Stock heads/rotating assembly, hot cam/vlave springs- how far can you go?

Magnum Engine Swaps

  1. MRGTX

    MRGTX Well-Known Member

    Messages:
    1,764
    Likes Received:
    588
    Joined:
    Sep 24, 2007
    Location:
    CT, USA
    Local Time:
    12:46 PM
    I realize that I've got three questions running at once on this forum. One on FI, one on head swap and now this...but they are pretty distinct topics and searches didn't quite answer all of my questions. Personally, it looks like I'm going to have to save up for a while longer to do the heads right (or just buy a new BP Engines crate motor :D )...so I'm looking for a stopgap measure to still be able to have some fun this summer. Perhaps a cam/valve spring upgrade could do the trick for now.

    Based on the Magnum 380 crate engine, it seems like there's at least 80hp to be had from a cam/valve spring/intake upgrade over a stock 5.9L which is pretty amazing. Unless I'm mistaken the difference between the Magnum 300 (which I have) or a junk yard 5.9 are relatively minimal.

    My question is about whether or not this is the best we can do on the stock heads/rotating assembly or if people have done better with a custom grind? If you've gone this route, how did your motor come out? Is it possible to get some good lope/overlap sounds?

    Would the use of a dual plane intake be a detriment? I have to figure that Mopar Performance went with the single plane for a reason...

    So the question was asked in general so that it might benefit other forum members....but before anyone asks, here's my application: '73 Sport, nearly full weight (fiberglass hood and a few weight reductions here and there. The drivetrain consists of a somewhat built 904 (TF2 shift kit, ~5800 rpm governor weight, stronger bands/clutches, deep pan), a TCI Streetfighter 2600 rpm stall, aluminum driveshaft, Moser 8.75" with Eaton helical limited slip, 4.10 final drive.

    Almost all of my work so far ha s been suspension/steering/brakes, all focused around handling. I prefer to use my car for general backroad hooligan driving so I really want a motor that breathes and feels relatively happy revving out upper 5ks at least. Can that be accomplished with stock heads? Is it worth the trouble?

    Once again, any experiences or opinions are extremely welcome.
     
  2. Garrett Ellison

    Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

    Messages:
    2,018
    Likes Received:
    1469
    Joined:
    Jan 1, 2018
    Location:
    Southwest VA
    Local Time:
    1:46 PM
    Hydraulic roller cam? This is one of of those times I’d be talking to a custom cam grinder.
     
    • Agree Agree x 3
    • Thanks! Thanks! x 1
    • rumblefish360

      rumblefish360 So close, yet so far away

      Messages:
      36,701
      Likes Received:
      8533
      Joined:
      Jun 21, 2005
      Location:
      New York, on a Island
      Local Time:
      1:46 PM
      Holy chit that’s a lotta questions. I’m going to break it up.
      This shouldn’t be to hard, but you may be disappointed.
      True! The difference is a cam, intake and I also think the suggested header and carb sizes.

      Better? What is better? If more HP is better, then it will happen at a higher RPM than the cam issued by MP. There will be a lack of torque to go with it down low.
      The Rhythm of the over lap sound can be enhanced. But the question is, will the new timing events work well?
      IMO, the MP dual plane would not be good on the 360/380 engine. MP used there own single plane intake because it suites the intended purpose better than the dual plane does. The RPM, IMO, would be the intake to use on the 360/380 engine. But that is not a MP intake and that’s the reason they didn’t use it.

      This reads like a street car that’s able to lay down a decent strip number for what it is. But if you use that MP 380 cam, I think that stall is a bit on the “Way Low” side.

      There ability to rev is controlled by the valve spring.
      There ability to make power is limited by the amount of air they can flow.
      Actual RPM really has nothing to do with it. Though the small stock window and what the head can flow is a limiting factor, I do t think I could put a RPM point on the head and say, that’s all there good for. Though a larger cam would make more power, with a limited flowing head, the power band window becomes smaller.

      If you want to make that “For now” change until your other engine is done, I suggest a copy of the 360/380 engine. But! You probably can not get that cam anymore. Which I think is a good thing. Comp Cams has a very similar mechanical cam that will have more lift with the 1/6 rocker since there listed lift is based on a 1.5 rocker.
      You can also search for a similar spec roller cam.

      In addition to the better cam, I would most certainly use a Edelbrock RPM for the Magnum engine.

      Hughes engines has a Trick retainer and spring package for the Magnum head. IIRC, they said it was good until a .540 lift.
      I don’t see a need for a custom grind cam for this temporary engine.
      You can always talk to the cam grinder and ask to move the centerline to a 108 if you wanted to. That would also lend to “That Sound” you mentioned about.
       
      Last edited: Jan 8, 2020
      • Like Like x 2
      • Thanks! Thanks! x 1
      • roccodart440

        roccodart440 Well-Known Member

        Messages:
        5,378
        Likes Received:
        4374
        Joined:
        Apr 19, 2010
        Local Time:
        1:46 PM
        With the eddy RPm vs. the victor there is a difference in peak HP, but under 500hp it is nominal and the power under the curve is better with the dual plane. IMO I'd use the DP on anything under 500hp especially if it will se a decent amount of street time.
         
        • Agree Agree x 2
        • Thanks! Thanks! x 1
        • Bobzilla

          Bobzilla Well-Known Member

          Messages:
          583
          Likes Received:
          399
          Joined:
          Aug 10, 2017
          Location:
          Livonia, Michigan
          Local Time:
          1:46 PM
          Do I understand correctly; you have an actual Mopar Performance 300 HP crate Magnum? Is that running in the car now? If so, how many miles on it?
          If your goal is to do Trick Flow heads, don't bother with stop gap upgrades. It will cost more in the long run.
          Mopar 380 crate Magnum camshaft would have performed less than stellar with that tight converter, but the 4:10 gears would have helped. I would not copy that camshaft for your build.
          Mopar always gave shitty support for their parts. I never got to check the pistons in a 380 crate engine. There was some indications it may have had higher compression than the 300 HP version, but who knows.
           
          • Agree Agree x 1
          • MRGTX

            MRGTX Well-Known Member

            Messages:
            1,764
            Likes Received:
            588
            Joined:
            Sep 24, 2007
            Location:
            CT, USA
            Local Time:
            12:46 PM
            Thanks to everybody!

            rumblefish360, you've come through with great answers to my questions many times. It's always extremely appreciated. Thank you.

            Very good points about the limitations of the heads and the sacrifices in the low end in favor of higher rpm performance...that is all understood. A net improvement in power with a bit more joy up high in the band would probably be enough to keep me happy for a while.

            I realize that the current setup reads as if it might be "ok" for a street/strip setup but there's just something off about the combo and it seldom feels good. I believe the 3spd transmission and the short gears are amplifying the "short legged" feel of this motor.

            So...It sounds like I might do well with something similar to the Magnum 380 cam, the Hughes retainer and spring package and the Edelbrock RPM Airgap intake? It also sounds like you're not optimistic...

            Correct. The engine is a Mopar Performance Magnum 300. It's running and doing fine. I don't know the exact mileage on the motor. I'm the second owner but has always been cared for as far as I can tell. It has the original Mopar M2 aluminum dual plane and a 650 carb. It runs well but does the usual Magnum thing where it falls on its face pretty early in the rpm range. Again, nothing wrong with the engine, it just feels like it would be more at home in pickup truck or a full sized van.
             
            • Thanks! Thanks! x 1
            • MRGTX

              MRGTX Well-Known Member

              Messages:
              1,764
              Likes Received:
              588
              Joined:
              Sep 24, 2007
              Location:
              CT, USA
              Local Time:
              12:46 PM
              I guess the question for me is whether or not the Eddy Airgap is worth spending the $300ish compared with the Mopar dual plane that I already have. I had been under the impression that the M2 manifold was nearly as good as the Edelbrock but please correct me if I'm wrong...
               
            • Garrett Ellison

              Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

              Messages:
              2,018
              Likes Received:
              1469
              Joined:
              Jan 1, 2018
              Location:
              Southwest VA
              Local Time:
              1:46 PM
              You could try milling the plenum divider out of the MP dual plane and putting a one in spacer under the carb first, but it's still not going to match the RPM. Edelbrock really did put a lot of R&D into the small block Chrysler RPM intake, it's pretty safe to say it's the best dual plane ever made for the A type engine. With 4.10 gears, I myself would look for a good LA single plane and convert it to the Magnum heads and block the exhaust crossover. The top contenders for the street would be Weiand 7545 Xcellerator or Edelbrock Torker II (Too bad Holley didn't make a Street Dominator with 340/360 sized ports).
               
              • Thanks! Thanks! x 1
              • Agree Agree x 1
              • rumblefish360

                rumblefish360 So close, yet so far away

                Messages:
                36,701
                Likes Received:
                8533
                Joined:
                Jun 21, 2005
                Location:
                New York, on a Island
                Local Time:
                1:46 PM
                @MRGTX

                Your welcome, glad to help.
                Im not really optimistic because this route often ends in people being unhappy about the in between mods.
                I am in the middle of doing just what I suggested without any plan to upgrade the engine later. IF and when I decide to do another engine for the car, it will be a stroked big block & a 6 pack.

                Anyways, back to you.... yes, I’d use the Edelbrock RPM intake because it is a much better part for the task at hand. The MP dual plane is a copy of there earlier OE 4bbl manifold. It is fine for small cams and drivers.

                The MP single plane M1 is race intake. IF I was using one, I would be ignoring all power below 4500 rpm, and I would be targeting a very low car weight and E.T.’s in the 10’s for starters. No higher than 11’s.

                The Edelbrock RPM fills the gap in between with excellence and can run in the low 11’s. That’s the intake to use. Sell the MP dual plane and roll the money over into the RPM.
                 
                Last edited: Jan 8, 2020
                • Like Like x 1
                • Thanks! Thanks! x 1
                • rumblefish360

                  rumblefish360 So close, yet so far away

                  Messages:
                  36,701
                  Likes Received:
                  8533
                  Joined:
                  Jun 21, 2005
                  Location:
                  New York, on a Island
                  Local Time:
                  1:46 PM
                  I would not bother cutting the divider down on the MP dual plane. Waste of time IMO. I also would not recommend a single plane for the street most of the time but even more so with his 2600 stall converter. The RPM can make an honest 500 ratio plus HP, out torque and match the HP of any single plane intake in a street performance arena.

                  Keeping in mind his 2600 stall converter and not spending his money on a new one for a good savings, I’d recommend a smaller cam than the MP 230@050 for sure. I’d recommend a cam of 224@050. This one below performs very well in my ride.

                  4AF67626-7FB4-4EF2-AF57-DD1D1CD8E956.jpeg

                  If he wants to purchase a new torque converter, then the next can of worms is opened!
                  :lol:
                   
                  • Like Like x 1
                  • Thanks! Thanks! x 1
                  • Agree Agree x 1
                  • AJ/FormS

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

                    Messages:
                    17,081
                    Likes Received:
                    5621
                    Joined:
                    Jan 19, 2014
                    Location:
                    South-Central Manitoba,Canada, 900ftelevation
                    Local Time:
                    12:46 PM
                    I just wanna say this
                    Backroad hooligan driving used to be my passion too. But I kept it below 50 mph, cuz our ditches are often,mostly; deep and steep; And I know what a sudden stop feels like at 30 so I wasn't interested in finding out anything more than 50.
                    That said, my backroads are gravel, and I had 3.55s with a 4-speed. So for me 50=4200,40=3360. So for me, power at 5500 didn't mean spit.
                    But for you with 4.10s and a 1.45 second gear , 50=3900 @5% slip, even 60=4650@5% slip, so again, power at 5500 don't mean spit.
                    Those 4.10s will hit 5500 at about 71 mph. So if you're blasting gravel backroads at 70 plus mph , you're either waaay braver than I ever was, or IDK what either,lol.
                    But on hardtop, Ok I concede the point.... but then the question is; how long are you expecting your engine to last, blasting at 5500?
                    I did that one time, and said goodbye to #1 rod bearing. Another time #3 went out.
                    Have you done any oiling mods to her?

                    You know a 318LA-2bbl cam will rev to upper 5000s right. It just takes the complimentary valve gear. I mean it won't make much power up there, but it will rev to there.
                    Be careful what you wish for; Rumble posted a well-thought-out answer.
                     
                    • Thanks! Thanks! x 1
                    • Agree Agree x 1
                    • RustyRatRod

                      RustyRatRod Weenie idiot loser. FABO Gold Member

                      Messages:
                      57,370
                      Likes Received:
                      26845
                      Joined:
                      Jun 7, 2010
                      Location:
                      Georgia
                      Local Time:
                      1:46 PM
                      Crate engine companies work within some fairly restrictive parameters. The end result has to satisfy the customer, while making the company a decent enough profit to cover all their costs involved and make money on top of that. So, you can bet there is room for improvement. I'll use Blueprint, for example. None of their engines come with any type of solid lifter camshaft. We all know which can make more power, everything else equal. They do that, ultimately to cut down on errors the customer might make and to help assure a good, successful installation and engine break in and good, dependable service. Lets face, it a hydraulic cam engine has room for fewer things to go wrong, since valve adjustment is generally not done except after initial break in and all of Blueprint's engines are pre-run, so all of that has already been done.

                      That being said, as I've said a lot before, "whatever" engine you build will have some power somewhere left on the table. That's just "how it is". To me the question would be can you come up with a better all around package, including dollar spent, verses value and reliability. Maybe......maybe not. It all depends on "how good" the crate engine company is. IMO, Blueprint is now probably one of the best.
                       
                      • Like Like x 1
                      • JunkyJimmy

                        JunkyJimmy FABO Gold Member FABO Gold Member

                        Messages:
                        7
                        Likes Received:
                        6
                        Joined:
                        Jun 2, 2017
                        Location:
                        Rising City
                        Local Time:
                        12:46 PM
                        I did a cheapy 5.9 many years ago, $100 running core with 185000 on the clock. Both heads had cracks Ray Charles could have seen, a few exh guides were a little loose, cam bearings were toast. Everything else looked good. Ball honed it, cam bearings with 1/8" holes, simple valve job, hot pressure washed it all. Reused heads, valves, rockers,oil pump, and rest of short block. Pistons were all 053" ish in the holes. China air gap,Oregon regrind, 1121 head gaskets, hughes springs and retainer kit, pushrods, fuel pump thingy, $35 timing set. Napa cast rearing kit, homemade pan and pick up,spent maybe 2 hours smoothing out the pockets and took 3/8" off bottom of intake guides. Old girl runs like a beast for what it is, kind of wish I would of put valves in it, but didn't want to spend the dough, have a little over $1000 in it with some elbow grease. No machine work except for the valve job. Turns low 6s all the time,(rpm). Really thought it would have spit the bit along time ago.
                         
                        • Like Like x 3
                        • roccodart440

                          roccodart440 Well-Known Member

                          Messages:
                          5,378
                          Likes Received:
                          4374
                          Joined:
                          Apr 19, 2010
                          Local Time:
                          1:46 PM
                          IMO it's worth getting the RPM airgap. I believe it's the best option. Even if it's "nearly as good" it's worth having the best on there. PLus there is the air gap as an advantage as well.
                           
                          • Like Like x 1
                          • Thanks! Thanks! x 1
                          • MRGTX

                            MRGTX Well-Known Member

                            Messages:
                            1,764
                            Likes Received:
                            588
                            Joined:
                            Sep 24, 2007
                            Location:
                            CT, USA
                            Local Time:
                            12:46 PM
                            Ripping around on gravel roads sounds like an absolute blast. I'm with you on pulling it back a bit where the consequences of a mistake get scary...I'm definitely not braver than you. I know my limits and the limits of the car and that has always kept me safe (so far!) but I'm no professional driver!

                            I hear your point about how useful power may or may not be at a particular RPM...that's very valid depending on the application. For me, the local backroads that I enjoy are all paved. I have this one amazing up-hill country road with a series of three chicane like turns in it. Getting down the rhythm of the road, keeping the engine right in the power band, ready to blast off on each corner exit has been so much fun. Being an up hill stretch allows me to put down more power longer before going into orbit. It's a great piece of road but so far, the Dart just doesn't have the punch to make that road as much fun as it has been in other cars. I'd love to be able to hold 1st gear a bit longer and do more than just make noise above 4.5k.

                            How long do I expect the motor to last? Well, I didn't think that 5500-6000 was overly stressful for this rotating assembly and I didn't anticipate any premature mortality for the engine. I don't plan to hold those RPM for prolonged periods of course but your reports about losing rod bearings are worrying.
                            So far, I am on the stock oiling system...am I gathering that this is a significant vulnerability.

                            Good points here. I guess the idea is to be slightly less conservative than the engine makers and reclaim a piece of that performance that was left for the sake of durability but not so much that you smoke your engine.

                            Often you'll see this with late model cars. Tuners are confident enough to go slightly more lean with AFRs or they're willing to raise a redline a little. It would be a risk for the OEM to tune this way but individual owners may know enough to push the limits.

                            This is encouraging...
                            It sounds like the stock oil pump is holding up which is good to hear. Does your custom pan/pickup offer any advantage over the car style (LA?) type pans that most of us use? IIRC, these pans do not have a windage tray...

                            I hear you on this. I suppose that this manifold can be transferred to the next motor anyway.
                             
                          • MRGTX

                            MRGTX Well-Known Member

                            Messages:
                            1,764
                            Likes Received:
                            588
                            Joined:
                            Sep 24, 2007
                            Location:
                            CT, USA
                            Local Time:
                            12:46 PM
                            Well after some hard thinking and teeth grinding, my plan is much less ambitious for this summer.

                            Edelbrock RPM Airgap with 1" spacer
                            Rebuild Demon 650
                            Recurve distribtutor
                            Possible: New oil pan with windage tray.
                            tune, tune, tune
                            Drive and enjoy as much as possible.

                            Otherwise, it will come down to taking care of the engine to keep it healthy, so I can sell it as a strong running basic motor next year and buy a stroker/aluminum head crate engine.
                             
                            • Like Like x 1
                            • Agree Agree x 1
                            • rumblefish360

                              rumblefish360 So close, yet so far away

                              Messages:
                              36,701
                              Likes Received:
                              8533
                              Joined:
                              Jun 21, 2005
                              Location:
                              New York, on a Island
                              Local Time:
                              1:46 PM
                              @MRGTX Sometimes, having an engine up and running so you can enjoy the car is better than having it’s engine just sit on the stand.

                              I went this route with my Magnum engine in my ‘79 Magnum. I get to drive the car! It’s not as powerful as I wanted, but I’m driving it. That was more important to me. Adding a cam or better cylinder head later is easy enough. (when the money allows.)

                              ENJOY THE CAR!
                               
                              • Agree Agree x 2
                              • MRGTX

                                MRGTX Well-Known Member

                                Messages:
                                1,764
                                Likes Received:
                                588
                                Joined:
                                Sep 24, 2007
                                Location:
                                CT, USA
                                Local Time:
                                12:46 PM
                                I totally agree!
                                Not being able to drive this car after all I went through to get it back on the road would really hurt.

                                I'm glad to hear that you're getting to drive that 1979 Magnum. It sounds like you're in a similar spot with that car.
                                Compared to a lot of the cars that we talk about in this forum, that's easily one of the rarer mopars of the last 50 years. Every time you take it out, someone will be seeing a Magnum for the first time. It's practically a public service! :D

                                Once you have a hot motor in there, it will be fun in a whole new way.

                                I don't know about you guys but while I do ok with income, these expenses are big ones for me. That crate engine (assuming nothing catastrophic happens between now and next winter) will represent sacrifices to other parts of my optional spending. I can't thank you guys enough for the advice as I try not to let my enthusiasm run away with my wallet. Hopefully the discussion is helpful for future readers too.
                                 
                              • rumblefish360

                                rumblefish360 So close, yet so far away

                                Messages:
                                36,701
                                Likes Received:
                                8533
                                Joined:
                                Jun 21, 2005
                                Location:
                                New York, on a Island
                                Local Time:
                                1:46 PM
                                Oh I hear ya there!
                                I agree. So far it has a stock ‘00, 5.9 long block, RPM intake, 600 AFB and headers spinning a 727 & 3.55’s. Nice cruiser. The pipe dream? Good heads and a moderate cam to compliment. It doesn’t need to be a powerful mill. I have an A body for that duty.

                                To bad this rare one doesn’t equal $$$$$!
                                 
                                • Like Like x 2
                                • Bobzilla

                                  Bobzilla Well-Known Member

                                  Messages:
                                  583
                                  Likes Received:
                                  399
                                  Joined:
                                  Aug 10, 2017
                                  Location:
                                  Livonia, Michigan
                                  Local Time:
                                  1:46 PM
                                  If you already have the M1 dual plane intake on that engine, you'd probably be money ahead to keep that and put the money into a good camshaft and springs. You'll see more usable performance that way, and you won't lose hardly anything with that combination compared to running the existing camshaft with the RPM intake.
                                  I am not against the RPM intake, but if the engine is changing again later, at least get a price on a camshaft selected for that combo. Several guys here recommend Oregon cam grinders.
                                   
                                  • Thanks! Thanks! 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.