Cure for lazy Magnum...Has anyone built a Magnum for 7k+ revs?

Magnum Engine Swaps

  1. MRGTX

    MRGTX Well-Known Member

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    Just tossing this around in my head this morning...looking for your thoughts and opinions here.

    So I have to say it; I find the Magnum 5.9L to be pretty uninspiring in stock form. I'm not expecting a big block killer/hot rod motor or anything but it seems to be lacking a "spark" that makes an engine fun and engaging. Yes, it makes decent power down low but it feels like it's all done midway through the 4k rev range, after which it's just noise...it feels like a very good "truck engine" (which it is)...in all of the good and bad ways that this implies. It just sort of does it's thing and sounds ok (not great despite headers, flow-through mufflers) doing it.

    My old stock 318, despite making much less power and being even less happy to rev, was just more smooth,responsive and rewarding. That was one of the first engines that I ever loved...I know this is totally subjective but the Magnum 5.9L isn't winning my heart the same way.

    I'm not really interested in the usual stroker mod path. I know it's a great way to make more power but I suspect that it would accentuate the things about the motor that are already there, low end grunt, reluctance to rev... Please disagree if I have that wrong.

    Has anyone ever built one of these motors to make power above 6k? How about 7k? Has anybody built one to have a personality more like the LA 340?

    IIRC, the heads are the biggest bottleneck to breathing at high RPM....does that still apply with the new Trickflow heads?

    How did you go about matching a cam/intake manifold?

    What lighter weight pistons have you guys had good luck with?

    Any thoughts an opinions are welcome. For the record, outside of this forum, I'd never speak ill of a Mopar V8...let's keep this between us. :D
     
  2. dano

    dano Evil Handy Man

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    So give us a rundown of you 5.9 like mileage, compression test, etc . Also what are all the items attached to the long block because this may be a tune issue. What have you tried? It could be mechanical, flat valve springs, worn rings, etc.

    Yes, a 5.9 can be built to run and run really well. There are good flowing Mag heads, if you need them.
     
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    • 318willrun

      318willrun Utube channel 318willrun

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      there is nothing that defines your definition of "lazy". 1/4 mile times of 15.2's? 14 flat? 13.3's? 12.4's? What is your build, gears, transmission, car, and what is it that you are calling lazy?
       
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      • toolmanmike

        toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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        No need to rev a small block that tight.
         
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        • rumblefish360

          rumblefish360 So close, yet so far away FABO Gold Member

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          Hey Mr.GTX. What you are experiencing is about normal due to a few facts that one you even stated, it is a good truck engine. I’m not sure if I’d take the stock engine short block to 7K, though it is an interesting thought..... LOL!

          First item in upping the lower in an OE engine is its ability to breath in and out only followed by the supporting parts. Now, what does that mean and what parts are we looking at for this air pump? Let’s start at the inside and take note of the camshaft. (I can’t remember what the specs are but) The camshaft is small and good to around that early to mid 4K RPM mark. That’s all that cam really has.

          As a cam basic guide line, the replacement cam you choose should then operate in the power band your going to be using. Error on the side of caution for the street.

          The supporting parts to that puzzle piece would then be the springs. They will allow the cam to do its job by keeping the valves opening and closing as dictated by the cam. IMO, it is best to gather all the associated parts from the cam grinder. AKA - all Lunati parts, all Comp parts, etc...

          Making use of stock or stock modified heads or aftermarket heads is your call. The new trick flow heads offer a bolt on solution to help. They enable the stock Magnum front acc. drive to be used and the use LA intakes. The better it flows, the more power you make.

          (OK, that’s a DUH! NO CHIT SHERLOCK! Statement, but an excellent high flowing and high quality head extends the lower making abilities of the cam.)


          Which brings us to..... the intake and carb.
          Which should also be high quality and high flowing.

          Intake manifolds are also like cams, there also given a listed operating RPM band/range. Depending on the cars usage, weight and camshaft being used,
          (this is a build dependent & vehicle usage thing. It can get a little dicey)
          somewhere around the 3500/4000 rpm range is where a single plane intake would be of great benefit. But also don’t be surprised if you get beat by a dual plane intake.
          If the car is not light enough or slightly off on the combo or not taking full advantage of the engines power.... loose you will.

          IF your driving this primarily in the street, I would be looking at a RPM or Stealth that is worked on. Port matched and ported up the runners, some plenum work as well. A spacer if needed. And only if needed.

          Just because an engine can and does turn 7K doesn’t automatically dictate a single plane intake. You can turn this RPM with a medium size street cam and actually make power there. You may very well turn in a lower ET with a dual plane if the car is on the heavy side.

          You asked about the lower end. As a minimum, for north of repeatedly 6500 RPM blasts on a track, a better piston should be employed. You could use a Hyperutecic very well. I personally like a flat top, 2 valve reliefs. You can find that with a KB-107 or the Speed Pro (H116CP) slug pictured below.
          94F64606-4D84-4331-BB30-3DB38F12E741.jpeg D9F2EDFE-3BC4-460C-B12D-6BB08CC87C37.jpeg C939A9CD-07DA-4077-BBC3-17899B7E3D88.jpeg
           
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          • j par

            j par Well-hung Member

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            • jos51700

              jos51700 Well-Known Member

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              One thing to be sure of...if the motor is a newer design, the engineers were really good at filling in any dips in the midrange torque curve. This makes an engine seem less like it's 'coming onto the cam' and it seems like it isn't as snappy, because it never really wakes up. It's awake the entire time.

              That said, put a cam matched to your intake and exhaust in it, and get back to us ;-)

              And I'm wondering about your assessments. I've yet to see a 318 that didn't like to rev less than a 5.9.
               
            • toolmanmike

              toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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              You need to look closely at the Nascar engines. They are designed to run 7000 + rpm and you need to duplicate that with your Magnum. Good luck! Every rpm you go over 4000 you will loose power from idle on up.
               
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              • DrEamer

                DrEamer I suffer from cars on the brain!

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                • RustyRatRod

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

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                  Naw man. Yall go ahead. LOL
                   
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                  • Kern Dog

                    Kern Dog Well-Known Member

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                    WTF ??
                    What is the point of revving to 7000 rpms? Engines like that are hard on parts and have less low speed torque than a Harbor Freight flash light. You have a heavy car that needs torque to get it moving. High rpms get horrible mileage too.
                     
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                    • Slantsix64

                      Slantsix64 Well-Known Member

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                      you need to recurve the dizzy also, the 5.9 camshaft has less duration and lift than the stock 5.2 magnum camshaft. I say dizzy with fbo limiter plate replace the heavy spring with mr gasket mopar kit, swap that camshaft for something 268/270 should rev good, but dizzy first
                       
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                      • rumblefish360

                        rumblefish360 So close, yet so far away FABO Gold Member

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                        He has to get a proper distributor first since the Magnum distributor is empty inside.
                         
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                        • 72Dart6pack

                          72Dart6pack Well-Known Member

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                          Nascar guys push 9400 rpm all the time. 7000 rpm sounds like your building it for Grandma. Step up to the plate and go Big or go Home.
                           
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                          • mopardude318

                            mopardude318 Well-Known Member

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                            Damn you guys sound like a bunch of old ladies.

                            I like twistin ‘em high! That’s good music.
                             
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                            • Kern Dog

                              Kern Dog Well-Known Member

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                              Yeah....LOTS of NASCAR 50 year old cars seen in commuter traffic....where 9400 rpms make the most sense.
                               
                            • dano

                              dano Evil Handy Man

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                              But the LS guys can get a JY engine for $50 put a cam in it and make 800hp, rev to 10k, get 30mpg, solve world hunger and drop all the panties!
                               
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                              • SSVDP

                                SSVDP FABO Gold Member FABO Gold Member

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                                The big limitations on the 5.9 are
                                1) intake manifold, it doesn’t tune and cuts HP.
                                2) intake valve size -add 2.02”
                                3) compression ratio- a little bit more will help
                                These three together with the ‘98 Jeep 5.9 calibration work well together.

                                The stock exhaust systems are extremely restrictive too.

                                Sadly the LA rocker shaft was replaced for the Magnum engines. I think getting some of the valve train stiffness back would extend RPM range but not sure exactly how much this would help.
                                 
                              • rumblefish360

                                rumblefish360 So close, yet so far away FABO Gold Member

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                                Is he using the stock FI & computer in his hot rod?
                                If not, add a RPM (or knock off) 650/750 carb, a nice distributor w/ignition & headers.

                                Adding a cam is a plus.
                                A bigger valve size is a plus.
                                The 9.0-1 ratio is OK.
                                 
                              • RustyRatRod

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

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                                He can just get the Hughes Magnum shaft mounted rockers.
                                 
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                                • MRGTX

                                  MRGTX Well-Known Member

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                                  Excellent information and thoughts all around, guys.
                                  @rumblefish360 , you're the best, sir. Tons of great info points there. I'm looking into those pistons...do you think the stock crank and rods are up to the job?

                                  The engine is a relatively fresh (~15k miles) stock Magnum 300. Stock cam (195@50, .433 lift IIRC), stock 62cc heads, stock ~9:1 compression (though I haven't compression tested mine to be honest), Mopar dual plane intake, 650cfm carb, Doug's headers. 16* initial timing, ~35* all in. I have the FBO ignition box and a generic billet distributor from Jegs.... I've tried to free up some responsiveness and hp with electric fans and manual steering too. Don't get me wrong, the engine is fine. It just doesn't set my pants on fire.

                                  Sadly, it's spinning (mildly built) slush pump auto but a manual conversion is in the works...hopefully in in time for the spring driving season. It has been a long time since I've driven a performance-oriented car with a manual gear box that can't rev into the 7k range.

                                  I hear you...and we do not need to agree on this.
                                  First, what's your definition of "heavy?" No, it's not a Porsche 914 or Lotus Elan...but it's no Caprice either! Heck, it's not even as heavy as a modern compact.
                                  In any case, once I got a taste for higher revving engines, I recognized that as something that I loved and wanted more and more of. Yes, there are lots of tradeoffs...efficiency, durability, low end power...none of that matters to me once the cam switches on and the motor comes alive with the revs "turned up to eleven." Ask the guys who drive first gen Z/28s and Boss 302s why they love their high winding "tiny" engines!
                                   
                                • toolmanmike

                                  toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                                  Really? Hey, what is your age? If your engine is out of a Magnum it's probably a Gem 3 Hemi. What is it?
                                   
                                • MRGTX

                                  MRGTX Well-Known Member

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                                  Has anyone attempted to replicate a Nascar build? I have to imagine that this could be pricey but I do love that idea...
                                   
                                • toolmanmike

                                  toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                                  Please answer post #22
                                   
                                • MRGTX

                                  MRGTX Well-Known Member

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                                  I think I was writing post #23 at the same time.

                                  The engine is a Magnum 5.9 crate engine.

                                  What's your age? Did you forget information from earlier in the thread already? :D
                                   
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