Magnum M1 2bbl vs. 4bbl

[jos51700]

I've been wondering this for a long time, searched, and recent discussions have prompted a post.

Is there any real difference between these two? Does the 4bbl M1 intake allow the use of the OEM-style alternator bracket? Does the 2bbl?
Does the 4bbl offer an apples and apples performance increase over the 2bbl? I'm sure there's an airflow restriction with the 2bbl at some point, but where is that point? Bigger 2bbl throttle bodies allowed a pretty big increase on the Magnums, as I recall.
Is there a single-plane and dual-plane version of each/either?

Let's assume that we're running EFI in any case, so the Airgap intakes don't count. Mopar M1 only.

 

[rumblefish360]

I can only say that I’ve read a couple of race teams finding over 500 hp with the 2bbl single plane M1. The throttle body being a limitation to the intake is the only obvious problem I see starting with what throttle body your working with.

Opening up the area where the throttle body sits is easy enough. But after that, how that intake flows past the throttle body into the plenum and into the runners, down the runners into the head, I’ve never seen a slow bench report or any words on how it is.

Where is “Bel-Ray?”

 

[Professor Fate]

I've been wondering this for a long time, searched, and recent discussions have prompted a post.

Is there any real difference between these two? Does the 4bbl M1 intake allow the use of the OEM-style alternator bracket? Does the 2bbl?
Does the 4bbl offer an apples and apples performance increase over the 2bbl? I'm sure there's an airflow restriction with the 2bbl at some point, but where is that point? Bigger 2bbl throttle bodies allowed a pretty big increase on the Magnums, as I recall.
Is there a single-plane and dual-plane version of each/either?

Let's assume that we're running EFI in any case, so the Airgap intakes don't count. Mopar M1 only.

I can't answer all your questions, but I can tell you this.
I had run the M1 2 bbl. a few years back, and it was a substantial improvement over the kegger. Didn't run out of breath at 4500 and no noticeable loss on the bottom end. The 2 bbl. throttle body (I had one that had been opened up a bit) breathed well enough for the cam I was running, a relatively mild street grind.
It accepted all the stock Magnum serpentine bracketry and accessories, and factory fuel rails.
It was a tall manifold, however; I believe a touch taller than the stock kegger. I had to shave a bit off the top flange to get the hood clearance I wanted in a '68 Dart; I think it was about a half inch. Luckily there's lots of meat up top.
Your results may vary.

 

[autopar3000]

Check this out:

https://www.allpar.com/threads/testing-intake-manifolds-for-the-5-2-5-9-magnum-v8-engines.229969/

270 cfm vs 280 cfm. Obviously there's more to it besides flow... specifically I'm thinking runner length is a big part of what dictates an intake's power band. Longer runner being a bit lower in the band is probably more suitable for a street engine anyway.

 

[rumblefish360]

I can't answer all your questions, but I can tell you this.
I had run the M1 2 bbl. a few years back, and it was a substantial improvement over the kegger. Didn't run out of breath at 4500 and no noticeable loss on the bottom end. The 2 bbl. throttle body (I had one that had been opened up a bit) breathed well enough for the cam I was running, a relatively mild street grind.
It accepted all the stock Magnum serpentine bracketry and accessories, and factory fuel rails.
It was a tall manifold, however; I believe a touch taller than the stock kegger. I had to shave a bit off the top flange to get the hood clearance I wanted in a '68 Dart; I think it was about a half inch. Luckily there's lots of meat up top.
Your results may vary.

If you don’t mind, can you remember the combo and cam specs to that engine as a general, “I did this” as some point of reference for us all here?

 

[autopar3000]

I can only say that I’ve read a couple of race teams finding over 500 hp with the 2bbl single plane M1. The throttle body being a limitation to the intake is the only obvious problem I see starting with what throttle body your working with.

Opening up the area where the throttle body sits is easy enough. But after that, how that intake flows past the throttle body into the plenum and into the runners, down the runners into the head, I’ve never seen a slow bench report or any words on how it is.

Where is “Bel-Ray?”

I put a 53 mm throttle body on top of my M1 last year and was surprised how well it works. I expected to lose a bit of power down low, but I think it's actually better.

 

[rumblefish360]

I put a 53 mm throttle body on top of my M1 last year and was surprised how well it works. I expected to lose a bit of power down low, but I think it's actually better.

Nice! Thats for that Allpar write up that helped a lot! Well done!

As I looked at that intake before, it did certainly seem to have longer runners. But never held it in my hands. I can say the plenum area also looks smaller but did t know by how much. Interestingly the writer put an approximate CID limit on it at 370 cubes. I’ll assume that is the guess limit to the manifold “As Cast.”

 

[jos51700]

I can only say that I’ve read a couple of race teams finding over 500 hp with the 2bbl single plane M1. The throttle body being a limitation to the intake is the only obvious problem I see starting with what throttle body your working with.

Opening up the area where the throttle body sits is easy enough. But after that, how that intake flows past the throttle body into the plenum and into the runners, down the runners into the head, I’ve never seen a slow bench report or any words on how it is.

Where is “Bel-Ray?”

LOL Belton/Raymore, Missouri, just south of Kansas City.

 

[Professor Fate]

If you don’t mind, can you remember the combo and cam specs to that engine as a general, “I did this” as some point of reference for us all here?

This was about 10-15 years ago, I'll see what I can dig up on the cam specs.
I ran 2 different cams, one was actually a stock LA roller from a 90ish 318- specs at .432/.432, 31* on a 113 centerline. Sounds a bit mild, but remember the Magnum uses 1.6 rockers, so the lift works out to closer to a touch over .460 - that thing pulled like a freight train even with 3.23 rear gears, and played very nicely with a factory PCM.
My subsequent Lunati I was never happy with, could never get it dialed in where I was happy with it. Must have sent the PCM back and forth to the tuner a half dozen times (before the time when everybody and their brother had PCTuners in their shop) and eventually went back to the LA roller cam with a mildly modded PCM.
I'll see if I can dig up some specs for the Lunati, but I gave all those parts and paperwork to the new owner when I sold the car.
Edit: I believe the Lunati was a #60711 grind; 264/270, 213/219 @ .050, .485 lift, on a 106 CL.

 

[autopar3000]

Interestingly the writer put an approximate CID limit on it at 370 cubes. I’ll assume that is the guess limit to the manifold “As Cast.”

Ha ha, interesting for sure.

"Anything over 370 CID I would just jump to the 4bbl and be done with it..."

If the 2 barrel M1 is only good up to 370 cid then what's the max cid for the kegger? Definitely less than 360!

I guess he's talking about trying to get every possible HP out of a combo, more of a racing scenario. And that article was probably written 15 years ago when you actually just buy one of these intakes new.

 

[rumblefish360]

LOL Belton/Raymore, Missouri, just south of Kansas City.

Oh, OK. If you were in Florida, I know a guy that would do it for free. Then offer to port it & make a heck of a you tube video series on it.

Ha ha, interesting for sure.

"Anything over 370 CID I would just jump to the 4bbl and be done with it..."

If the 2 barrel M1 is only good up to 370 cid then what's the max cid for the kegger? Definitely less than 360!

Honestly a good question. Or what’s a good rpm ceiling for a given engine size. We already know the 5.9 & Kegger are good to 5K.

I guess he's talking about trying to get every possible HP out of a combo, more of a racing scenario. And that article was probably written 15 years ago when you actually just buy one of these intakes new.

I didn’t notice it was 15 years old. Still informative though.

 

[Bobzilla]

I've been wondering this for a long time, searched, and recent discussions have prompted a post.

Let's assume that we're running EFI in any case, so the Airgap intakes don't count. Mopar M1 only.

The Hughes Edelbrock RPM airgap intake does have the injector bosses cast in, so could include it if you want. Edelbrock does not directly sell that one though, so you have to get it from Hughes or someone who sells Hughes parts like Mancini Racing.

Does the 4bbl M1 intake allow the use of the OEM-style alternator bracket? Does the 2bbl?

If you are asking about the Magnum alternator bracket, it does not mount to the intake manifold iteself, other than the one reinforcement bracket on top that also serves as a support for the truck air cleaner on those trucks. So, yes you can mount the Magnum alternator bracket to Magnum heads when running an M1 single plane two barrel or four barrel intake, and the Hughes intake too.

But, the M1 single plane four barrel intakes were offered in several configurations so you have to know what you have or what you want. There are LA intake mounting versions that were available with or without EFI bungs cast in. Then, those were offered with LA thermostat location and bypass hose OR Magnum thermostat location and bypass hose.