Injector line routing

[Huw Powell]

>  > What about the o-rings?  What is the purpose of the black ones?  Do they
> just pilot the injector further down in the head?
> 
> Oh, yeah. Forgot. They do help locate the injector tip but,
> I believe, they also provide an air seal for the air "shrouding"
> pressure. Higher pressure air from before the throttle body
> is routed into an air passage in the head which feeds each
> injector position. I don't have one in front of me to verify this,
> but there must then be small air openings in the injector body
> between the two o-rings to allow this air to be forced through
> the injector. The purpose of the shrouding air jet is to further
> atomize the spray of fuel as it exits the injector tip.

I thought the shrouding air was to cool the injectors, to improve warm
starting.  One of the many little things done around '84 to try to make
the cars run a bit better!

Anyway, now that i am back from looking at Brendan's freshly pulled NF
head and some grotty injectors, let's follow that air.  It is always
available from before the throttle plate, so is drawn most at idle.  It
goes to a nipple in the middle of the head which is plumbed to a 1/4"
dia. manifold running along the head to the outside of each injector
seat.  the injector seats have a couple of holes in them to allow this
air to flow into the space around the injector and inside the seat
tube.  Then the only place it could go, due to the injector tip being
sealed by the little o ring to the seat, is through tiny spaces in the
injector shroud and then into the intake valve area by way of the tiny
ring of space in the center of the shroud, which is also where the fuel
flows.

So I would have to agree, it might also function to improve or alter the
spray pattern as well as cooling the injector tip directly.  When you
are off idle though, especially much, not much air would be drawn
through since the direct route would be available.  at idle there would
be a strong vacuum at the intake port to draw this air from its source.

> 
> This is still metered air so the a/f mixture control has no problem
> with this small amount of air that bypasses the throttle plate.

agreed.

anyway, what the heck was the question?

If you have your injectors out, whether to replace or just play, all new
seals and even seats (they should be cheap...) would be in order.

big fat seal at base of injector, little one at tip (usually premounted
on new injectors and tough to replace), and the seal for the seat as it
screws into the head.

now I have to wash my hands.  how come engine parts get to darn dirty???

-- 
Huw Powell

http://www.humanspeakers.com

http://www.humanthoughts.org