Injector placement

[donsboy]

I saw a homemade fuel injection setup for a 390 ford using a 351c tunnel ram. The owner has the injectors tilted for clearance instead of square to the intake runner. Will this affect performance? Everyone I've ever seen including stock is square to the runner. Is there a reason?

[peejay]

Most injectors I see are NOT square to the runner, they are angled down into the port, in many cases spraying directly on the intake valve(s) or as close as possible to that.

[David Redszus]

Most injectors I see are NOT square to the runner, they are angled down into the port, in many cases spraying directly on the intake valve(s) or as close as possible to that.

For a street engine running at lower rpms, the injectors are placed close to the inlet valve and sprayed on the back of the valve.
But for high speed applications, this does not allow enough time for fuel evaporation. Now the injectors are moved further from the port, sometimes even at the end of the inlet duct. Injectors are made with various spray cone angles to allow the spray to be aimed so that it will not impinge on the inlet tube wall.

If high speed operation is intended and the injector cannot be moved or replaced, use a fuel with a lower distillation point to assist evaporation.

[donsboy]

The injector is usually mounted straight up. It may not be square but these injectors are mounted visibly canted toward the center of the engine not pointed to the intake valve at all. Will this make the engine more susceptible to build up on the intake valve? Or more susceptible to fuel pudding or even reversion?

[pamotorman]

I believe that NASCAR has a rule where the injector can be place in the runner leg.

[mk e]

The injector is usually mounted straight up. It may not be square but these injectors are mounted visibly canted toward the center of the engine not pointed to the intake valve at all. Will this make the engine more susceptible to build up on the intake valve? Or more susceptible to fuel pudding or even reversion?

The more fuel you spray at or on the maifold and port walls the more difficult it is to control mixture during warmup and throttle transitions. OEMs have very strict limits they need to meet so they generally spray at the closed intake at lower power to get as much of the fuel vaporized as possible. If you don't have the limits and just want the engine to work it makes a lot less difference.

There is some HP advantage to making sure you are spraying the fuel into the air and not onto the port/manifold because you want the vaporizing fuel to cool the air as much as possible instead of cooling the port/manifold. High performance application normally focus their attention here and live with whatever they get at low power.

Injection angle and injector sizing helps too. With big injectors you can only spray into the moving air stream to maximize the air cooling. That makes it harder yet to control low power fuel so injectors that are fully charaterized like those from injector dynamic have become popular to allow good control of very short injector pulse widths then spraying when the intate is closed like OEMs at low power and at intake open at high power gives you the best you're going to get.

[FloydODB]

maybe one day they will figure out how to inject it right into the cylinder.

[Kenova]

maybe one day they will figure out how to inject it right into the cylinder.

Now that is just crazy talk!

Ken

[K.P.]

I thought direct fuel injection was just that, injecting fuel directly into the combustion chamber!

[wyrmrider]

Germans Beat you to it

[Circlotron]

OEMs have very strict limits they need to meet so they generally spray at the closed intake at lower power to get as much of the fuel vaporized as possible.

What is done with a four valve head where you have two inlet valves to aim at, with maybe two separate ports?
I asked this once before and have forgotten the answer.

[user-612937456]

I thought the new Corvette LT1 was direct injection?

[user-23911]

OEMs have very strict limits they need to meet so they generally spray at the closed intake at lower power to get as much of the fuel vaporized as possible.

What is done with a four valve head where you have two inlet valves to aim at, with maybe two separate ports?
I asked this once before and have forgotten the answer.

2 holes in the injector, one sprays at one valve, the other sprays at the other.
Use the wrong sort of injector and it won't work properly.
More failed upgrades when you don't know.

[mk e]

OEMs have very strict limits they need to meet so they generally spray at the closed intake at lower power to get as much of the fuel vaporized as possible.

What is done with a four valve head where you have two inlet valves to aim at, with maybe two separate ports?
I asked this once before and have forgotten the answer.

2 holes in the injector, one sprays at one valve, the other sprays at the other.
Use the wrong sort of injector and it won't work properly.
More failed upgrades when you don't know.

or mount higher so the moving air will pull the fuel where it need to go - most sport bikes do this.
or aim the injector at 1 port of the other.

[roc]

I thought the new Corvette LT1 was direct injection?

Not just the Corvette, but Tahoe, Suburban, Silverado powered by the EcoTec3 5.3L V8 engine.