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What's the ideal injector trajectory angle?

General engine tech -- Drag Racing to Circle Track

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gmrocket
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What's the ideal injector trajectory angle?

Post by gmrocket » Sat Aug 24, 2019 9:47 am

For an injector placement about 3.5" from the valve?

I always see bungs welded on that places the spray pattern almost straight down into the runner floor, which don't make sense to me other than it's easy to build the rail on top of it.

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Re: What's the ideal injector trajectory angle?

Post by Walter R. Malik » Sat Aug 24, 2019 10:56 am

gmrocket wrote:
Sat Aug 24, 2019 9:47 am
For an injector placement about 3.5" from the valve?

I always see bungs welded on that places the spray pattern almost straight down into the runner floor, which don't make sense to me other than it's easy to build the rail on top of it.
Whatever will cause the most fuel Atomization. That is probably different in almost every scenario.
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Re: What's the ideal injector trajectory angle?

Post by gmrocket » Sat Aug 24, 2019 11:02 am

Walter R. Malik wrote:
Sat Aug 24, 2019 10:56 am
gmrocket wrote:
Sat Aug 24, 2019 9:47 am
For an injector placement about 3.5" from the valve?

I always see bungs welded on that places the spray pattern almost straight down into the runner floor, which don't make sense to me other than it's easy to build the rail on top of it.
Whatever will cause the most fuel Atomization. That is probably different in almost every scenario.
That makes sense to me.

I'm doing a port injection intake and want to get the bungs angled right.

I just don't think shooting it at the port floor is right.

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Re: What's the ideal injector trajectory angle?

Post by PackardV8 » Sat Aug 24, 2019 11:37 am

Yes, agree; most aftermarket conversion intake bungs are positioned for ease of fuel rail installation.

No, there's no one best/only angle. Define the intended use. Idle and emissions want different timing and angle and distance to the valve than does WOT power.

Maybe, do some research. For example, some IR race-only EFI systems mount the injector at the top center of each IR runner, spraying downward into open intake air flow.

Maybe, note later OEM heads designed solely for EFI will have a notch at the top of the intake port to accept and direct the EFI spray.
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Re: What's the ideal injector trajectory angle?

Post by Walter R. Malik » Sat Aug 24, 2019 3:30 pm

gmrocket wrote:
Sat Aug 24, 2019 11:02 am
Walter R. Malik wrote:
Sat Aug 24, 2019 10:56 am
gmrocket wrote:
Sat Aug 24, 2019 9:47 am
For an injector placement about 3.5" from the valve?

I always see bungs welded on that places the spray pattern almost straight down into the runner floor, which don't make sense to me other than it's easy to build the rail on top of it.
Whatever will cause the most fuel Atomization. That is probably different in almost every scenario.
That makes sense to me.

I'm doing a port injection intake and want to get the bungs angled right.

I just don't think shooting it at the port floor is right.
Toward the middle of the backside of a hot intake valve is accepted in most O.E.M. instances however, making the most power is not their first concern.
Being able and finding a position to do that is not so easy in a lot of applications.
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Re: What's the ideal injector trajectory angle?

Post by ptuomov » Sat Aug 24, 2019 4:18 pm

ITBs or a plenum manifold? With ITBs and a street car, one wants to minimize the volume between the intake valve and the throttle plate. That means getting the injector sprayingbas close to valve as possible.

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Re: What's the ideal injector trajectory angle?

Post by mk e » Sat Aug 24, 2019 5:05 pm

ptuomov wrote:
Sat Aug 24, 2019 4:18 pm
ITBs or a plenum manifold?
Doesn't really matter, straight down the runner is the accepted "best".

After that distance from the valve varies with rpm...more rpm, further from the valve so the fuel has time to vaporize but not time for the now cooled charge to reheat....that's the theory anyway. Building on that theory bigger injectors with lower duty cycle, like around 35% that only spray into the moving charge have been shown to make more hp than the standard 80-85% DC sizing....if the injectors are properly characterized and mat hed and injection angle optimized blah blah blah......lots of variables to play with beyond angle.

I can tell you the spraying straight at the opposite wall of the runner because it fits well like that just plain sucks...the fuel puddles and dips into the cylinder in an uncontrolled way so the mixture ( particularly low power) is inconsistant, been there, done that and it's a sh!t setup. Aimed at the center of the runner 3-4 inches from the injector tip seems about perfect.
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Re: What's the ideal injector trajectory angle?

Post by gmrocket » Sat Aug 24, 2019 8:18 pm

I should have mentioned this is for a low rpm high tq set up. Long hi velocity runner.

Max rpm no more than 4500, peak tq down low.

Cruising/towing rpm at 60mph about 2200 2300

I'll be using the megasquirt

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Re: What's the ideal injector trajectory angle?

Post by Circlotron » Sat Aug 24, 2019 9:08 pm

Walter R. Malik wrote:
Sat Aug 24, 2019 3:30 pm
Toward the middle of the backside of a hot intake valve is accepted in most O.E.M. instances however, making the most power is not their first concern.
For a two valve head, yes.
What about for a four valve head?
You can't aim at both inlet valves at once.

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Re: What's the ideal injector trajectory angle?

Post by digger » Sat Aug 24, 2019 9:18 pm

Circlotron wrote:
Sat Aug 24, 2019 9:08 pm
Walter R. Malik wrote:
Sat Aug 24, 2019 3:30 pm
Toward the middle of the backside of a hot intake valve is accepted in most O.E.M. instances however, making the most power is not their first concern.
For a two valve head, yes.
What about for a four valve head?
You can't aim at both inlet valves at once.
yes you can

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Re: What's the ideal injector trajectory angle?

Post by mk e » Sun Aug 25, 2019 9:00 am

Circlotron wrote:
Sat Aug 24, 2019 9:08 pm
Walter R. Malik wrote:
Sat Aug 24, 2019 3:30 pm
Toward the middle of the backside of a hot intake valve is accepted in most O.E.M. instances however, making the most power is not their first concern.
For a two valve head, yes.
What about for a four valve head?
You can't aim at both inlet valves at once.
There are injectors with split spray patterns for that purpose. If you are that 3-4" away from the port split a single straight cone pattern seems to work fine.....not testing I did a testing I've seen data from.
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Re: What's the ideal injector trajectory angle?

Post by gmrocket » Sun Aug 25, 2019 9:57 am

Two vale head

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Re: What's the ideal injector trajectory angle?

Post by gruntguru » Sun Aug 25, 2019 7:01 pm

As mentioned above - OEMs usually aim at the back of the valve. This works best for driveability when cold and at low speeds where fuel can puddle on cold metal. If this liquid fuel streams along the back of the open valve and across the seat, it is more likely to break away and enter the chamber than fuel that is streaming along the port wall and across the chamber valve seat.

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Re: What's the ideal injector trajectory angle?

Post by gmrocket » Sun Aug 25, 2019 7:22 pm

It would be nice to be able to move them slightly and test.

Being about 3 or 4 inches away , only a slight movement at the top of injector would move the spray pattern at the valve quite a bit.

Shouldn't be that hard to do.

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Re: What's the ideal injector trajectory angle?

Post by af2 » Sun Aug 25, 2019 7:41 pm

The best is in the chamber... SO why is it a problem shooting at the floor like all the sprint cars do?
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