383 Upgrades

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    Offline jrig383

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    383 Upgrades
    « on: July 18, 2006 - 10:28:42 PM »
    383 Upgrades

    Can anyone help me out here?

    -NEWBIE-

    I have a 71 Challenger with a stock 383 and a 2bbl carb. It’s auto with 727 trans and
    2.76 gears. It’s my daily driver and its getting 8 mpg. That’s Terrible when your paying almost $4 a gallon. The trouble I’m having is its sluggish on take off like it’s going to die out. When at a stop I have to keep it revved up in Neutral or it may die. It’s also been dying at will when accelerating on the freeway or even cruising. When I pull over the side of the road it will startup and idle fine, sounding very healthy. The motor has 115,000 miles on it. These are driver miles no racing or hot roding miles. The oil gets changed every 1500 to 2000 miles and eats a quart of oil every 800 miles. Everyone says my problem is carburetion. They say rip that 2bbl off and put on a 4bbl. So if that’s the case what 4bbl combo will suit me best? I am looking for gas mileage in the 12-16 mpg if possible. I have been doing some homework and This is what I came up with:
    Edelbrock PERFORMER intake
    Road demon 625 carb
    Does any one see a problem with this setup? I am on a budget to. It needs to fit under a stock hood. I think I might have hood clearance problems if I go with the PERFORMER RPM intake. Are there any problems I might have with kickdown? I know that the engine is going to need rebuilding at some time, but until then I just want the car to be drivable. Any suggestions?
    Thank you for any one reading this post.

    Thanks for the help in advance

     
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    Offline Chryco Psycho

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    Re: 383 Upgrades
    « Reply #1 on: July 19, 2006 - 12:45:22 AM »
    Welcome
     before changing anything I would tune the life otu of the engine & do a compression test too
    try setting the initial timing around 20* with total timing in the 38* range this should pick up the bottom end response
    if you decide to replace the intake use a good intake like the Mopar M1 or Weiand , the performer is a waste of $$ also the 383 needs a 750 , I would look at a Proform or Holley over the demon & ther are a lot of choices depending on what you want as far as choke , vacumm secondary or mech secondary etc , at last count I think Holley has 14 differnt 750s available
     do the tuning & tests first let us know the results
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    Offline moper

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    Re: 383 Upgrades
    « Reply #2 on: July 19, 2006 - 05:25:59 AM »
     :iagree:
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    Offline tactransman

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    • 1973 Challenger- Member here since April 14, 2006
    Re: 383 Upgrades
    « Reply #3 on: July 20, 2006 - 07:09:49 AM »
    800 miles to a quart of oil if you are not leaking it is too much oil consumption. Do the compression test like Chryco said first. You can tune it till your blue in the face and your not going to get it right if you don't have good compression.
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    Terry-tactransman 
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    Union, Mo.
    Give a man a fish and he eats for a day,teach him to fish and he eats for a lifetime.

    Offline Follicly Challenged

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    Re: 383 Upgrades
    « Reply #4 on: July 20, 2006 - 10:28:03 AM »
    383 stroke is 3.38
    318 stroke is 3.31
    Even a 360 is 3.58 for crissakes.
    Do the compression test to insure the patent integrity of the rings etc., first.
    800 miles/per quart seems excessive at this point.

    Above is just for comparison of arm length only, but you get the "basic" picture. Yes, many other variables are involved, but, for this, thats enough.
    Without a bunch more "push" involved on the arm ie; compression, hotter burn, the WEE-83's inherently have a tough time "getting going" down low. The same things, that makes them great revers "dimensionally" up high, kill 'em down low.
    If ya can't "tune it out" as Chryco says, get a little bit of stall, in the way of a small convertor in the 727 trans, to let it "get a run" at it's power band, the low deck "B" engines LOVE THAT. Nothing crazy, just enough to let it catch some wind off the line. Sometimes, in the long run, on an otherwise tuned properly, and "Patent" wee-83, the slightly extra stall speed is the best "Snap" for buck spent "off the line".

    FC out.
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    Offline jrig383

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    Re: 383 Upgrades
    « Reply #5 on: July 22, 2006 - 05:09:11 PM »
    All right Just did a Compression test. Hears what the numbers look like

    115 8      7 105

    110 6      5 110   
         PSI
    110 4      3 99

    110 2      1 105

    I am not sure what the spec tolerates? The number 3 cylinder spark plug has always had a lot of build up I bet that’s were my oil is going. Just added another quart today. I tweaked with the timing, hard to tell if it made a difference. I tried putting on the AC today but it dyed out when coming to a stop. The only time that seems to work right is at wot on the freeway. I think that’s more of an electrical problem. So want are my options here? What would to do? I am starting to get blue in the face.

    Thanks
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    Offline 71383bee

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    Re: 383 Upgrades
    « Reply #6 on: July 22, 2006 - 09:41:44 PM »
    Well I would venture a guess and say that your motor is tired, but not quite out.  Did you try and squirt some oil in the cylinders and re-do the test?  If the pressure goes way up then it is an indicator that you rings are going. 

    Average pressure of around 110 is a bit weak.  Also it is interesting to see that the left bank is all lower in psi than the right side which could indicate some head related issues too.

    However, 99 versus 110 average is not huge...CP and moper what is Bad compression variation for a tired motor...greater than 20?   :clueless:

    Like everybody else says i think the motor really needs a good old fashioned tune up.  Get new wires, new plugs, new rotor, set total timing around 34-36 BTDC, check initial timing, and tune the carb.  Maybe rebuild it (the carb) if necessary.  Keep it simple.  Maybe a bad PCV or a old cracked vacum hose is giving you trouble.
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    Offline ntstlgl1970

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    Re: 383 Upgrades
    « Reply #7 on: July 23, 2006 - 12:54:15 AM »
    I agree with what others have said, check the basics first and go from there. If you have access to a fuel pressure gauge, would be good to make sure the fuel pressure is adequate. Check the float level in the carb. Also with the timing light, make sure the timing advances when you rev the engine up. Also check the vacuum advance on the distrubutor to make sure the diaphragm isn't blown. When I first got my car it had a 440 with 2.76's, stock intake, stock carb (holley 600 vac) and it would get about 12-14mpg and the motor had some compression issues similar to what you have. Let us know what you find.
    « Last Edit: July 23, 2006 - 12:56:44 AM by ntstlgl1970 »
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    70 Cuda, 7.0L Gen-III Hemi, Viper T56 w/9310 gearset, 3.91's, Megasquirt MS3x v3.57, Innovate wideband, Firm Feel upper arms, torsion bars, springs and strut rods, QA1 DA shocks. I did everything on this car except the fancy paint stuff and I drive it...and I can't seem to stop messing with it....

    Offline Chryco Psycho

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    Re: 383 Upgrades
    « Reply #8 on: July 23, 2006 - 02:03:02 AM »
    Generally more than 15 lbs difference is the break point where the heads or cylinders need work 
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