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Discussion Starter · #1 ·
There have been so many posts on this subject but they might be outdated. I figure if i'm going to spend 1k+ I want the right parts. I own a 97 GSR contemplating the comptech exhaust because I've heard nothing but good things (so far) about em, plus it's quiet sound. Cops are crackin down around here on imports. Figure if i'm more quiet, gives me a better chance of not having a big $$ fix it ticket/fine.

Is there any special header/exhaust combination? I mean right now my car is sluggish as the shizzos. I need something that will be good for the car without spending mad $$$ I'd like to keep it under 1500 if that's possible. I've got some loud tip on there that the former owner put on there. I believe it's still stock piping though.
If you've got any suggestions please let me know. I'm sure people would really enjoy your suggestions on Headers/Cats/Exhaust as a little update.

Thanks a bunch. TI forums are awesome.

31,217 Posts
MichaelDelaney on Jan/23/04 said:
I suggest you may want to take a look at the header basics article to try and understand what happens to the peak torque location (powerband location) and peak power when you change certain aspects of the header. This way you can decide for yourself where the power comes in and if this fits your package's needs. When you already know your rpm upshift points and where you want your powerband and how much peak power you are looking for, the choice of product comes pretty easy. It's great when you have an educated eye and know what to look for when you are shopping rather than knowing nothing and accepting whatever the salespitch is.

It'd be nice to get a collection of specs of these custom headers in terms of diameters (just after the flange, first turn at the oil pan, at the secondary merge if there is one, just before the collector merge, type of collector merge, ID or OD of the collector) and lengths of the primaries/secondaries, and port area at the flange. No-one has done that as a honda board group membership. Even though honda-tech has these headers promoted every time they first come out, no-one asks "can we get the specs?" so we can compare the designs. I've been trying to get us to be the more enlightened group to start doing this but....

There's just too many competing headers in same price range with similar features to say that this separates them from the herd without an objective measurement test. I'm not a big fan of hype, customer endorsements without proof of bias, and guessed promotional opinions.

Here's the latest UP TO DATE (third) great header test with fuel tuning but does not include the SMSP or AN-R headers.

here's the UP TO DATE TI article on a buyer guide

here's my header buyer guide (need to log in)

here's the TI article on header tech to understand the specs and what they do to the powerband and peak torque location , to help you decide smartly.

here's a nice link from that thread on header tech

here's a another nice link on header tech from Burn's stainless

here's a recent thread on an RSX header where I quote on some header tech from the header tech article:

Quote: MichaelDelaney on Feb/04/04

it's how you combine the diameters with the length assuming that we don't talk about primary pairing here.

Diameter is what determines top end. Length is what determines midrange (if we ignore pairing and collector design). Remember adding length does not move the peak torque like diameter changes. The peak torque remains at the same place. However, the torque curve is "tilted" in such a way that at the rpms below the peak, the torque is tilted upwards like the high end of a see saw with the peak being the fulcrum.

We can then turn to the steps in diameter and where they are located along the length of the header, as well as the merge collector design. These 2 other design factors also determine the flow energy that you get up top. We also know that sequential pairing gives you more kick up top over the traditional 1-4, 2-3 nonsequantial pairing.

The exhaust pulse leaves the head exhaust port at over the speed of sound (mach 1). Maintaining the momentum of the flow speed is the key for the top end stuff.

Obviously when the import world finally decides to catch up with the motorcycle world, we'll begin to see electronically controlled exhaust valves and not these primitive "want some backpressure all the time" manually controlled exhaust valves. This also will give you the same effect as the hybrid headers...2 powerbands (or more).

I think I said all of these things in the header tech article using Jim McFarland's lectures. At the highest levels of custom header design these "undergraduate" principles are modified and the rules/conventions are challenged. Dave was telling me that when he was developing that B20VTEC extra long hybrid header, they unexpectedly got more top end using an even longer secondary section (i.e. expecting to see more kick at the upshift rpm landing point which they got also). It may've been related to the bigger collector and diameter at the secondary though.

But if you want to read more about this sort of thing:

BTB Racing Exhausts in the UK used to have a nice write up on header theory summarized as well on their website by Joe Ellis.:

Quote: Original Author Joe Ellis BTB Technical article on header design - Jan/01/02

The design of exhaust manifolds is governed by two basic principles. The first calls for the efficient extraction of exhaust gases from the cylinder after combustion. The second is the controlled development of a standing pressure wave in the manifold pipe to encourage over filling of the combustion chamber with inlet charge.

The first is the easiest to understand if we merely think of the engine as a pump. After the combustion stroke has taken place the piston has to return to top dead centre. As it returns, the hot exhaust gas has to be expelled past the open exhaust valve into the exhaust pipe. At this point the objective is the efficient expulsion of exhaust gas to allow the piston to return as quickly as possible. The pressure against the piston as it rises determines the speed of its movement, this is known as the pumping loss and is simply the work done by the piston against the exhaust gas. In order to minimise pumping losses, the flow of exhaust gas has to be maximised. This does not necessarily mean the largest diameter pipe. Because the gas travels as a fluid, too large a duct will lose gas velocity and the gas flow will stall, (imagine a small stream reaching a large lake, the energy of the flow is lost as the stream decides where to go, and silts up the lake).

Conversely, too small a duct will restrict the flow and increase the pressure (damming up our analogous stream). Determining the optimum size of the exhaust duct largely depends on the capacity of the engine, and the amount of revolutions per minute at which it is operating. Supercharged engines will need bigger exhaust pipes as they effectively have a greater capacity. We can determine the theoretical perfect size for the exhaust through a series of calculations. Ironically, in the most widely used formula, these calculations rely on us already knowing the theoretical perfect length. Also very important is the need for a smooth parallel-sided duct with the minimum number of bends on the largest possible bend radius, because hot exhaust gases do not like to change direction too abruptly. We must also avoid sudden changes in diameter or mismatched ports, and encourage smooth transitions where one pipe meets another. So, in summary, this aspect of exhaust design is essentially a fluid dynamics exercise and is usually heavily compromised by packaging restraints once an engine is mounted in the chassis.

The rather more scientific wave tuning aspect of exhaust manifold design requires us to understand standing waves. For an acoustical analogy consider the case of a pipe organ, where different notes are formed from blowing air across the open ended mouth of different diameters and lengths of tubes. If we consider the case of a single cylinder engine with a straight exhaust pipe exiting to atmosphere, the pulsing flow of gas causes a standing wave to be formed in the pipe. A standing wave is best illustrated by stretching a "Slinky" spring between two people, if one end is oscillated at a consistent frequency a clear pattern can be seen in the coils where bunching indicates a high pressure zone and stretching shows low pressure. We have already seen how important it is for an engine to be expelling gases into a low-pressure pipe, but for a high performance engine a standing wave can be especially beneficial. This is because at high rpm in a tuned engine both the inlet and exhaust valves are open at the same time as the piston approaches TDC to begin its inlet stroke. At this point if we can ensure that a low pressure zone exits just behind the exhaust valve, inlet charge can start to be drawn into the cylinder even before the piston starts to travel downwards on its "sucking cycle". This ram effect is crucial to the "over filling" of the cylinder prior to combustion that leads to increased engine power. Of course these days most engines have more than one cylinder and therefore the interaction of the ram effect between the cylinders is paramount. A typical formula for calculating lengths and therefore diameters is as written in A.Graham Bell's excellent book 4 stroke Performance Tuning in Theory and Practice, published by Haynes.

850 x ED
P= ---------------- - 3

Where P is primary pipe length in inches
ED is 180 + the number of degrees that the exhaust valve opens before bottom dead centre Rpm is the tuned engine speed in revolutions per minute.

This gives an excellent starting point to exhaust manifold design by suggesting a primary length for a theoretical 4-1 design. Using this we can then calculate the Inside Diameter of the primary using the formula:


ID = S ----------------------- x 2.1

(P+3) x 25

Mr Bell goes on to suggest a way of calculating lengths for a 4-2-1 design. This relies on a theory that the length of the primary pipes for a 4-2-1 should always be 15 inches. Whilst again this may be a good starting point it is generalising too much to suggest that all 4-2-1 exhausts should have the same primary length. Over the years we have tried many alternatives to this with sometimes surprising results. The most popular capacity range for race engines in the UK is from 1300-2000cc and in this range almost always a 4-2-1 design has proved to be better than 4-1. It should however be emphasised that, long primaries of the length calculated for a 4-1 but subsequently merging into two short secondaries appear to give the top end performance of a 4-1, without the flat spot at low revs that a 4-1 usually has.

The best way to establish the exact optimum layout and dimension for a specific engine is by trial and error on an engine dyno. This gives the tuner ample opportunity to try many different iterations of length, diameter, collector design and tailpipe size. Not to be forgotten of course is the inlet tract, which also will generate a standing wave and its length including plenums, trumpets and butterflies has to be tuned in conjunction with the exhaust. It is clear that exhaust pipe length and diameter dimension will be a function of the quantity of exhaust gas that is being expelled and the length of time that it is being expelled (period of stroke). Hence a short stroke, big bore engine will require a shorter and larger diameter pipe than a longer stroke narrow bore one. Altering the design of the inlet and exhaust can have a dramatic effect on the characteristics of the engine and often just looking for one peak power figure at a specific rpm doesn't produce as competitive an engine as considering the performance across the whole usable power band of the engine. The successful engine designer's holy grail is to get the maximum area under the torque curve, as this will provide the most opportunity for accelerating the car for the longest period. This partly explains the emergence of quirky manifold designs where theoretically the wrong cylinders are linked together in the layout of the manifold. This seems particularly to be the case in highly tuned motorcycle engines where instead of linking cylinders 1 & 4, and 2 & 3 into a 4-2-1 design, pipes are paired 1 & 2, 3 & 4.

Although initially this would appear to be so that the pipes can sweep under or around the engine frame more easily, it also gives a more even spread of torque with less peakiness. This unusual design layout has also been favoured in Touring Cars, where (in common with motor bikes) traction is at a premium and therefore a nice progressive power delivery is more desirable than a peaky wheel spin inducing one.

If it is not possible to optimise the exhaust manifold design on the dyno, then it is a good idea to make the pipes with slip joints between the pipes and collectors, so that different lengths can be experimented with during testing. It may be found that on a track with a high proportion of long straights a shorter primary that will give more power at higher revs provides a quicker lap time. Equally, on a tight track or a hillclimb with a standing start, a longer primary will boost acceleration from low revs.

The reason that a 4-2-1 works better over a wide range of rpm's than a 4-1 is that each combination of pipes will work best at a specific rpm and therefore the more combinations that are available the more possible solutions arise. A current trend in Formula 1 is to have steps in diameter at certain lengths along the primary.

Again, each step will create a standing wave at its own rpm, and these steps can be made to magnify existing waveforms at certain revs. Whatever the design, the object is the same. Sudden steps in the primary will contradict my earlier smooth gas flow theory, but it has obviously proved itself to be a compromise that the designer is willing to make. High revving short stroke racing engines have a very short time available to fill the cylinder with air fuel mixture and as such rely on ram tuning from the combined effects of the inlet and exhaust tracts to achieve their high specific outputs.
You better know: your eventual displacement, NA vs FI, your peak power goal so that you get a header that's big enough diameter-wise (at the primaries, secondaries, collector) for it , your tranny upshift landing points and powerband (torque) location so that you can choose the right layout (i.e. 4-1, tri-Y, or hybrid tri-Y).

Exhaust combo? make sure the diameter is the same all the way through and choose the right diameter , like we told you a million times everywhere already (see exhaust tech articles).

I hope you have time to read because that's what you need to do. All the ideas and opinions and answers are all already stated in these links. Get back to us for some help, if you still don't get it...
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