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Thread: Weber tuning

  1. #1301
    smart ? i don't know.... just trying out some things i read. According the GT40 guys formula i should now be at max HP just below 6000 rpm with the 38.5 mm venturis.
    I must admit that on most graphs the 36 mm i started with are on the small side... but kept in mind one can always drill it out larger , not the opposite.

    O well ,next dyno will show it... if now mains 135 or larger and air correctors 190 or smaller .. that's what i have

  2. #1302
    we had again some HP gain.... but still way to rich in the upper rev's.... till i had seen the air filters !! They started to be eaten by that engine holes as from mice....

    Seems at WOT that foam is sucked into the trumpets ..... there is no metal cage inside. No wonder it's always to rich .

    Did some street tests without the filters and got it +/- at 12.5 AFR ... a lot better now , and with 155 mains instead of 135 !

    Now to build a scoop ....

  3. #1303
    Senior Member Funding Member RedBarchetta's Avatar
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    Good progress, Barry. Me personally, if I ran Weber’s I’d just use metal screens to keep large objects out and ditch any filtering. Seems more times than not I’ve read that filters on these carbs really choke them down and mess up A/F and overall driveability.
    -Dean

    "...tires spitting gravel, I commit my weekly crime."

  4. #1304
    I need some sort of filter.... sure in rally if you should catch up on a car .
    My idea now is to make a "scoop" ( closed above so no direct rain in it ) and in the rectangular opening a filter screen.
    Underside rubber sheets that pop over the trumpets ( against heat from engine )

    What we do not know so far is either opening at the front ( Ram air ) or the rear ( positive pressure zone , front negative )

    Luchtweerstandmeting.jpg

    i'm in favor for opening at "10" .... in the positive pressure zone.

    and i read that carbs ( venturi effect ) don't work well with ram air .... i assume as the air get denser but velocity stays the same it would lean out with speed... or one should have the same "pressure " on the fuel bowl.
    Last edited by belgiumbarry; 04-01-2021 at 06:48 AM.

  5. #1305
    Senior Member Funding Member RedBarchetta's Avatar
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    Quote Originally Posted by belgiumbarry View Post
    i'm in favor for opening at "10" .... in the positive pressure zone.
    I have always seen that referenced here as "cowl induction." Look at a '69 Z-28 Camaro or a 1970 Chevelle with the "flapper door" at the rear of the bulged hood for examples. Both worked well off the same principle.
    -Dean

    "...tires spitting gravel, I commit my weekly crime."

  6. #1306
    Dean , do you think Silver can still follow this science ?
    I think he will keep out.

  7. #1307
    GROUCHY FUC***G OLD APE Funding Member Silverback's Avatar
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    What the hell are you blabbering about now WaffleHead.

    Remember, it was me that said the hood scoop on the SRT/10 was in a low pressure area, and along with Shawn proved it. He took the raw data measurements I requested and I did the calculations.

  8. #1308
    April 1 Silver .....

  9. #1309
    Senior Member Funding Member
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    Good one Barry....you sucked him right in!

  10. #1310
    GROUCHY FUC***G OLD APE Funding Member Silverback's Avatar
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    There is no April Fools day on the Ape Calendar.

  11. #1311
    haha, some pressure tests... no at the windshield it won't work.... must be "ram" air.
    scoop test.jpg

    Made a scoop as was .... but way to big . Ugly and no visibility , sure not for right corners. That was a drag race model....
    Found and ordered lower trumpets ( 32 mm instead of the standard 56 mm ) ... so changed the scoop to 24 mm lower. Already a lot better ! Second model....
    But with shorter trumpets i could not reach the rear ones with the rubber gasket to seal from engine heat.... so i had to lower the bottom plate level with carbs.... Third and final model.

    Still some tack welds and kit to finish... and paint.

    What seemed a simple project became almost 2 days playing with idea's..... and grinding/bending alu.

    SAM_3541.jpgSAM_3545.jpg

    don't know what ram air "pressure " can be , but as the fuel bowls air inlets are on top under a little screen i can open that in the rubber gaskets to have the same "pressure".
    Otherwise denser air would lean the mixture with speed .... here the injection boys running on O2 sensor have that advantage. Carbs vaporize with air speed , not density.

  12. #1312
    GROUCHY FUC***G OLD APE Funding Member Silverback's Avatar
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    Look at it this was WaffleHead. At least you had something to do over the weekend besides drink.

  13. #1313
    weekend ? didn't notice it. And i took some drinks too ... as on a work day . Work day ? what's that ? between the weekends ?
    We are still in lockdown.... nothing to do outside .....

  14. #1314
    seen by coincidence.... here we are with the BMW 2002 in a rally in 1984.... damned, 37 years ago...
    we drive by at 8:00 and 9.30.

    https://www.youtube.com/watch?v=yqNS5jxsFSU

  15. #1315
    GROUCHY FUC***G OLD APE Funding Member Silverback's Avatar
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    That was you WaffleHead. I would have recognized you anywhere.

  16. #1316
    nice memory anyhow... never seen a rally movie of that time with "us" .... private video cameras were still rare and expensive....

  17. #1317
    Administrator Funding Member Ron77's Avatar
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    That was interesting Barry. Thanks for posting it.

    Ron


    MY ALBUMS

  18. #1318
    Senior Member GianM's Avatar
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    I thought about Barry when I watched this...

    This is driving on the very edge, with some great commentary from the late, Murry Walker.
    These guys had real driving skills, and for the most part, were in full control of how the car performed and not reliant on computer assisted functions and gadgets. We also had the Ford Escort XR3 out here in SA, but not the turbo option.

    I just enjoyed watching this, but Barry might have more insight...

    https://www.youtube.com/watch?v=-U-zmmGlXG0

    Of all the things I've lost, I miss my mind the most...

  19. #1319
    GROUCHY FUC***G OLD APE Funding Member Silverback's Avatar
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    I agree Gian that the racing was better before all the electronic shit came along.

    And I could not believe they let the car with the blown turbo seal stay out there and race.

  20. #1320
    Gian , this is rallycross , not so directly my favorite. Rather short track with asphalt and gravel sections. Ideal for spectators.
    Drivers must know every corner very well by doing it a hundred times....like F1 but total other discipline.
    Must be great racing that close... with the usual damage of course.

    But nice to see rally cars back in the days ... now they are all the same , Peugeot,Ford,Skoda, Citroen.... one has to look at the badge to be sure.

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