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Mopar 340 Intake Question

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  • Mopar 340 Intake Question

    My friend has a 73 Challenger with a slightly warmed over 340 with "J" heads. He's currently running an Edelbrock Performer Intake Manifold (that we snagged from a Junkyard) with a 750 CFM Edelbrock carb. He had a Weiand Dual Plane Intake on it before. It seems to like the Edelbrock alot better than the Weiand. My question is...is this the best Intake for this engine or do you reccomend another? Like I said before, it's mostly stock with a cam that's warmer than what was in it before. I don't have any cam numbers (the engine was rebuilt sometime in it's life before he bought the car), but it idles well (with a little lope) and the engine doesn't produce vaccum for crap. I've worked on Mopars for a little while, and I think the manifold he has right now is good enough but I thought I'd post this here and see what answers I get back. Fellow Mopar guys, please feel free to answer...

    And since we're talking about Mopar engines, I would like some clarification on the small block heads if y'all can help. I've been told that the "X" head is better than the "J" head. Is this true? We swapped a pair onto a 340 Duster once and the guy said he could tell a difference. Since I never drove the car before he did the swap, I wouldn't know one way or the other. I was told by another Mopar guy with some experience that there's no difference whatsoever. Any help you guys can give me is much appreciated!

  • #2

    Re: Mopar 340 Intake Question

    Re: Mopar 340 Intake Question

    With bigblocks, I know the Performer RPM intake is a pretty good intake.
    I believe I've read the regular 'Performer' intake is mostly just a aluminum 'copy' of the castiron factory intake.
    Not sure if this is the same with smallblocks.
    I couldn't give you any info about the heads.
    www.BigBlockMopar.com

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    • #3

      Re: Mopar 340 Intake Question

      Re: Mopar 340 Intake Question

      Thanks anyway BBM. Maybe Dave can help out with this one. From what I understand, he's an intake manifold god. It also helps that he's a Mopar nut.

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      • #4

        Re: Mopar 340 Intake Question

        Re: Mopar 340 Intake Question

        can't comment on the weiand manifold, but I do know the performer is really the same level performance wise as a stock 340/360 4bbl intake. it even has the smaller 273/318 ports! Best intake for a mild engine IMO is the discontinued LD340 or an Air Gap. Even Edelbrock has said there's no real performance gain going from an LD340 to an Air Gap. And they are good even for more mods later on, they really flow well.

        X heads and J heads are really close performance wise. X's are pre-71, Js followed. If the Js are running 2.02 valves it really is close. If they are the later 1.88 Js, that can choke a 340.

        The one thing that worries me is the lack of vacuum. A mild cam should be producing PLENTY. Also, anything else done to the engine? in 73 the 340s were pretty smog laden (low compression ratio) so a change in pistons could really add a lot of POP for the buck...

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        • #5

          Re: Mopar 340 Intake Question

          Re: Mopar 340 Intake Question

          I agree, the LD340 or the Air Gap is the way to go. But first I'd put a Holley or Demon on it if you're looking for peak performance potential.

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          • #6

            Re: Mopar 340 Intake Question

            Re: Mopar 340 Intake Question

            Thanks for that info CudaZappa. I didn't know about the LD340 intake. I've learned something new today. The cam and the pistons are the mystery part of the whole equation. I've tried to convince my friend to pull the motor so we can rebuild it. That way we know what parts are in the engine. He's reluctant to do that because, and I quote, "It isn't burning any oil". I do know that if you try to run anything less than 91 octane the car will act the fool. I also know that the power brakes are good for one stop, then they go to crap power wise. After the vacuum has had time to build back up, they're good for another stop and the whole process starts all over again. The only thing I haven't done, and my friend hasn't let me do it yet, is measure vacuum at idle. That way I can isolate the problem to engine vacuum or the power booster. I'd have done it by now, but it isn't my car...

            And Dave, funny you should mention Demon carbs. I said the same damn thing. The Holley he had on there was junk, and since he doesn't like Holleys anyway, he went with the Edelbrock. Now don't get me wrong, I like Edelbrocks. I think they're a great carb, but with the performance potential of that 340, I think the Demon is the way to go too. Thanks for answering. You just reaffirmed my position. And for anyone else who weighs in on this, I appreciate your input too.

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            • #7

              Re: Mopar 340 Intake Question

              Re: Mopar 340 Intake Question

              "it isn't burning any oil" is a pretty good reason to leave the engine alone. And if by "act the fool" you mean it will ping or knock on low octane fuel, then it probably has the early higher compression pistons already. Wife's dart has the low compression pistons, almost stock cam, never pings on 87.

              I can't help on the intake, wife's dart has a stock 69 340 intake that I swapped a new LS-7 flywheel for....

              My fabulous web page

              "If it don't go, chrome it!" --Stroker McGurk

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              • #8

                Re: Mopar 340 Intake Question

                Re: Mopar 340 Intake Question

                True about the not burning any oil part. I really want to check the vacuum before I recommend anything else to him as far as the internals are concerned. However, if the engine vaccum is the culprit, he either needs to do something with that cam or run a vacuum canister. I'm pretty sure he wants to keep the power brakes, and there isn't a hell of alot of room underneath the hood of that Challenger. Fitting a vacuum canister in there will be a bitch unless I put it near the radiator (actually near the headlight bucket). It was always my understanding that you want to get the vacuum cansiter as near the booster as possible. If I'm wrong, someone please let me know. And yes, by "act the fool" I mean the car pings and generally runs like a dog.

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                • #9

                  Re: Mopar 340 Intake Question

                  Re: Mopar 340 Intake Question

                  sounds like a careful tuneup is the first thing to do. Might want to run a compression test, and a leakdown test if you have the equipment available. Of course, if he won't let you hook up a vacuum gage, good luck on pulling a spark plug out (let alone all 8 )
                  My fabulous web page

                  "If it don't go, chrome it!" --Stroker McGurk

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                  • #10

                    Re: Mopar 340 Intake Question

                    Re: Mopar 340 Intake Question

                    I've done a tune up. Replaced the plugs (she likes autolites) and wires, replaced the distributor cap and rotor, and installed an "orange" ignition box. Haven't played with the springs inside the distributor yet, and I haven't been able to check the timing. My timing light is busted and he doesn't have one. > She's also running a little hot. That's one of the reasons why I want to check the timing. Once I make sure the timing is okay, I want to flush his radiator and put a cooler thermostat in it. He has a 195 degree thermostat right now. I've told him he needs to step that down to at least 180, but he hasn't bought one yet. I've already replaced the water pump when his crapped out, so I know that's good. Speaking of timing, do any of you guys have a recommendation as far as what I should set the initial timing to, or should I go with what's in the book? I usually go with what's in the book, but I know there are some Mopar gearheads around here that might have some info I don't. He's already running high octane fuel, so I want to be able to take advantage of that.

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                    • #11

                      Re: Mopar 340 Intake Question

                      Re: Mopar 340 Intake Question

                      Don't forget that a stock 73 340 probably has pistons 0.080 in the hole and a junk chamber design. No quench at all. It would not surprise me to see it detonate on 87.

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                      • #12

                        Re: Mopar 340 Intake Question

                        Re: Mopar 340 Intake Question

                        .080 down? Sheesh, why would they do that? To reduce compression? Mine are down .024 and I think that's a little deep.
                        BS'er formally known as Rebeldryver

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                        • #13

                          Re: Mopar 340 Intake Question

                          Re: Mopar 340 Intake Question

                          About the 'orange' ECU, make sure he keeps the original one in the trunk.
                          I don't know about the current status of these things 'cause I stopped buying them ages ago, but at least until recently these ECU's were crap and could leave you stranded in the most inconvenient places... Ask me how I know ;)
                          I think the chrome Mopar ECU's are a notch better and give a more/better spark aswell. Don't buy the gold ones 'cause they are race-only and heat up pretty fast.

                          I usually tune by ear at idle. Then take the car out for a drive and check if it pings in high gear when you get on the throttle. If it does, back down the timing until it stops.
                          Too much heat in an engine will cause early pinging aswell. Definitly loose 195 stat and go for a 185 or a 160.
                          Also make sure the radiator really can cool the engine at all times otherwise switching stats won't help that much in the end.
                          www.BigBlockMopar.com

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                          • #14

                            Re: Mopar 340 Intake Question

                            Re: Mopar 340 Intake Question

                            The last time I tore a 340 apart was about 12 years ago (my friend's 73 Duster). From what I remember, the pistons are dished in the 73 340. I was thinking a set of hypereutectic pistons with a slight dome like this one would fit the bill and bump up compression a little...



                            Now Dave just said that the chamber is basically garbage so with that in mind, I was thinking of dumping the stock heads and getting a set of Edelbrock Performer RPM 340 heads. For a cam, I was thinking of Comp Cams 'High Energy' 268 Series. I think all of this, plus a Demon carb would make a good package for this daily driven 340. If anyone has any other ideas, please let me know. Remember, the engine needs decent vacuum at idle for the power brakes.

                            And last but not least, this is just in the "idea" phase. This isn't my engine. I have to talk my friend into all this! :D This is what I would do if it were my car.

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                            • #15

                              Re: Mopar 340 Intake Question

                              Re: Mopar 340 Intake Question

                              I have lots of experience with 340's.

                              Ditch that performer and stick on a stock iron 68-70 340 intake - you will make more power. The LD340 is a good intake also but has some mixture distrbution problems. The current best intake for milder cars is the Performer RPM Airgap. If the car has some gear and a converter where you can drop power under 3000rpm, the M1 single plane is a killer with factory heads.

                              It sounds like that engine has the early 10.5:1 compression pistons in it and probably a milder cam. The J heads ports are identical to the X heads - the only real difference is that most of them have smaller intake valves (1.88") and induction hardend valve seats. I Have gotten [email protected]" out of X heads with 2.02 valves when ported.

                              73' 340's didn't have much smog gear from the factory and the loss of HP was mostly from the big drop in compression.

                              The Eddie heads are good heads. Just get someone to check the valve seats. A lot of the time they are not concentric. That cam is to small. Go with the XE268HL if you want to stay with comp (I think they make it for the small block), but personally I would look at the Lunati, and Crower offerings, or the old standby mopar performance cams. Its still hard to beat them.

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