Reverse Split Pattern Cam - 318 Magnum Head swap

Small Block Mopar Engine

  1. cal30_sniper

    cal30_sniper Member

    Messages:
    21
    Likes Received:
    10
    Joined:
    Sep 22, 2019
    Location:
    United States
    Local Time:
    4:31 PM
    Not how I wanted my intro post to go, but I'm stumped on a cam question and figured I'd better ask the experts...

    BLUF: Should I even consider a reverse split duration cam on a 318 roller build with Magnum heads?

    I'm working on a roller cam 318 LA build from an '88 Fifth Avenue that I parted out. The plan is a bigger roller cam, EQ Magnum heads with stock valve sizes, a '71 340 intake that I picked up, and a rebuilt mid-80s Chrysler Quadrajet. This will all be going in my 3000lb manual everything no-A/C Volare daily driver. I'm looking for lots of mpgs with something that will still merge with traffic and put a smile on my face.

    While perusing cam choices, I came across the Lunati 20200714. Unfortunately, sometime in the last few years since I bought a cam, it seems that all of the manufacturers have taken down cam cards off of their websites. I don't know why, but used to you could open all the info straight up from the product pages at Comp Cams or Lunati. Now they give you the pre-school numbers and leave the rest up to a call to tech support.

    I figured I'd google the part number and see if I could find a cam card. When I did, the first hit was an Amazon Prime listing for that same Lunati cam part number for $140. I figured for that price, it was worth a shot to see if it was real or not, and potentially get a roller cam with specs that I liked for half price. You probably know about where this is headed now...

    For reference, the cam page from Lunati is here: Voodoo Hydraulic Roller Cam - Chrysler 273-360 (W/ Long Snout) 258/264

    It lists 207/213 .485/.485 with a 112LSA and 106ICL. Assuming those lift numbers are at 1.5:1 ratio, because it doesn't say.

    Well, the cam came in today, and it is a brand new Lunati roller cam. The cam card part number is 20200714. So far so good. The number stamped into the back of the cam is 20200714. Even better. Then I looked harder at the cam card, and noticed something interesting...

    uMYHO2j.jpg

    Although the part number is the same, this cam card lists a 213/209, .480/474 on a 112LSA and 106ICL...

    What gives? I would think if it was a custom grind, it wouldn't be carrying an off the shelf part number. I searched these cam specs and came up with nothing, so it's not some other grind that got mixed up. Either its a cam card typo, a custom grind with an OTS part number, or somebody botched the cam grind and boxed it anyways. I plan to call Lunati tech support tomorrow to see if they can answer those questions. I'm guessing this is why it was $140. I checked today and the price was $300 on the same Amazon link now, so maybe they were just trying to dump a botched grind on an unsuspecting customer.

    Now, on to the meat and potatoes of the post...

    Is there any merit to trying a reverse split duration cam with my build? It seems like there are a few posts here and there where certain individuals recommend a single pattern cam, or even a reverse split cam with magnum heads since their exhaust ports flow fairly well relative to intake flow. That makes sense, and I might even buy it with headers. Only problem is, given the extreme budget nature of this build, I had planned to run scrapyard magnum exhaust manifolds and save the header cash for gas money. So is it worth trying this thing, or should I go through the hoops to return/exchange it for the grind I really wanted (while probably paying twice the price in the process).

    Thoughts? Opinions?
     
  2. perfacar

    perfacar Well-Known Member

    Messages:
    1,079
    Likes Received:
    263
    Joined:
    Mar 1, 2006
    Location:
    renton,wa
    Local Time:
    3:31 PM
    when the exhaust port flows too good, it sucks intake charge out, and burns in header, on the overlap stroke. been down this road before, the 576 head mopar sold did that. I tested in on flow bench, up to .250 the exhaust out flowed the intake. this is the overlap area. there is a loss of a lot of power. headers will glow red.
     
    • Thanks! Thanks! x 1
    • cal30_sniper

      cal30_sniper Member

      Messages:
      21
      Likes Received:
      10
      Joined:
      Sep 22, 2019
      Location:
      United States
      Local Time:
      4:31 PM
      That's what I gathered. Seems like if taken too far, you could get into EGR-by-cam pretty quick though.

      So do the magnum heads/exhaust manifolds flow well enough to warrant a reverse split cam, or is this just going to be a waste of time that needs to go back?
       
    • yellow rose

      yellow rose Overnight Sensation FABO Gold Member

      Messages:
      27,518
      Likes Received:
      23749
      Joined:
      Jun 19, 2015
      Location:
      Central Washington
      Local Time:
      3:31 PM



      I'd call Lunati and ask them. That's strange. They did help the exhaust on the magnum head but I'm not a fan of split duration, let alone a reverse split. I don't mind the reduced lift on the exhaust, but why lose the duration? Especially if you are using exhaust manifolds.

      That's all I got. It's worth exactly what you paid for it!
       
    • yellow rose

      yellow rose Overnight Sensation FABO Gold Member

      Messages:
      27,518
      Likes Received:
      23749
      Joined:
      Jun 19, 2015
      Location:
      Central Washington
      Local Time:
      3:31 PM
      I believe perfacar's explanation much better than mine.
       
    • PRH

      PRH Well-Known Member

      Messages:
      2,999
      Likes Received:
      4452
      Joined:
      Dec 14, 2018
      Location:
      So. Burlington, Vt
      Local Time:
      6:31 PM
      In the Lunati catalog it’s not a reverse dual pattern cam.
      You could put it in and check it yourself to verify exactly what it is.
      But first I’d give Lunati a call and see what they say.
      It wouldn’t surprise me one bit if the cam card was just filled out incorrectly.

      It also wouldn’t surprise me that it’s an early version of that part number and it is what the cam card says.
      The recent catalog shows the specs as 258/264, 207/213.
       
    • teringer

      teringer FABO Gold Member FABO Gold Member

      Messages:
      878
      Likes Received:
      225
      Joined:
      Feb 22, 2011
      Location:
      kenly nc
      Local Time:
      5:31 PM
      could be a turbo/blower cam the intake side is bigger.
       
    • mullinax95

      mullinax95 Well-Known Member

      Messages:
      11,537
      Likes Received:
      399
      Joined:
      Oct 25, 2006
      Location:
      Anderson, SC
      Local Time:
      6:31 PM
    • Krooser

      Krooser Reform School Graduate

      Messages:
      2,869
      Likes Received:
      2371
      Joined:
      Jul 19, 2015
      Location:
      Central Wisconsin
      Local Time:
      5:31 PM
      CamCraft grinds a lot of cams with smaller exhaust durations... an anti reversion deal.
       
    • MileHighDart

      MileHighDart Well-Known Member

      Messages:
      4,449
      Likes Received:
      4133
      Joined:
      Jun 3, 2004
      Location:
      Lyons, CO
      Local Time:
      11:31 PM
      Hmmm, interesting. I almost bought that cam off amazon because of the low cost.
      Ended up getting the next step up 20200715, it was also very cheap compared to every other retailer. Got it for $159. When I bought it said (1 left) If you look now its like $295.

      Just checked the cam card that came with it. Cam is advertised as .213 - .219 at .050
      Cam card says .211 - .219 at .050
       
    • AJ/FormS

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

      Messages:
      20,236
      Likes Received:
      7768
      Joined:
      Jan 19, 2014
      Location:
      South-Central Manitoba,Canada, 900ftelevation
      Local Time:
      5:31 PM
      Well if it is backwards ,
      I sure wouldn't put it in at 106*.. unless your Scr is really really low.
      In at 106 it sets you up for an ICA of 56* which is great to make compression with, in a Low-C engine. But that stinking 112LSA then makes the power stroke just 106* which ain't the best for fuel economy. But if your Volare has 2.45 gears well then she'll need all the cylinder-pressure you can find. For this reason; I'm no fan of wide-LSA cams.
      However if the Volare has something like 3.23s, now, for mpgs,she'll want some help in power extraction. So then IMO an install of 110 to even 114; would make some potential for mpgs. However, the cylinder pressure would fall significantly at 114*.,requiring an increase of about 10% in Scr to overcome, which works out to about 10cc less total chamber volume. Since the top end is coming off anyway, just shave the heads and presto!
      Because this is a 112 LSA cam, and say you put it in at 110 and 8.8Scr with any sub 3.55 gear; the power delivery is gonna be somewhat like an electric motor. It won't feel very powerful, but watch the speedOmeter, they don't lie.
      I hope you also kept the automatic from the Fifth, she's a 2.74/1.54/1.00 unit, most likely with a loc-up feature. That's a great trans for this combo.

      But if it's not backwards, I'd install it at ~108 for an Ica of 60* and extraction of 110*, good to go with shaved heads.

      Here's my theory; if the extraction is less than 100* she will be a gas hog. Between 100 and 108, she just gets poor fuel mileage. From 108 to 116 it's getting somewhere. By 120 or better yur passing filling stations and smiling.
      The above is only true when the cruise rpm is kept reasonably low, yet high enough to keep the engine out of reversion.
      And the cylinder pressure is close to as high as possible for the fuel you are using.
      In other words;
      A)you can't expect fuel mileage with big cam, like a 276/284/112 cam at 8/1 Scr with ANY gear, especially one that keeps the engine in reversion. Partly because it has no decent pressure, partly because some of what little it has is going back into the intake, and mostly because at cruising-rpm,power extraction is just too short, and a lot of energy is going straight out the tailpipes.
      B) the stock 318 does pretty good with the 240/248/112 cam in at 8/1 with nearly any gear. Partly because nearly all the pressure it makes, goes into compression, partly because at hiway-rpm it has no measurable reversion, and partly because it has a very long extraction period.
      If these guidelines are used, then the lower the rpm, the higher the fuel economy will be.
      So, if you want BIG mpgs all you gotta do is select a small cam with lots of power extraction,in an engine that makes a lotta cylinder pressure, and gear the car to idle down the hiway. and after that 3000 pounds is waaaaaaay better than 4000; at the high end,every pound counts.
      Well there comes a point ,lol where power extraction could I suppose become too great for what little fuel it is drawing in, but Ima thinking the factory 318 cam (240/248/112) is about as small as anybody would ever install, and it, in at 112, about as retarded as one might consider;still has a ratio of 128 compression to 120 extraction (48.387% exhaust); whereas your 264/260/112 in at 106, has a ratio of 122 compression to 108 extraction (46.96% extraction).
      So no worries.
       
      Last edited: Oct 3, 2019
    • cal30_sniper

      cal30_sniper Member

      Messages:
      21
      Likes Received:
      10
      Joined:
      Sep 22, 2019
      Location:
      United States
      Local Time:
      4:31 PM
      That's one heck of a response, AJ. Thank you.

      I'm going to have to do some more reading and thinking about some of the stuff you mentioned, it does make sense, but my knowledge in that area is a little thin. From what I can gather, my SCR should be between 8.8 and 9.2 with the 62cc Magnum heads. I'll have to pull off the LA heads and see how far the slugs are down in the hole to know for sure. I plan to push as much CR as I can. I'm at over 5000' elevation, so I can afford a little more squeeze on the cylinder.

      The Volare currently has 2.94 gears. The stock 7.25" was 3.23s, but it was on it's last legs (that's how I ended up in the junkyard in the first place). I grabbed the 8.25" out of that Fifth and swapped it in first, but I just couldn't stop thinking about the low miles roller 318 and sweet M-body instrument panel that I'd left behind, so I went back the next weekend, and the next, haha (had to get that V8 K-frame too). I wanted the 904, but the joker that forked the car into the yard broke the bellhousing. That's okay I guess, the car will hopefully end up with an A500 swap down the road anyways.

      I've built a few econo-cruisers along the way, and learned something every time. My best so far was an '87 Firebird with a high compression roller cam 305, a mild Comp Cams grind, backed up by a short ratio T56 and 2.73:1 rear gears. I got over 30mpg with that car on several occasions with a Quadrajet and HEI. That car had a lot better aero than the brown brick that is the Volare though.

      I'm hoping to get on the phone with Lunati tomorrow and figure this out. If I don't get a good answer from them, I'll probably just get with Amazon and pursue an exchange or refund. If I have to pay full price, I'll probably go with the small Magnum grind from Hughes Cams and pair it with some of their EQ magnum complete heads.

      NDUPBYj.jpg
       
      • Like Like x 2
      • cal30_sniper

        cal30_sniper Member

        Messages:
        21
        Likes Received:
        10
        Joined:
        Sep 22, 2019
        Location:
        United States
        Local Time:
        4:31 PM
        Yep, same with mine. Said last one left, and then went up to $300 the next day.

        Maybe they had a batch of grinds that were just far enough off the speed shops wouldn't sell them, so they pushed them to amazon sales.
         
      • Slantsix64

        Slantsix64 Well-Known Member

        Messages:
        2,894
        Likes Received:
        1176
        Joined:
        May 11, 2014
        Location:
        SGV
        Local Time:
        5:31 PM
        I used roller regrind by oregon cams number 1006 260intake 264exhaust. 1989 318 roller block 302 head mild port job ld4b intake 904 9:5CR with a shift kit recurved dizzy msd blaster coil mopar ECU 3.55 gears getting constant 15mpg city (i live in Los Angeles that where all my driving is). Motor is a beast, best build i have done yet!
         
      • cal30_sniper

        cal30_sniper Member

        Messages:
        21
        Likes Received:
        10
        Joined:
        Sep 22, 2019
        Location:
        United States
        Local Time:
        4:31 PM
        Yep, I read all through your thread. Lots of great info. I think we've got pretty similar build goals. I'm going to spring for the Magnum heads, but plan on running Magnum exhaust manifolds, valvetrain, and a factory 4bbl intake to help even out some of the cost. I considered the regrind, but I think a new factory grind opens up the door for a bit better overall package.
         
      • Slantsix64

        Slantsix64 Well-Known Member

        Messages:
        2,894
        Likes Received:
        1176
        Joined:
        May 11, 2014
        Location:
        SGV
        Local Time:
        5:31 PM
        Yup magnum exhaust manifolds are a great upgrade! I like magnum heads with the 1.6 ratio rockers but remember you need a magnum style intake cause of the bolt pattern which new are almost 400.00 bucks. Only thing that sucks theres not alot of intake options on the magnum carb route, why i have no freaking idea lol. but if you got those 302 heads sell em help out with the cost.
         
      • Slantsix64

        Slantsix64 Well-Known Member

        Messages:
        2,894
        Likes Received:
        1176
        Joined:
        May 11, 2014
        Location:
        SGV
        Local Time:
        5:31 PM
        By the way that cam specs are pretty good to me, thats a damn good price too
        running manifolds split duration works best, the stock magnum camshaft duration is 252/264 .435/.435.
         
      • cal30_sniper

        cal30_sniper Member

        Messages:
        21
        Likes Received:
        10
        Joined:
        Sep 22, 2019
        Location:
        United States
        Local Time:
        4:31 PM
        You can actually get them drilled for the LA bolt pattern instead of the magnum pattern, that’s my plan. I little pricey up front, but I’ve never gone wrong putting money into good heads.

        I picked up a 71 340 Intake the other day from a great Mopar guy on Facebook Marketplace. It should work perfect for what I’m doing.
         
        • Like Like x 1
        1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
          By continuing to use this site, you are consenting to our use of cookies.