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Testing intake manifolds for the 5.2 / 5.9 Magnum V8 engines

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Testing intake manifolds for the 5.2 / 5.9 Magnum V8 engines

story and photos by Daniel Bennett

Recently, there has arisen a debate about the merits of certain intake manifolds versus other intake manifolds specifically for the Chrysler 5.2/5.9 (318/360) Magnum motor.

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Small block Chryslers are esoteric enough to most people, without the added affliction of being a late-model fuel injected Magnum style motor, that, as far as I know, no one has attempted to put this depth of information together before in one place. We have had some informal dyno tests on stock motors, or modified motors, etc., but those tests will favor whichever intake is better aligned with the motor, as modified.

This test is not to determine the best intake of the bunch, but it's a tool that should be used in conjunction with head intake port CFM numbers to determine which intake might be the best fit for your combo. This is a tool, nothing more.

What originally started as only 4 intakes, grew into almost every possible option for a fuel injected Magnum motor. Thank you in no particular order to Joe Monar (Champion Racing Ported 4bbl M-1), Mark Knapcik (Hughes Airgap), Jim Jenkins (modified stocker), James Marsh (2bbl M-1) and Chris Orlando (Indy Modman with 4bbl top plate) for the loan of certain intakes to help round out this field. Four of them are from my own stash of carefully hoarded parts: the stocker, the stock four barrel M-1, the Indy 360-3M, and the W9 tall deck intake (a/k/a The Ringer). Take a closer look at the intakes below so you can see the variety of styles that were included in this test.

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With intakes loaded into the bed of one of the Dakota R/T's, which seems eminently appropriate, I headed off to my local machine shop of choice, Action Machine. They have been serving the greater Seattle area since the 1960s, and had agreed to run these manifolds on their Seanz J-600 flowbench, and allow me to be part of the setup and testing.

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I had given them the smallest and largest of the intakes a few weeks before, and they made an adapter plate that would allow us to bolt the intake directly to the flowbench in a very precise and controlled fashion, so that we would have as much consistency across the tests as possible.

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We blocked every orifice and port other than the runner that we were testing (either #1 or #2 on every intake) so that the air was only being supplied via the throttle body mounting area. This included plugging injection ports, vacuum ports, and sensor port as needed. This was done equally on every intake. All testing was done at 28 inches of vacuum, which is the main industry standard. We also laid a rolled ring of clay around the throttle body mounting pad to help simulate a smoothed air entrance to the intake vs having it just draw across the sharp edge of the entrance.

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Now that we have established the who, what, why, and how, it's time to share the results.

The following chart is to be used as a guide only. The advantage of what was done, is that it was done all on the same day, and on the same flow bench. But as with any testing procedure, the numbers are not to be taken as literal gospel, it's the relationship between the intakes that we established, not "definitive" flow numbers, as you would not get two flow benches to agree with each other in most cases.

Also keep in mind that all CFM numbers are an average. When they are on the bench they don't find a number and stay steady state, there is fluctuation, up to 50 cfm; in most cases, the swings were not small. So we took an average of the high and low numbers.

As another point of reference, the generally accepted CFM rating of the stock Magnum head is 190 CFM on the intake. Most of the aftermarket bolt on heads are in the 250-260 CFM intake port as cast, and they will almost all end up around 300 CFM with competent port work. These are the numbers that you would use to narrow down your intake choices to just a few. CID and operating range would take care of the rest of it for you.

The order of the intakes was arbitrarily chosen by me, based on the order that I thought that they would perform. As you can see, I was generally right, but a couple of those middle ones jumped up and bit my assumptions - hence the need for this test.

DescriptionPartCFMAvg Runner
Avg Port
1Stock 1992-2003stock18012"1.94"5531cc5n/aNo
2Plenum area modified from stockstock19010"1.94"66375n/aNo
3M1 two barrel P50078522706.75"2"4924n/aNo
4Indy Modman four barrel top plateModman MA-X3203"2.62"26362.75n/aNo
5Hughes AirgapHUG 55092556"1.96"5952 and 4360Yes
6M1 four barrelP50077902806"2.28"8033.35468No
7Ported M1 4bbl (by Champion Racing)P50077903206"3.19"8033.35n/aNo
8Indy 360-3M prepped by Shady Dell360-3M3656"4.34"12045.75n/aNo
9W9 tall deck 4159 as castP48761623405.5"3.18"6323.15n/aNo

Some commentary and basic descriptions of the intakes:

#1: "The Stocker" Known alternatively as the Keg, or Beer Barrel, or Beehive intake, this was the standard intake on all V8 Magnum motors during its entire production run. Yes, there are some minor differences in years, but the port and the throttle blade openings remained consistent throughout the production run, and really that is all that we were really worried about. For reference, this one was the original intake off of one of my 98 Dakota R/Ts. It's rather lackluster showing was of no surprise to anyone really. It's meant to be a low end grunt manifold, and it does do that well. The other stuff? Well, it's never been known for performing that well past 2500 RPM without a lot of massaging.

#2 The "modded" Stocker. This was a typical garage modified stock intake, with shortened runners and belled openings of the runners to provide a "better" air path. Without further work of the entire runner, there are little to no flow gains to be had from this plenum modding. Now what this test does not show, but I can verify from personal experience, is that this plenum and runner shortening mod adds about 1000-1500 usable RPM to the middle range of the RPM band making the intake more friendly from 2500-4000 RPM. It still suffers beyond that point without more runner work.

#3 The Mopar M-1 2bbl 270 cfm. This was one of the big surprises of the test. I had been told before that this intake was only good for stock headed motors, and would not flow enough air to support aftermarket heads. Guess what, that's not true.

At 270 CFM (average), it really showed that it can hang almost up there with the 4bbl M1 (280 CFM avg) and with only a bit of runner work could equal the M1 4bbl in flow. The one big downfall to this intake is the plenum size. This was designed originally as a direct bolt on replacement for the stock intake, and was even being considered for production vehicle status at one point.

Anyway, as a result of being a direct bolt on single plane style intake, the plenum is small, and that will not work well with high RPM or larger CID motors. Anything over 370 CID I would just jump to the 4bbl and be done with it, especially if the "standard" aftermarket heads are being used.

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The numbers on this one shocked me so much, that after we tested all of the other intakes, we re-tested this one just to make sure we hadn't messed anything up. Nope. It stayed consistent. I even took a picture of it during the test for proof. I tried to get a pic of it while it was more in the middle of its swing, but as you can see I failed. Do not use the number in the pic as your gospel, that was the peak of the swing and I just happened to catch it on camera.

#4 Indy Modman MA-X w/4bbl Top. Here we have another surprise, although upon measuring the port CSA, it was apparent why it kicked out the numbers that it did. Normally, this intake would not merit consideration, as we have plenty of good and readily available choices out there, BUT, Chris Orlando at Z-Code Performance uses this intake as the basis for his upgraded Kenne Bell twin screw blower kits. I would say it's a plenty good foundation to work with for his goals! He offered one up with a 4bbl plate as a tester, and who am I to say no?

#5 Hughes Air-Gap. This intake was a bit of a letdown for me, as I was expecting it to be closer to the M1 4bbl territory, than to be the lowest of all the aftermarket intakes. I think part of the problem is that this is a modified carb dual plane intake, and as a result there is some built in perturbation in the airflow to help keep fuel atomized and suspended when put into the top of the intake. With direct port injection, we do not have to worry about keeping fuel atomized and suspended in the intake tract, so volume and flow can be the focus.

I have run the carbed version of this intake on my own L'il Red Express, and love it. It just has too many compromises to be used as an injected intake, in my opinion - although bolted onto a stock heads/cam motor, this intake would perform beautifully. But so does the M1 2bbl, and when you compare pricing between the two - well, it just places this intake in a difficult spot. Great quality piece, though, and well done, just not the best choice for a direct port application. I would have no hesitation at all recommending this style intake for a moderate carbureted build.

#6 M-1 4bbl unported. Great for an economical straight bolt on with a set of aftermarket heads. This is the intake that everyone else compares theirs too. Old style (LA style thermostat and bypass hose) and new style (Magnum thermostat and bypass) use the same runners and plenum, so no worries if you have one or the other, they will both perform equally well. Unlike in a carbureted application, this intake should have little to no low end loss of power, as long as you have a proper tune for your application.

#7 M-1 4bbl ported by Champion Racing Heads. This was another big surprise for me. I expected gains to be had from porting this intake, but man oh man, did this one gain a bunch: 40 cfm. That is significant, and puts this intake out of the range of all of the cylinder heads it can be bolted to! Great and consistent port work from the guys at Champion.

#8 Indy 360-3M gasket matched by Shady Dell Speedshop. I expected this intake to place right at the top of the list, but I did not expect it to outright win it with only gasket matching being done, even beating the ringer.

To clarify, gasket matching usually involves just about 1" of the intake port where it would meet the cylinder head, and opening that up to the standard gasket size. That's all that was done on this intake. With more port work and more plenum work, this intake could conceivably end up in the 400 cfm range. Although there are no heads that use this intake pattern that will flow those kinds of numbers (Raised port Indy 360-1s are in the 365 CFM range fully done), it is nice to know that this intake will keep up with whatever is thrown at it.

#9 W9 Tall deck, also known as "the ringer." This is an as-cast, Mopar W9 head intake. W9 heads can be made to flow in the low 400 cfm range (for very large displacement small blocks, 450-500 CID) and there is plenty of meat in this intake to open it up to flow at those numbers or larger. I figured this one would take the outright win, but it got upstaged by the Indy 360-3M. Nonetheless, it still offered impressive flow out of the box.

That concludes this test. Some surprises, and some confirmations, but all around good info for everyone to have and use.

Thanks again to everyone that loaned intakes for this test, and most especially to Action Machine for letting me waste a couple hours of shop time doing this test.

Additional comments from "dana44"

[As Dan wrote,] if no changes are done to the heads themselves, you aren't going to be changing anything overall. Doing a port job (including removing the sharkfin on the intake port) won't do any good if it is still restricted once the fuel/air hits the combustion chamber/valve pocket and stalls and swirls because of the eddy effect (due to the clearance). You'd still be stuck on almost stock flow due to restrictions there. [In one case I know, the owner] did was a radius cut around the intake valve in the combustion chamber itself to relieve the edge of the intake flow, and gained 50 cfm in flow. The total port job increased about 75 cfm, deshrouding the valve 50 cfm on its own.

Daniel replied: This is good, but he is speaking of is pure CFM, but the intakes also change the RPM tuning of the combination, so even just an intake swap can make the stock heads and cam function up to 5600-5800 RPM effectively, where with the stock intake, that falls off way early (4500 or so) because of the intake design.

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