Catback?

[Ntegra Dryvr]

I'm looking at getting a set of headers and a hayame cat back exhaust sys. What is the difference in performance between the 4-1 and the 4-2-1 headers? And 2nd, since a cat back exhuast system is from the cat back....... then the stock pipe inbetween the headers and the cat would be a downer on performance wouldnt it? The catback is 2.25" should I switch out the stock pipping to something else? If so what should I switch it to? And any idea on how loud this would all be resonator is included with the system and i would get a high flow cat. Thanks for replies.

[90CRXZCSi]

4-2-1 is more for low end and the 4-1 is for higher power like the ITR. When you buy a catback, it is from the CAT--> BACK. You can still use the stock cat and it will bolt right up to that. If you want you can get a high flow, but it doesnt really do that much and IMO, it makes your car stink because of the fumes.

[whtteg]

OK this is IMO get the 4-1 header if you do alot of high rpm driving ( agressive driving) and get the 4-2-1 header if you do alot of stop and go city driving. Second get a carsound cat, and then a good catback, DC Sports, RSR, Skunk2, or my personal choice (other than RSR) Vibrant.

[Ntegra Dryvr]

Doesn't the stock pipe from the end of the headers to the cat limit you? Once I buy my cat back and install it should I have a replacement pipe put in for the stock? If I have the header and the cat back which is 2.25 what size if so? Thanks for your replies!

[spender1326]

This is part 2 of an article from the Compact Sports Car web page

Enjoy!

Headers
Why headers work is an arena full of old hot rodder's old wives tales and myths. Headers can produce substantial amounts of power on a engine with very few negative compromises. Headers work so well in producing extra power that they are a rare, win-win modification with hardly any negative trade-offs. This makes them a mod that is almost essential for any serious engine build-up.

For space, cost and catalytic converter light-off reasons, most cars come with a crude, cast iron, log-type manifold stock from the factory. A log manifold is simply a tube with stubby legs connecting the exhaust ports to the main tube. This is good for conserving heat to quickly light off a catalytic converter during cold starts, and it is compact, preserving valuable under-hood space within today's crowded engine compartment. However, a log manifold is detrimental for power production. Some Japanese sport compacts come with crude cast iron approximations of headers. This is better than nothing but it is still far from optimal.

Tri-y headers like this one tend to have a broader powerband at the expense of slightly less peak power than a four-into-one.

A header is an exhaust manifold fabricated from tubular sections of pipe. Full radius mandrel bends are preferred so the pipe's tight radiuses will not be crushed down. Each individual exhaust port is treated to its own separate primary runner instead of merely dumping into the shared main pipe of a log manifold. The equal length, or close to equal length primary pipes converge at a single, larger-diameter point called the collector. The collector then leads to the main exhaust pipe. An old hot rodder's tale is that headers produce more power by reducing backpressure and by the long individual runners preventing the exhaust blast from one cylinder from blowing into the next cylinder, contaminating the charge on overlap. While this is partially true it is not the primary reason why headers produce more power than a stock manifold.

Headers make more power by primarily using resonance tuning to create a low-pressure, reflected wave rarefaction pulse during the overlap period. (The overlap period, remember, is between the end of the exhaust stroke and the beginning of the intake stroke. At this time, both the intake and exhaust valves are open at the same time for a few degrees of crankshaft rotation. Now don't you wish you read Part One?) Engine designers take advantage of this overlap period to help the engine breathe better.


To work right, a header must first exploit the inertial force of the outgoing exhaust gas. This rapidly moving, high-mass, high-pressure pulse creates a suction in its wake to pull burnt exhaust gas out of the cylinder. This first negative pressure wave helps evacuate the cylinder of burnt exhaust as the piston nears TDC and slows down.

To get the best breathing and to help pull as much fresh fuel/air mixture into the cylinder as possible during the overlap period, it is best if a low-level vacuum or rarefaction can be created and maintained past the initial low-pressure wave in the primary pipe. A well-designed header can use acoustic energy to maintain low pressure near the exhaust valve during the overlap period.

Four-into-one headers typically work best over a relatively narrow powerband. Like anything, there are exceptions, and this particular AEBS header had excellent low-rpm performance as well.

The way a header is tuned is much like how an organ pipe is tuned. The optimal length used is the one needed for the primary pipe to have a fundamental note corresponding to the time when the exhaust valve opens. When the exhaust valve opens, a high-pressure pulse of hot, expanding exhaust gas travels down the exhaust port at approximately 300 feet per second. This wave of hot, moving, high pressure gas has mass and inertia of its own which pulls a suction or a low pressure rarefaction behind the pulse.

Depending on the engine, the pulse can have a positive pressure of anywhere from 5 to 15 psi with the low pressure rarefaction behind the pulse being anywhere from 1 to 5 psi of negative pressure. As this low-pressure rarefaction is several milliseconds behind the initial high pressure pulse, it can be exploited to help suck residual exhaust gases out of the cylinder toward the end of the exhaust stroke as the piston approaches TDC. The build up of this negative pressure and its timing in the exhaust stroke is closely associated with the primary pipe's length and diameter, just like an organ or other musical instrument.

A standard, low-cost collector like this one can still be effective, but ultimately does not flow as well as a true merge collector. This type of collector can be extremely restrictive if carelessly designed and constructed.

As the exhaust valve starts to close and the intake valve starts to open, the engine enters the overlap period. During the overlap period the piston is starting to slow down as it approaches TDC and gets ready to reverse directions. To maintain good scavenging, a negative pressure must be maintained near the exhaust valve to help continue to suck stale exhaust gas out of the cylinder to make room for fresh fuel and air. As the main column of high pressure gas is almost out of the end of the header's primary tube, the pressure near the exhaust valve starts to rise again. All is not lost, however.

As the pulse of high-pressure, high-energy gas leaves the end of the primary tube and is diffused in the larger diameter header collector, a reflected pulse of sound energy just like a musical note is generated, much like that of a organ. This reflected sonic pulse travels down the exhaust pipe at the speed of sound, which is usually around 1100 to 1900 feet per second in thin, hot exhaust gas, causing a slight rise in pressure at the valve. The wave is then reflected back toward the open end of the primary pipe. Just like the initial exhaust pulse, the reflected sound pulse has an area of rarefaction, or low pressure, behind it. If the pipe is of proper length and diameter, this reflected wave can be exploited to lengthen the amount of time the condition of low pressure exists around the exhaust valve.

These phenomena are harnessed by the smart header designer to tune the pipe to help get the maximum amount of burnt gas out and to help pull the most fresh fuel in. Of course, because a header is tuned like a musical instrument, a header can only be optimized to produce the greatest scavenge-improving vacuum in a band of several hundred rpm.

Without going into a lot of math, there are some general guidelines you can use for selecting a header. Shorter primary runners and/or larger-diameter primary runners are better for top-end power. This has to do with the tuning of the pipe's fundamental note for reflected wave tuning and the travel time of the main initial exhaust gas pulse. Just like a piccolo is a higher-pitched instrument than a clarinet, a shorter, fatter primary pipe is better for higher rpm. Conversely, a longer and/or smaller diameter primary tube is better for lower rpm for the same reasons as above. Camshaft design and the duration of the exhaust cam are a large factor in header design. Generally, the later the closing point of the exhaust valve, the shorter the header primary pipes must be.

The way the primary pipes gather together is important also. This area of convergence, called the collector, is critical for proper header function. It must be of larger diameter than the primary tubes because it must be large enough to acoustically represent the end of the pipe (this is necessary to get the reflected sound wave to help scavenge the exhaust), and it must be big enough to support the flow from all the cylinders without creating excessive backpressure. Usually the collector is just a junction where all of the pipes are stuffed and welded into a larger pipe that may or may not neck down into the final size of the exhaust pipe. A well-designed collector, pairs cylinders opposite in the firing order with each other so an exiting pulse from one cylinder will not hamper the evacuation of the next cylinder. Adjacent cylinders in the firing order are kept separate so the exiting pulse of one cylinder cannot contaminate the next cylinder that may be on the overlap part of the power stroke. In a typical inline four cylinder, that would mean paring cylinders 1 and 4 and 2 and 3.

The best collectors are called merged collectors. This is a collector where the two opposite cylinders are paired together in a smooth taper before being introduced to the flows of the other cylinders. Merged collectors usually produce a wider powerband and sometimes more top-end power. Not too many production headers are merged due to the difficulty in fabrication, except for those headers found on real race cars.

Many headers presently available for popular sport compacts are of the tri-y design. For street cars, tri-y's are usually the best as they are forgiving to camshaft design and other tuning factors that the header builder has no control over, unlike a real race car designer who knows exactly what is in his engine. Tri-y's also promote a wide power band. A tri-y design pairs the opposite cylinders in the firing order together in a short "Y" and then brings the two pairs of "Ys" into a single collector, hence the name tri-y.

When a pulse travels down the primary of a tri-y header to the collector, it mostly goes down the main branch of the primary. When it reaches the collector, the reflected wave also travels back up the main primary to the exhaust valve and back out again. However in a tri-y, the branch that goes up to the opposite cylinder, since the exhaust valve is closed for that cylinder, acts like an interference branch, creating a pulse and an assisting wave of its own, slightly out of phase with the main pulse and wave. This widens the bandwidth of rpm over which the additional scavenging is effective and makes the pipe less sensitive to rpm-induced pitch.

The tri-y pipe becomes "in-tune" for a wider band of rpm, widening the engine's powerband at the expense of slightly reducing peak power over a 4-into-1 design. Since some of the pulse's energy is dissipated in the interference branch, the main pulse is not as strong and the scavenge is not as complete for the tri-y. Peak scavenging efficiency is compromised for having good scavenge over a wider range of rpm. That is why many full race engines where peak power is important use 4-into-1 designs, while many headers that are designed for best driveabilty like street engines or rally engines use tri-y headers.

For the most part, the majority of street performance drivers are better off either with a tri-y or a 4-into-1 header optimized for midrange power with either long runners, small runner diameters or both.

For street cars it is essential that the headers you purchase have provisions for all of the vehicle's stock O2 sensors, EGR fittings and any other emission controls that the vehicle originally had fitted to the exhaust manifold. Most modern emission controls do not rob any horsepower at wide-open throttle. The common EGR valve, which reduces toxic oxides of nitrogen, closes and has no effect at wide open throttle. Most air injection devices only operate either on cold start or under closed throttle deceleration on most modern cars. Removing these controls does not help power and does pollute the air.

On a more sinister note, on the new OBDII cars (1995 and later), if any of the emission controls are not hooked up, the car's ECU will start recording the error codes generated. In many states, you cannot register a car if the ECU has uncorrected error codes in its memory. There are many in our government that would like to closely monitor these codes and restrict our driving privileges if these codes can be found in our ECUs.

Just because your headers have provisions for all of your smog equipment, don't assume it is street legal. Due to the intelligence of some of our local government agencies, unless an aftermarket part is CARB approved with a CARB EO number, it is not legal in some states, no matter how clean the gsses coming from the tail pipe are! If having no smog certification hassles are important, either check local laws before installing or make sure the part you buy has a CARB EO number. A parts dealer should be able to answer that question.

A power gain of about 5-to-15 hp at the wheels can be expected from a well-designed header on most cars depending on how bad the factory exhaust manifold was. If you drive at a regular speed, (not exploiting your new-found power too frequently) you can expect better mileage with a header due to the improved pumping efficiency it produces. In buying a header look for thick-wall mild steel tubing, at least 16 gauge, and preferably 14 gauge (the steel is thicker on lower gauge tubing). Rust- and heat-resistant ceramic coated or stainless steel primary pipes are preferred for longer life. Look for thick flanges also, as these will resist exhaust leaks and last much longer.

[Green96GSR]

i just hacked off my muffler and surpisingly it sounds really good but i also have an injen intake on it. also it is loud as hell outside but not too bad inside. almost sounds like a bike. as for header i was trying to figure that out as well. im looking at dc sports stainless but i dont know if i want 4-2-1 or 4-1 i understand that it all goes into 1 in the end but what is the best way. also are eurolite gauge faces any good.

[Ntegra Dryvr]

Thanks for that last post, not sure I understood what it said but I sure do feel smarter cause of it. So if I read correctly I should choose a 4-1 for my car?? And I dont suppose anyone knows whether I should change out the stock pipe from the header to the cat if I were to get a cat back system?

I'm not sure exactally either but I'm looking at a dc sports stainless steel , 4-1 or 4-2-1?? Which do i Pick!??!?!

[billab2ong]

4-2-1 Ceramic...DC is the best. 4-1....if you wanna rev to 6000 rpm every shift...get those but i shift at 3500 rpm about and 4-2-1 is the best for that. im not getting headers though... turbo is better

[spender1326]

Ntegra,

There is one line in that article that sums it up best

"Tri-y headers (4-2-1) ... tend to have a broader powerband at the expense of slightly less peak power than a four-into-one."

So if you're a profession racer or someone who is very good at keeping the engine in a certain rpm range, and you have a very close ratio'ed tranny, like 98+ spec lsd tranny from the type R, then go with 4-1. Otherwise, I would say 4-2-1 is better for a broader range of power. especially if this is going in to a street car. If track car, tight road course with low speeds, a close ratioed tranny specifically tuned for the course, where the engine is always between 6k - 8k rpm, then 4-1.

Bill

I'm thinking turboing my 94 ls. Actually, my originally plan was to swap in a B18c5, but turbo has better bang for buck, and I won't have to deal with the whole smog referree thing when it comes to engine swaps in CA. So my question is where did you get your turbo for $2000. I've been looking online and the best price for Greddy units are $2500 but no intercooler and it's not for 94 ls only 96+ ls. Cheapest Drag kit is $3100, it has intercooler and it's for the 94 ls. Please let me know where you got your kit. Or did you piece the kit together yourself. If so where did you buy the parts, and what is the complete list of parts for the turbo.

Thx.

[sameintheend01]

Originally Posted by spender1326

Ntegra,

There is one line in that article that sums it up best

"Tri-y headers (4-2-1) ... tend to have a broader powerband at the expense of slightly less peak power than a four-into-one."

So if you're a profession racer or someone who is very good at keeping the engine in a certain rpm range, and you have a very close ratio'ed tranny, like 98+ spec lsd tranny from the type R, then go with 4-1. Otherwise, I would say 4-2-1 is better for a broader range of power. especially if this is going in to a street car. If track car, tight road course with low speeds, a close ratioed tranny specifically tuned for the course, where the engine is always between 6k - 8k rpm, then 4-1.

Bill

I'm thinking turboing my 94 ls. Actually, my originally plan was to swap in a B18c5, but turbo has better bang for buck, and I won't have to deal with the whole smog referree thing when it comes to engine swaps in CA. So my question is where did you get your turbo for $2000. I've been looking online and the best price for Greddy units are $2500 but no intercooler and it's not for 94 ls only 96+ ls. Cheapest Drag kit is $3100, it has intercooler and it's for the 94 ls. Please let me know where you got your kit. Or did you piece the kit together yourself. If so where did you buy the parts, and what is the complete list of parts for the turbo.

Thx.

yeah, but you are gonna still have to deal with CA emission laws. Make sure the turbo kit you get is carb approved or you will kill yourself.

[billab2ong]

buy a used greddy or another CARB legal kit

im getting a used greddy kit w/ fmic(only 2-3k on it) for $1100

turbos add up

$1100 for turbo and everything
$450 hondata s100b
$350 Clutch
$3-500 on exhaust(all depending)
$50 on boost gauge
$150 on EGT gauge
$275 Help installing turbo, clutch, gauges and so on

Adds up pretty quickly eh? Turbo kits should come w/ boost gauge!

[Ntegra Dryvr]

Thanks for helpin me make my decision I appreciate it. I dont suppose anyone knows whether I should change out the stock pipe from the header to the cat if I were to get a cat back system?

[spender1326]

Bill

Thx for the reply, lets us know how your teg turns out. Post pictures and dyno results when complete. I'm thinking about going the same route.