Lazeum Posted December 18, 2011 Share Posted December 18, 2011 I believe not. I think their a ratio to take into consideration into the flow equation, something such as the ratio of the sections. Venturi effect would be more important on 45 than on 40 since 18²/22.5² << 18²/20² Ratio would be 0.64 for the first one and 0.91 for the second. Suction would be 30° more important on 45DCOE. Flow however should be identical with the same "restriction". I need to get back to the basic math of venturi effect (Bernoulli & flow equations). Maybe I'm wrong but this is the way I would attempt to explain the difference Quote Link to comment Share on other sites More sharing options...
duragg Posted December 18, 2011 Share Posted December 18, 2011 Interesting. Hope some others have thoughts too. I can choke up my 40s to 36mm choke or swap to 45s with 36 chokes. So for apples apples how do they perform differently. Obviously there is more work in starting over with 45s but ultimately have more capacity. Quote Link to comment Share on other sites More sharing options...
duragg Posted December 19, 2011 Share Posted December 19, 2011 Found this graph from an unknown source on an Alfa BB. If this chart is accurate it suggests diminishing returns past about 34mm chokes on DCOE40 and is certainly plausible. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 20, 2011 Share Posted December 20, 2011 I ran 32 venturis in my Dellortos to get it running right. I even had a set of 28s on hand just in case that didn't cut it. I think most of the kits were sold with verturis too large. Unfortunatly, none of the parts interchange with Weber. I think you are doing the right thing to down-size your venturis. Quote Link to comment Share on other sites More sharing options...
duragg Posted December 20, 2011 Share Posted December 20, 2011 But I am goint to upsize (from 34 to 36 or more). According to the Weber selection manual with my Power peak at 6800+ and 470 / cylider volume I should be at a 36 as a minimum (at 34 choke now). Going to 36 on my 40s is easy and cheap. Going to 36 on new 45s is a massive process including relocation of the Progression Port. Makes more sense to spend more money go ITB.. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted December 20, 2011 Share Posted December 20, 2011 The doc above is interesting (and depressing for the ones like you & me who are thinking about going up in ventur's size above 32mm) As you said, choking up our carbs is easy. However, I don't understand your comment about depression ports with 45DCOE. On the bright side, I'm in the good side of the ocean when talking about DCOE, nobody knows how to tune them but they're everywhere in classifieds Quote Link to comment Share on other sites More sharing options...
duragg Posted December 20, 2011 Share Posted December 20, 2011 I had to machine a new progression port so the butterfly would sit in the ideal position underneath for perfect throttle response (and closed the old one). Lota of work, carbs on / carbs off / resetting everything. To realize gains beyond 34 choke means the investment in DCOE45s, bunches of new jets, couple grand? No way I could justify that. I'd go ITB. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted December 20, 2011 Share Posted December 20, 2011 (edited) got it! it would make sense. My DCOE 18 did not need any rework of progression ports. As far as I'm concerned, I can switch for 3 45DCOE to refurbish for about 600€. then I can still sell the 40DCOE to cover some of the cost. it might be an option for the future Edited December 20, 2011 by Lazeum Quote Link to comment Share on other sites More sharing options...
duragg Posted December 20, 2011 Share Posted December 20, 2011 Supposedly DCOE40-151 progression is much different than -18, and isn't suitable for L2x I'm my experience. Same with Dcoe45-152. But there is a later model (152g?) That might be better. Probably all more expensive here in the distant colonies. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted December 20, 2011 Share Posted December 20, 2011 (edited) Interesting. I run the 151's on my 240Z L28, and have always battled a progression issue. However with gradual throttle, they work fine. If you spike the throttle below 2800rpms, you get a bog. I always considered this an accel pump issue, and plan to mess around with the accel jets. Here is an interesting observation. I looked down the progression ports and set all the butterflies with their front edge EXACTLY lined up with the front edge of the first progression hole. Then I started the car. It idled at about 2000 rpms. I had to move the butterflies top edge quite a way forward (closed), away from the progression ports, to get a regular best lean idle. This corroborates with people having to drill new progression holes in the 151's. From a designers perspective, Weber cast a pretty large, accessible well for the progression ports.  This tells me that they left room for experimentation, because they knew that each application would require hole location experimentation. The position of the butterflies at idle will vary depending on timing, idle vacuum, and jetting. Edited December 20, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
Lazeum Posted December 20, 2011 Share Posted December 20, 2011 Probably all more expensive here in the distant colonies. For what is worth, this is the link of the web store I use to get all my supplies for DCOE. Fast Road Cars They have new DCOE for 277£ (40 & 45) Quote Link to comment Share on other sites More sharing options...
duragg Posted December 20, 2011 Share Posted December 20, 2011 Interesting. I run the 151's on my 240Z L28, and have always battled a progression issue. However with gradual throttle, they work fine. If you spike the throttle below 2800rpms, you get a bog. I always considered this an accel pump issue, and plan to mess around with the accel jets. Here is an interesting observation. I looked down the progression ports and set all the butterflies with their front edge EXACTLY lined up with the front edge of the first progression hole. Then I started the car. It idled at about 2000 rpms. I had to move the butterflies top edge quite a way forward (closed), away from the progression ports, to get a regular best lean idle. This corroborates with people having to drill new progression holes in the 151's. From a designers perspective, Weber cast a pretty large, accessible well for the progression ports. This tells me that they left room for experimentation, because they knew that each application would require hole location experimentation. The position of the butterflies at idle will vary depending on timing, idle vacuum, and jetting. I battled the same for years and tried everything. When I put in the Wideband I saw the stumble was lean and perfectly matched the progression position. So one day I just drilled the darn new hole further forward and closed off the old 1st hole (closest to engine). Problem solved. Its perfect now. The progression port is the "canvas". Quote Link to comment Share on other sites More sharing options...
BrianW Posted January 26, 2012 Share Posted January 26, 2012 Damn Im having this issue currently. My 45's will idle good around 1000 rpm with throttle plates adjusted quite a bit forward of the 1st progression hole but bogs down as soon as I hit the gas and spits and sputters everywhere under about 3000 rpm. When I cover the 1st hole the transition is smooth but my idle is around 2000 rpm. I can go from a smooth 2000 rpm idle at 2.5 turns out on the mixture screws to under a 1000 rpm idle and running like crap at 2 turns out. Also Im getting alot of gas in the air horns with it set like this. I wonder if I switch to a 50f9 from a 55f9 would it help any. I would hate to have to drill holes in new carbs. Brian 36 chokes F 16 E tube 145 main 55F9 Idle 170 air corrector Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted January 26, 2012 Share Posted January 26, 2012 Simple answer: Electronic Fuel Injection Quote Link to comment Share on other sites More sharing options...
Leon Posted January 27, 2012 Share Posted January 27, 2012 Simpler answer: drill the holes. There is no way of getting around poor progression hole placement. Quote Link to comment Share on other sites More sharing options...
BrianW Posted January 28, 2012 Share Posted January 28, 2012 F............. Quote Link to comment Share on other sites More sharing options...
Leon Posted January 28, 2012 Share Posted January 28, 2012 I battled the same for years and tried everything. When I put in the Wideband I saw the stumble was lean and perfectly matched the progression position. So one day I just drilled the darn new hole further forward and closed off the old 1st hole (closest to engine). Problem solved. Its perfect now. The progression port is the "canvas". F............. Send duragg a PM, he has done this. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted March 19, 2012 Share Posted March 19, 2012 (edited) I will soon start again the car for the first time in nearly 2 years Before doing it, I need to order some parts for my 40DCOE. Besides the regular main, idle, air jets & chokes., I'm also looking at accel pump rod. Car besides bog at low rpm was quite snappy with no hesitation during normal operation but was not working well at low rpm (like we all experienced?) Since bog at low RPM is showing lean AFR after rich peak, I was wondering if it would worth a try to get some different pump rod design to pump more fuel during accel. My first move was to measure what I've got today in my carbs. I ended up with part number 015 in the chart below (in millimeter). My question is actually easy: what should I do to get more fuel during accel event? Obviously I need to make the stroke longer but I don't have any clue how! I foresee 3 options: 1- I reduce B length - I see no option on the chart. 2- I increase A length - easier since there're some choices; pn 012 or 016 would do the trick. 3- I get A & B to change but what kind of results should I expect? I don't also know the effect , would 1 extra millimeter of stroke make a significant difference? Should I go big to check? Rods are around 15$ per carb, I'm tempted to try Edited March 19, 2012 by Lazeum Quote Link to comment Share on other sites More sharing options...
didier Posted March 20, 2012 Share Posted March 20, 2012 Longer A and shorter B would increase the fuel flow (more capacity at rest), so i 'll go for PN 016 or much more PN 012 . Quote Link to comment Share on other sites More sharing options...
Lazeum Posted March 28, 2012 Share Posted March 28, 2012 I'm placing soon the order and I've looked at how the accel system works. Pump rod change might not be the smartest move to perform. It seems I should investigate other parameters first. I've made a picture with comment to illustrate my thought. Spill Valve (the jet at the bottom of the fuel bowl, #23 on diagram) seems to be the way to go if it is not fully closed yet. I haven't seen anybody to try this route yet... Quote Link to comment Share on other sites More sharing options...
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