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 9751 times)

    Offline Chryco Psycho

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #60 on: May 31, 2009 - 09:35:36 PM »
    maybe not Zero deck but you will want to be within .60 to get the quench working for you , the closed chamber heads could be used either way
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    Offline moper

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #61 on: June 01, 2009 - 08:17:01 AM »
    Quote from: willard on May 29, 2009 - 01:45:11 PM
    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.

    Your elevation isnt much different tthan where i live, basically close to sea level. So the numbers you get are similar. But, the 14.7:1 result is assuming the valves are closed and the cylinder sealed at Bottom Dead Center on the intake stroke and the rings are 100$% sealed. So the compressing of the volume would be exactly 9.5 times the swept volume of the piston. Unfortunately, the valves are not closed at Bottom Dead Center and there is always leakage of some number around the rings. That is why you can't really use the cylinder pressure to figure the engines mechanical compression ratio. The intake usually closes somewhere between 30 and 60° of crank rotation after BDC. It's the intake valve closing point that determines the cylinder pressure. I dont have the spec for you cam but it should be on the cam card. Now, as far as the cylinder heads... Mopar heads are always LARGER than the factory spec. If the car had a valve job or two as most did in it's younger years, that chamber size effectively gets bigger as the valves are made smaller and the seats sunk. Most I measure now are closer to 90-94cc prior to any work, and after even using new seats and valves you have to mill to get them down to 84-88cc. Which is why I'd be really surprised if you had anything close to 9.5:1. The close dchamber idea has erit, but the way to address the issue is to simply replace the pistons with something that is taller to get that compression back. Just be careful, the Euro 95 octane is figured differently and I believe it equates to about 91octane US. So you will want to keep the cylinder pressure as you measured it (a few turns) to less than 180psi. By advancing the intake closing point by 8°, I raised the cylinder pressure from 120si to 185 with the factory 335hp stock cam. It does not take much to get higher pressures but by doing it with the cam rather than the piston or head you give up horsepower to gain torque. 383s need to be well rounded...lol.
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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #62 on: June 01, 2009 - 09:11:46 AM »
    Thanks Moper,
    I see that if I don't want to extract the engine (cost of tools, no place to do that..., leaving car at a workshop...) 99% I won't avoid milling the heads thus having to correct the valvetrain geometry.
    I played with the compression calculator at Kb site and maybe I'm wrong but it seems that getting a factory 9.5 CR on a 383 is really not easy with open chamber heads (flat top pistons must be exactly zero deck+0.02 gaskets).
    Stroker 438 kit is very temting but the price + shipping + complete disassembly and machining work is a killer. But winter in Poland starts in october so there are 5 months to do that ;) and I can start gathering parts $ cash right now.
    I'm afraid of one thing more - I can't rely on machinist's / mechanic's knowledge because the can only fix BMWs and fiats - so I have to measure everything and just give them simpe instructions what to do.
    I wih a had a large garrage and a reputable workshop/machine sop nearby, like you ;)

    As far as gas is concerned Eu 95 is US 91 and we also have EU 98 which is like your 93 octane.
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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 #63 on: June 01, 2009 - 11:53:59 AM »
    I'm not a huge fan of stroking 383s, as a 400 will get a better result. Maybe with the Euro exchange rate buying a complete assembled long lock might be easier for you. Not cheaper, but easier. Also, milling doesnt change geometry on a shaft-rocker system. It just means you need (possibly) a shorter pushrod to fit. It is hard. I use a flat top KB hypereutectic in at zero deck, and mill the heads down to 78cc and run the std Felpro 8553PT-1 gasket. That comes to 9.5:1 true, and I've run the steelies to get a little more when I needed it. As far as Polish machinists... I have several that I know of that own their own Aeropspace businesses here. You should be able to find one... BMW machining is a damn site better than anything mopar ever did..lol. Fiat... we wont talk about Fiat...lol
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    Offline Chryco Psycho

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #64 on: June 02, 2009 - 01:54:08 AM »
    excessive milling of the heads & or block can cause headaches fitting the intakes though
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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #65 on: December 25, 2009 - 06:21:00 AM »
    Ok, the engine has been partially disassembled and  have 366NP (federal mogul, flat top) pistons sitting 0.1" in the bore, 906s have 84-85cc and have been slightly milled. Block 0.30 over.
    Putting KB400 pistons i(-6cc dome) instead of 366NP gives mi little advantage (CH 1.908" instead of 1.848").
    Now I shlould have a CR of 7.7:1 (wow...)
    With KB400 and 0.02" gasket it rises to 8.3:1
    To get 9.5:1 without touching the block I'd have to go from 85cc to 70cc chambers - i.e mill heads 0.0042" x 15 = 0.063" isn't that too much?

    If I decide to mill the block deck 0.1" and have the 366NP pistons at zero deck. Leave 85cc heads  with 0.02" gaskets it leads to 9.8:1.

    Questions:

    Is it necessary to pull out all bearings, freeze plugs from the bock?
    Does the milling of the block deck of 0.1" cause pushrod change (I have hydraulic lifters)?
    Is it safe to mill 0.1" of the deck? Or it's better to take 0.063" off the heads?
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    1970 383 R/T SE

    Offline Moparal

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #66 on: December 25, 2009 - 12:30:42 PM »
    Decking a block 100 thou is a lot. Almost 1/8th inch.  I would find another piston.  You have better options milling the aluminum heads to. Or even buying some 915 heads for that matter. 
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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #67 on: December 25, 2009 - 01:06:01 PM »
    I recalculated with KB400 pistons (-6cc dome). With stock 9.98" deck height and KB400 1.908" CH they should sit 0.0265" in the bore and with a thin (0.028) gasket and 85cc chambers that results in 9.6:1. No deck/head milling, no problems, just new pistons. This should be the easiest way but:

    - do I need to hone the bores (they were honed approx 2000 miles ago and look good) ?
    - do I need to rebalance the whole set with new pistons ?

    My budget is limited so as of new heads are no go.
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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 #68 on: December 25, 2009 - 01:12:52 PM »
    if the block can be easly cleaned you can just rough the bores quickly with a hone to give the surface a better surface to seat in new rings
     you need to weigh the pistons , if they are off by more than a few grams you shoudl rebalance to the new piston weight
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    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #69 on: December 25, 2009 - 01:31:46 PM »
    Sorry for my english - I meant balancing the whole assembly (crank+rods+pistons) - if the new pistons are lighter/heavier than the old ones wouldn't that cause troubles (vibrations, premature wear?).
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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 #70 on: December 26, 2009 - 12:29:30 PM »
    if the pistons are different in weight it wil cause vibration & possibly wear issues
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    Offline Topcat

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #71 on: December 26, 2009 - 01:20:25 PM »
    Quote from: Chryco Psycho on December 26, 2009 - 12:29:30 PM
    if the pistons are different in weight it wil cause vibration & possibly wear issues


    I looked up the non balanced weight on the pistons and it came up with this:

    Piston weight 779g, pin weight 190g. This is without rings.
    http://www.summitracing.com/parts/UEM-KB400-030/Application/?prefilter=1
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    Mike, Fremont, CA.

    Offline willard

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #72 on: December 30, 2009 - 07:16:21 AM »
    Wasted half a day on looking for these FM 366NP pistons weight. No data available. However I found that OEM pistons in a 383 were 770g (pison only). So will approx 9g a piston (KB400 vs. OEM) make a huge difference and need rebalancing?

    Also do I need extra wrist pins (or they sell piston+pin set?) for KB400 hypers  (summit says the pistons are both press/float type) or I should use the old ones from 366NP pistons (they are press pin). Of course I need new rings.

    I know my questions are noobish but the shop I have my challenger disassembled in, seems to be lacking knowledge on engines in relation to this board. The say I need to mill the block/intake if I mill heads (I told them that milling surface needs milling intake side proportionally  too). Thy event did not calculated CR with different pistons available on the market...
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    1970 383 R/T SE

    Offline swede-cuda

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #73 on: December 31, 2009 - 05:18:15 PM »
     :horse:hej,im sure it will turn out good in the end,just want to say that there are a set of 516 heads for 270 $ on www.nitroz.se or maybe it was www.moparsweden.com or se.915 heads comes up to from time to time to but for the double amount of balobas,or more.you could take the ferry to sweden and get them if shipping is unreasonable.also for example,www.generallee.com has new 0.30 pistons in his ad that cost twice as the 516 heads,without rings.no idea what pistons it is.anyway just wanted to let you know.good luck,Anders
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    Offline Moparal

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    Re: I'm disassembling my 383 and need some feedback
    « Reply #74 on: December 31, 2009 - 08:05:37 PM »
    New pistons come with the pins. The kb400's will for sure. The pistons will be lighter than stock. So rebalance the assembly. Jegs and summitt racing sells a steel shim head gasket made by Mr Gasket for 15 bucks a pair, they are  .018/ .020 thick this bumps the compression up about 1/2 a point more then the paper type, then if you go to a closed chamber head like a 915, this also bumps up the compression about another 1/2 a point up. The kb pistons will have valve reliefs cut in the pistons so piston to valve clearance is good up to about .625 lift and this is at zero deck.
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