I have always wondered WHY Acura would design the car like this, never found an answer around here, but did find this informative info (from following a link in 3G Garage)


HIGH-FLOW EXHAUST SYSTEM WITH CLOSE-COUPLED CATALYZERS

To reduce weight and move the engine's to primary catalytic converters as close as possible to the combustion chambers, the TL exhaust manifolds are cast right into the cylinder heads. A 900-cell per-square-inch high efficiency converter mounts directly to the exhaust port of each cylinder head for extremely rapid converter light off after the engine starts. This mounting system has the added benefit of eliminating traditional exhaust header pipes, which saves a total of 17.6 pounds.

To ensure optimum flow and reduce backpressure, a hydroformed 2-into-1 collector pipe carries spent gases down to a 350 cell-per-inch secondary converter under the passenger cabin. The design for the exhaust system downstream of the secondary catalyst, including the dual silencers, further reduces back pressure and is 11 percent lighter than the comparable Type-S arrangement...

Full article

 

Nice idea on Acura's part, but too bad we can't gain 30 whp and get 300 hp at the crank by simply swapping out the headers as can be done for the 02-03 TL Type S's

 

The TL doesn't come with headers and neither do most cars.. although a fair amount do.

 

most cars don't? I'm curious....name some of them, please

 

what exactly does a header do.....

 

It's simply the first piece of your exhaust system outside of the motor

 

this process also allows the engine to develop 270hp and be ULEV compliant, as the cats closer to the engine heat faster reducing emmisions, it is becomming more comon place, the new volvo 4.4L V8 does the same thing to get ULEV emissions.

 

 

Headers are not the "first piece of your exhaust system outside of the motor" on most vehicles. That's the exhaust manifold.

A header is a tuned exhaust tubing setup, one tube per exhaust port, frequently but not always, with equal-length tubes. Exhaust manifolds are generally cast iron and are not equal length or tuned. Grab any gearhead magazine for drag racing or NASCAR and I guarantee you'll see somewhere in there, pictures of an engine with headers. Or visit a website by one of the well know header manufacturers such as Hedman or Hooker and you'll see info on headers.

So to recap, a header is a specialty product usually reserved for the after-market industry. but can be found in some factory cars which have been designed and built for the enthusiast.


To NFLblitze1;

What a header does is a better job at purging the cylinders of spent exhaust gases than conventional exhaust manifolds. This is due to the fact that each cylinder has its own exhaust runner and with the better headers, all of the runners on each cylinder bank are of equal length. This allows the exhaust pulse to reach and exit the collector with out interference from other exhaust pulses. Inn fact, with equal length headers, each pulse will impart a pulling effect on the next cylinder's pulse in the firing cycle to increase cylinder purging even more.

Hope this helps.

 

I should add that headers and exhaust flow are a whole science of their own. Very complex theories and physics can be applied and seen in this area of engine tuning.

 

so how does this affect a car?

 

Here's three websites with pictures and info on headers for those of you who are not familiar with or know what a header is and does.



http://www.hedman.com/pages/hedmanmain.html

http://www.jbaheaders.com/cat4ward.asp

http://www.edelbrock.com/automotive/...act/index.html

 

To NFLblitze1;

Increases both horsepower and torque.. but again, that depends upon the manner in which both the header and the engine and its bolt-ons are tuned. Headers will increase intake manifold vaccum which means you can use a higher CFM carburetor (if your engine uses such) or a larger throttle body (fuel injection) and a freer breathing intake system to add more power.

Headers allow more complete purging exhaust gases from the cylinders. This enables a better fuel/air mix during the following intake stroke which results in more power. With engines which have been race-prepped with high lift long duration cams, more exotic intakes, and head work, headers can actually over-scavenge an engine.

 

so is the exhaust manifold welded or not, jlucas from the Honda R&D team that ran the TL said they weren't but the specs posted above say it is... i am confused

 

No, it's not welded. The exhaust manifold is cast into the head.

 

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Most cars have exhaust manifolds, and make concessions either to material, longevity, quiet operation, emissions, or all of the the above - generally a header involves some sort of design involving a collector, where the shape and length of the tubing acts to "scavenge" exhaust gases. Years ago, they were made of cast iron for durability, and not optimally shaped. Today's cars often come with stainless steel "headers" that are light years ahead of the old cast iron pig metal - but on the other hand, the days of huge power gains from adding an aftermarket header are similarly reduced.

The TL design makes for cleaner emissions - I also do not believe there is anywhere near 30 HP sitting on the shelf. I had the CompTech headers on the 2002 Type-S, and determined they were not worth the money. Whatever power they provided was so far up the power bandwidth that the practical benefit on the street was minimal. I regretted spending the money - plus, my performance measurements did not see a significant increase.

This is more of a bling-bling mod in my opinion - "bragging" rights for Internet Forums.

 

Good data and cool, new avatar!

 

i doubt that a type-s would be capable of 30hp from just headers. usually for N/A engines large gains like that from one mod are not likely. if it was a turbo or supercharged car then those gains are more reasonable.

 

The header is just another name for exhaust manifold...no one ever calls their stock manifold a header....it's usaully said for an after market manifold...header jus basically means first piece, think about it..it only takes comon sense

 

To back this up on the 04/05 models, look for the thread with info on the Racing TL that came in 3rd in the endurance race in CA recently. One of the guys from AHM R&D posted alot of info here and linked to another thread with even more info. One of the things he said is the 04 TL Exhaust Manifold/Headers are actually pretty good. They focused their attention right after the header where the first CATs are located and then from there back.

 

headers are only one piece to a complicated breathing puzzle. if you're gonna do headers you should work on intake, exhaust, and a ecu re-map.

without doing the extra work your time/effort to get headers on really goes un-noticed, with potential power/torq still locked up.

 

Does anyone have some photos of the integrated headers on the 3rd gen TL? I think that would clear up the Bolted/Welded/Cast argument.

 

the TL does not have headers. This si what headers look like:





Previous TLs had exhaust manifolds then couple together and passing throught one CAT.

The 04 TL has 2 CAT's attached directly to the exhaust ports, then couple and the rest (mufflers, resornators, piping)

 

A header is not "just another name for exhaust manifold". In the context of internal combustion engines, the terms "header" and "exhaust manifold" describe two entirely different entities. While the task they perform is essentially the same, the manner in which they perform it and the resulting affect is different.

The three links I supplied clearly show headers. And Bitium's photos (thank you) most clearly show headers in use.


To cvajs;

You wrote, "without doing the extra work your time/effort to get headers on really goes un-noticed, with potential power/torq still locked up".

Not entirely. Adding a header (4-cylinder) or headers (two-bank engine) will always have an affect on performance, but sometimes the affect can actually be in the negative. Thus, your statement, "headers are only one piece to a complicated breathing puzzle. if you're gonna do headers you should work on intake, exhaust, and a ecu re-map" is true. Though the the re-mapping of the ECU may not be necessary as long as it contains software that will just relearn the new environmental parameters.

I once owned a 1966 SS 396/360HP L34 Chevelle. This engine, as most Chevies of the day, was shipped with a "log" style exhaust manifold. VERY restrictive to good exhaust flow and therefore a real power robber. The stock carburetor was a single-feed 660 CFM Holley, capped by a fully exposed air cleaner (filter was visible all the way around the top and bottom pieces). I checked the intake manifold vaccum before installing a set of equal length Hooker headers and it was 21 inches of mercury at idle (I already had a straight through exhaust on the car - glasspack mufflers and no resonators). After header installation, the intake manifold jumped up to 23 inches. Tremendous throttle response but the engine basically died after around 4000 RPM because the headers were allowing it to demand more than the 660 CFM carb could supply. So there was an improvement but were I to go out racing, I would have gotten burned pretty badly.

So that same week, I replaced the stock carburetor with a dual-feed, center-pivot, 780 CFM Holley (model R3310) and manifold vaccum dropped down to 20 inches with a nice little lopey idle. Now the engine was able to get all it needed. It felt like a whole new engine with power estimates of an additional 50 horsepower and around another 20 to 25 lb/ft of torque. In other words, it screamed big time!

When Road Rage says, "I also do not believe there is anywhere near 30 HP sitting on the shelf", I agree with this statement and the reason is pretty simple. To get 270 normally aspired HP out of 196 cubic inches in a street driven machine is getting close to the end of the game. My example above with a 396 Chevy engine was unencumbered by EPA regulations or any such nonsense. And 396 cubic inches is nearly twice the size of a 196 cubic inch engine, hence more room to work out more power. I assume he means 30 HP at the wheels which would be around 36 to the flywheel, or 306 total.

I have a friend who has a 2002 Altima SE, much like the one I had. With an engine of 214 cubic inches (3.5 liters) rated at 240 HP and 246 lb/ft of torque, most were dynoed at around 201 to 205 HP at the wheels. He had the following mods on his car:

Full greddy catback exhaust
HotShot headers w/Y pipe (removes both pre-cats and main cat)
UR UDP (Unorthodox Racing Under Drive Pulley)
Berk WAI w/Apexi filter
Ignition timing advanced 3 degrees
Throttle hesitation problem fixed (this was a TSB)

After these mods, his car dynoed at 244 HP and 244 lb/ft of torque TO THE DRIVE WHEELS. Let me tell you, this thing WAS quick. But two things allowed for this. 1) the stck intake and exhaust was pretty restrictive on this engine. 2) More cubic inches gives a little more room to play. I have seen our TL engines dynoed around 229 HP to the wheels, so you can see, Honda has not left a lot of room in the stock intake and exhaust from which to free up a lot more power.

 

That's along the lines of what I was thinking when I made the first post about it.

 

Here is something I found:


Headers are one of the easiest bolt-on accessories you can use to improve an engine's performance. The goal of headers is to make it easier for the engine to push exhaust gases out of the cylinders.

When you look at the four-stroke cycle in How Car Engines Work, you can see that the engine produces all of its power during the power stroke. The gasoline in the cylinder burns and expands during this stroke, generating power. The other three strokes are necessary evils required to make the power stroke possible. If these three strokes consume power, they are a drain on the engine.

During the exhaust stroke, a good way for an engine to lose power is through back pressure. The exhaust valve opens at the beginning of the exhaust stroke, and then the piston pushes the exhaust gases out of the cylinder. If there is any amount of resistance that the piston has to push against to force the exhaust gases out, power is wasted. Using two exhaust valves rather than one improves the flow by making the hole that the exhaust gases travel through larger.

In a normal engine, once the exhaust gases exit the cylinder they end up in the exhaust manifold. In a four-cylinder or eight-cylinder engine, there are four cylinders using the same manifold. From the manifold, the exhaust gases flow into one pipe toward the catalytic converter and the muffler. It turns out that the manifold can be an important source of back pressure because exhaust gases from one cylinder build up pressure in the manifold that affects the next cylinder that uses the manifold.

The idea behind an exhaust header is to eliminate the manifold's back pressure. Instead of a common manifold that all of the cylinders share, each cylinder gets its own exhaust pipe. These pipes come together in a larger pipe called the collector. The individual pipes are cut and bent so that each one is the same length as the others. By making them the same length, it guarantees that each cylinder's exhaust gases arrive in the collector spaced out equally so there is no back pressure generated by the cylinders sharing the collector.

 

To BIGFISH;

This is a simplistic, but very good explanation of what headers and exhaust manifolds do. He deliberately left out the more complex stuff, but for his text, that's just fine.

I had written in a previous post that headers can actually over-scavenge an engine. What this means is they can "pull" some of the fresh fuel/air mix entering the intake valve, out of the cylinder along with spent exhaust gases. This happens when the individual runners are of such a diameter and length (and also the collector) that Newton's Law of inertia really comes into play. The exiting gases will actually impart a pull on the next cylinder's runner when they hit the collector because they will create a partial vaccum due to their speed of exit in the collector. This is where extensive tuning of the headers comes into play.

Nice simple write-up, though.. thanks.

 

there are "headers" and there are "tuned headers". most off-the-shelf headers are not tuned, they simply fit and relieve some issues experienced by crude manifold.

however, off-the-shelf parts are cost effective. a tuned header will be more expensive and total costs will usually skyrocket because of the need to do work on the exhaust side.

IMHO, Honda should be able to get off-the-shelf header for same costs as the manifold.
check out this site
http://www.burnsstainless.com/

 

Ditto. I replaced the stock "manifold" on a Prelude with DC Sports "headers". Both attached to the block at one end and the cat at the other. Sheesh.

rw