Stu, did you check fuel volume over time with and without injectors on in the end?

Great thread and great info! Kudos to stup for doing the tests and explaining the procedure!

Now to throw the spanner in the machinery:

OEM pancake intake is badly made and flows unevenly to cylinders. The very final touch would be to take off the air-injector plug and connect a copper-tube leading to WBO2 sensor (WBO2 needs very small gas flow to be accurate).

Then you could fine-adjust injector flow to each cylinder to same AFR. Middle cylinders will generally have higher AFR's than others. Also, you could add a tad more fuel to cylinders 1,2 in order to compensate for worse cooling they recieve :)

[QUOTE=beepbeep;4652009]
OEM pancake intake is badly made and flows unevenly to cylinders. The very final touch would be to take off the air-injector plug and connect a copper-tube leading to WBO2 sensor (WBO2 needs very small gas flow to be accurate).
QUOTE]

Won't the WBO2 sensor's accuracy be affected by the back pressure of directly coupling the sensor to the cylinder or will the normal pressure flow of the exhaust be enough to maintain accuracy?

I was under the impression that a WBO2 needed to be in a flow stream for accurate results.

Great idea!

Jim

I had thought accepted the unballanced air flow thought at one time.

However, for the most part I believe that while it is true that if you put a manifold on a flow bench you will see some unbalance at the flow rates they operate at, I mostly believe that once on boost the same amount of air flows into each cylinder as the intake port size becomes a nozzle and when the intake valve opens, the cylinders fill until they reach the same pressure as the intake manifold.

Just my thought. I do not think an of us know for sure.

The way to really do this would be to put EGT's at each primary exhaust tube. Some racers have done this on turbos, MFI, and carbs. Then if you have a cylinder that is running hotter than the others, it can be balanced out.

For now, we are likely best served for getting them balanced like when they left the factory.

Goran,
thanks for your invaluable input. I was thinking along those same lines as the inefficiency of the pancake manifold. I was wondering about the SC 3.0 intake runners with a homemade plenum attached. They're equal length, easily obtainable. Do you know what the size of the primaries are? Larger, smaller than 3.3l intake runners?

If the intake maiflod is of concern it is easyest to just have it Extrue Honed to even up the air flows. Also can make the motor run a little more efficent so you migh pick up a few poines.

I have 2 allen head wrenchs that fit those and they don't have size markings on them. They probably came with something like a steering wheel hub... I guess they are 9/64 or 3.5mm, and yes they were in tight.
They came loose with a little snap and I put them back in tight.

The ones I removed were in a euro fuel head and they are almost black colored steel so I think they are made of 12.8 hardness high carbon steel.
The allen head wrench shouldn't strip out the female points if it fits snug.

A little Kroil and a little courage and I broke them loose.
Thanks.

Now the fun starts...
Keep a garden hose and a fire extinguisher nearby if you have one.

A 6 pack of bottled water for the plastic bottles works good.
It's fun getting the injectors to fit in the bottles without bending the lines.. so get small short water bottles less than 12oz. if possible.

I pulled the plug on the back of the fuel head and then grounded the overboost wire to turn the pumps on and off while the ignition was on and the ignition wires were on the plugs.

It's interesting to play with different heights of the sensor plate to see how much gas comes out.

What does the plug on the back of the fuel head do?

There is a switch on the back of the CIS unit next to the back side of the sensor plate and it turns the fuel pumps off if there is no air being sucked into the engine and the sensor plate at rest while the ignition is on.
It's a safety feature so the car won't burn down if you're in a bad accident and leave the ignition on.

Pulling the plug off it makes the pumps run all the time if the ignition is on.
Then it's easy to turn them on and off by touching the low voltage, non sparking overboost sensor wire to ground where the pumps will run, or leave it in mid air and the pumps shut off.

If thats confusing do a search on fuel pump wiring, overboost sensoer and relay circuts, and the blue fuel head safety switch or whatever they call it.

[QUOTE=911st;4652354] The way to really do this would be to put EGT's at each primary exhaust tube. Some racers have done this on turbos, MFI, and carbs. Then if you have a cylinder that is running hotter than the others, it can be balanced out.QUOTE]

This approach might have merrit.

I can envision getting a 6 channel digital temperature meter with thermocouple wire inserted into the air pump injection ports of each cylinder. Measure the individual cylinder exhaust gas temperture in that fashion and tweak the fuel head to get even EGT's. Cross-check this against your WBO2 sensor in the exhaust feeding your AFR gauge and a person should be able to precisely balance the fuel flow to each cylinder. Get your EGT's balanced at idle and from there make overall system adjustments with your control pressures to center the AFR where you want it. A full system tuning approach.

All theory, of course!

Balance at idle may not necessarily translate to balance at WOT.

There are reasons to run CIS a bit fat. One being possible variances in AFR's per cylinders from ware and or design limitations.

The other is due to the fact that the system can not compensate for things like changes in ambient air temperatures like a good EFI system dose and pull back timming or add more fuel. Even then most makers of new Turbos (i.e. Subi STI...) run them fat (in the 10's on boost) as protection. If one is going to run in the low 12's make sure the system is fuel ballanced and set the CO on a cool day. This will give you more fuel on the hot days and a bit of safety.

Best practices is to have the injectors cleaned and checked for balance. Then, and then, check the head for balance or have it serviced and bench tested.

Could read your spark plugs from time to time I guess.

Not much more to be gained beyond that. Extrude honing the manifold might be the only other thing that may or may not be of benifit.

Enjoy.

I think just machining the downcomers a little bigger for 1, 2, 4 and 6 would be enough.
Has anyone seen any flow data that indicates that 3 and 5 really flow more?

Again, I suspect the manifold is not the restriction, the little tiny intake ports that were made that way in ensure good mix with air of the fuel that sits in the intake port waiting for the intake valve to open. On a normal aspirated motor they can use the piston top to create a swirl to ensure a good mix for better combustion and lower emissions. That is not possible with the Turbo's flat top pistons.

If you have your intake ports open up to 41 or 43mm like the 935's it might be a different story. :)

Another easy way to do this might just be with a hand held infrared temp detector?

Wouldn't buying 6 EGT's would be costly?

How would you know they were all 100% accurate to each other? (Like the problem we are trying to correct :))

Oh, how hot would it need to read?

Sorry for late reply guys,,House refurbing last week or so:(

Nathan:
At wide open meter plate with injectors FITTED my car flowed between 120ml-124ml per 30 seconds(tested twice and results the same both times)..approx all within 3% at WOT...Copied that from earlier,,hope that helps...tested control pressure flow rate also and it was towards upper limit of specs 160-240ml per minute...i was at 220ml..that was the fuel line into the wur.

replied to you pm 911nut.

J fairman.
Be very carefull re-fitting 9/64 allen headed screws back into head as its only alluminium and is a very fine thread which is easily cross threaded especially considering access!

Beep Beep would be good to complete that test as you mentioned or even extrude honing intake and may do this if anything has to be removed in future!

Car made 383 bhp at the wheels last time running 1 bar boost plus my other mods.....Had car on rollers last week and since i have completed flow matching fuel to each cylinder i swear the engine sounds so much sweeter and is now pulling much more harder!!!
Now it made 401.4 bhp at the wheels and on a second run still made over 400 at the wheels(roughly 440-450 at fly).

I am now running a frequency valve dropping control pressure under boost through a Greddy controler and my fuel curve is perfect..
Cruise 14.5 afr, drops into 12's boost onset,11.8afr between 4000 to 5200 and 12-12.2 at max revs...fuel curve line is straight as a die,, so all good!;)

Great numbers Stu, really pleased for you! I take it you've dumped the Digi unit then and gone back to using an adjustable WUR, what's the story there?

"Be very carefull re-fitting 9/64 allen headed screws back into head as its only alluminium and is a very fine thread which is easily cross threaded especially considering access!"
True, the silver color USA heads are aluminum and light in weight.

I have 3 - 930 fuel heads and the one that I removed the button head allen screws from is a black euro fuel head and they are cast iron and heavy.
I used a little L shaped allen wrench that would kill your fingers before you could strip the threads with it :)

It's also alot easier to remove the top center control pressure line from the USA heads because Bosch machined grooves into the sides of the two injector line raised banjo bosses behind it so you can fit a 12mm socket in between them to get at the control pressure banjo bolt.
With the black euro heads you can't fit a 12mm socket between those two rear most injector bosses so you have to use a 12mm box end wrench to get at it and only a thin wall box end wrench will fit in there.
Thicker walled box wrenches like some older sears ones won't fit in there unless you grind the box end thinner.
High quality more expensive box wrenches are thin wall and will fit.

I like the newer aluminum USA heads better because of that, the lighter weight, and they are plumbed with the option to mount a frequency pulse valve between the lower port/side of the differential valves and the return line port on the fuel head.
That allows more options for controlling the air fuel mixture either with the factory 1986-94 lambda system for emissions, or a custom unit with an aftermarket frequency valve controller like "911st" has mentioned in other posts for another way of trimming or richening up the mixture where you want it.

Cheers jonathan,
For the time being i fitted a self build system!

It works perfect and is pretty simple once all is installed,,still using my original wur although the boost enrichment line is disconnected and i am using the greddy fuel injector controller to control a frequency valve which is hooked up in line to wur fuel line.

Basically you control the valve to open up at any percentage at whatever revs versus whatever boost pressure which in turn drops the control pressure to give you more fuel when and where you want it!.

Reliable as you will get and once you programme it thats you.

I thought was going well before but now with this other work i have completed recently it feels night and day again!..

Was away on Porsche club(TIPEC) run the other week there up through glenshee in Scotland etc and even though there was some well spirited driving going on at many stages the car still returned 23 mpg on average of the 270mile drive.
Reckon would acheive a bit better with lighter foot though.