Small block combo suggestions

Small Block Mopar Engine

  1. jeff1

    jeff1 Active Member

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    hello all. I'm looking for some suggestions on tweaking my combo.
    67 cuda convert, 360 .030 over KB 107 pistons , X heads ,six pack intake XE 262h-10 cam 195 thermostat
    Auto wt 2500 coverter ,3:55 rear gear
    PS,PB wt front disc , CruiseControl
    Carbs are stock jetting PV 6.5
    Timing is 15 Int wt 35 total.
    All n by 2300 rpm
    I'm in to detonation wt just about any full throttle application. Have backed the timing down to 30 total.
    So I'm fighting surging at 2200 in cruise and detonation on acceleration I'm installing a innvoate LC2 and hope to gather more data.
    My ideas to solve problems are slow advance rate and look into transition circuit. Vacuum at idle in gear is 15"
    Cam is installed straight up as instructed wt 110 LSA .
    All opinions entainered
     
  2. Hipo65

    Hipo65 Yeah I'm "That Guy"

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    Yes slow the rate of advance! All in by 2300 is pretty aggressive for 3.55 gears! More like by 3000 rpm. A wide band is a great tuning tool aswell. Im sure it surges some with aalmost all timing in at 2200 & a slight load.
     
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    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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      Solid roller @ .640 lift on a 102.
      Fully port the heads and mill to 50cc's.
      Up swept headers through the hood.
      6000 stall

      Your now good To go!
       
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      • jeff1

        jeff1 Active Member

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        Rumblefish360
        Thanks for your input while I do feel that imitation is the sincerest form of flattery I would feel guilty copying your combo. Besides I know you have put a lot of work and thought into it. I'm going to have to go wt something a little milder. So please keep those ideas and suggestions coming. Thanks I'm fortunate to have caught your eye as I've seen plenty of your post and have always found them to be informative.
         
      • dano

        dano Evil Handy Man

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        Are you looking to change what you have (as in parts) to fix what you have?
         
      • 496 polara

        496 polara moparts id gch

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        Try a 180* (or 160* if you prefer) thermostat as well.
         
      • RustyRatRod

        RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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        JUST .640? Pussy.
         
      • yellow rose

        yellow rose Overnight Sensation

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        Damn you guys are on fire. Like a 2 dolla whore on a crack pipe.

        Golden.
         
      • yellow rose

        yellow rose Overnight Sensation

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        Yep , that's pussy lift for sure, but the upswept header seals the deal.
         
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        • jeff1

          jeff1 Active Member

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          496 Polara
          The thermostat does help but from some testing I've done on another six pack car. It causes the fuel to puddle in the bottom of the intake. Drives an A/F gauge nuts. But it does delay onset of detonation. I would like to run a 180* in it and have one sitting in the box.
           
        • jeff1

          jeff1 Active Member

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          Dano
          Looking to work wt what I have but have not ruled out a cam swap.
          I had run a similar combo for about 15 yrs so thought I would just raise compression on this build and that sent me down this road of refining a new combo. But hey that what makes this stuff challenging and fun Thanks
           
        • Marcohotrod

          Marcohotrod Well-Known Member

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          all in at 2300 is too early. what temp does it run at? do U also have vacuum advance? cam is small. with 15" vacuum go up to like 8.5" power valve for earlier enrichment
           
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          • jeff1

            jeff1 Active Member

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            Marcohotrod
            It runs at 195. All day even in traffic. Like cruising the coast traffic. Could try the 8.5 Pv. Was going to try and finish A/F gauge install before changes to have a base line but I do agree that would enrich earlier good idea.
            Yes it does have vacuum advance. Ported total advance at cruise is 48 btdc
             
          • Marcohotrod

            Marcohotrod Well-Known Member

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            what spark plugs? how do they look? maybe go colder. what octane?
             
          • jeff1

            jeff1 Active Member

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            Sir. Autolite 64. 63s foul pretty quickly. On plugs. MSD 6al ing
            A gray/tan. 93 octane
             
          • Marcohotrod

            Marcohotrod Well-Known Member

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            sounds good
             
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            Post #1 is full of info
            but the most important info is missing. How much cylinder pressure is that engine running and at what altitude is it operating?

            KB107s are flat-tops and in a 360 sit down in the hole. X-heads are open chamber items. The 262 has a very early ICA. But unless you have done a lot of machining, the engine should not be detonating. Well yeah your timing is all in a little early, but there is something you haven't told us,namely the cylinder pressure..

            A little detective work,; with no machining, this is a 9.5 engine. the 262,in at 106 makes an ICA of 59*. This conspires to make a Dcr of 7.9 and cylinder pressure of 158 at sealevel;just about perfect,for iron heads.And should not require 93.
            Soooooooooo, what's your pressure.
            Three things lead to detonation; too much heat, and too much heat, and too much heat; for the fuel.The heat can come from excessive pressure,too-early timing, a hot-running cooling system,hot-air intake,hot spots in the chambers,restrictive exhaust, or lean AFRs.
            Did I miss anything?
            Oh yeah, too high a load.As in secondaries coming in too soon.

            -If it detonates after 4000, you can probably rule out your timing. That combo should run full-timing ok at 180*engine temp.If you have a scoop, you can rule out hot-air. If you have headers and duals exhaust looks covered. That leaves just; pressure,hot-spots and AFR.
            -But if it detonates right from the get-go, Perhaps the secondaries are coming in too early,or the exhaust is not getting out,or as you have already surmised, the timing is all-in too early.
            -If it detonates between say 3000 and 4000, then cutting back the timing should help.But you tried that and even at 30* it is still detonating.
            Soooooo, what's the pressure?
            -If the pressure is below 160psi,and timing is under 36*,and it still detonates after 4000,then you have three choices,I think; Hot spots in the chambers,Lean AFRs, or hot inducted air.
            It's all about too-much heat,or too much load.
            Ok here's a wild card; the heat could be from something in the chamber that should not be in there,lol. Like exhaust,engine oil, something in the gas,or not in the gas that should be in, or a gasket overhanging the top of the bore,or plain old carbon. I would clean out the chambers and start over.
            -If the pressure is over 160, you are gonna have to be sharp on the tune.
            I like this combo;it should make a ton of torque, and be a pleasure to cruise around in. I also see lots of tire-smoke
             
            Last edited: Dec 15, 2016
          • rumblefish360

            rumblefish360 So close, yet so far away FABO Gold Member

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            Jeff, thanks for accepting my sense if humor today.
            Seriously, more cam would be my "Up the anti" choice.
            A surge is lean & the distributor needs a tuning. Not coming in so fast.

            RRR, is there a smiley that is giving out razzbeeries by chance?
            Insert here ---->
            LMAO

            YR, you should have left a link to your post, "Help me choose a cam!"
            And "I'm all over like a drunk out of a weekend lock up that just ran into the liquor store with a hundred bucks!"
            (Funny thing is, my hot rod guzzled gas like that on a regular bassis! AKA W.O.T.! )
             
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            • MOPAROFFICIAL

              MOPAROFFICIAL FABO Gold Member FABO Gold Member

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              Unless you have over 170 cranking psi on un prep'd chambers ...Primary jetting is lean=surge at cruise.
              The old mp .490 lift solid would be great for your combo, with 1.6 even better.
               
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              • the wall

                the wall Well-Known Member

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                You need to look into carb tuning see were that is. Rumble got the right idea here if you don't change any thing else a more agressive cam will help. Please do not believe the advance curve is to fast. When you changed the timing from 35 to 30 you changed initial to 10. reduce the amount of advance in the dist and bring your initial back to 15 or higher especially if you go with more duration and over lap on the cam. All smart engine guys never use slow advance they go with even faster. My engines start at 15 initial as soon as it fires it goes straight to my total. The only time you slow the advance is if you can't get it in fast enough and hold it high and you put your automatic in drive, that drops idle speed just enough for the timing to drop and effectively stalling the engine.if you have any other reason for slowing your advance you have big tuning issues to deal with.slowing advance is the same mentality as you cant put 3 inch exhaust on cause you need back pressure for the street. And that is wrong.
                 
                Last edited: Dec 16, 2016
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                • 360duster

                  360duster Well-Known Member

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                  did you try with out vacuum advance? Maybe it´s too slow coming back under full throttle....

                  Michael
                   
                • Lelo Dart

                  Lelo Dart * FABO Gold Member

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                • qkcuda

                  qkcuda Well-Known Member

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                  Disconnect and plug the vacuum advance and reset the timing to 35 degrees and report back on driveability. I had exactly the same problem with my big block, also with 3.55 gears, and disconnected the vacuum advance and the surging and detonation were gone. A good test is just to bring the revs up slowly in neutral, if it starts to miss, you have too much advance. Disconnect the vacuum advance and try it again.
                   
                • jeff1

                  jeff1 Active Member

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                  AJ. Great points all
                  I'll try to answer some of your questions
                  The motor has about 2000 miles since built. About 2 yrs.
                  I have the 1967 barracuda hp exhaust. Which is a single muffler and resonater . Converting to duals soon.
                  The combo that u described is exactly what I had come up wt and was shooting for. The heads and block deck were just touched to insure straightness. We tried not to take any more metal off than absolutely necessary to ensure it was true
                  I live in south Louisiana which is for most of the year is under sea level. Lol
                  I believe you are confirming what I have been slow to discover. Heat heat heat
                  Single exhaust and 195* thermostat are contributing to problem.
                  I will have a new cranking pressure number in the next few days. I should have included it in the opening statement
                  It's a six pack setup and I have run it wt and without the outer carbs installed
                  When I dropped timing back to 30* I took it out of the advance so was able to keep the initial at 15*. It actually likes 18* initial better.
                  Heat heat heAt.
                  I'll report back Thanks for taking the time to respond.
                   
                • jeff1

                  jeff1 Active Member

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                  QKcuda I will try that
                  It will be a week or so before I can report back as weather here is headed in the crapper. The 35* degrees was just initial plus mechanical. Wt the vac advance it's up around 48* at cruise.
                   
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