Information about the 934 CIS Injection
 

Hi there!

I´ve read some posts here and I can see great interest in the 934 race cars CIS system and some frustration due to lack of information so maybe I can give you some help.

The system are race parts from Bosch motorsport. Usually Bosch product numbers starts with a "zero" but motor sports products and prototypes starts with a "B" or includes an "E"
Volvo motorsport used exactly the same system on their Volvo 242 Turbo Group-A race car and Peugeot on their 205 T16 Group-B rallycar as well.
I have a complete race CIS system so let´s take a closer look.
I will borrow some pictures that I found here.

We start with the air flow meter. Take a closer look on these two pictures and you will see that the housing differ a litte bit.

http://forums.pelicanparts.com/uploa...1331769573.jpg

http://forums.pelicanparts.com/uploa...1331769603.jpg




The race car used a specially designed air flow meter with changeable cones with different sizes to suit different tracks, height and power output.
The Number on this unit is B 438 120 363 928 001

http://forums.pelicanparts.com/uploa...1331770213.jpg

http://forums.pelicanparts.com/uploa...1331770234.jpg

http://forums.pelicanparts.com/uploa...1331770256.jpg




The fuel distributor. V8 heads modified by Bosch with bigger metering slits and nozzles. Early ones cast iron and later aluminum heads.
Volvo used the aluminum model and it can support fuel for over 400 Hp with only 4 outputs and over 600 Hp with 6 outputs.

http://forums.pelicanparts.com/uploa...1331771932.jpg

http://forums.pelicanparts.com/uploa...1331771953.jpg




Here you can see the different size of the nozzles between the stock 911/930 head and the race head. I don´t have any pictures to compare the metering slits.

http://forums.pelicanparts.com/uploa...1331772401.jpg

http://forums.pelicanparts.com/uploa...1331772421.jpg

Greetings from Sweden!

Daniel

Excellent first post and welcome to Pelican. Thanks for checking in.

Can I ask where you got these parts?

http://forums.pelicanparts.com/uploa...1331774754.jpg




Control pressure regulator no. 4 on the drawing.
Manually adjustable 3-5 bar. Volvo run with 3.8-4.2 bar. The number on this unit is B 280 500 049

http://forums.pelicanparts.com/uploa...1331774806.jpg




VDO Pressure sensor no. 2 on the drawing.
Connected to the control pressure regulator and a gauge in the compartment to measure and read the control pressure, the most important pressure.

http://forums.pelicanparts.com/uploa...1331775401.jpg




No. 7 on the drawing is the return from the recirculating relief valve.

Greetings from Sweden!

Daniel

Daniel, where have you been hiding? I am fascinated by the interchangeable "cones" on the fuel head (more appropriately, I would call them venturies). Those would definitely change the air flow characteristics and metering arm deflection. I think we're on to something here....

Danial:

Welcome and a million thanks !!!!!!!!!

I was familiar with the fact that the 934 CIS was different and that
the fuel heads would flow more fuel as well as having a different air
metering assembly. The problem was I could never find any information
about either. The information you have provided is priceless. And your
pictures are worth a thousand words. I know the 934 unit would
be serious overkill for a street car, as well as being way out of my price
range, but the pictures and information provides much clarity.

That is my 930 CIS in your picture and as you can tell I am a die hard
934 fan. My build is, as I stated, a street car but I tried to make the
modifications from the 934 that I felt could be incorporated into a street
car and would enhance performance while being true to the 934 Marque.
I installed the 934 headers and relocated the turbo and CIS in an effort
to reduce lag and shorten the intake track. The CIS itself has had the
the tapers inside metering cone modified to change the fuel curve.

The issue I have been trying to solve is the optimization of the metering
plate arm travel to insure we are getting all the fuel available in the stock
unit. A builder in Oregon " Jeff at Rothsport Racing" discovered, with a
stock 930 engine on the dyno, that at full throttle you could reach in and
push the air metering plate down further and actually find more fuel that
was previously unused. Jeff found that modifying the top of the metering
plate allowed full travel of the arm and resulted in more HP. Jeff felt that
the stock air filter was not allowing enough air to completely get all the
travel out of the metering arm. We were trying to further investigate the
934 air intake configuration to see if we could solve the issue.

Again I thank you for the incrediable information and if you have any
insight on the extra arm travel I would greatly appreciated.

Cole

Cole,
I've been thinking about this a lot since the recent threads on the Bosch metering units. Regarding what Jeff at Rothsport Racing discovered; if the metering plate will travel further down after pressing on it, why wouldn't lowering control pressure do the same thing? Afterall, when there's 0 psi control pressure, doesn't the plate naturally lower to the bottom of the plenum due to gravity?

Dave:

Good to hear from you !!! Hope all is good with you and yours !!!

As a matter of fact I have. I have a DWUR that I have never installed and with the issues they have had I don't feel comfortable doing a fresh start up with it so I sent my WUR out to Brian to get it modified to adjustable. I saw Leask's plug on this new RPM controlled solenoid valve and it got my wheels turning about
possibly using it to chop the control pressure at high RPM. Thought I would get my feet wet with the new WUR and then give Leaks a call and pick his brain about using the RPM Solenoid to quickly drop control pressure up top.

Cole.

I had one of those B280 500 049 gizzmos on my beast when I got it - between my WUR and fuel head on the CP line. Could never work out what for. Took it off.
My part # search told me it was a Mercedes fuel enrichment device - mine is fractionally different and has Bosch # 0 280 161 007.
But it looks like it allows another adjustment to the CP. It is basically a spring loaded/adjustable diaphragm which the CP fuel runs across.
Cole, I KNEW you would be dribbling over this post. Wipe your chin.
Daniel - TELL US MORE. Don't leave us hanging here. Where does Cole get this stuff?
Alan

willtell:

Thanks! Very hard to find but I found it here in Sweden it´s meant for the Volvo race car.

Mark:

Yeah I like it too!

Cole:

You are welcome I´m glad to help!

Why do you need that exta fuel is it running lean?
Do you need extra fuel on all rpms or just on full throttle?
If you just need it on full throttle then I can give you a tip, a trick Volvo did.
They took a frequency valve but instead of being connected to the lower chamber on the fuel distributor like normally they coupled it in parallel with the control pressure regulator, or in your case the WUR. Then when it´s operating the control pressure will drop. You just have to find a way to trigger it, for example a pressure switch, rpm switch, nock senor, manually etc.

Picture of it installed on a Volvo race car.







http://forums.pelicanparts.com/uploa...1331865706.jpg

Daniel

Daniel:

The reason there was so much interest in the 934 set up is that above about 350 HP the stock 930 runs out of fuel and goes exceptionally lean.

It was found that during a recent 930 dyno pull at full throttle the metering plate could be pushed down further using a long screw driver. In other words the metering plate will not go to the end of it's full travel and thus is not allowing all the full fuel available to be used. On this particular 930 build they added a flap of some kind to the top of the metering plate, which allowed full metering arm travel, and gained significant HP without a lean condition. The tuner attributed the fuel shortage to the intake air not being sufficient to get full travel of metering arm. I am trying to make sure I get full travel of the metering arm and accessing all the available fuel.

The interest in being able to get full fuel by getting full metering plate
travel led us to trying to find out what modifications were done on the 934 CIS that might give us the answer. Due to the fact there was never any definitive
information on how the 934 CIS supported 480 HP we were speculating until
you posted.

The frequency valve addition certainly gives us another viable option !!!!!

THANKS !!!!!!!!!!

Cole

Alan:

You are correct, I've been drooling over all this since Danial posted. This
clears up all the questions we have had about how a 934 got more fuel.

I realize the 934 CIS is impractical for a street car but also now
understand how it got more fuel. The multiple air metering heads tell us a
lot because we know more air means more fuel as long as more fuel is
available.

What we have seen with Daniel’s kind contribution is the lengths the factory went to in getting enough fuel. Obviously the air metering modifications are the answer. Which also lends credence to Jeff’s statement about more inlet air. I pulled the next few paragraphs from my old files and they are interesting reading when you look at the 934 CIS mods. The recontouring of the funnel
That Steve Wiener has done for years now makes a lot of sence. Steve did mine for me a couple years back.


The intake air quantity serves as the main actuating variable for determining
the basic injection quantity. It is the appropriate physical quantity for deriving
the fuel requirement, and changes in the induction characteristics of the
engine have no effect upon the formation of the air-fuel mixture. Since the air
drawn in by the engine must pass through the air-flow sensor before it
reaches the engine, this means that it has been measured and the control
signal generated before it actually enters the engine cylinders. The result is
that, in addition to other measures described below, the correct mixture
adaptation takes place at all times

The basic adaptation of the air-fuel mixture to the operating modes of idle,
part load and full load is by appropriately shaping the air funnel in the air-flow
sensor If the funnel had a purely conical shape, the result would be a mixture
with a constant air-fuel ratio throughout the whole of the sensor plate range
of travel (metering range). However, it is necessary to meter to the engine an
air-fuel mixture which is optimal for particular operating modes such as idle,
part load and full load. In practice, this means a richer mixture at idle and full
load, and a leaner mixture in the part-load range. This adaptation is achieved
by designing the air funnel so that it becomes wider in stages. If the cone
shape of the funnel is flatter than the basic cone shape (which was specified
for a particular mixture, e.g. for ì = 1), this results in a leaner mixture. If the
funnel walls are steeper than in the basic model, the sensor plate is lifted
further for the same air throughput, more fuel is therefore metered by the
control plunger and the mixture is richer. Consequently, this means that the
air funnel can be shaped so that it is possible to meter mixtures to the engine
which have different air-fuel ratios depending upon the sensor-plate position
in the funnel (which in turn corresponds to the particular engine operating
mode i.e. idle, part load and full load). This results in a richer mixture for idle
and full load (idle and fullload enrichment) and, by contrast, a leaner mixture
for part load.

I was thinking if we take the information here there are several things
that could be done to improve stock 930 CIS performance.


Cole

Cole:

Then I have important information for you!
The metering arm only needs to travel 37 +/- 1 mm down to open the hole metering slit. That´s about 8 mm before full travel.
If it travels more than that the control plunger goes upp too high and starts blocking the fuel from entering the barrel.
One old engineer at Volvo motorsport told me that, and I have checked it by my self, and I´m pretty sure it´s the same with standard Porsche and MB units.
see pictures.

Have you tried to increase the fuel flow by adjustning the spring tension on each outlet on the distributor?
If that´s not enough then you have to raise the system pressure.



http://forums.pelicanparts.com/uploa...1331874157.jpg

http://forums.pelicanparts.com/uploa...1331874176.jpg

http://forums.pelicanparts.com/uploa...1331874205.jpg

Daniel

Hi Cole, that's not what the RPM solenoid is for, see it as an on/off valve cut into the vac/boost line from your manifold to your WUR. Let's say you put a 4200rpm chip in it, this means it will open at 4200 RPM. The point being is that vac/boost line going 'unrestricted' to the WUR allows to WUR to enrich the fuel FAR too early, hence the huge 'fat mid range' fuel curves we see on a lot of CIS cars.
Main reason being, the stock system had that lazy old 3LDZ turbo, restrictive exhaust etc etc etc..... So it did a decent job on a stock engine.
With a quicker spooling turbo, a freer flowing engine all round, direct manifold pressure to the WUR will see premature dumps of fuel in the mid range.
The RPM solenoid irons this out. When you first Dyno the engine, you may see it getting pig rich at a little over 2000 RPM, then start to come good again up around 3800 RPM. So you fit a 3800 chip in the solenoid and it stops the manifold pressure getting to the WUR, hence preventing the diaphragm moving and dumping all that unnecessary fuel in, until of course you need it, then the solenoid opens, you may get a simigin of over richness for a second, and then you are back on track.

Look at leask's graph below, The blue line on each graph (the fuelling bit at the bottom of each Dyno sheet obviously) shows the run without the solenoid connected, just unrestricted manifold pressure going to the WUR. Then the red line shows the RPM solenoid holding off that manifold pressure until the fuel is actually needed....... You couldn't really ask for a better fuel curve really, without EFI that is about as good as you can get, and frankly as good as it ever needs to be, more power, less fuel, happy days ;-)

http://i139.photobucket.com/albums/q...0/7faf66a2.jpg

That's what the old Andial fuel enrichment systems did. I had one, it worked pretty well actually, but adjustable WUR's enable a better fine tune.

"Have you tried to increase the fuel flow by adjusting the spring tension on each outlet on the distributor?"

If you do that with a painted cast iron euro fuel head be very careful and only turn the 6 individual 3mm allen heads (that are under the 4mm allen head button screw covers) that adjust spring tension pushing down on the stiff stainless steel individual injector final fuel metering diaphram a tiny bit clockwise at a time or the metal diaphram will possibly be dented or dimpled and that'll damage it's ability to accurately and consistanly meter fuel against the small fuel orifices above it permanently.

You also have to do an injector flow test on the motor while you have the injectors inserted into 6 individual bottles to collect the fuel sprayed from them. 8 ounce plastic water bottles work good for that.

Then measure the fuel in the bottles while adjusting so all injectors flow equal amounts. If 2 flow more than the others put those injectors in #2 and #5 because those heads and combustion chambers run hotter than the rest.
It's a slow tedious process because you have to remove the injector line banjo fittings to remove the 4mm plugs underneath and adjust the 3mm spring tension adjusters over and over a little at a time until you get them as close to each other as possible.

With an aluminum lambda fuel head the diaphram seperating the upper and lower chambers is made of a very flexible synthetic material instead of stainless steel and it has 6 round fuel metering discs bonded to it under the upper chamber fuel metering orifices that lead upwards to the injector line banjo fittings.
That means you have alot more final and individual injector fuel metering adjustability with a lambda head and it is why the aluminum lambda fuel heads used from 1986-1994 can flow more fuel than a cast iron euro fuel head.

The aluminum fuel heads also weigh alot less than the cast iron heads and they won't rust in the bottoms of the lower chambers when water gets in there and stays there because water is heavier than gas.
That's where the rust people find in the conical CIS injector fuel screens is probably coming from. The stock fuel filter would stop rust particals coming from the gas tank and any that are small enough to pass through it would go right through the 6 fuel screens around the control plunger cylinder that fuel flows through entering the cylinder and also the conical fuel screens in the injectors.

"If that´s not enough then you have to raise the system pressure."

I know hydraulic control pressure and lower chamber pressure have nothing to with each other and are isolated from steady system pressure by small fuel orifices but hydraulic control pressure fuel pushing down on the top of the control plunger will go up at the same time fuel system pressure is raised so the control pressure regulator will have to be adjusted to return more fuel to the tank to lower hydraulic control pressure.. if you want more fuel from the injectors.

Another modification along with the rest of them to get more fuel is enlarging the 6 fuel metering slits in the control plunger cylinder wall that lead to the 6 individual upper chambers. They can be enlarged in a tapered fashion. I don't know if anyone actually does that but it would probably require CNC machining to enlarge them all the exact same amount.

Daniel

Great inputs and pictures from you !

I am also agree with your information concerning the metering arm travel . There is no any "hidden" fuel flow additionnal capacity by trying to get more excursion !

Yes I agree with Jfairman the later aluminum distributor is a much better choice!

Thierry25:

Thanks!

I changed my post, I did a control today it is 8 mm before full travel measured from the center screw and straight up or 37 mm down from its rest position.

Volvo did this on some cars. They drilled one of holes that holds the distributor in place straight through and installed an adjustable stopper against the counter weight so the arm only could travel 37 mm.



http://forums.pelicanparts.com/uploa...1331943876.jpg




Picture of a very early car they used a Porsche 928 air flow meter and a MB V8 aluminum distributor with two outlets connected to one injector to get enough fuel. Same here.


http://forums.pelicanparts.com/uploa...1331944207.jpg

Daniel

Daniel:

One thing for sure is with all this information I can forget everything
I read, herd, supposed, or was previously told about 930 CIS. I sincerely
appreciate all your help with this. I at least feel I have a valid starting
point. I can set the correct metering plate travel, dial in all the pressures
correctly and then work from there. I have an Innovate LM-1 logging all
the pertinent engine parameters so I should be able to make sense out
of all this, finally.

While we are here have you got any information on that metering plate
cone that can be seen on top of the metering plate on my motor ( the pic
you posted earlier) ?

THANKS !!!!!

Cole

I ran across this issue when tuning my CIS last year. I increased the system pressure to max but no changing of boost control pressure would allow the system to run in the sweet spot of 11.0 - 12.2 afr. It was pig rich all the time. My engine is stock so I couldn't use the extra fuel. When I dropped the control pressure to minimum spec all was well and now runs like a raped ape.

Man, this is good stuff! Thanks for sharing!

Out of curiosity, what system pressures have you tried, and what do you run now?

6.7 bar was a no-go for reasons stated above. Currently running 6.1 bar and the engine likes it.

Great thread and has got me interested.
Once you flow balance all fuel to each cylinder in my opinion there is no need to go as rich as 11.0 Afr,the sweet spot is a bit leaner than that.My +400 whp 3.3 turbo barely sees below 12.0afr through midrange,maybe at lowest 11.8 through midrange and pulls cleaner/harder at those settings and has done for the last 2 years plus after several years of fine tuning and comparing results on mine and many several other 930 I have tuned.
Some excellent info coming through from this thread,keep it up ;-)
I am still a total believer in retaining cis on our vehicles if set up/tuned correctly as the engines can run perfectly with no real negatives if you plan to stay below 450 whp or maybe a bit more hp as threads like this maybe prove to us.

With all camera tech available nowadays and also editing software etc it would be a really interesting to see if someone could install a small bullet camera in top the air box above the metering plate and capture its movement in different shaped variations( cones etc) and log it along with obviously AFR ,boost rpm etc to see the effect airflow has on top and underneath it..just thinking out loud and this will prob never happen but it would be cool to see

I've thought about that and never done it but you could do it with just about any small pocket point and shoot digital camera with macro and video functions, and that's probably all of them these days.

With no air cleaner in place you'd mount the camera at a slight angle above the CIS air flow meter somewhow and also a 12 volt light or flashlight lighting it up. A small tripod with adustable leg angles and some bungee cords and duct tape to hold it and the light in place would probably do it.

Then start the video recording, get in and drive the car. The sound of the motor on the video would help you estimate throttle position, boost, and rpms from previous experience during playback.

I played around with my mixture last fall. I first tried 12.0 afr at 3000 rpm, ending up at 12.8 at 6000 rpm. Just for fun (and on the advice of an old engine calibrator that I work with) went to 11.5 at 3000 rpm, finishing up at 12.3 at 6000 rpm.
The car reaches 6000 rpm at little faster at the richer setting according to the data but it also seemed faster from a butt dyno perspective, so I would agree with you, Stu.

Here is a flow chart of Bosch CIS fuel distributors and all 911/930 distributors are listed. I guess the flow rate must be the factory setting from Bosch.




http://forums.pelicanparts.com/uploa...1332109911.jpg




Cole:

Do you have the 037 model?
Do a flow test. It´s very easy especially for you with your flexible fuel hoses and you don´t have to include the injectors, just put the hoses only in bottles, start your pumps and push the air flow meter down for 60 sec and then measure.

Fuel req. per injector:

6 cyl 300 bhp fuel req. 250cc +/- 10% = 225-275cc/min/cyl

6 cyl 350 bhp fuel req. 292cc +/- 10% = 263-321cc/min/cyl

Daniel

Cole:

No I don´t have any info about the metering plate cone but I can ask a guy at a Swedish forum, I will return with an answer.

Daniel

Pretty good acheiving those figures,way better afr than what it came with from factory.good going mate ;-)

I had these pics saved and was told it from a 934 style race car. They could be wrong but either way it looks quite different from a 930 air meter assembly.

http://forums.pelicanparts.com/uploa...1332135902.jpg

http://forums.pelicanparts.com/uploa...1332135917.jpg

http://forums.pelicanparts.com/uploa...1332135926.jpg

The secret is revealed!!! ;)

Daniel

Cole:

You gotta see this!!! :eek:

Daniel

Stu & Paul:

Great to have you two jumping in here !!!!! Great stuff your posting, it
gives us some real world numbers to compare to.

Ben:

That has to be off one of the race cars that Daniel has refereed to that
used the factory race CIS. Really an interesting metering plate cone on
that one, and defiantly one we have never seen before.

Daniel:

Man, your blowing my mind here, what a fantastic wealth of information.
Can't thank you enough this stuff is priceless !!!!!

My car is an 80 ROW 930 and it does have the 037 fuel head. I am 2-3
weeks away from pouring fuel in and starting to dial in some settings,
makes all this very timely. I'm going to be installing the new adjustable
WUR also. Once I get That done I'll see what the flows look like and get
them dialed in. Can't thank you enough for all the help.

I'll be looking forward to hearing what the next big surprise is !!!!!!



Cole

Hello Stup !

100% agree with you !

Here is measurement example with fat mid ( stock CIS behaviour ) VS correct AFR (with my CIS controller ).... The torque difference is clearly visible.

http://img231.imageshack.us/img231/4...puissances.jpg

The engine is much less responsive with too fat AFR.

Stup and Thierry: So you guys don't worry about the middle cylinders possibly getting more air and if fuel is the same they would be leaner. I wish someone would measure the AF at the headers.

Hello Smurf

How many % do you estimate the difference between middle and external cylinders ?

As you said, no one has made the real AF measurement at each output ? So how can you believe there is a strong difference between middle and external ?

Hi guys!!
Good to be back posting on interesting threads like this one with fellow enthusiasts;-)
I have not measured afr or egt's at each individual cylinder,measured injected fuel though to each individual cylinder on partial and full throttle and got this to less than 2% difference between all 6 cylinders after some adjustments via meter head...what I can confirm though is I removed my headers last year and the colouring of each individual header port looked the exact same and perfect colour,it just so happens I am removing my headers again tommorow to fix oil return tube leaks so I will try take picture to show the even colouring on each port,with this evidence I would then presume the air flow in each cylinder can't be that far out and must be pretty even

We hear lots of anecdotal evidence of that being the case but I've never seen any data to suggest it. Someone would have to have a wide band O2 sensor on each cylinder to verify this.
The assumption is that the middle cylinders would get more air because the intake path is shorter. That would only be the case of all intake valves on all cylinders were open at the same time, which obviously, they are not. I'm sure the flow under running conditions is more complex that I have just portrayed it to be so the truth might lie somewhere in between the two models.

I have asked about the stock 930 IM flow before with no replys and I haven't found any info over other sites either.
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/551523-stock-930-im-flow-numbers.html

I'm not saying 930IM flows unequal but carrera manifold seems to. It's a bit strange that there is no real info available about this even after 35yrs! It's true that boosted IM kind of softens the impact of flow test numbers.

Chris (tk) said he had asked for the 930 flowcharts from EH but could not get any. That 'could' imply that there was not much delta between the ports either?

Here are some flowcomparisons for the carrera IM:
http://forums.pelicanparts.com/porsche-911-technical-forum/198441-extrude-hone-worth-2.html

Copy paste below from that thread.
****************
Here's some real data for you, rather then a bunch of opinions and theories:

Before and After CFM on my 3.2L plenums:

#1 - 197/322 +125 CFM gain
#2 - 313/335 +22 CFM gain
#3 - 227/331 +104 CFM gain
#4 - 197/348 +151 CFM gain
#5 - 313/339 +26 CFM gain
#6 - 233/335 +102 CFM gain

********************

1 257.1 290.3
2 253.2 298.4
3 250.9 297.7
4 264.7 294.6
5 250.4 300.6
6 260.8 297.1

Sorry this has taken so long, Cole.
The dang thing just wont let me post the file.
So I have taken some pics.
This is out of a gen factory 934 man.

http://i1188.photobucket.com/albums/...ilips/0012.jpg
http://i1188.photobucket.com/albums/...ilips/0022.jpg
http://i1188.photobucket.com/albums/...ilips/0032.jpg
http://i1188.photobucket.com/albums/...ilips/0042.jpg

Not sure if this is of any help.

Cole, I can get you a copy of the factory info if you want.
A good friend of mine has a set.
He wont let them out of his hands, but I can get a photo copy for you.
Let me know if you want them. :)

On my build thread we were discussing Jeff's comments about
more air and the issues with insufficient air flow with the stock air
cleaner. We started looking at the original 934 air intakes and
discussing what we thought the theory was behind their design.

Marty / Copbait, who is a real turbo guru, mentioned he also
had a lot of interest in air flow, blowers and fans. He graciously
offered his learned opinion on the best properties for optimum air
flow. His explanation and comments lent credence to what was
actually used on the 934's and why. He also expounded on what
would work best if applied. This is what Marty Posted.


Cole-

"The plate weighs air mass flow.

What I see is basic optimizing of inlet conditions into the metering plate/orifice to eliminate turbulance. Turbulence in this location at higher mass flow could prevent proper metering. A bell-mouth flow nozzle and straight section of tubing (ideally one diameter in height) will accomplish this. Think velocity stack but stubby. (This is not what Brian has with his filter swap.) Probably could find one sold for a four barrel carb.

Looks to be a flow nozzle under the screen in the dirty engine 934 shot. You are not tuning a pulse, you are simply allowing the air inlet to pull in all that is possible and present a uniform column of air to the plate.

Why it is not done on the factory installation? Probably is more about packaging considerations (no room for an ideal situation). These compromises happen all the time. Plus this is a problem outside the normal operating range at their design power level.

Wouldn't mess with attempting turning vanes. One idea discussed
is a definite NO-NO. Never place guide vanes in the inlet of these turbo-compressors. The eddy currents they produce excite the inlet blades and can cause blade separation in very quick order."



I purchased the pieces to replicate an original style 934 air intake.

934 Air Intake

http://forums.pelicanparts.com/uploa...1332738300.jpg



Material to fabricate 934 Air Intake

http://forums.pelicanparts.com/uploa...1332738386.jpg


The Optimum Air venturi

http://forums.pelicanparts.com/uploa...1332738510.jpg


Any input, comments, or suggestions welcomed.

Cole