D-Series Exhaust Manifold Comparison

this page is a mirror of http://www.hadamotorsport.com/tech/review/dsemc/index.html

The chart below outlines some basic information for Honda D-series SOHC engines. The prices listed are in U.S. dollars and represent MSRP when available on the manufacturer website or the listed price on linked retailers in the 'Price' column. Data on primary diameter and collector diameter has been collected from various internet sources, via e-mails to the manufacturers, or by physical measurement by HADA members. All of the measurements are outer diameter (O.D.) unless otherwise specified. It is definitely preferrable to use inner diameter (I.D.) since this is what the exhaust gas "sees", so we will try to update the chart to include I.D. for all headers eventually.

Primary Dia.
Collector Dia.
4-2-1; one-piece stainless steel
4-1; one-piece mild steel or ceramic coated
1 5/8'' stepped to 1 3/4''
2 1/4'' merge; 2 1/2'' exit
each step is 13'' long; steps have inner tube overlays to prevent reversion 
4-2-1; one-piece stainless steel
DC Sports
4-2-1; one-piece stainless or ceramic
7 whp gain shown in SCC
4-2-1; mild steel
primaries -
1 5/8''
secondaries - 2''
2'' I.D.
also available in stainless steel
4-2-1; two-piece stainless steel
primaries -
1 5/8''
secondaries -
1 3/4'' 
data received from Greddy
4-2-1; two piece ceramic coated
1 3/8 to
1 5/8''
Powerplus model; stepped primary tubes & equalizer tube
HP Racing
4-2-1; one-piece chrome plated
primaries -
1 5/8"
secondaries - 1 3/4''
2" I.D.
4-1; one-piece ceramic coated
1 1/2 to
1 5/8''
new Pro-Step design; stepped primary tubes
JG Edelbrock
4-2-1; two-piece stainless or ceramic
1 3/4''
2'' (or 3'' race only)
4-1; two-piece ceramic coated
1 3/4''
2 1/2''
Endyn modified design
4-2-1; one-piece stainless steel
1 3/4''  
2 1/4''
7.4 whp on the dyno in Import tuner Magazine
4-2-1; two-piece ceramic coated
1 5/8''
2 1/4''
available uncoated for $199.95
Ractive (Toucan)
4-1; one-piece nickel plated
1 3/4"
2'' I.D.
also have a 4-2-1 two-piece model available
4-1; mild steel; available in ceramic coated or stainless steel
2 1/4''
ITA D-series header; other designs available based on level of engine modification
Spoon Sports
Spoon 4-2; top portion of a two-piece
will bolt onto a stock downpipe
4-1; one-piece ceramic coated
 1.5'' O.D.
32'' long
 Thanks to MistaBone from dseries.org for the measurements
4-2-1; one-piece stainless steel
1 3/4''
2 3/8''
JDM design; diameter measurements are O.D.
$174 + $300
4-2-1; two-piece; cast 4-2 piece, mild steel 2-1 piece
primaries -
1.3'' I.D.
secondaries -
1.5'' I.D. 
1.5'' I.D.
2'' O.D.
dealership pricing; used unit should be very cheap
D16Y8 ('00+)
4-2-1; two-piece mild steel
primaries -
1.4'' I.D.
secondaries -
1.8'' I.D. 

1.5'' I.D.
2'' O.D. 

measurements taken from a '00 Acura EL 1.6 (D16Y8) manifold 

Exhaust Manifold Design & Engine Power

For an excellent and extremely detailed discussion on exhaust manifold design, I highly recommend an article found at team-integra.net  You will have to register (free of charge, just need a valid e-mail address) to view the article, but it's definitely worth the trouble. A similar article can also be found at http://www.hondalife.com/articles/bseriesheader.htm  My analysis of the D-series headers pictured below is based on the design principles laid out on these (and a few other) websites.

One issue worth noting before having a look at the headers below is the ingition firing sequence. Since the D-series ignition firing sequence is 1, 3, 4, 2 (meaning cylinder 1 fires first, then cylinder 3, then cylinder 4, and finally cylinder 2), the smoothest exhaust gas flow will be attained by joining the 1and 4 cylinders and the 2 and 3 cylinders. The concept is to keep the exhaust gases flowing by not having two pulses enter the collector at the same time, which would cause excessive back pressure. This is called non-sequential pairing, and most of the D-series headers below apply this design concept. However, sequential pairing does allow for a broader powerband and better acceleration properties by pairing the energy from adjacent firing cylinders (ie. pairing 1-3 and 4-2). Given these different results, it is not suprising to see non-sequential pairing used for street headers that have longevity, well-rounded performance and ground clearance in mind, while a race header will benefit more from sequential pairing that harnesses the energy of adjacent pulses to create greater velocity and maximum power output. Or so the story goes. I'm not a header designer nor do I have enough experience experimenting with different header designs on a dyno to know which method of pairing primaries yields the best results on a D-series engine.

In response to the issue of primary pairing, David Stadulis of SMSP (one of the best custom header designers in North America, as evidenced by his products success in a wide variety of race series) sent me the following via e-mail:

The non-sequentially paired header design can do well if designed properly. Honda pairs them that way and that's probably one of the reasons all the aftermarket stuff is built that way. Yolu can get away with shorter primaries with a non-sequential 4-2-1 header where you can't as much with a sequentially paired 4-2-1. Sequentially paired 4-2-1s like primaries almost as long as traditional 4-1s and are therefore more difficult to build and likely to have ground clearance issues.

Headers are designed for street or race and most street headers are far from optimized. If you look at almost any aftermarket USDM header company, their offerings for the Honda/Acura cars are non-sequential 4-2-1 headers, for most 1.6 civics and maybe even some of the 1.5s up to 2.3 Prelude engines all use 1-5/8'' primaries and 1-3/4" secondaries. Why? I'd say it's not for performance but $. They can buy more tubing of one size and get a better price for it, tooling is less costlky, coating costs are less, etc.

The implications of this appear to be that sequential pairing of primaries is preferrable in terms of ultimate power output, but because of the difficulties inherent in this design approach it has proven more cost-effective and space-efficient for Honda and most aftermarket header producers to use non-sequential pairing. On the other hand, true race headers do tend to use sequential pairing for its greater performance potential and on a race car concerns such as cost and ground clearance tend to be secondary.

I think it's fair to say that there are pros and cons to all the header designs featured below. It's up to you to decide which one best suits your needs (ie. race use only, street/track use, street only use; stock engine, moderately modified engine, race engine) and your budget. Happy shopping!

APEXi GT 4-2-1 one-piece header:

Note the long primaries, which should provide strong low and mid rpm performance but cause a drop off in high rpm output. The primary to secondary merge appear to be smooth and there are no obvious restrictions given the lack of any severe or sharp bends. This should help keep velocity up. The short collector should increase peak power slightly. Also note the non-sequential pairing of primaries (1-4, 3-2). Overall, the APEXi header looks to be designed with street use in mind, given its emphasis on low and midrange power output.

'Bisimoto 4-to-1 Header:

This brand new header combines a number of cutting-edge design elements including: the equal length primaries with wide radius bends designed to maintain maximum velocity; equal length (13'') stepped primaries to prevent reversion; a true merge collector with a 2 1/4" venturi to a 2 1/2" exit pipe; and excellent ground clearance since only the downpipe travels under the oil pan. The design also appears to provide enough clearance to allow for the use of a full-width (ie. Integra) radiator. The fairly large primaries and downpipe should allow for increased volume and should therefore be very well suited for use on moderate to heavily modified engines.

This header is a very high-end design, similarly featured custom headers costing well over $1k U.S. At 'Bisimoto's price point, it seems like an incredible value for anyone looking for top flight performance out of a $500 header. And given 'Bisimoto's proven performance at the drag strip as the world's fastest SOHC Honda, it seems reasonable to conclude that this header will produce excellent power gains.

Well done 'Bisimoto!

This is a dyno graph supplied by 'Bisimoto Engineering of their 'Street' header on a D-series engine equipped with "78mm bore 11:1 compression motor on pump gas, with my ['Bisimoto] cam, valvetrain and RS Head". This header made 6 peak horsepower and 3 ft/lbs of torque more than the popular RS*R street header.
You can then imagine the hp gains above stock!

This is a dyno graph supplied by 'Bisimoto Engineering of their 'Race' header on one of their D16 high compression prototype engines. This header made 10whp peak and 3 ft/lbs torque more than the $1300 popular race header.

The above dyno test was performed on September 2nd, 2003 by the HADA crew at TAG Motorsports in Oakville, Ontario on their Dynojet.  The blue horsepower and torque curves were produced using my '93 Honda Civic CX equipped with a stock D16Z6 engine with a modified Z6 exhaust manifold where the downpipe was enlarged such that the inner diameter is 2.25'', a full 3/4'' larger than the stock downpipe (see the bottom of this page for more details). We know from experience that this modification improves midrange considerably and helps peak horsepower by as much as 3-4whp on some Honda engines (ie. B16a).  The 'Bisimoto header was then immediately installed and we produced the red horsepower and torque curves, showing an 8whp gain over our modified Z6 manifold.  For a race header to produce such significant gains over a modified Z6 header on a completely stock engine (with over 200,000km on it!) is very impressive and I look forward to testing the header again once I've installed my high compression Z6 block with ported Y8 head and a custom Exospeed camshaft. Stay tuned! (no pun intended...) 
Comptech 4-2-1 one-piece header:

The primaries are roughly the same length as the secondaries, indicating a balanced design looking to offer good low and mid rpm performance without sacrificing too much high rpm performance in the process. A short collector with a smooth merge should help keep velocity up and provide a slight improvement in peak power. Also note the non-sequential pairing of the primaries. The slightly shorter primaries in comparison to the APEXi header means the Comptech header will produce a bit more top end power. Overall the Comptech header appears to be a well designed street header that should offer well rounded performance under a variety of uses.
DC Sports 4-2-1 one-piece header:

This header is a classic 4-2-1 design, with fairly equal length primary and secondary tubing, gradual merging of the primaries to the secondaries, and a short collector. Also note the non-sequential pairing on the primaries. The overall design looks very similar to the Comptech header and should produce similar results. This design is ideal for street use, since it emphasizes good midrange power output.

Greddy 4-2-1 two-piece header:

Similar in design to the other 4-2-1 headers discussed, the Greddy header will be a bit heavier given the two-piece design. Also note the relatively short primaries for a 4-2-1 header, meaning maximum power output is pushed up the rpm range. The merges to the secondary runners and the collector appear a bit abrupt. This could create some unwanted back pressure and slowing of velocity. Overall, the Greddy header should produce good midrange power but the design does not appear to flow as nicely as many of the one-piece headers.

Hedman Chikara 4-2-1 two-piece with PowerPlus Technology:

Hats off to Hedman for designing a D-series header with a lot of interesting features. Not only does this design include stepped primaries, for improved velocity due to their anti-reversion inducing effect, it also includes an equalizer tube design to eliminate spent gases more efficiently. As a two-piece header it will be heavier than a one-piece (but easier to install) and it does appear to suffer from short primary and secondary merges, which look to be potential design limitations in terms of flow and velocity. Despite the merges, this header has a lot of potential to produce nice gains over a broad powerband and it's a very good value given the price and features like stepped primaries and an equalizer tube.

HP Racing 4-2-1 two-piece header:

This image is probably not for a D-series engine, given the resonator on the downpipe and the strange O2 sensor location. Nevertheless, it may give us some clues to the D-series header design from this company. In particularly, it would appear they use fairly long primaries for a two-piece 4-2-1 design, which will give better midrange output. However, the bend towards the collector on the secondaries seems rather sharp and thus potentially restrictive. The very long collector will limit peak rpm output but should enhance low and midrange performance. Based on this image, it would appear the HP Racing header is designed for good ground clearance and solid street performance in the low to midrange powerband. The fairly large primaries (1 5/8''), secondaries (1 3/4'') and collector (2'' I.D.) should provide good volumetric capacity increase and thus provide good gains for modified engines.

Holley Air Mass 4-1 Pro-Step header:

Holley should be congradulated for this innovative 4-1 design. Note the relatively short primaries for a 4 to 1 design (compare it to the more traditional 4-1 design of the Stillen header below), suggesting that the header is designed to maximize output at very high rpm. The relatively long collector attempts to balance this, since a long collector produces stronger midrange power (while a shorter, larger diameter collector increases peak output). The stepped primaries helps prevent exhaust flow from travelling backwards to the engine (called back pressure or reversion) as well as achieving a broader powerband. The overall design of the Air Mass Pro-Step header is quite different than anything else on the market and appears to be excellent for high rpm use, while the stepped primaries and long collector should help low and midrange output (and gives it better ground clearance than a standard 4 to 1 design) making it a streetable header as well.

JG Edelbrock 4-2-1 two-piece header:

Unlike the Hedman two-piece header, this header has very nice long and smooth merges, meaning less restriction to flow and velocity. The very short primaries will have the effect of pushing the sweet spot on the powerband up the rpm range, and the long secondaries indicate strong midrange output. The 1 3/4'' primaries are larger than most of the other D-series headers, a feature that modified engines with greater power potential will benefit from. Overall the JG header has very few obvious restrictions in its design, suggesting it should be a solid performer across a wide powerband.

Kamikaze Endyn Modified 4-1 header:

A unique D-series design, with its 4-1 two-piece layout, this header is the popular choice among supercharged Hondas because of the long and large diameter (2 1/2'') downpipe and collector. The short primaries will push peak power up the rpm range. The fairly large primary tubing diameter (1 3/4'') and the large downpipe are clearly designed to move greater volume than most D-series headers. This great volumetric capacity is something a highly modified naturally aspirated or supercharged engine will benefit the most from. A stock engine would likely lose power with this header due to lost velocity caused by too much volume.

Landspeed Racing Powercore 4-2-1:

Another classic 4-2-1 one-piece design, very similar in dimensions to the DC Sports and Comptech headers. Fairly equal length primaries and secondaries indicate a design philosophy aiming for balanced performance and good midrange output. Definitely a solid choice for a street header on a relatively stock engine and an excellent price value compared to the other 4-2-1 one-piece stainless steel headers in the group.

Pacesetter 4-2-1 two-piece header:

This two-piece header features relatively large diameter primaries (1 5/8'') and collector (2 1/4'') and as such has greater volumetric capacity than most of the other headers listed here. A heavily modified engine will be able to take advantage of this extra volume without losing velocity, but a stock engine may not be able to and could suffer some power loss at low rpm as a result. The longer than usual collector will aid midrange power, though the collector merge appears to be a bit abrupt. The primary merge appears to be longer and smoother than the collector merge. Overall this header should provide good midrange and high rpm power output, though low rpm performance may be weak when mated to a relatively stock engine.

Ractive (Toucan) 4-1 one-piece header:

Sorry about the crappy picture quality, it's the best I could find online. Despite the blurry image, you can still make out that the collector is a Tri-Y design, which gives better ground clearance than the more common box style collector (as seen on the Stillen 4-1). Given the fairly large diameter primaries (1 3/4'') and reasonable collector diameter (2'' I.D.), this header should provide good peak power gains and high rpm performance, even on a fairly modified engine. It should also be noted that with 4-1 designs like this there is a possibility of running into ground clearance problems with the primaries that hang quite low and can easily be flattened on a lowered car. Beware of manhole covers and high curbs if you're using a 4-1 header and your car is lowered more than an 1 1/2'' or so!

SMSP 4-1 custom header:

This custom-built header by SMS Products uses extra long primaries and a long collector to maximize velocity and volume. Headers like this have been dyno proven to make more power than mass-produced off-the-shelf units, especially for highly tuned and modified engines. Because of the extra length of a custom header like this you will need to relocate the catalytic converter (by shortening the exhaust b-pipe or using a shorter length test-pipe). Being a true custom-built header, be prepared to pay more, but if you've got the budget for it and you want the best SMSP is a good place to start shopping.

Spoon Sports 4-2 header:

As you can see, this header is the top portion only of a 4-2-1 design. It is apparently compatable with a stock 2-1 downpipe (which can be cheaply and easily modified by any reputable muffler shop to feature any collector size you want). The primary merges are long and smooth for a 4-2 design, suggesting very minimal restriction to flow and velocity. But at $677 U.S., is it really that much better than the other 4-2-1 design headers in this group? To a JDM addict, maybe.

Stillen 4-1 one-piece header:

A classic 4-1 design, the Stillen header uses a tradition box style collector, which stacks the primaries in a 2x2 pattern, a design element that is thought to aid peak power output but decreases ground clearance. Ground clearance is also an issue where the primaries bend back towards the collector. However, 4-1 designed headers do generally offer superior peak power compared to 4-2-1 designed headers, though they sacrifice low and midrange performance in order to do so. As such, 4-1 headers like the Stillen version pictured here are ideal for racing applications but less street friendly given the ground clearance and low rpm performance issues.

T1R 4-2-1 one-piece header:

This header uses a JDM style 4-2-1 design, with its long primaries which make the bend towards the collector before merging and large diameter primary (1 3/4'') and collector (2 3/8'') tubing. The long primaries do create a ground clearance problem, though their length provides excellent midrange output. The large diameter tubing and collector provide higher volumetric capacity and higher potential peak horsepower, provided the engine is modified enough to take advantage of these design elements. Overall, this header should provide excellent all around performance and should produce strong peak power gains on modified engines. The price tag is JDM too.

D16Y8 '00 4-2-1 two-piece header:

This is the factory original header off a 2000 Acura EL 1.6. It uses an unsequential pairing of the primaries like many of the aftermarket headers seen above and the merges look to be longer and smoother than most factory D-series headers. The primaries are longer and have a larger diameter than the cast 4-2 portion on a D16Z6 header, which should add midrange output. The secondaries are also larger diameter than on the D16Z6. This header would appear to offer a good OE low cost upgrade over earlier stock D-series headers and with a little modification could potentially perform just as well as many of the more expensive aftermarket 4-2-1 two-piece headers listed above. Food for thought!

D16Z6 4-2-1 two-piece header:

This is a 92-95 Civic Si header. Compared to the D16Y8 header above, the primaries are considerably shorter, though they are paired in the same unsequentially 4-1 2-3 manner. Though it's difficult to tell from the picture, the collector merges are shorter and more severe than the Y8's. The loss of tubing diameter on the bends toward the collector on the secondaries also appear more severe on the Z6 compared to the Y8. It's also worth noting that the inner diameter (I.D.) of the collector is only 1 1/2'' due to the double walled tubing. This is considerably smaller than the aftermarket headers that use a single wall tubing and lose a small amount of I.D. as a result. Cutting off the stock collector and having a 2.25'' (or larger) I.D. collector tube welded on is a cheap mod that will yield some peak horsepower gains and improve velocity. Overall the Z6 header looks to have quite a few restrictions in its design and will prevent optimal peak performance, particularly on modified engines.

Modified D16Z6 4-2-1 header:

The pictures on the left are comparing a stock Z6 header and one with a modified collector. As you can from the top picture, the inner diameter (I.D.) of the collector on the modified header (on the right) is significantly larger (3/4'' to be precise) than that of the stock header (on the left). The modified collector is also slightly longer than the stock one since the point at which the original collector is cut off is positioned slightly farther back on the secondary merge so that the outlet diameter of the merge will match the diameter of the larger collector tube. We will be testing this mod on the dyno very soon, but we're confident this simple modification to the stock header will produce some gains in peak output and quite possibly strengthen the midrange a bit too.

For a more detailed explanation on how to modify a stock D-series header, check out Moose's guide