Long tube headers vs. short tube headers.

[5.0stang]

I notice consistently in the aftermarket exhaust world that in the majority of cases, when a longtube is placed on an engine the low to mid-range power picks up.

This is also with the same size diameter primaries but different lengths.

So I am comparing:

Long tube:

30" primary tubes into a 7-10" collector before going into mid-pipe.

Short tube:

10-12" primary tubes into a 1-2" collector before going into mid-pipe.

Why do longer exhaust primary tubes create more torque and low-mid range power?

 

[david borla]

I notice consistently in the aftermarket exhaust world that in the majority of cases, when a longtube is placed on an engine the low to mid-range power picks up.

This is also with the same size diameter primaries but different lengths.

So I am comparing:

Long tube:

30" primary tubes into a 7-10" collector before going into mid-pipe.

Short tube:

10-12" primary tubes into a 1-2" collector before going into mid-pipe.

Why do longer exhaust primary tubes create more torque and low-mid range power?

Do the long tube headers you are referring to remove the catalytic convertors?

 

[turbo]

5.0stang, you keep asking questions related to exhaust scavenging, which is a very complex field. One of the things that impacts on exhaust scavenging is the duration of the exhaust pulse, which is inversely proportional to engine RPM. If you have relatively long primaries, the exhaust pulses are less likely to interfere at low RPM at the collector and more likely to assist in the evacuation of the other primaries, increasing efficiency. The easier your engine can "exhale" the more fuel-air mix it can process and the more horsepower it can produce.

 

[5.0stang]

I asked this question back in January, but I do not mind that it was brought back-up.

I just purchased Gordon Blair's book (D&S of a 4-stroke engine), and it goes into a lot of detail, that is hard for me to pick-up.

You guys put it in easier terms for me to understand.

David - Yes, the "cats" are removed.

Thank you thus far!

 

[bxtask88]

This is a question of exhuast gas scavenging efficiency. Effective scavenging is an extremely important factor to consider in maximizing your engine's volumetric efficiency, or "V.E." Although the most thorough answer is one that takes far too long to put in this post, Ill give you the shortened one.
Long tube headers are headers where your primary tubes are on average, at least 28" in length, they are also much more narrow that their short tube counter parts. These type of headers, generally speaking, are best when used on a street rod, or "smoke show" application. Basically, lighting up the tires from stoplight to stoplight, generally with a mid to low power band. This is because of the way the engine breathes at mid and lower RPM's.

At the low to mid end, the best way to maximize your scavenging effect, thus helping to maximize your engine's V.E., Is to move the exhuast out of the engine as fast as possible, or with as much velocity as possible. Long tubes work best for this because of their length, and their width (well, lack of width). Thier length allows an elongated path for the gas to flow, thus allowing the gas to leave the cylinder with more speed because the gas has more time to gain velocity before it hits the collector.

Now, you've heard car enthusiasts state that ANY restriction is bad for a motor, no matter what. This is not completely true, in your exhaust, small, strategically placed, smooth mandrel restrictions can be a good thing due to the fact that well place, correct sized restrictions followed by larger openings actually speed up exhuast gas flow. So the smaller diameter tubes actually serve your scavenging better in the mid and low ranges.

Mid and low ranges don't produce a lot of actual exhuast volume, so small tubes don't restrict or "back up" flow.

LARGE, SHORT TUBE HEADERS MAKE FOR "LAZY" EXHUAST GAS SPEED WHEN EXHUAST VOLUME IS LOW! (as it is in the low and mid range).

However, if you don't even begin to tip into your power band until about 3700, you may consider short tubes. High RPM operation in a big motor (not talking about 4 bangers here), yeild LARGE amounts of exhuast gas discharge. THIS is where you need the larger diameter tubes, to get more volume out of the cylinder. THIS is where you can loose power due to pumping losses on the exhuast stroke. In an ideal world, your exhuast system would be soooo effective, that by the time that pistion STARTS coming up on the exhuast stroke, your ports and headers will have scavenged all exhuast gas out of the cylinder during the duration of the exhuast pulse. If there's no sizable amount to push out, there in a low pressure area in the cylinder (also known as vacuum), almost causing a "pulling up" affect on the piston. So, your not loosing power by pushing, your gaining power by being pulled.

Hope this helped!

 

[Ranger Mike]

Some pretty good advice above...if you still are undecided about which way to go...please post answers to following:

How big (CID) is the engine?

is it 4 cylinder? 6? V8?
manual trans or automatic?
what car is it in? what manufactured?
is it singe or dual plane intake manifold

stock cam or aftermarket?
what type accessories ?/ air conditioning? power brakes?
is it for daily driver , weekend racer or full race?

remember, engineers have spent huge $$ and time to design a BALANCED intake/exhaust system and you are going to make significant changes to this design..you already removed the cat converter which will mess with the computer..if equipped...
when you go to aftermarket headers I can tell you three things for a fact
1. it will be a lot louder in the cockpit
2. unless you go to stainless steel,,they will rust
3. you will replace header gaskets frequently

 

[HowlerMonkey]

I would guess he's talking about a 5.0 mustang.

"long tube" vs "short tube" header discussion was extremely rare before the aftermarket started making headers for the fox body mustang.

This is because the market responded by offering "short tube" headers that flow better than stock manifolds but are much easier to install than the long tube headers.

 

[geojungle]

Hi-

This is assuming shorties w/cats, '04 F-150 5.3--

Is the scavenging effect nil after the collector? Does sizing down the exhaust pipe(cooling gases contracting) help scavenge in any significant way, or is it just less detrimental than having a too large pipe?

Any value to header wrapping the exhaust pipe a certain distance after the headers to keep exhaust gases hot?

 

[Ranger Mike]

Mufflers cause back pressure and are a necessary evil if your want to stay legal.

The piping that connects all of the individual components of the exhaust system is called the exhaust pipe. Contrary to popular belief, the largest diameter exhaust pipe is not always better. If the pipe is too large, the scavenging effect will suffer at low rpm, resulting in loss of torque and driveability . Running a pipe that is too large may also decrease a car's ground clearance, increasing the risk of the exhaust being damaged when the car moves over an uneven surface

Wrapping headers wit thermal tape will help but will cause rust. That's why the hi tech header guys fabricate these out of stainless steel. Huge dollars but they work.

Advantages
An increase in peak engine horsepower can be achieved. maye up to 25 HP
Gas mileage can be increased in a well designed aftermarket system.
Aftermarket parts can be cost effective replacements for stock parts when OEM parts are not readily available (or are more expensive).
Aftermarket parts are often available in longer lasting stainless steel, whereas many OEM exhaust components are made from mild steel and have a limited lifespan.
Disadvantages
Removing or bypassing a catalytic converter may interfere with emission laws in some jurisdictions.
A noticeable increase in noxious fumes may result (particularly when the catalytic converter is removed or bypassed, and/or when exhaust outlets are rerouted to the side of the car as with side-exit exhausts).
Engine sound may be more noticeable to both driver and pedestrians, resulting in increased noise pollution.
An incorrectly designed exhaust can cause loss of low-RPM torque, and a decrease in fuel economy.
Some modifications can void factory warranties.