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DCOE Installation FAQ

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I was surprised to see that there is currently no '02 FAQ for DCOE installations. After thoroughly researching the topic prior to my own recent dual sidedraft conversion, I wanted to post as much relevant information as possible so that future '02 owners contemplating DCOEs will have much of what they need--in terms of info--in one place.

Others are welcome to add or differ along the way--there are certainly many here with more expertise than me in this matter--and I will be adding more to this post as time and further reflection permit.

If any of what follows is helpful in any way, the credit goes to this website and the community found here. Enjoy!

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When I decided to put dual sidedrafts on the '02, I wanted the installation to be as original as possible. To this end, I located and purchased a used 2002ti intake manifold (BMW part no. 11611250591). Although I opted to mount dual 40 DCOEs to them, 45 DCOEs would certainly mount perfectly as well. Here are the BMW 2002ti parts needed to mount the MANIFOLD to the ENGINE BLOCK:

Gasket 11611727995 Qty 1

Gasket 11611727994 Qty 3

Flat washer 11610643134 Qty 1

Hex nut w/ flange* 11611713432 Qty 8

Flat washer 07119900052 Qty 7

* This subs for NLA hex nut (18114090251)

Here are the additional BMW 2002ti parts needed to mount the CARBS to the MANIFOLD:

Insulator 13110639028 Qty 4

Gasket 13119067015 Qty 8

Wave washer 07119932095 Qty 8

Hex nut 07119922856 Qty 8

As for the 2002ti insulators and gaskets (see pictures), these are significantly more expensive (~$130) than two pair of Weber DCOE soft mounts (Weber part number 99005.145, about $30). There are several reasons why I urge the use of the BMW parts in this case, however. For one, they were designed for the ti intake manifold and its stud bolts. As such, the ti manifold stud bolts are too short to use with Weber soft mounts. More importantly, most whom I have consulted have soundly rebuked the soft mounts as leak-proned crap that fail to deliver as intended. As long as the carbs being installed have Weber's newer plastic float bowls, they will operate just fine (according to some, older brass float bowls could conceivably crack from vibration when used in a 4-cylinder application). My own experience with the 2002ti mounts from BMW gives them the strongest recommendation; my twin Weber '02 has worked flawlessly across diverse driving applications.

There are a lot of opinions about what to do about the vent at the top of the engine cover. Some run a hose to a catch can. Others run a long hose to drain into oblivion. Others fit a small K&N filter. To each his own. Given the aims of my conversion, I opted for a ti vent hose. Interestingly, the side width of a Ramflo dome-shaped filter perfectly covers the diameter of the tube running back into the air filter, so any oil/air mixture that may make it that far is filtered prior to reentering the carburator. Here's the part number:

2002ti vent hose 11120623134 Qty 1

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Thanks to Tom Jones here at the FAQ, I decided to use a mechanical fuel pump from a Bavaria to supply my dual Webers. This fuel pump has the high flow, low pressure characteristics that DCOEs need. And the dimensions of the Bavaria fuel pump will clear Weber DCOEs without issue, in my experience (see picture). The fuel pump has delivered the goods for me through daily driving, autocrossing, and track days. Tom's rationale for its use can be found here:

http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,294242/start,0/postdays,0/postorder,asc/highlight,/

Here are the parts needed:

Bavaria fuel pump 13311260677 Qty 1

Push rod (107mm) 13311250398 Qty 1

Insulator 11111721614 Qty 1

Insulator bushings 13310075752 Qty 2

Wave washer 07119932095 Qty 2

Hex nut w/ flange* 11611713432 Qty 2

* This subs for NLA hex nut 18114090251.

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Whether you plan to convert to dual sidedrafts or a single DCOE/Lynx manifold setup, you'll need to bypass the lower coolant hose than ran into the original downdraft intake manifold. Fortunately, there are parts that can be used from a E21 320i to solve this problem:

Return pipe 11531266817 Qty 1

Water (reducer) hose 11531266472 Qty 1

Water house outlet 64211356170 Qty 1

On the top side, the E21 320i divider* (aka, water neck) can be used to keep the top radiator hoses tidy without interfering with dual carbs:

320i Divider 11531267535 Qty 1

Screw plug 07119919228 Qty 1

Gasket ring 07119963200 Qty 3

Wave washer 07119932095 Qty 1

Hex nut 11611713432 Qty 1

* I have read that a E21 318i divider can be used as well, but it will need an additional screw plug to stop an extra orifice. If so, the 320i part is recommended for purely cosmetic reasons.

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Probably the biggest--and unfounded--fear in a DCOE installation is getting the carbs to syncronize properly; that is, to choose an effective and trouble-free throttle linkage. A poor design choice or installation will severely limit the success of the entire project, which will only add to the prevailing ignorance that dual sidedrafts are in some ways mysterious gremlins, hell-bent on turning "Freude am Fahren" into "Schadenfreude".

Weber offers bar linkage kits (99006.105), center-pull, interlink kits (99006.110), and so-called deluxe cable linkage kits, in either top-mount or bottom-mount variants (99006.101 and 99006.102, respectively). Of these three choices, the recommended choice for 2002s is the deluxe cable linkage. An important feature of the deluxe linkage is that it incorporates its own return springs, which reduce wear on the carbs own throttle return springs. A downside is that they are aesthetically displeasing to some. These retail for about $120 these days.

Another option is the TEP cable linkage kit. It is a center-pull design that uses the brake booster as a lower mounting point. It costs $125 at present. Although it does not include its own throttle return spring, the stock 2002 return spring can easily and cheaply be mounted between the Weber's external throttle lever and the engine block cover to relieve wear on the carb's internal return spring (see pictures). With this simple modification, this is the linkage I have been using without issue.

A third, costlier option is to combine the cable and brake booster parts from the TEP setup with the Weber deluxe spring return mechanism. Those who have spent the extra for this setup have given it high marks at this site.

A final option is the 2002ti linkage reproductions available for $115 from Lars Gunther ([email protected] ... certain critical parts of the linkage are NLA). One day I may get one of these to finish off the factory look of my own installation.

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Okay, so the Weber DCOE conversion kit you found on sale at website XYZ really makes you think it will make a great bang-for-your buck upgrade. Don't get me wrong, I pray at the DCOE altar every morning when I drive to work and every evening when I return home, and there is nothing I regret about my decision to convert. So here are some of your possible choices:

1) A Lynx cross-over style intake manifold mated to a single Weber 45 DCOE. A new conversion kit and extra 320i coolant bypass parts, air filter, gaskets, soft mounts, etc. will set you back about $900. You may be able to cut a little off of this by fashioning your own coolant bypass parts like MacGyver.

2) A dual Weber 40 or 45 DCOE conversion kit. Prices may vary, but $1200 new is ballpark for 2 Webers, a Cannon intake manifold (no. 99002 093), gaskets, soft mounts, etc. But then comes the fun part--you'll need the 320i coolant bypass bits, plus a new fuel pump (stock '02 fuel pump is too anemic and won't fit next to a Weber DCOE). The Carter 4070 electric fuel pump seems to be frequently recommended. Consider opting for Ramflo style air filters to clear the stock '02 brake booster if necessary. Anyway, the Weber conversion kit with low-pressure electric fuel pump, 320i bypass fittings, and Ramflo filters run about $1500.

3) Dual Webers (40 DCOEs in my case) fitted to a 2002ti intake manifold, using a new Bavaria mechanical fuel pump, Ramflo air filters, 320i bypass bits, and BMW insulators, gaskets, etc. This option set me back about $1600, some parts new, some old. Given the cost of the alternatives, it was worth it (to me) to keep everything in the family, so to speak.

4) Your best choice; that is, mixing and matching from the above and from elsewhere (e.g., Dellortos, Mikunis, etc.) to intelligently suit your own aspirations and you car's application(s).

NOTE: In all cases, a mechanical 2002tii distributor is recommended (or a suitable electronic ignition) to provide the best advance to suit the DCOEs. Alternatively, I have been told that a stock '02 distributor's vacuum advance can simply be unplugged and the unit's timing increased to about 15 degrees to compensate for sidedraft use. For God's sake, find a nice used tii distributor--new ones are like $600!

NOTE: Make sure one of your Webers has a T-shaped fuel inlet (10536.034) to feed fuel to both carbs. The second carb can use the standard Weber fuel inlet (10536.035), which is L-shaped.

NOTE: The DCOE cold start mechanism is useless and is typically oriented backwards for our application. Simply leave as is (i.e., pitch your old downdraft choke cable) and garnish, possibly, with Weber starter system covers (52135.008). By the way, in my experience with the Bavaria fuel pump, DCOEs are impossible to flood, so the cold start circuit is superfluous.

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great idea for a faq! thanks for starting. we should add pics of dcoe installs to show intake, manifold and linkage options. i have italian dcoe's on one car and spanish dcoes on the other, both with pierce linkages. i will take some picks and add them to this post.

edit - many pics of my dcoe installs in the photo bucket link in my sig.

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Thanks! Pictures were the one shortcoming of my own installation, as well as experience with the idiosyncracies of other sidedrafts out there to round out this FAQ.

By the way, isn't the linkage that Pierce Manifolds recommend the deluxe Weber top mount? That was my understanding when consulting with them.

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I haven't built a 2002 solely for racing yet, so I'll leave any contributions to this FAQ pertaining to any Stage 2 modifications to others with such experience. Instead, I'll share my own perspective and opinions regarding exhaust manifold choices that are well mated to DCOE street use.

For my 2002, I simply decided to pair my twin 40 DCOEs with a used ti/tii exhaust manifold (11621265449). This setup is inexpensive and is about as close as Stage 1 engine modifications can make a stock 2002 perform like the venerable 2002ti. The stock '02 lacks the ti's higher compression ratio, but Weber DCOEs tend to produce a bit more power than the original Solex units. Furthermore, the ti/tii exhaust manifold permits additional flow while retaining BMW's original torquey character. This can be a relevant factor to consider for those, like me, with a standard 4-speed gearbox. And most importantly, for me, the overall improvements in throttle response and acceleration--from any speed--were noticeable without requiring extensive brake and suspension upgrades to keep everything balanced. Acceleration (or deceleration, for that matter) is instantaneous yet not outrageous. For now, my car retains the stock '02 downpipe--resonator--muffler (same as a 2002ti), but a tii resonator and muffler or stainless Ireland Engineering exhaust system could be used instead.

When mounting a ti/tii exhaust manifold, you can use the one-piece gasket from a E21 320i (11621723876), which includes a heat shield that separates the header from the spark plug wires above. From a functional standpoint, many consider this as an updated specification that supercedes the manifold's original metal heat shield that is currently NLA. Use eight hex nuts (11621744323) to attach the manifold to the engine block as well as one gasket (18111728363) and three hex nuts (18301737774) to attach the manifold to the downpipe.

Alternatives to the factory ti/tii exhaust manifold are the Ireland Engineering "shorty" header and the 02again Tii replacement exhaust manifold (currently sold out).

The next step up would be a four-in-one exhaust header (that typically replaces the stock manifold and downpipe) mated with a free flowing resonators and mufflers, including perhaps 2002 turbo parts. Four-in-one headers are probably the most common recommendation to complement a dual DCOE conversion, as they offer the most potential for increased performance. Stahl and Ireland Engineering make durable, well-respected headers for the 2002. In these cases, additional mechanical upgrades (e.g., cooling, braking, etc.) may be needed to maintain a balanced package.

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Let's preface this section with the obvious caveat that DCOEs were designed to be flexible, so the possibilities are truly limitless. That being said, these systems have been used very successfully by many drivers for many years--we're not reinventing the wheel here, folks. If your DCOEs aren't working for your application, please don't whinge about it; such rants only dissuade others who could be getting more out of their '02s. Yes, I will concede that initial carburetor choice and setup can be frustrating for some, but the root of such feelings typically lays elsewhere than in the Webers themselves. I personally spent months researching the supposed pros and cons of DCOE conversions before finalizing all the variables, but the result was a painless, intuitive installation and bulletproof performance afterwards.

In my opinion, the DCOE, and two of them at that, are the ultimate carburetor(s) for the BMW 2002. Period. The M10 engine is an inline 4-cylinder; a pair of either 40 DCOEs or 45 DCOEs (chosen dispassionately for the intended use and based upon concurrent upgrades) will outperform any other carburetor choice. The only advantage of the stock Solex or Weber 32/36 DGAV is the economy of the parts. Mated to a 2002ti or similar intake manifold, no other setup than twin DCOEs will deliver a more precise dosage of fuel and air to each individual cylinder. No other choice will perform better, as twin DCOEs give incredible freedom in tailoring the exact nature of that performance (e.g., power vs. economy, etc.) to your own desires. In short, I find it plainly one dimensional to think that DCOEs only equal more power—there's so much more to their beauty than that....

Enough soapboxing; let's examine the choices available to us. Before laying out the various sidedraft choices, let's briefly reaffirm the merits of downdraft offerings. A well-tuned stock Solex or Weber 32/36 DGAV is a fine setup for many, is ridiculously economical hardware, and delivers high fuel mileage. The Weber 38/38 downdraft--mated to a properly ported intake manifold--increases power and torque cheaply, quickly, and easily. Certainly, the 38/38 DGES is arguably one of the best bang-for-your-buck, do-it-yourself upgrades available. Unfortunately, the 38/38 DGES was designed for larger engine capacities (e.g., 3L engines) and, like the original downdraft, treats all four cylinders equally, which is less than ideal (e.g., cylinders 2 and 3 can run at different temperatures than 1 and 4; the lengths of the inner and outer pair of intake manifold runners are unequal, etc.). These factors force an inevitable compromise upon the M10 that meddles between a flat spot somewhere on acceleration and a rich, less-optimal mixture.

A single sidedraft and Lynx crossover intake manifold mitigates this compromise in at least two ways. One, a DCOE is simply more tunable than a DGAV or DGES, so you have more ways to reach stoichiometric consensus. Additionally, the crossover intake design allows each barrel to sequentially feed its mixture to only two cylinders as the engine cycles through its ignition sequence--a relative advantage to downdrafts when fine tuning the entire setup for optimal performance. As such, a single 45 DCOE/Lynx will certainly outperform a 38/38 DGES, but will also cost appreciably more time and money to install. Given the extra cost, most who go the Lynx route choose a 45 DCOE over a 40 DCOE to maximize the return on their investment. Those who have opted for a single 45 DCOE/Lynx setup over traditional dual sidedraft conversions may argue that it represents a good compromise between performance and mechanical parsimony, especially on otherwise stock '02s.

Whether single or double, there are several choices available for sidedrafts (e.g., Weber, Mikuni, Dellorto, Solex). As I am most familiar with Weber DCOEs, I will concentrate on Edoardo's offerings here.

For the BMW 2002, you will most likely be choosing between 40 DCOEs and 45 DCOEs. Other than the primary Venturi (i.e., choke) diameters, these are nearly identical carburetors (same outward dimensions, minimal internal differences) that mount and install the same. Generally speaking, the choke size(s) needed given your range of applications will determine whether the 40 or 45 is the best option. This is the time to be absolutely honest with yourself and determine what your present and future plans are for the car. A stock or near stock '02 would obviously be better served by dual 40s than dual 45s; however, some would argue that dual sidedrafts are perhaps overpriced and under-utilized on an otherwise stock 2002. While I disagree with this opinion (in my opinion, DCOEs offer more than just more "power"), I concede that these additional performance improvements may appear too subtle on a stock '02 for some to justify the expense.

Look at it this way: What do you want to turn your 2002 into? A stock 2002 puts out about 100 hp. The 2002ti about 120 hp. The 2002tii about 130 hp. Weber 40 DCOEs utilized on an otherwise stock ’02 engine with some combination of Stage 1 modifications, including free-flowing exhaust headers, resonators, and mufflers, and maybe a Pertronix ignition, will put you somewhere in 2002ti territory. In these cases, 30 mm or 32 mm primary Venturis (i.e., chokes) will produce a nice balance of drivability, power, and economy which performs well with the standard 4-speed gearbox. Although additional Stage 2 engine upgrades (cams, increased compression, etc.) can push the 40s to help pump out about 150 hp, this is well into the area where the 45 DCOEs excel. As a result, 45s with 34 mm or 36 mm chokes to begin with are typically the preferred choice if Stage 2 upgrades are implemented on a 2002.

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Books

Braden, Pat (1988). Weber Carburetors. New York, NY: HP Books.

Hammill, Des (2003). How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors. Dorset, UK: Veloce Publishing.

Legg, A. K., Peers, D., Maddox R., & Haynes, J. H. (1999). Haynes Weber Carburetor Manual. Clifton Park, NY: Thomson Delmar Learning.

Macartney, Mike (1998). BMW '02 Restoration Guide. Cobham, UK: Brooklands Books.

Passini, John (2008). Weber Carburettors: Tuning Tips and Techniques. Cobham, UK: Brooklands Books.

Weber Tuning Manual

Websites

http://www.bmw2002faq.com/

http://www.tjwakeman.net/TR/WeberDCOEinfo.htm

http://www.teglerizer.com/dcoe/index.html

http://www.fordcaprilaser.co.uk/weber_dcoe_carbs.htm#Chart%20Showing%20Main%

http://www.aircooled.net/gnrlsite/resource/articles/dualcarb.htm

http://www.inglese.com/Information/ (then click on FAQ section)

http://www.webernorthamerica.com/

http://www.redlineweber.com/html/Tech/Table_of_contents.htm

http://www.carburetion.com/Weber/adjust.htm

http://www.piercemanifolds.com/products.htm

http://www.racetep.com/webtechpage.html

http://jameng.com/

http://www.bmw2002.com/

http://www.kormanfastbmw.com/2002.htm

http://www.jaymic.co.uk/

http://vesquared.com/ramflo/index.htm

http://www.webcon.co.uk/

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Two things:

1. does that pump push enough fuel for the DCOE's?

2. shouldn't you put the fuel filter before the pump?

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Just two things:

1. does that pump push enough fuel for the DCOE's?

2. shouldn't you put the filter before the pump?

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