Nick's Garage just dyno tested a 440 using factory HP exhaust manifolds, max wedge manifolds and headers.
Results:
HP manifolds---- 375 horsepower------ torque- 389
Max Wedge------ 410 HP ----------------- torque-446
Headers ---------- 419 HP ----------------- torque-463
The headers (1 7/8" tubes) increased 44 horsepower. Back in the day everybody claimed they only gave you 15 more horses.

And I still hear guys today saying the HP manifolds are just as good as headers, lol. Of course they are always the car show type...scared to have to prove anything.

Boy, those Max Wedge manifolds sure do a nice job. I was not expecting that big of a difference between HP and Max Wedge.

Thanks for posting that.

All depends on the combination. Those dyno tests can be "rigged" by changing the camshaft. The results also will change a lot depending on the muffler and tailpipes that are used.

I always invite car show guys to the dragstrip and they never show...

Car show types wouldn't like the Pure Stock Drags. Most of the cars there are show worthy, and will kick their ash on the strip to boot.

He didn't change anything on the engine except the manifolds. Go to Youtube and type in Nick's Garage, he's a Mopar guy too.

I have sure replaced a lot of manifolds with headers over the years and the headers always helped. But 44hp and 74lbs more torque sounds like an awful lot. The advertising departments sure missed their chance on that one. Frankly, it's been a long time now since I swapped manifolds for headers, but I don't remember that spectacular of a difference. At least not normally on a stockish combo.

Watch the video - the aerial portion above the carbs.

Notice the fuel atomization differences between the three setups.

more airflow = higher atomization!

I saw that too, interesting. Glad someone posted the numbers, I couldn’t understand a thing he said lol. I’m guessing the difference between the Max and headers is the collector and length-size of tubes. But just bolt on stuff was cool.

Andy's comment is valid... when you have a cam with a bunch of overlap, the power difference between manifolds and headers will be magnified - headers support scavenging and manifolds don't. As soon as I saw the vacuum gauge reading around 11 in-hg with a pretty lumpy idle, I knew you'd see a big difference. It was impressive to see the max wedge manifolds hang with the headers. When running a factory-type stock cam, I've seen engines only pick up 10-15 hp with headers on back-to-back dyno pulls.

Given what the power output will be w/ a factory stock cam...10-15 hp w/ headers is still a big gain.

Look again. Notice the pulsing.

Back in the day I recall 30-40 HP being tossed around by advertisers & bench-racers, but dynos & ET/MPH slips tell the truth.
Obviously, as the saying goes, "it's in the combination"; witness the F.A.S.T. guys for one example.
I recall a SoCal engine builder telling me (mid-90s) that his dyno headers were about 40 HP better than the headers that allowed a C/SA 440 to fit a '69 Cuda.
Some work ($$$) was needed to get some of that back.
The Maxie stuff in that test scored well, but those things are big, and heavy.

<---> this is where it is...... the correct cam and combo will help overcome the lack in exhaust efficiency . an effective cam would pick up the power on manifolds and there would be little if any from the addition of headers.......

If you have ever lifted them you may be surprised. Max exhaust are heavy, but not nearly as heavy as they look.

you’re both missing the point, it wasn’t an all out dyno session of many combination of parts, just three different exhaust types and how they worked on THAT engine. Heck he could’ve put Indy heads, roller cams, you name it, the purpose wasn’t for extracting every bit of HP, just what if. Take what he did and go have a coffee break. Sheesh

We're not missing the point, we know what the point is since we've done it ourselves many times. I can do a dyno test just like that and have very little difference between HP manifolds and headers. I can also run a dyno test where there is a big difference between manifolds and headers. The test itself is kind of meaningless since it can easily be rigged to provide a wide range of answers. I can do the same thing with rocker arm ratios. I can "prove" that rocker arm ratio doesn't matter or I can "prove" that it matters a lot. All I have to do is use a different camshaft. And if I don't tell anyone what cam is in the motor then most guys won't know the difference. They'll just accept what the magazine article says as fact.