CIS injector flow limitations?
 

Some of us have been debating if the injector is a limitation to how much fuel we can deliver.

I tend to believe they are not.

With EFI injectors, gross flow is determined at the injector based on injector size (20, 30, 55lbs...), fuel pressure, and how long the injector is open (duty cycle).

With CIS flow is determined by the CIS fuel distribution head. The upper lower pressure differential acting on the diaphragm and springs, the system-pressure level, and the internal orifice size -- mostly being what determines our gross fuel delivery capacity.

So, as long as the injector orifice is not smaller than the heads internal orifice, I would not expect a larger injector to be a source of increasing gross fuel delivery.

However, my "theory" is not enough to convince even me. What we need to do is some type of test.

What would this look like.

Maybe test a fuel head on an injector bench with the metering pin at the max delivery position without an injector.

Then to test a CIS injector at the same pressure and make a comparison.

I might suggest a pressure just under the system pressure regulator level to take that out of the equation and ensure the head orfice and injector see the same pressure.

What do we think?

I contacted an Injector Test and cleaning company with some questions to see if he could help.

This is his reply:

If we can get together the different 930 injectors (US, Euro, and 3.6) I would be willing to pay to test them against each other. This is not the best test but it might give us some clues.

If Pelican could source a new one of each for the cause, it might result in a bunch of sales should say the 3.6 injector proves to have more gross flow potential. If so, it might be a better fit with a HF fuel distribution head.

I can maybe contribute some here...
Recently when flowmatching injectors on a customers car,i found several failed spray patterns...Swapped his failed standard 1988 930 euro injectors with a few spare euro standard 3.3 964t ones i had and i am 99% sure if memory dont fail me with the 964t ones in place they flowed quite a bit less fuel!

Different orifice size and part number on the injectors also.

Spray pattern and cracking pressure seem to be the recommended tests for CIS injectors.

I guess if they do not all "crack" at the same point, the week one is going to drain down with shut down.

Is there a way to just measure the orifice size on different CIS injectors?

I have not had one in my hand for a long time.

Keith,

I buried with work right now and can't contribute much. You might consider calling John at specialitauto.com. He has more Porsche CIS parts and info than anyone in the US.

Cole

Keith

That's a good idea to create this thread ! :)

Ok, on my side I have 6 pces of 3.6T injectors that I bought with the a complete 3.6T kjet body & head.

As you know, my clutch is failing and I need to replace it. This will be done in few weeks.

As the car will be at the workshop and as I scheduled to change my injectors ( using the new 964T 3.3 injectors) in the mean time , I will take some time to make comparison.

It will be the same head , same fuel pressure, same everything .... I will push the metering plate at full excursion in both case. So I will just switch from 3.3 to 3.6 injectors.... Then we will see if the flowed fuel volume is the same or not.

In the mean time, as my kjet will be fully accessible, I will measure exactly the cone OD /shape and compare it with the 3.6 cone.


How do you think ?

Can't ask for more than that ;)

Thierry,

You are the man!!! :D

Might test with half the injectors 3.3 and half 3.6 at the same time then poor the gross from each side into its own measuring beaker.

Or what ever you think is best.

Just use cheap set of digital scales (£10/$16) and there is no need to measure anything in a beaker..Far quicker and more accurate!
1 gram = 1 ml

I the next few weeks i could find out the difference between standard injectors on a euro 1978 3.3 turbo i have coming in and then test with 1992 3.3 964 turbo injectors in place.

Dude, your post on measuring CIS injector flow is really good so I'm pasting the link to it.
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/461843-meter-head-flow-adjustment-question.html

Using those common 12 oz. ribbed drinking water bottles from a 6 pack is good for quick comparing the fuel delvery/level form each injector.

J,

Agreed. Everyone should consider doing this. Maybe even with there valve adjustments.

I love your suggestion for testing the cam spray bar for blockage. (Lost a couple lobes my self once.)


T,

I do not know if it makes any sense to measure fuel delivery without any injector at all against the 3.3 & 3.6 units on the end of the injector line as a reference?

Exciting stuff!

Thanks Cole and JF for the refural to John at Special T. They specialize in CIS FD heads and WURs for Porsche and other cars.

I asked his opinion of the injectors being a limiting factor.

Here is his reply:

The specific gravity of water is 1.000 g/ml. The specific gravity of unleaded gasoline is 0.739 g/ml. Picky point I know but noteworthy.

Cracking pressure and spray pattern are the parameters I use to reject a bad injector. Flow rate is used to adjust the fuel head.

Just a thought, addational pressure is probably the best way to get more fuel.

There are a lot of potental restrictions along the fuel delivery path that could become a bottle neck.

Enlarge the metering slits and we may just get fuel earlyer but not any more. Ream the orfice's and the injector might not let it pass.

Bumping system pressure and playing with the upper and lower head pressure differential keeps these issues from arising.

MFI runs at around 230psi so we should have room if we can get fuel pumps that can accommodate us. Seems two 044's linked can get us to maybe 160psi. Also seems the stock pumps start to top out around 100psi or so.

Just a thought.

Not picky at all, Brian. ;)

I remembered water's density to be 1 metric tonne per metre cubed, and that oil floats on water (i.e. is less dense). But didn't have the exact figures, so let is pass.

However, relative masses were all that was necessary for Stu's fine work on Cylinder Fuelling ratios.
:cool:

Not sure what the S/G of water has to do with "CIS injector flow limitation"?

Here is the guy that builds the HF heads replyed about injector flow:

The injectors don't seem to be a restriction from my experience.

I've mentioned this experience before:
When I first put one of Larry's M007 flowtech modified USA fuel heads on my car after installing an HFS turbo the car would not run above 4000rpm at all because it was getting so much fuel.

The Brian Leask adjustable control pressure regulator allowed me to raise boost control pressure alot higher, and steady cruise control pressure a little higher than what Brian set it up for before sending it back to me.
After doing that the modified fuel head works quite nicely on my car which has 964 cams, B&B headers, Garretson longneck intercooler, and 1 bar wastegate spring.

The M007 flowtech modified fuel head did not make the idle mixture any richer than the stock fuel head. The idle CO did not change much at all after I installed it. This is why I think he tapers the metering slits in the control plunger cylinder to a larger diameter towards the top when he CNC enlarges them. I havn't removed it and measured them so I don't know though.

I forgot to mention in an earlier post on these Flowtech M007 fuel heads that he also adds a thin shim to the shim stack under the spring in the fuel heads system pressure regulator to raise system pressure to 97psi on the fuel head I have.

JFairman,

Good heads up warning of the need to rebalanced the WUR / control pressures with a HF FD.

I knew we would have issue with the AFR curves with the first head I talked Larry into doing for Brent930. It flowed 17% more fuel at all points along the metering pin travel. No issue getting idle right, cruse was a little issue, however first on boost was the biggie. We tried getting control of it with the WUR but could not get the first boost enrichment where we needed it. He set his WUR to delay enrichment till a higher boost level but it blew through and it only delayed enrichment a small amount. He adjusted the on boost enrichment CP higher and could make improvement but lost the high rpm enrichment we needed. We ran it w/o any enrichment and got a near perfect AFR curve except it went lean at the top but what a nice on boost AFR through the mid range even without lower CP on boost. That was when I suggested using an rpm switch to clamp the boost signal until much later in the RPM range.

Imagine my surprise to come back to the boards 5 years later to see such a large adoption of the HF fuel distributor and the MSD switch/ solenoid enrichment clamp.

We got some 17% increase if fuel with I think just readjustment of the spring tension and the height at the internal orifices along with higher system pressure (which was not a big secret at the time) without any machining or hard mods.

I have no idea what he and Stephen came up after the first head to get more fuel except for modifying the Lambda head to work like a non Lambda head. That was brilliant!

My dream at the time was to try building a HF FD that kept the Lambda function and dial it in with a 25% duty cycle at the frequency valve. Then bump it up to 75% to get even more fuel than the non Lambda head. Unfortunately, my turbo head was changed to a euro head and I could not find a reasonable C2 Turbo core at the time on the cheap.

Have you confirmed any of the other hard mods like machining to the slits or any other? Stephen or Larry did say they had not done anything to the pin but not sure about the other.

If the slits are larger in gross than the internal orifice that could just accelerate fuel delivery without adding to the total. If the orfice can flow more, such a mod might help w a restriction.

A perfect taper on the slits it could tune and fatten up the later part of the pin travel so that we might not have to play w the WUR.

Seems system pressure and reducing restriction from the fuel regulation function around the orifices is what has gotten most of our increases. Getting more might require a larger opening in the orifices if they are the bottle neck. Maybe then the injectors would become the bottle neck if they are not already.

However, I could be wrong on this but that is how I learn.

----

Many experts have told us fuel is not the ultimate restriction, air is.

It was not until I started thinking about your comment about the turbo snorkel restriction that I stared thinking about this and start to understand that we are approaching the air flow limits of the CIS. Appreciated!

Do or anyone know how large the exit on the metering assembly?

It seems that will set the limit of how large of Turbo intake we can go up to and only if we do not have restriction in the path way to the turbo.

Unless come up with some type of air bypass around the metering system that should set the ultimate limit as Turbo efficiency drops off quickly when it tries to suck air through a to small straw increasing the pressure-differential about the compressor wheel.

Anyway, back to the topic at hand. It seems the injector has up until now, not kept increases in fuel we have found at the head from making it through the injectors.

I am worried that at the higher flows, if the injectors are near becoming a restriction, they may contribute to unbalanced fuel delivery. If the 3.6 injectors are bigger they might be a good insurance. Your encouragement of doing the injector balance test is a very, very good idea.

K