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Info on Weber 40 DCOE sidedrafts

Discussion in 'The Hokey Ass Message Board' started by denis4x4, Oct 13, 2010.

  1. red baron
    Joined: Jun 2, 2007
    Posts: 596

    red baron
    from o'side

    I ran dual 45 DCOE's on an O/T ca, ran great, decent mileage, and plenty of power. Embarrased lots of people with it, and even won a burnout contest with it lol. I have a video of said burnout somewhere on my laptop.
  2. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,716

    Tech Editor

    In one post you talk about 360deg seperation, in the next you say 180.

    One complete 4 stroke tract is 720deg.

    Take the head off any 4 inline and you'll see that the middle two cylinders move op and down together ( get to BDC and TDC at the same time )

    So those two are 360deg apart, in firing order. ( only two firing orders are possible... 1342 and 1432, 1342 being the most common... )

    The two outside ones move in sync as well.

    That means the two pairs, mirrored from the center ( in other words 1&2 and 3&4 ) follow eachother.

    So the pulses are 180deg and 540deg apart through the complete two rotations, not 360 and 360.

    That gives an uneven-ness over that pair of cyinders.

    Which WILL affect the sizing of the carb...
  3. SimonSez
    Joined: Jul 1, 2001
    Posts: 1,632


    Many years ago I talked my mother into buying a second-hand Datsun 120Y SSS which was a NZ only limited edition with twin 40mm Dellortos on a 1200cc engine. They had a mild cam, and exhaust headers and ran very well for the time. When the original engine wore out, we put the intake and exhaust onto a standard 1200 engine and it still ran good with the twin side-drafts.

    So properly sized and jetted, they will be just fine on 1800 cc.
  4. CutawayAl
    Joined: Aug 3, 2009
    Posts: 2,144

    from MI

    I am running out of ways to explain this. And amazingly, your post makes my point. I agree with everything you posted, until the final two sentences.

    An intake stroke is 180 degrees. Whether those occur 180 degrees apart or 360 degrees apart, the carb serving those two cylinders doesn't know the difference. When one cylinder is drawing on the carb the intake valve on the other is completely closed. With respect to carb flow they are two completely separate and independent events. The flows at the overlap on siamese ports with 180 degree timing are so low they have no bearing on carb max flow requirement.

    The asymmetry of intake pulses you described WILL affect intake tuning/resonance. Most twin carb inline 4 cylinder engines with siamese ports have a balance tube. The primary function of that tube is to tune out and dampen the ratty intake pulses you mentioned. Most people think the balance tube is there for performance enhancement, but inside those tubes is generally some sort of restrictor(damper), or, on engines where the intake runners are longer and additional volume is not needed, the balance tube will be small its entire length.
    Last edited: Oct 14, 2010
  5. mart3406
    Joined: May 31, 2009
    Posts: 3,055

    from Canada

    As long as you mount them on an 'Isolated
    Runner-type' manifold (- ie - a manifold
    with a separate runner and carb venturi
    for each cylinder, *without* a common plenum
    chamber connecting the venturis together),
    the '40's won't be too big. If anything, they
    might even a bit on the small side, depending
    on what else has been done to the engine.
    Engines with I.R-type manifolds require carbs
    with about 2 or 2 1/2 times more airflow capacity
    than what would be usual and prudent for a
    given displacement, horsepower output and rpm
    range with a plenum-type manifold. A rule of thumb
    too, requarding plenums - generally, the larger the
    plenum volume of a manifold, the smaller the carb
    that is required to support a given displacement,
    horsepower and rpm.

    Last edited: Oct 14, 2010
  6. 50Fraud
    Joined: May 6, 2001
    Posts: 9,885


    I had a Lotus Super 7 for many years with twin 40DCOEs on a 1340 cc pushrod Cosworth Ford. I can't really take any credit for it, as I didn't set it up, but it was an absolute rocket and totally tractable. The carbs were mounted with O-rings and spring washers, as Metalshapes has described.
  7. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,716

    Tech Editor

    As long as we can agree on that, not all is lost...

    Because if it does ( and it does...), it automatically follows you'll have to adjust a carb ( any carb ) to compensate for that.
  8. aldixie
    Joined: May 28, 2008
    Posts: 1,644


    I ran twin 40's on a ford 1.6 back in the UK. It was a screamer and would easily out run a fuel injected equivalent. Fuel consumption was on the high side though. I ended up selling them after I canon balled the engine. They are now living on a Caterham 7 somewhere. I'm now looking at running one on a MG Midget that I am building at the moment.
  9. 64cheb
    Joined: Sep 27, 2010
    Posts: 74


    Ive ran DCOEs on Harleys, but like andy said, sync them, and leave them. I had to rejet every DCOE and DHLA I had every day. A 103ci stroker I built had so much flow throught the manifold and heads, there was frost on the manifold from how much CFM a DCOE pulls
    Also don't make a right side carb into a left, real PITA.
    I would run IDF's on your application, they are more reliable and adjustable.
    but if you already have a DCOE, give it a try. Just make sure you have the tuning guide. Those are very valuable when it comes to the fine tuning.
  10. If you ran a DCOE on a Harley what is there to Sync? It is a single, two throat carb, with a single throttle shaft for both throats. You certainly didn't run two of them (a total of 4 throats) on a V Twin did you?
    And Carb / Manifold icing has nothing to do with the flow. It is caused by the vaporizing of the fuel which vaporizes the air around it. With an aluminum manifold it turns quite cold causing condensation the exterior of manifold or carb. On air cooled airplanes, pilots learn to turn on a small valve that blows heat over the manifold to stop this from happening any time the RPM drops below 2000. The more humid it is the worse the condition, regardless of air temp. If it gets severe enough the fuel quits flowing and the motor stalls, not a great thing on final approach.
    As for running IDF's on an overhead cam in line 4 cylinder, it is not practical in most cases, both for hood clearance and a lack of available manifolds. Having said that Esslinger does (or at least did) make a manifold for 2.3 liter Ford's with downdrafts - I ran that setup on my Off Road truck as the cage and shock towers made it tough to run side drafts.
    Last edited: Oct 14, 2010
  11. Here's my 2000cc Pinto with twin 40's. I had them dialed in, then did some engine work, now I need to fatten them up some.

    Attached Files:

  12. Jonny69
    Joined: Jul 24, 2007
    Posts: 275

    from England

    Careful now, the Ford Kent engine has a 1243 firing order.

    Yes it does. More flow through one carb means more fuel vaporisation concentrated in one carb body. With two DCOEs they rarely get cold enough to ice up, but when you use one they do have a habit of icing up because of the increased flow through the single carb.
  14. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,716

    Tech Editor



    And its an extra silly mistake, because I own one.:D

    U2 Engine 002.jpg
  15. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,716

    Tech Editor

  16. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,716

    Tech Editor

  17. zman
    Joined: Apr 2, 2001
    Posts: 16,594

    from Garner, NC

    The uneven firing order mimicks the power delivery of the 90° V4 with a 180° crank. "The idea of this technology is to reduce internal crankshaft torque, thus giving the new R1 a more linear power delivery." The idea was for the best of both worlds motorcycle wise "the low end torque of a twin and the pace of an inline four"
  19. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,716

    Tech Editor

    Thanks Zman and Hotroddon.

    Those guys will try anything....:D :D
  20. I don't know where this conversation is going but... regarding 40mm dcoe's I would take a very good look at them and if they haven't been ruined, missmatched or suffered any other abuse give a serious thought to useing them. Like any other componant on your ride once they're right they're right.

    I have a 1966 Alfa Romeo Giulia Sprint GT resting in my garage, I drive, with a 1600 motor and two 40 dcoe's on it. This is not a super gee wizz racer but a production car sold to the masses and the 40's were screwed on by the factory.

    It idles great, runs great and has never left me with any concern regarding the carbs. Hot days, cold starts, city traffic it's as smooth as yur mom's Caddy.

    After 44 years I gotta tell you, I still love it. My 2 cents, your call.
  21. denis4x4
    Joined: Apr 23, 2005
    Posts: 3,766

    from Colorado

    Thanks for the input. Found the correct manifold(s) on the shelf in Gilroy and ordered them this afternoon. I've been amazed at the availability of brand new parts and pieces for an engine that went out of production in 1978!

    Thanks again.
  22. Weasel
    Joined: Dec 30, 2007
    Posts: 6,693


    I have had several of them thar Alpha Romeros:rolleyes: - damn furrin cars ya know....;) I always insisted on Webers and a couple of times I had the dealer remove the factory supplied Solex junk and put on Webers or I would not take delivery. Soft mounts are de rigeur on Alfas. The poor old US cars were fated to receive the dreaded SPICA injection from 1969 on. This was an adapted diesel injection setup and in the mid eighties they switched to Bosch. Nowadays you can get DCOE flange compatible throttle bodies in various sizes all the way up to 50mm from TWM - - which can be adapted to run with the SPICA .

    I have a pair I am contemplating using on an Alfa engine for a hot rod build.

  23. Just Jones
    Joined: Jan 11, 2005
    Posts: 928

    Just Jones

    I used a pair of DCOE 40s on a 1.8l motor and it ran beautifully. It was a Volvo p1800S with a rally cam, headers, and all that kind of crap . . . but damn, it ran great. Very streetable, yet loved to rev. The faster you went, then faster it wanted to go. Yet it didn't bog on the bottom end, either.

    So in that case, it was a perfect match.
  24. Artiki
    Joined: Feb 17, 2004
    Posts: 2,008

    from Brum...

    Good thread, fellas.
    Here's something I was working on a few years ago. A 46 IDA on a four-banger. Unfortunately, I broke my crank before getting it sorted, so it's now shelved.

    Last edited: Oct 16, 2010
  25. Heo
    Joined: Jan 8, 2010
    Posts: 524


    When i was young back in the stoneage we use to run(i think everyone did) a pair of
    45s or 48s on Volvo B18-20 (1.8-2.0 liter) runs great with
    the right chokes and jets and dont forget velocity stacks
    one thing thats important to. Viton tiped floatvalve needle
    tune them right and forget them.If you have to fidle with something
    get a girlfriend or something but leave the carbs alone
  26. Kenneth S
    Joined: Dec 15, 2007
    Posts: 1,527

    Kenneth S

    My O/T 72 Pinto 2.0L with dual 45 DCOE's, ran strong!
  27. So what motor are you running? Datsun L series?
  28. denis4x4
    Joined: Apr 23, 2005
    Posts: 3,766

    from Colorado

    Running a 1975 Ford Courier SOHC 1.8 (same as a Mazda B1800) with a new Crower Cam, domed pistons, ported, balanced and lightened flywheel. Transmission is a ZF 4-speed. Since I'm splitting the wishbones and the engine is shorter than an A, we modified the pan to hold 2 extra quarts of oil. The Courier and the Model A Huckster are pretty close on wheelbase, tread width and GVW.
    Last edited: Oct 18, 2010
  29. It's funny, but when they imported the Courier for Ford it had an 1800 version of the motor but the Mazda version had the 1600, even though Mazda built both. Of course Mazda did have the Rotary powered truck, and they Hauled Ass!
    They were all replaced by the B2000 version and Ford offered the 2.3 Pinto motor as well - which was better than the others.
    Then they offered the 2.6 version which was actually a Mitsubishi motor that was also used in Dodge and Plymouth D50 trucks!

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