I'm disassembling my 383 and need some feedback

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    Author Topic: I'm disassembling my 383 and need some feedback  (Read 9746 times)

    Offline moper

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #45 on: May 27, 2009 - 11:59:37 AM »
    I would have expected a bit more pressure than that, especially with a cam change to something a little more modern. Is the shortblock original? IMO, you still don't need a convertor. The engine is wheezing. You need to know why. Can you get your hands on a leak down testor over there?
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    Offline Hemi Dude

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #46 on: May 28, 2009 - 04:38:48 AM »
    I can't believe no one asked the simple question yet willard!
    What type of fuel are you running in that beast of yours? It could be the answer to all your problems. Now since you are in Poland i am courious if there is any good quality fuel available for serious muscle cars that demand 93+ octane.
    Another note, your compression figures are a bit on the low side. From a healthy 383 i would expect to see around 140-150 psi at least.

    Hemi Dude
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    '70 Hemi Challenger (modified)
    '74 El Camino SS 454

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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #47 on: May 28, 2009 - 08:00:16 AM »
    I use european 95 octane gas plus lead additive. I run my volvo s80 on this gas too and it is good. My firm has a long term contract for fuel with this fuel station.

    I listed 2 numbers for the compression - should I take into account the one I got after 3-4 compression strokes (closer to 130) or the engine should put the targetted value on the first stroke? In every case 2 first crank revolutions make a 20 psi lower pressure than the 3rd and 4th. What's the proper method?

    The shortblock is original # matching HP block. I did not disassemble it but the seller claimed the engine was rebuild with stock mopar parts.
    There's no vac leak, sticking valves, worn guides, choked muffler, leaking head gasket - the vacuum test denied that.

    Speaking about leakdown tester you mean pressurizing a cylinder at TDC and searching for escaping air (valves, rings)?
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    1970 383 R/T SE

    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #48 on: May 28, 2009 - 11:52:07 AM »
    Can't believe it but it happened. I started fro mthe cratch and checked tha carb - if throttle opens fully and wanted to set idle mixtur once again.  I took the car for a ride and on a parking lot advanced the timing "some" th engine definitely LIKES that and was running smoother, I also got 14 in of vac in gear. While adjusting idle mixture I noticed that unscrewing (enrichening) has literally no effect on idle quality, rpm and vac - be it 1.5 turn or 3 turns - the same... I set it on the best lean side.
    I took it for another run and the acceleration was far better than before, no pinging, etc (vac advance is off).

    When I came back to the garrage I checked the timing with the strobe light, guess what. 30 deg BTDC of initial timing! When I add 24 deg of mech advance this gives 54 and I can believe there was no pinging.
    When I was assembling the cam, timing chain, I verified it more than twice that the damper marking is a true TDC (dots lined 6 and 12 oclock, damper pointing at 0 deg). I can only guess it slipped?
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    1970 383 R/T SE

    Offline moper

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #49 on: May 28, 2009 - 12:42:12 PM »
    No, you have a low compression 383. It's the factory parts used in the rebuild, and it's common. The HPs are much closer to 9:1 then 10.5, and that's using the thin steel head gaskets. If you have composite ones, it's closer to 8.5:1 static. That is why you have low cylinder pressure, and why changing cams did little for you. It's also why so much ignition timing is needed. Did you degree the cam? I dont recall. but you could degree it and maybe advance it to get more low end.
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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #50 on: May 28, 2009 - 01:50:15 PM »
    Yes, cam was finally degreed and is correctly installed. I'm really reluctant to make the mess once again and advancing the cam...
    It seems that the previous owner cut the expenses on rebuild. The block has matching vin and on the top p/s pad has "HP" and some numbers embossed so I assume it is from this car. That's a pity that there's no other way to improve the performance than changing pistons (the heads are 906s).

    Last question then - is it safe to advance the timing more? I feel that the idle could be better and rpm could rise with another 5-10 degrees...
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    1970 383 R/T SE

    Offline Chryco Psycho

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #51 on: May 28, 2009 - 07:04:43 PM »
    YEs it is safe , this is why I tossed my timing light , give it more timing unless it pings
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    Offline moper

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #52 on: May 29, 2009 - 12:43:38 PM »
    If the numbers are on the pad, and there is no step where the block was decked, yes, the guy cheaped out on it. I have gotten a totally stock 383HP/335hp rebuild (no blueprinting done) 383 to get to 180psi by advancing the cam 4°. But it is a lot of work and "your results may vary". You can throw timing at it like CP said. Eventually you go too far and it simply loses power but I doubt it will ever ping...lol. Maybe take it apart some other time.
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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #53 on: May 29, 2009 - 01:45:11 PM »
    The facts are that after the cam swap and some adjustments the car runs better than before. I did the cam swap for the first time and some time has to pass before I start removing radiator, compressor, pumps etc to advance the cam and see the results... maybe I wait till winter and remove it from the car to have it disassembled, verified ant then put a stroker kit in it  :clapping:

    As far as compression is concerned I thought it felt within an acceptable range (according to FSM) and 140 psi is approx 9.5 atmosphere ie. 9.5 more than normal pressure which should give 1:9,5 compression. 120 psi is only 8,2 atmosphere.

    Last thing - should I rely on the first number (after 2 crank revolutions) or the second (always higher) after a total of 304 compression strokes?

    Anyway thanks for input.
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    1970 383 R/T SE

    Offline Chryco Psycho

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #54 on: May 30, 2009 - 01:28:27 AM »
    both compression # are useful the first # shows how fast it will build compression usually a sign of wear in the engine the second is more what the best compression the engine is making at 500 rpm cranking speed , with RPM Dynamic compressioin can rise a lot
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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #55 on: May 30, 2009 - 04:00:09 AM »
    I did some research and I found that with 906 heads (88cc) it is damn hard to get even the 9,5:1. When I calculated the stock flat piston, zero deck, it's around 9:1. Taking into account stock engines were not zero deck the compression dramatically falls.
    What type of pistons would you suggest to get into a 9.5-10 compression range?
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    1970 383 R/T SE

    Offline Chryco Psycho

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #56 on: May 30, 2009 - 04:16:15 AM »
    I use 516 or 915 heads to get the compression up to 10:1
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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #57 on: May 31, 2009 - 11:18:35 AM »
    Ok, so I have a few options to chose from:
    1. simply changing heads to 516s (I found a nice set @ moparts) - according to a CR calculator this will give me a slight rise (0.6) thanks to 10cc smaller combustion chamber. cheap, easy to do. Question is 0.6 worth it. Let it even be 0.8 with 0.02" head gasket.
    And 516 have smaller exhaust flow.
    2. milling the 516s - less cheap, easy to put on the engine but will cause valvetrain misalignment and need of intake side milling, shimming stock rockers arms.. the milling will also make future piston-valve colission more possible (?).
    3. extracting engine, disassembly, zero deck with installed pistons (if possible), leaving 906s on. this should give me 9.1 with 0.039 gasket and perfect 9.5 with 0.02". However I don't have place and tools to pull out the engine...
    4. as above but putting in a 438 stroker set from 440source. the most costly one but will give me the best result ;)

    The problem is the piston head - block deck distance which can only be milled. How much can be milled from a stock 383 block deck? 0.1"?

    What do you advise?
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    1970 383 R/T SE

    Offline Chryco Psycho

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #58 on: May 31, 2009 - 11:28:48 AM »
    the 516 heads with some port work & hardened exhaust seats work great , th elarger 1.72 or even 1.81 valve can be installed into the 516 heads , use the steel shim gasket & you will get good results from that .
    The next step would be the stroker kit for best results .
     Messing around with milling decks & trying to correct the geometery is a pain for the amount of gain you get
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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #59 on: May 31, 2009 - 01:34:00 PM »
    ok, but with a stroker kit I have to zero-deck the pistons anyway...
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    1970 383 R/T SE
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