madmog
Club Retro Rides Member
Posts: 1,160
Club RR Member Number: 46
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Thinking of adapting some carbs onto a Mercedes M103 engine. In my research on what might suit, the IDF and DGES (or DGMS, DGAS - choke cable, electric or water choke function) come up as well as twin 1/34 SUs - I'll come to them after. First question is what is the functional difference between IDFs and DGES? I can see that a DGES would be suitable on a V6 Ford Essex or Cologne feeding a plenum but up to how many bhp? The M103 varies between 160ish bhp and 200ish bhp (2.6 or 3.0). I can also see IDF's popular on VW porsche air cooled flat 4s and 6s often in pairs. The numbers on IDFs suggests more flow (40, 44 & 48 IDF) vs 38 DGES but the uses I can find suggest the DGES is more suitable. Second question, is the Weber water choke rubbish or reliable? Third question, is the F.I. M103 manifold, going to create problems of de-atomization due to it's long inlets or general shape? I've seen people have stuck carbs on the Merc manifold on Youtube but now comparisons of how much worse it is than (good) original F.I. Just in terms of work in fitting, a downdraft plonked (painstakingly grafted!) onto the manifold is simplist. BUT There are a few 6 cylinder cars of similar capacity that had twin 44mm SUs; one carb per three cylinders. Eg Rover SD1 2600. A made up manifold would be a lot more work but would give a smoother path from carb to inlet valve. But I've also read that a carb feeding a plenum shared by all inlet throats makes it's whole capacity available to each throat since they don't all need fuel at the same time. Ie a 38 DGES on a plenum offers 2 x 38 mm chokes to any cylinder while the Twin SUs each feeding 3 inlets would only offer the single 44mm choke, not both. Going by areas alone: 44mm diameter = 1519sq.mm 2 x 38mm = 2266sq.mm Is this the correct way to compare Use is for a reliable cruiser, not outright performance. I don't want bike carbs and I don't have the original Mercedes FI with the engine and am not inclined to seek one out. And I didn't ask which carb (design) is best, SU or Weber  |
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Water chokes are generally tuned to the specific application, you would be better with a manual. Twin choke Webers basically come in 2 flavours one where both buterflies open at the same time and the other where a small primary opens first, this gives better drivability on a road engine but a bit slower response.
Sus will be eaaier to set up, rover v8 uses a pair which would be a vood starting point. Most of the twin set ups have some sort of balance tube so they are linked anyway.
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melle
South West
It'll come out in the wash.
Posts: 1,999
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Read the excellent book "Weber Carburettors Tuning Tips and Techniques" by John Passini. He starts by discussing carburettor principles in general and then focusses on different types of Webers and how to set them up for specific applications. Webers in general are excellent carbs if set up correctly, I have no experience with SUs, so can't comment on those.
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www.saabv4.com'70 Saab 96 V4 "The Devil's Own V4" '77 Saab 95 V4 van conversion project '88 Saab 900i 8V
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madmog
Club Retro Rides Member
Posts: 1,160
Club RR Member Number: 46
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Thanks all, I'll get that book ordered now.
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Personally I'd stay away from water chokes and stick to a manual... but that's just me. I like things simple for maintenance, manual for control, and isolated so that one system doesn't impact another. My last car had two SUs feeding a straight six. I forget what size they were but they were off an XJ6 feeding a 3litre. I never had any problems with them (until I had a big problem that was not their fault) and they can be balanced quite easily. I'm not sure I buy into the argument that they are any easier than a Weber to live with though. A Weber is largely plug and play and tuning them is easy, as it re-jetting them, and once set up they pretty much stay right. SUs do require regular fiddling in my experience. As for Webers, given the description of your driving intentions I'd say the 38 will be ample for your needs. Its synchronous carb rather than progressive so you get both barrels all the time as opposed to the 32/36 which opens the smaller first followed by the larger. People use the 38 way past the power range you mention, so the 40+ could well be overkill for cruising. The only other thing that struck me was if you have to fabricate an inlet manifold to use twin SUs anyway, why go for two feeding three and not three feeding two?  |
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madmog
Club Retro Rides Member
Posts: 1,160
Club RR Member Number: 46
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Thanks Quatermass. More food for thought. I've found several sources explaining the difference between DG V and DG S and some explaining difference between IDF and IDA but nothing that explains difference between DGS and IDF.
I've got a cheap Rover 2600 SD1 manifold coming from Ebay. That had 2 x 1 3/4 (as did I think the 3 litre XJ6). I'll see if there's natural point where the Merc and Rover branches could be cut and spliced for SUs.
One plus for the Webers is that you can buy them new, let alone all the parts. Another is that there are (or seems to be) many more people out there who can tune a Weber than SUs
I did think of triple but that looks like a lot of balancing work plus I've only seen triples using the 2" HD8 type which are much less common and hideously expensive on Ebay. It would even out the manifold length for all inlets though.
Agree on the manual choke.
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Darkspeed
Club Retro Rides Member
Posts: 4,839
Club RR Member Number: 39
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IDF's are typically for individual choke applications like a DCOE If looking at down drafts Edelbrock / Weber 4 barrels are also an option worth consideration. US and AUS been doing it for eons in the sort of configuration you describe.  |
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Last Edit: Jun 4, 2019 23:03:12 GMT by Darkspeed
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but nothing that explains difference between DGS and IDF. I've never used an IDF so I may be talking out of my harris here, but as I've always understood it IDFs are in effect two separate carbs sharing a common body and mechanisms. In terms of air, mixture and delivery they are two chambers set wider apart by the central location of all the mechanisms and floats in the body. The wider body has a wider delivery base with more distinct ports, so used at 90º to opposed cylinder banks it will feed each side better than a standard two barrel - cleaner flow, less manifold turbulence. A DGS is a standard two barrel and the chambers are closer together so the delivery is re-merged more as it enters the inlet manifold (sorry for my appalling terminology my brain isn't working yet). On my Essex the two DGS outlet ports feed a single aperture in the inlet manifold. Its divided, but it's very narrow and will ultimately merge more inside the inlet manifold. An IDF on a good manifold will generally do a better job of feeding one bank each (which is why they are used a lot on VW flat four engines I guess). So if an IDF was sat parallel to a straight six it would probably do a better job of feeding three cylinders each with the right manifold design, versus a DGS. With the wrong manifold design it would probably be no better (but no worse either) than than the standard two barrel DGS design, except the IDF offers a range of larger flow sizes. Edit, added: Really though what would be better depending on available space would be a side draught DCOE, but I guess that depends on whether you have more room vertically to fit a downdraught, or more room horizontally for a side draught. I would imagine being a straight six you would have room for a DCOE which would give you a more direct flow. |
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Last Edit: Jun 5, 2019 9:18:01 GMT by Deleted
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madmog
Club Retro Rides Member
Posts: 1,160
Club RR Member Number: 46
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Thanks Quatermass, what you said makes complete sense. Just noticing your Scimitar, were you at Retro Rides France a few years ago?
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Thanks Quatermass, what you said makes complete sense. Just noticing your Scimitar, were you at Retro Rides France a few years ago? Well, it's just a guess and I hope if there's a better or more accurate description of the difference somebody will correct my explanation. My car hasn't been to RR France in my ownership. I do know that the previous owner bought it with his son specifically to drive it to Le Mans for a weekend gathering of some description which would have been 3 - 4 years ago now, so it's possible he was at RR France too as they did a bit of a tour in it around France and Belgium, but the car looked a little different at the time...  |
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Last Edit: Jun 5, 2019 9:12:23 GMT by Deleted
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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You will find it's a bit easier to get the bits to tune the IDFs than the other Weber's. That said the SU is a better option for road use than most people may think so don't write those off
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melle
South West
It'll come out in the wash.
Posts: 1,999
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DGV/ DGAV/ DGEV and DGAS/ DGES/ DGMS parts availability is very good as far as I know.
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Last Edit: Jun 5, 2019 14:55:42 GMT by melle
www.saabv4.com'70 Saab 96 V4 "The Devil's Own V4" '77 Saab 95 V4 van conversion project '88 Saab 900i 8V
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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You can get it all yes but you will find the dcoe/idf parts (emulsion tubes etc) are much more common and rolling roads etc will have more available to swap. The last thing you want is to have to shell out 100s on various parts to set them up perfectly. Also SUs are good as you can 'make your own' needles rather than needing to have 100s of types to hand to swap.
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madmog
Club Retro Rides Member
Posts: 1,160
Club RR Member Number: 46
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Starting to lean more towards SUs as a simpler choice and it's for road day to day duties, not thrashing. Burlen seems to make most parts for common carb formats.
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dreadspeed
Part of things
1972 triumph 2.5 pi on carbs
Posts: 66 
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My mk2 Triumph 2500cc has a pair of 1-3/4" su hs6 carbs fitted as standard to the straight six engine, yes burlin have most parts for su carbs, ive never had a problem with the su hs6 carbs on my triumph, if your going to buy a pair of used su carbs whatch out for worn spindle bushs also check the pistons move up and down freely,
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Feels a bit odd to put SU on a Mercedes engine.
Mercedes-Benz used Solex on their carb'd engines so that be worth a look.
The M110 used Solex 4A1 carburetor, which is a 4 barrel setup like Darkspeed suggested.
So maybe a Weber 500 or an Holley 500 for a Rover V8 might be the ticket.
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ChasR
RR Helper
motivation
Posts: 10,243
Club RR Member Number: 170
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Jun 10, 2019 21:37:52 GMT
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A Holley is tempting for simplicity. But to prolong engine life, it's well worth doing your research and 1) Be willing to buy a decent AFR gauge to tune the car yourself, with an assortment of needles and knowledge 2) Pay a decent RR to set it up for you . The last thing you want is to have a dead engine due to either being run too lean or or being bore washed to death. Even the Weber conversions for the M130 engines IME are rarely tuned right coming out of the box. Despite what people say, a normal engine should idle smoothly and rev freely on a well setup carb, not spit and make that 'pufff pufff' sound of the occasional misfire all of the time. I'm very surprised my Stag carb was tuned right however to be fair, but that was also far from a cheap conversion, but it paid dividends at the pumps compared to a well known competitor's conversion. As for the carb design, SUs IME are easier to setup, but the needles can get expensive. It may be worth buying Des Hammill's book on how to tune them. I've had Holleys before and TBH I've found them fairly simple to setup too. IDFs are in theory but IME they do tend to be fiddlier to do, and the people who can do them right are getting few and far between now, and for their own semi-valid reasons aren't too willing to share the knowledge out. As for the DG*S carbs, it goes as follows: DGMS - Manual Choke DGAS - Auto Aqua (Water) Choke DGES - Auto Electric Choke They can be a very handy carb however. I will be honest though. The chokes on Fixed Jet carbs IMHO are much of a muchness. They really are a very crude tap chucking more fuel into the engine. My Holley on a manual choke would almost flood the Stag engine unless I backed it off as soon as I started it up. |
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pxr5
Part of things
Posts: 198
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Jun 11, 2019 22:23:19 GMT
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SU carbs, the best choice, easy to set up & very good, any carb that needs a squirt to mask a flat spot is 3rd rate,
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madmog
Club Retro Rides Member
Posts: 1,160
Club RR Member Number: 46
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Jun 14, 2019 15:01:55 GMT
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Feels a bit odd to put SU on a Mercedes engine. Mercedes-Benz used Solex on their carb'd engines so that be worth a look. The M110 used Solex 4A1 carburetor, which is a 4 barrel setup like Darkspeed suggested. So maybe a Weber 500 or an Holley 500 for a Rover V8 might be the ticket. I think there'a a Solex on my W123 200. parts are very hard to get, I think there's a Holley and/or Weber (prob DGV or DGS) conversion for that but it works fine for now. I've now got the Merc M103 2.6 in my shed and looking at the remains of the old F.I. (most missing) the simplicity of carbs seems hard to beat, albeit at a fuel and power penalty. As background, this engine combo is for my Merc W114 which had a knackered M180 engine. I was going with a modern Merc OM611 diesel transplant but in the time I've been fixing someone's botched welds, diesels have become the spawn of satan and will be expensive to drive in London. More importantly our daily C220CDi and a friends modern Merc diesel have had a 'all the electrics and engine died suddenly & unexplainably on a fast A road' event. Our car got 'better' by itself after the AA couldn't get it going and towed it home. Our friend's car coasted to the side and got written off by an inattentive driver. Probably digressing but the paranoia of adding so many fail points with F.I. and partial CANBUS when a carb will do the job is extremely appealing. Mechanical diesel might have been nice too but as someone pointed out, an M103 will fit and get you running or you could spend years and years messing around with different engines while you could be driving. As Dreadspeed said above, SU spindle wear is the main risk. I think someone out there reams out the spindle holes and adds a sealed bearing for long life without air leaks. M103 on (I think DG?S) |
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Jun 14, 2019 17:59:00 GMT
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Seems to running nicely on that carb. i just wonder why they running that dizzy?
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