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Thread: Update on my CIS trials & tribulations

  1. #1
    Join Date
    Oct 2004
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    Ohio
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    E21 320i, e39 540i/6

    Update on my CIS trials & tribulations

    OK, I've been working and researching quietly on things for quite awhile and its time to fill you all in. I've probably learned more about CIS over the last month that I have in 3 years of lots of studying. For those of you that don't know, I've been working to resolve a lean condition above 5500 rpm since I finished my turbo system almost 2 years ago.

    I started with a volvo 240 turbo fuel distributor mounted to what I THOUGHT was a Porsche 931 air flow meter. I bought this setup brand new on ebay in 2001 for $125. It was listed as being a fuel distributor for a turbo 4 cylinder. Before I knew what I was doing I decided to port the air flow meter thinking it would be a good idea to reduce restriction as much as possible. It then sat on a shelf for 5 years until I decided it was time to take the plunge and design a turbo system for the car. Early on I determined that the fuel distributor was off of a volvo 240 turbo by a part number search. Through pictures I determined that the AFM was from a 931 (a part number search didn't give me anything).

    To correct my lean condition I started by installing a fat hoss 911 turbo fuel pump capable of fueling up to 450 hp. I then cranked system pressure up to 95 psi and installed a set of brass 6.9L mercedes injectors. At the very end I even tried an experimental flap inside the bowl that could be adjusted with a set screw to change the shape of the bowl. This made no change to the fuel curve, no matter what it would lean out at 5500 rpm.

    When I ported the AFM I mistakenly put a radius on the very bottom edge of the bowl and I thought this was the cause a my lean condition, so I bought an unmolested 931 AFM and FD from a board member on 924.org, and after cleaning and inspection I realized that even though the castings are the same, the AFM I've been running is not off a 931.

    Here is my original system next to a stock e21 AFM & FD, showing most of the port job:







    compared to my "new" 931 afm:







    I've now determined that it is off of a Volvo v6 (the same v6 used in the Delorean), which is why the 6 cyl casting of the volvo FD was able to bolt to it. When put next to the 931 AFM, it was apparent the bowl shapes of the 2 AFM's are VERY different. The sensor plate of the 931 AFM is 76mm compared to 80mm of the Volvo 260 AFM, and the "enrichment" curve at the bottom of the bowl comes in much sooner. Here are the 2 bowls side by side, the 931 on the left and the Volvo 260 on the right:



    I installed the "new" AFM and FD last week and the car ran terrible. I was getting 10:1 AFR at part throttle. I realized that the Volvo WUR and the way it is plumbed with boost & vacuum lines was completely wrong for the 931 system. At 19" Hg vacuum (at idle), my control pressure would go from 53 psi to 47. Then at part throttle my control pressure was dropping from 47 psi to 30 psi and it would go pig rich.

    The stock 924 turbo control pressure is ~53 psi, which is what my WUR is set at with no vacuum/boost, so I decided to unplug it to see what happens. What a difference! I now hit 12:1 AFR and it holds that AFR all the way to 7k rpm. Running with no vacuum enrichment is not ideal so now I'm in the market for a 924 turbo WUR which is vacuum sensing only. This should give me slightly better throttle response and better part throttle/midrange mixture while allowing healthy afr's at WOT.

    To recap, the major lessons I've learned here:
    1) The Volvo 240 turbo and Porsche 924 turbo FD's/AFM's are NOT interchangeable. The Volvo has the 6 cylinder bolt pattern and the porsche uses the 4 cyl. FD bolt pattern.

    2) Make sure you use an AFM that was originally designed for a turbo application. Bowl shapes are different and they WILL have an effect on fuel curve. In my case I've been trying to make the AFM from an NA v6 work on my 4 cyl. turbo the whole time under the false assumption that it was from a 924 turbo.

    3) If you use the Volvo setup, you need to use the audi 5000 S or volvo WUR. If you use the Porsche setup, you should also use a Porsche WUR. You will save time in tuning in the long run. They are constructed differently, function differently and are plumbed different. I could go into enough detail on this to start a whole other thread (Which I plan to do).

    As a result of all this I was able to turn the boost up to 13 psi tonight (which drops to 12 psi after 4500 rpm) and my AFR still holds steady at 12:1-11.9:1. I am wary of turning the boost up any higher at this point, though if I get gutsy 14 psi should net me about 250 hp, which should be enough to put a 2400 lb e21 into the mid 13's in the quarter mile. Right now at 13 psi I'm estimating about 240 hp. I hope to get the car on the dyno and also down the strip soon to see what it does. I can say that it is noticeably faster, and it's a glorious feeling to have it just keep pulling past redline instead of falling flat 1000 rpm before redline.

    I'll try to post some updated pics of the engine bay tomorrow.

    '81 320i turbo | t25, 931 CIS, 240hp, 13.92@100mph | 2.2L m10 Turbo Build | My E21 Videos |

  2. #2
    Join Date
    May 2006
    Location
    Mountain view, CA
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    83 320i (M20 Powa)
    im ganna have to re read this tomorrow it all went right over my head haha. but as i get closer to thinking about fuel im getting more nervous about if im doing everything right. if i was a better fuel pump which would i change... the intake or the inline? also after reading this and the other thread i have come to your conclusion that i have the volvo 240 FD atop the top half of AFM attached to the bottom of the e21 AFM, right? if this is correct then according to you i would want to use the volvo 240 or audi 5000 WUR right? (btw i took my wur apart and man that thing is dirty inside, maybe the cause or my hard start warm and cold). now once i figure out that that wur is the right one i have no idea what pressures i would want the fuel at each stage in the warm up of the car as well as run...? and another thing when i went to test the fuel injector line figment, they didn't reach what other options do i have for lines other then the vw SS lines? ok sorry i was asking questions and thinking out loud. and josh i think im ganna have to call you one day and pick your brain haha

  3. #3
    Join Date
    Oct 2004
    Location
    Ohio
    Posts
    6,763
    My Cars
    E21 320i, e39 540i/6
    Finally, here are some updated pics of the engine bay with the new fuel distributor. I had to run new injector fuel lines and re-bend one to fit over the center port on the FD. I also sacrificed an old volvo fuel line to make the one going to my pressure gage/WUR. Notice the main infeed fuel line to the fuel distributor is using a reshaped e21 fitting with new hose crimped on. Also notice a rest pressure of over 30 psi after the car had sat for over 30 minutes. New accumulator, check valve and pressure regulator o-rings FTW.









    Last edited by jrcook320; 09-04-2008 at 12:24 AM.

    '81 320i turbo | t25, 931 CIS, 240hp, 13.92@100mph | 2.2L m10 Turbo Build | My E21 Videos |

  4. #4
    Join Date
    Feb 2006
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    94062
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    '71 Bavaria
    Looks great! Runs good huh?

  5. #5
    Join Date
    Oct 2004
    Location
    Ohio
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    E21 320i, e39 540i/6
    very, very good.

    A few weekends ago I ran a 13.92 1/4 mile at 100.6 mph. That same night I beat a '99 camaro z28 (LS1 6 spd) who managed a best of 14.0, and also an '01 mustang GT, who ran a 14.6.

    '81 320i turbo | t25, 931 CIS, 240hp, 13.92@100mph | 2.2L m10 Turbo Build | My E21 Videos |

  6. #6
    Join Date
    Feb 2006
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    94062
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    '71 Bavaria
    Quote Originally Posted by jrcook320 View Post
    very, very good.


    A few weekends ago I ran a 13.92 1/4 mile at 100.6 mph. That same night I beat a '99 camaro z28 (LS1 6 spd) who managed a best of 14.0, and also an '01 mustang GT, who ran a 14.6.
    Thats amazing! good job again! do you have pictures of your interior/ trunk etc. also, good pics of where you mounted the front sploiler?

    If i had an m10, I would be doing what you and DJ have done.

    -Rick

  7. #7
    Join Date
    Jan 2008
    Location
    WI, USA
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    '69 2002
    Quote Originally Posted by jrcook320 View Post
    very, very good.

    A few weekends ago I ran a 13.92 1/4 mile at 100.6 mph. That same night I beat a '99 camaro z28 (LS1 6 spd) who managed a best of 14.0, and also an '01 mustang GT, who ran a 14.6.

    I trust you'll be bringing her back through SE WI to let me test drive it again, right?
    Kanye West is a gay fish.

  8. #8
    Join Date
    Apr 2004
    Location
    Boston
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    7,444
    My Cars
    1979 323i BMW. 2003 GTI 20 V Turbo
    Looks great.

    So the main problem was that you where running a fuel component that was not really what your where told it was? I can see why this became a problem.

    With the light weight nature of the car, that turbo setup with the fuel system dialed in must make your car really fly. I see a big smile on your face as you blow the doors of the competion.

    PS: my calipers should be there soon.
    "..Horsepower is a measure of work done over time, or the rate at which work is done."




    http://www.cardomain.com/ride/579694/1


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