Location of secondary injectors
 

Ok have some differing opinions about this.

I am running 8x injectors using the APS tumbler. The primary injectors are in the standard location and the secondaries are a little higher.

Now my question is and would like some answers to it..

1) What is the best location of secondary injectors and why?
2) Some people say that its better to have all the fuel right near the factory location, why?

discuss..

The closer you can get the injector to the inlet valve pocket the better.

The reason?
There is more turbulance behind the valve head than anywhere else in the inlet tract, this turbulance prevents the fuel from wetting the inlet port walls and ensures a more even fuel air mix inside the cylinder.

I had dramas when I added 4 extra 550 cc injectors to a 13b turbo (TO4E, large extend port) the bosses were welded in to the inlet runners (1 per runner) 6 inches higher than the stock injectors (that fired directly into the inlet ports).

The issue this caused for me was fuel condensing on the manifold walls at low to moderate boost levels - throwing the afr's all over the show. It was solid at full power on the dyno (440rwhp) but would foul (wet the plugs) cruising around on the streets, when on boost for short periods of time.

In the end the only cure was to fit 4 x 1000cc injectors & modified rails to the factory injector bosses and cap the whizz bang welded in bosses......

Yes but in my case the secondaries come on at 300 hp atw. So there should be enough air flow to direct the air to the port. Why I was thinking it's better to have them on the runner was that the fuel and air got time to mix nicely before going to the port?

The problem with the runners is that the airflow is smooth and not very turbulent, leading to poor charge stratification...... The long manifold runners on the subaru's would encourage smooth airflow to my minds way of thinking.

Another point to note is that the further away from the port you are the earlier you have to fire the injector in relation to the actual valve opening, in acount of the volume of the air column inside the runner.

Also worth noting how hard it is to get the injector to spray down the runner rather than across it to wet the opposite wall of the runner. It's pretty hard to get a good 'shot angle' with weld on injector bosses and very difficult to get all 4 uniform on the same angle.

Why not go for larger injectors in the stock location?
Wouldn't that save the expense of someone butchering the manifold (and possibly getting it wrong)?

[QUOTE=LegacyRS]
Why not go for larger injectors in the stock location?
Wouldn't that save the expense of someone butchering the manifold (and possibly getting it wrong)?[/QUOTE]

He wants an economical 600HP....

[url]http://www.maperformance.com/aps-tumbler-delete-aux-injector-manifold-housing.html[/url]

Sexy bit of kit, no butchering.

[QUOTE=Hurtenstein]He wants an economical 600HP....

[url]http://www.maperformance.com/aps-tumbler-delete-aux-injector-manifold-housing.html[/url]

Sexy bit of kit, no butchering.[/QUOTE]


Yeh I know I've already got that. That is how I'm running my 8 injectors.

But have been told that the further the way the secondaries the better fuel atomization.

Nice comparo. But I'd be looking at sitting the injectors on top of runners. So they would be pointing straight down and not ok the side.


[QUOTE=LegacyRS]The problem with the runners is that the airflow is smooth and not very turbulent, leading to poor charge stratification...... The long manifold runners on the subaru's would encourage smooth airflow to my minds way of thinking.

Another point to note is that the further away from the port you are the earlier you have to fire the injector in relation to the actual valve opening, in acount of the volume of the air column inside the runner.

Also worth noting how hard it is to get the injector to spray down the runner rather than across it to wet the opposite wall of the runner. It's pretty hard to get a good 'shot angle' with weld on injector bosses and very difficult to get all 4 uniform on the same angle.

Why not go for larger injectors in the stock location?
Wouldn't that save the expense of someone butchering the manifold (and possibly getting it wrong)?[/QUOTE]

[QUOTE=trainwrex]Yeh I know I've already got that. That is how I'm running my 8 injectors.
[/QUOTE]

I know. =) It was for Ross's benefit =)

Have you spoken to MoTeC about where they recommend them? Stace was saying soemthing about V8 supercars having the secondaries further up the inlet manifold as it encourages beter mixtures. I don't believe Ross's "wetting the wall" theory when there is 30psi of pressure pushing on them

[QUOTE=jEstEr?]Have you spoken to MoTeC about where they recommend them? Stace was saying soemthing about V8 supercars having the secondaries further up the inlet manifold as it encourages beter mixtures. I don't believe Ross's "wetting the wall" theory when there is 30psi of pressure pushing on them[/QUOTE]
Exactly. Apart from the show side of it, big hp carby V8's sometimes have great big in-let runners that stretch from the valley right through the bonnet. Looks hell bogan spec but the whole idea is to give the fuel more time to mix thoroughly with the oxygen before it gets sucked into the combustion chamber. More torque = bigger skids

[url]http://www.youtube.com/watch?v=o_QyUD6V5_I[/url]
One of my favourite videos on how good mixture is achieved, ordinarily there would be a cover over the top of the inlet plenum.