another ECU were junk...one cap feel off but luckily got caught in the bung. 3 others were loose (after maybe 10 min of running).

FWIW, the Ford injectors have the 4 small holes, the another ECU had the little needle-looking thing at the pintle.

Trying to decide whether to spend my money at the speed shop helping me look at the tune, trying different injectors, or trying another intake (Super Vic). I just had the Fords cleaned flowed...all matched perfect.

[Matt Cramer]

I've never heard good things about Venom injectors. But I'd agree - if the injector is "aimed" at the manifold walls, a wider spray pattern makes for better atomization. An extreme example of the wide spray pattern / no target school of design is a GM TBI, where the injectors "puff" the fuel all over the place. "Squirt gun" injector patterns are best if you're aiming the injector at the valve, and probably work well if they're being fired down a long length of runner.

[grtskydog]

This is just a theoretical physics/fluid dynamics kind of question, mind you. I would think if most "squirt-gun" type injectors didn't work well with the MPFI carb-style manifolds, the alerts would be all over the place on efi boards like this. Likewise, if a certain brand/spray pattern injector was pretty much mandatory for say, a Super Victor EFI, then Edelbrock would certainly have that in their notes...they seem pretty good about that. I would think that kind of info would be all over the web as well.

In the end, I'm likely over-thinking something that will wind up being stupid-simple to solve.

[grtskydog]

Then I found this quote on performancefuelsystems.com Tech corner:

In many production engine applications, injector spray patterns play a minimal role in combustion performance because the spray is usually not aimed at the intake valve. Instead, the spray is aimed at the intake runner wall or floor. This is done for many reasons such as for emissions or packaging constraints. In these cases, atomization occurs after the airflow picks-up the fuel either in flight or as it splashes off the runner. In performance applications where emissions are not an issue, injector aiming should be optimized towards the valve and atomization techniques should be utilized.

So take from that what you will. Doesn't sound too critical, as long as the fuel atomizes off the floor. In the case of most "Spyder" type manifolds, the fuel is actually hitting the floor of the head port just shy of the valve...not the intake floor.

[Matt Cramer]

This is just a theoretical physics/fluid dynamics kind of question, mind you. I would think if most "squirt-gun" type injectors didn't work well with the MPFI carb-style manifolds, the alerts would be all over the place on efi boards like this. Likewise, if a certain brand/spray pattern injector was pretty much mandatory for say, a Super Victor EFI, then Edelbrock would certainly have that in their notes...they seem pretty good about that. I would think that kind of info would be all over the web as well.

In the end, I'm likely over-thinking something that will wind up being stupid-simple to solve.

It's not a huge difference. And I suspect the biggest thing that's affected is emissions, followed by some of the X-Tau AE coefficients.