360 Advice Needed - Autocross / Street Engine Build

Discussion in 'Small Block Mopar Engine' started by Kicker92, Oct 12, 2017.

  1. Kicker92

    Kicker92 Well-Known Member

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    Hi Guys, I'm looking for some advice with my project, in particular cam selection and static compression ratio.
    It's a 72 demon, that was previously an all original restoration. It will now be a sleeper type build, used for street driving and AutoX / HPDE days.

    I want to keep the engine looking like it could have come from the factory, no chrome / bling, and will have these key parts as limitations:

    - Original air cleaner assembly (cutout in back for airflow)
    - 360 exhaust manifolds (ported on the short turns, and polished inside)
    - Stock valve covers (will spacer to clear rockers)
    - Turbo style Dynomax 2.5" mufflers, dual exhaust
    - 91 octane pump gas
    20170728_065425.jpg

    So far, I have the following setup on the engine:
    - 360 block, 0.030" over
    - KB107 pistons, +0.005" deck height
    - 0.032" squish, closed chamber heads
    - Edelbrock heads, OOTB RPM
    - RPM Air-Gap Intake
    - Edelbrock 800 cfm carb
    - Comp Cams 275 DEH, Hydraulic, 219/235 @ 0.050", .462"/.482" lift
    (previously installed to work with exhaust manifolds)
    - 1.5 roller rockers
    - Static Compression ~11:1

    The car has a 3000 stall converter, 3.91 gears, and will have 26" tall 245/45/17 RE-71R tires.

    This engine will spend most of it's life at 3000-5000 rpm, but needs to idle when stuck in some traffic. I don't care about vacuum inches, it's manual brakes & steering.

    Questions:
    - With this cam / compression combo create too much cylinder pressure? (for pump gas)
    - Should I change to 1.6 ratio rockers for more lift?
    - Cam intake centerline is 106°, should I advance or retard it a bit?

    - On the cylinder heads, I plan to reduce the head bolt lump, de-shroud the valves, and do a light bowl blend.
    - Any other tips on these heads to maximize flow around the valves at 0.300"-0.400" lift?


    I know it's hard to make recommendations over the web, but this is only the second engine I've fully built, so really needing some help.


    Thanks,

    Ryan
     
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    • autoxcuda

      autoxcuda Well-Known Member

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      Seems well thought out. I would worry about that compression and 91 pump gas though.

      3.91's might be a bit for a track day. But depends on your track.

      Knock any rough spots in chamber. Debur that triangle point were the valve machining circles come together. Match head chamber bore to block bore on sides.

      But andouble pumper probably give you better throttle response all the way around.

      One with adjustable throttle blade helped me fine tune drivability just that extra bit.
       
      Last edited: Oct 13, 2017
    • rumblefish360

      rumblefish360 so close yet so far away

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      Your cam is way small, step up in duration.
      Do so move to a 1.6 rocker.
      Install the cam as per spec card and try it out from there to see how it performs. Experiment on it later after you get a good base line of how it performs.
       
    • Kicker92

      Kicker92 Well-Known Member

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      Thanks autoxcuda & rumblefish360, your posts on other threads have been a great help in figuring out this build so far, especially the chassis setup.

      I will certainly smooth out any hot spots on the head chamber, and probably pick up a couple cc's in volume there while maintaining good quench. I've got a burret on order to balance out the chamber volumes.

      Our local track is relatively low speed, I should be hitting about 110mph on the one long straight, but it's just lapping days so can always lift for a bit there.
      Track.JPG
       
    • Kicker92

      Kicker92 Well-Known Member

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      For the cam, I had gone with a split pattern to try to help with the exhaust restriction.

      Looking at the cam card though, it seems to have a pretty slow ramp compared to other:

      Comp 275DEH:
      • Advertised Duration (Int/Exh): 275/284
      • Duration @ .050 (Int/Exh): 219/235
      • Gross Valve Lift (Int/Exh): .462/.482

      Looking around at other similar cams, I see Lunati's version:

      Lunati 10200704:
      • Advertised Duration (Int/Exh): 276/284
      • Duration @ .050 (Int/Exh): 234/242
      • Gross Valve Lift (Int/Exh): .513/.533
      This has far more duration at 0.050", so I would assume a much steeper ramp.

      How much larger on the camshaft would you suggest as a starting point?
      And does the longer exhaust duration make sense?


      Thanks,

      Ryan
       
    • nm9stheham

      nm9stheham Well-Known Member

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      I ran your numbers and would put in a .050" thick head gaskets. That will put the static CR at 10.6. You can put in a thicker head gasket to drop SCR and DCR, but that will do away with your quench gap; that effect helps to fight detonation.

      DCR with you original cam and a .050" thick head gasket is 8.5. I think you can run it with the AL heads but you're gonna have to stay on top of your tune. And be ready to do some octane treatments if need be. Don't go high on the ignition timing; IMHO, you have all sorts of compression and torque so it won't be needed anyway. And if you smooth the chambers and add just 2 cc's to the volume, your SCR and DCR are gonna drop a bit over 0.2.

      The DCR number above is based on the original cam at a 106 ICL. I would not advance it at all.

      I think RF360 is concerned with the DCR and is suggesting you go for a longer duration cam as in a 284 duration type. I agree on being cautious on this engine but would try it myself at this combination if I wanted to get as much as I could out of it. Keeping low RPM torque is important for this use, and the higher the cam duration, the less low RPM torque you get. The Lunati may or may not lower the DCR; the .050" durations have less to do with DCR than the advertised duration. (But that also depends on the DCR calculator you use....) The Lunati will give you more breathing for the same advertised duration, but with the heads you have and the RPM band of use, peak HP is less of an issue. (BTW, my racing discipline has been rally, and it is the same deal: a wide torque band trumps peak HP aaaaaall day long.)

      As for the torque converter, I seriously would go to a 2200 or 2500 stall TC. Here is the reason: When you pile into a corner and get ready to pick up the throttle to exit the corner, it is gonna take another few tenths of a second for the TC to lock up hard with the higher stall speed. That few tenths of a second is an eternity for road racing and rally, in terms of getting the torque to the rear wheels and setting the car, transferring weight, etc. You have an engine that is gonna have gobs of torque waaay down towards 2000 RPM, plus a 3.91 gear; it is gonna break the tires loose at will with even a 2000 RPM stall TC!

      Hopes this helps... sounds exciting!
       
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      • Kicker92

        Kicker92 Well-Known Member

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        Out of curiousity, what is the DCR calculator that you use? I've only been thinking in terms or static CR and cylinder PSI because that's what I'm familiar with.

        Longer duration = hopefully more scavenging on the overlap and the later intake closing for lower DCR?

        Stepping up a notch for a split pattern would be this one from Lunati:
        • Advertised Duration (Int/Exh): 284/292
        • Duration @ .050 (Int/Exh): 242/252
        • Gross Valve Lift (Int/Exh): .533/.552
        • LSA/ICL: 110/106
        Not sure if this would start to be pushing it for still keeping a streetable idle?

        Good point about the converter, I have the stock one and the 3000 stall 10" TCS unit.
        Perhaps I should sell both and find an 11" - 2500rpm one.
        Were the factory TC's around 1600-1800 rpm?

        I appreciate the help! and I am looking forward to getting this setup on the road.

        Here it was as restored: (the white GTI is what it needs to keep up with!)
        20170715_133342.jpg 20170715_143220.jpg 20170715_133350.jpg
         
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        • nm9stheham

          nm9stheham Well-Known Member

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          I use the Pat Kelley calculator; it is online as a downloadable program. Look near the bottom of this page: Dynamic CR

          You can quickly compute SCR on tab 3 and then put in your cam info on tab 2 , then stroke and rod length on tab 1 and then go back to tab 3 and check the DCR box and get DCR. (The trick around a 'bug' in the program is that when you change the cam, then you have to:
          - recompute the 'dynamic' stroke on tab 1
          - go back and uncheck the DCR box on tab 3, compute the SCR again, and then check the DCR box and compute the new DCR. It seems to need that process to fetch the new cam and stroke info from tabs 1 and 2.)

          The DCR is an indicator of what the compression will really be with the intake valve closing angle, and thus is a better indicator of how prone the engine is to detonation. That is all modified in a good way with your quench gap and the AL heads. I ran a low 8's iron headed engine with quench, for years on the road, and towed and did all sorts of low RPM stuff with it, and did not have detonation issues. I did have to run it on premium, and I did have to limit total ignition advance. With you AL heads, you should be better off and can run up into the mid 8's DCR with some care.

          Yes on the stock TC stall speeds. BTW, I always rallied with a manual trans, so that is part of my aversion to a high stall TC. You are already going to lose the advantages of 'setting' the car with engine braking through the trans. I'd be curious to hear from others on this point.

          As for the cam.....mmmm I personally still would go with the shorter cam durations and work with it. IMHO, it is all about a wide torque band and that starts with a low RPM torque curve, which starts with short cam durations. But it is a somewhat a matter of comfort with the DCR situation; some are averse to getting into the 8+ range, and others will work with it.

          As a side note, the Lunati Voodoo cams with their steep ramps put more stress on valvetrains. Ditto with the 1.6 rockers. The better lift-to-duration ratio of both helps with breathing but there is a cost in stress. I chickened out on my son's 340 and used a milder ramp Crane cam (less valve train stress) but with 1.6 rockers (more valvetrain stress).
           
        • cookietruck

          cookietruck Well-Known Member

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          this is what i was going to mention. i would run smoother lobes. better reliability, better valvetrain stability...less worries.
           
        • autoxcuda

          autoxcuda Well-Known Member

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          I'm at 9.7:1 with my 416 and 274-S cam. On California 91 octane, I'm on the verge of pinging. SRT-8's don't pass me on power in the straights.

          I think the 11:1 needs to be knocked down a full point. Now that I look at it more the 11:1 l, 3.91's, and the cam seem a little mismatched.

          3.91's and that 110 mph straights will be tough on valve train for 7-10 lap sessions. Have you consider a solid cam?
           
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          • Kicker92

            Kicker92 Well-Known Member

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            Ok, playing around with the calculator a bit:

            If I kept the 0.032" quench, but shape the chamber out to 68cc (similar to other CNC heads, so the meat is there):
            Static CR goes to 10.3 (vs 10.9)
            DCR goes to 8.3 (vs 8.8)

            Does that sounds like it's closer to a reasonable limit if I can keep it running cool?


            As far as the track goes, the hard corner just after that main straight about 30mph, so lifting on that section really saves the brakes from cooking.

            Most of the rest is about 80mph tops (hence the 3000-5000 rpm band), so similar to street driving.

            The bottom end is fully balanced, and I should be able to redline around 6500rpm if it's still making power.
             
          • nm9stheham

            nm9stheham Well-Known Member

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            Are you using AL or iron heads? Open chambers? Quench? AL heads are good for 0.5 to 1 full point more in detonation tolerance, and open chambers detonate more readily than closed ones. Plus the Edelbrock chambers are fairly smooth out of the box which helps. And with your 274 solid cam lashed properly, the actual duration at .006" valve lift is gonna be more like a 265-267 duration, so that is making your DCR being relatively higher than with a hydraulic 274. So let's be sure to compare apples to apples. (BTW, it sucks that the west coast is stuck with 91 octane...)

            BTW, OP..... .032" quench is getting too tight IMHO.... the pistons will rock and piston-to-deck heights will vary cylinder to cylinder due to deck variations and rod length variations. Put the quench gap at least up into the high 30's, or IMHO preferably the low 40's.
             
            Last edited: Oct 13, 2017
          • autoxcuda

            autoxcuda Well-Known Member

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            I'm using Aluminum Edelbrocks. I have quench too. And I've smoothed any sharp edges for hot spots and fit cyl head chambers to block to un-shroud valves and reduce point for hot spot.

            I've seen some engine builder say that aluminum head 1/2 to full point detonation resistance is over exaggerated.

            California 91 is high oxygenated too.

            What's the gas quality in Vancouver WA like??
             
          • MOPAROFFICIAL

            MOPAROFFICIAL Well-Known Member

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            .030-.035 quench is fine.
             
          • Kicker92

            Kicker92 Well-Known Member

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            Close, it's actually Vancouver, BC, Canada. And our gas here is pretty poor. Most is 10% ethanol, to get to 91. I can get "94" at some stations, that is about equal to the 91 in Washington state. Our GTI is running 16psi, and likes the 94 or else pulls 3-4° timing. That's a high compression direct injection motor, so a bit more complex.

            As far as the quench goes, my machine shop held that to a pretty tight tolerance.
            Haven't assembled the bottom end yet though, so will measure carefully the installed piston height.
            I figured starting at that number leaves thicker head gaskets as an option during assembly, like the Felpro SD509.

            What would be the advantage of a solid lifters in this case vs the hydraulic?

            There's very few older cars out at the track here, most are drag racing. It's been hard to get info locally on setups, so I appreciate the help.
            At what point is there just going to be too much torque on corner exits to make use of with a 245-255 tire?
             
          • nm9stheham

            nm9stheham Well-Known Member

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            With the 3.91 gears, you are already going to be able spin tires at will in 1st. At what point up the curve they will spin in 2nd is perhaps more of the question. But that is what your brain and right foot are for... to manage that. Having the torque and managing it is better than not having the torque. Try rallying someday... in loose gravel, mud, snow, ice..... a stock Hyundai 1.8L in 4th gear will spin the tires LOL

            BTW, who would pull (grind) the material out of the heads? 2 cc's is not all that hard. But finding 5-6 cc's of material and not going into the worn area gets harder; it was quite worry to me when I ground out 6-8 cc's from some iron chambers a long time ago. If the bottom end is all together, then I can see not wanting to touch the pistons.

            And as for the quench gap.....there will be piston and bore wear and the pistons will rock more and more over the long term. So if you want to keep this engine for a long period of time, then keep that in mind as you think about piston-to-head clearance; .030" is the minimum that the local racers around here use but that is for engines that get torn down and refreshed regularly. More is wise/necessary for long term use.
             
            Last edited: Oct 14, 2017
          • nm9stheham

            nm9stheham Well-Known Member

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            Tnx. that is good reference info. And, yes, I generally think of a half a point of advantage being what you can count on with AL heads. So then the timing and effectively smaller cam and the fuel come into play.

            When running oxegenated fuel, the combustion speed is lower and so timing would logically be increased, but the slower burn of MTBE may still make the combustion slow enough to increase detonation possibilities. Gasahol burns faster so is better in that regard.
             
          • Kicker92

            Kicker92 Well-Known Member

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            "With the 3.91 gears, you are already going to be able spin tires at will in 1st"
            This is the part that I'm trying to figure out... The previous build was a mild 318, and traction was already pretty limited in 1st.

            Getting a bit off topic from the engine build, but:
            Would 3.23 gears and an 11" converter be a better combo?

            Street tires only allow for so much of a holeshot at traffic lights, and one the track / autox 1st gear may be useless?
             
          • nm9stheham

            nm9stheham Well-Known Member

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            Well, I have been wondering why the 3.91.. but with a 318 that makes more sense. I was thinking 3.55 would be better all around and you're still gonna be able to spin tires at will in 1st. But IMHO, it depends on the track(s): I personally would set the rear gear to match the peak engine RPM (minus a few hundred RPM) in 3rd gear at peak expected speed on the long straights. I personally would not set the rear gear 'just' to limit rear wheel torque... again, torque management are what your brain and right foot are for.

            And I would expect you to use 1st in some auto-x's that are set up tight to be fair to smaller, low HP cars.

            And IMHO yes on the 11"..... stall in the lower 2000's range; better torque control from the throttle with the TC locked up is my thinking. (But realize that I come from a racing world where traction is very limited and torque control is really vital.) Autoxcuda may have a better viewpoint.
             
          • autoxcuda

            autoxcuda Well-Known Member

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            In autocross, most auto cars run in 2nd gear in SCCA course. The 1st is just too much torque multiplication. Too "hard on, hard off". Not smooth. Most run 3.23 gears. You may launch in 1st. And might have that 1-2 super tight corners that you dip to 1st. But that usually upsets the car. Smoother and what seems to be "slower" is usually faster.

            At the track, you'll never use 1st. And your experience will heavily dictate your speed/mph. I think at 5500 rpm up sustained you are going to get some loss of lift and/or valve float. The weak link to RPM is usually valveteain before bottom end.

            I ran about 4 full track days with my 340 auto (.450/.455 268/272 "761" hyd), AVS, Stealth DP, 3.23 with stock oil pan. Then I had a pro instructor drive the car. He carried much more speed into, during, out of corners. In two laps the lifters collapsed. Oil pan starved, foamed and/or oil stuck in valve cover.
             
            Last edited: Oct 14, 2017
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            • 72bluNblu

              72bluNblu FABO Gold Member FABO Gold Member

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              I'm late to this show, and I think autoXcuda's input is better than what mine would be anyway. But, I can comment on this cam if it's still a consideration. I run that lunati 60404 in my 340, which is a .060" over '68 340. Compression is 9.8:1 with the KB 243's .018" over the deck. Heads are iron 308's, chambers are 65cc's, 2.02/1.60 valves, stage II ported and flowing 264 cfm @ .500". I run it with a eddy air gap, holley ultra 750 double pumper, doug's headers, and currently have it in front of an 833 with a 3.09 first gear, 26" tall tires and 3.55's.

              Idle for the street is getting a little borderline, it only pulls about 11-12" of vacuum at idle, which is around 750 rpm. I had to play with my timing to run California 91 octane, I'm at 22* initial but I run heavy springs in my distributor and my total is limited to 32* all in mechanical. Advertised power range is 2200-6400, and that's the truth. It does not like to pull below 2200. And really it's not happy until its at 3k if you're going to stomp on it. Past 3,500 it will push you back in the seats hard, and it goes from 3,500 to 6k in a heartbeat.

              Overall, it's a big cam for the street. For the daily driving I do it can be a bit of a pain. On the track you'd want to keep it at 3k or higher, stall is supposed to be 2800 or more. The 3.55's are smaller than what the cam wants, my plan is 4.30's and a T56 to keep the top end speeds, but still have 2 gear with the revs up for autoX. Here's the idle



              ***Edit***
              Here's the compression and DCR info for it, as I said I've had to pull timing to manage this for 91 octane
              compressionR-DCR340.jpg
               
              Last edited: Oct 14, 2017
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              • MOPEkidD-3

                MOPEkidD-3 Torsional Member

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                Remember the OP intends to use factory 360 log manifolds so that will definitely influence the cam choice... I don't see a built 360 with log manifolds being able to make power at 6000 RPM but that's just me. I understand the reliability and stock-looking aspect but with a fully built engine like you're planning the log manifolds will be a HUGE choke point and will seriously reduce power and efficiency unless the cam timing is set up for it; if I were you I would get a custom-grind camshaft.
                 
              • Kicker92

                Kicker92 Well-Known Member

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                Thanks to all you guys for jumping in to help, this is exactly why I'm asking the questions at this stage.
                It's seems that I have some mis-matches in this setup, if I understand correctly:

                1.) DCR is generally too high for 91 pump gas: Baseline @ 8.8:1 , goal would be to reach under 8.2:1
                Possible solutions with current bottom end:
                - Increase cc's of cylinder heads (I think some CNC prepped edelbrock heads are 68cc's, drops DCR to 8.3:1)
                - Increase head gasket thickness (0.054" gasket would drop it to 8.4:1, but quench height would become 0.049")
                - Increase cam duration from 275 to 284 (only lowers to 8.7:1)
                or a combination of the above???

                2.) Gear ratio / high stall converter:
                - Seems like 3.55 gears with a 2500 stall would be an ideal compromise here.
                - Alternative might be to keep the 3.91's, but put in the stock 11" converter.
                A bit slower off the line, but the gearing puts me at about 5600rpm at 110 mph, and backroad cruise of 2000rpm at 40mph

                3.) Manifolds:
                - I'd like to look of it being mostly factory, and the lack of headaches that seem to come with headers.
                - That said, if this thing is going to die off after 4500-5000 rpm, or have heat issues from choking that off, I may need to change.
                - Headers would need to be shorty style, any suggestions who makes a good pair for the a-bodies?

                4.) Oiling issues?
                - I have a windage tray, and a high volume pump.
                - Other than that, the oiling system is stock and I haven't considered it much.
                What did you end up doing to keep it picking up oil at the track?


                Thanks,

                Ryan
                 
              • autoxcuda

                autoxcuda Well-Known Member

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                Is cutting the pistons a possibility? How much needed, is there enough meat?

                Only shorties I would bother with are TTI's. Not as tricky to install in car as oil
                pan. They are expensive.

                Do you have HiPo cast manifolds?

                Oil pan would be the milodon. It's a tight fit. What Kmember are you running? But hard to put on a fit with motor in car. Protects motor investment. Also not cheap.
                 
              • MOPEkidD-3

                MOPEkidD-3 Torsional Member

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                Have you measured the volume of the chambers on the new Edelbrock heads yourself? Sometimes they can vary from advertised spec. I didn't quite understand your first post did you mean the engine is already assembled with all those parts?

                Your short block is like a 360 I did, same pistons but they weren't .005" above deck, was your block decked? Is this something you or your machinist measured after assembly or is it based off just numbers-crunching? Also I think the Fel-Pro #1008 head gaskets would be close to ideal, .039" compressed thickness on those.

                That Comp 275DEH you have might work well with some 1.6:1 rockers to bump up the lift, large split pattern is nice for manifolds. And I agree with the lower converter stall and taller gears in the back, 3000 RPM stall and 3.91 gears is more of a drag racing setup IMO.