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On a 2276 T4, EMPI long manifolds with 40 mm ITB's

http://matsgarage.com/?p=1014 You can see the manfold and injector angle in the second Picture.

So, would there be any benefit from using the thick phenolic spacers thats used with the stock Djet injection or will the warmup of the manifolds just aid atomisation of the fuel?

Those injectors are so far back from the intake valves, I don't think a spacer would have much effect either way. The angle of the injector looks correct, not too steep or too low.

I suspect the reason for those phenolic spacers was to prevent the fuel in the injectors/rails from boiling after shutoff, which can cause restart issues, esp hot.
Short: Insulation.


In Texas summers, they help carbs more IMHO, (bowls can boil dry just sitting in direct sun, much less from engine heat)
In cold weather, they hurt more than help with carbs IMHO.
If your pressure regulator holds pressure as it should (~20 PSI or better), and/or you have a programmable injection system with a proper pump priming run at key on, which will flush out ~any vapor, there is no issue.
They really don't hurt anything, tho.
They may slightly hurt or help injector aim... but that's pretty minor in this case.
YMMV.

Try it both ways.

Well I can only dream about hot Texas summer days here, a really hot summer day we see about 30-35C and this past summer we had maybe one day upwards of those temps.

Piledriver wrote:I suspect the reason for those phenolic spacers was to prevent the fuel in the injectors/rails from boiling after shutoff, which can cause restart issues, esp hot.
Short: Insulation.


In Texas summers, they help carbs more IMHO, (bowls can boil dry just sitting in direct sun, much less from engine heat)
In cold weather, they hurt more than help with carbs IMHO.
If your pressure regulator holds pressure as it should (~20 PSI or better), and/or you have a programmable injection system with a proper pump priming run at key on, which will flush out ~any vapor, there is no issue.
They really don't hurt anything, tho.
They may slightly hurt or help injector aim... but that's pretty minor in this case.
YMMV.

Try it both ways.

No really....they are not for insulation. The injectors in D and L jet do not physically contact the intake manifold or the head. They are suspended in a rubber grommet in the metal bolt down hasp....and terminate in a viton ring with no injector contact on the intake manifold.....unless and until the injector seals get old and crush down....and at that point they usually crack and leak.

The primary reason for these phenolic spacers is to correctly distance the injector from the back of the valve so that the width of the injector spray pattern/cone is where it needs to be with relation to intake valve diameter.
Try removing the phenolic spacer in a well tuned engine.....and it makes a difference in fuel atomization at idle and just off idle. The engine runs differently. Ray

Interesting...

In that case it depends on your injector spray pattern.
Anyone know the stock injector spray cone angle?

Note they also ran thinner phenolic spacers on WBX...
Seems like they would have just made the manifolds 4mm thicker if it was solely injector aim...

Of course they forgot a lot of lessons learned from the T4 by the time they did the WBX (oil system, particularly the serial through another lifter bore lifter oil feed on several bores like T1, which was probably stupid in 1937, and done right on T4s)

I'm using Bosch 350 cc/min injectors from a Saab 9-5 Aero (brick brown colour) No idea about the spray angle on them but I suspect 30 years of development should make them better than the stock Djet injectors and since I'm not using the stock inlet tubes either its even less relevant then. I'll just run without the spacers to start with and keep monitoring the temp buildup in the intake manifolds, if they get excessivly hot I may add the spacers.

I dont think you will have a problem. Its not just a specific spray pattern. This is primarily a D-jet issue.
Bear in mind that the original problem with D-jet injectors is that they are low impedance and low pressure...comparatively. When they get right up around 35 psi...at higher rpms they tend to revert to a stream. They also have huge pintle diameter. The D-jet had a narrower angle of pintle. The later modern injectors have a wider pintle and spray pattern.

The big deal with this is that D-jet was paired injection. The type 4 head has a pretty long/deep port...when you add in the length across the runner pocket itself. Its like 4" long. They needed just a little more distance to allow the rather narrow spray cone to develop into a proper cloud....and most importantly keep the fuel cloud off the port walls until the valve opened. It was mainly an angle thing with the mounting of the injector.
If you think about it....moving the injector inward without changing its angle in its mounting clamp...produces an injector aim that is more angle slightly to spray more on the floor of the port.

This was only important at idle and low rpm. With the paired injectors ...two ports already run wet in D-jet.

Once you get above about 1500-1800 rpm...its happening so quick that it just does not matter.

The reason it mattered with D-jet as the factory delivered it...is that the factory state of tune was slightly rich in the first place to prevent excessive lean at part throttle. The rich idle made enough of an issue that they worked hard on atomization and to keep the fuel off the port walls from everything I can tell.

and...I figured most of this out...because if you experiment....with injector angle on D-jet while you are tuning it leaner for better throttle response....injector angle and atomization are really critical elements in the system when tuning. They make a big difference in idle quality and off the line throttle response. And...throttle response from injection pattern...makes a difference in how the outer full load stop on the MPS can be tuned, Ray

Thanks for sharing your knowledge Ray. Now I've learned something new today.