FinP Posted October 2, 2014 Report Share Posted October 2, 2014 Did anyone see these at Goodwood? Made available for Classic Jaguars, No doubt also available for TR's and other Classics. I do have the contact details for anyone interested. They are based North Midlands. Quote Link to post Share on other sites
Peter Cobbold Posted October 2, 2014 Report Share Posted October 2, 2014 FinP, Interesting, they look like 2inch. Wonder if they sell just the casting? Would be good to feed the blower. Pls PM me their details. Peter Quote Link to post Share on other sites
ctc77965o Posted October 3, 2014 Report Share Posted October 3, 2014 They are available on eBay Quote Link to post Share on other sites
stuart Posted October 3, 2014 Report Share Posted October 3, 2014 Dont look entirely complete from those pictures, in fact the bodies look like new bare castings so good luck with trying to find the rest of the bits, they were only ever any good for flat out race operation which is why SU stopped making them after around 50 odd units were made. Stuart. Quote Link to post Share on other sites
FinP Posted October 3, 2014 Author Report Share Posted October 3, 2014 They are unfinished casting having just been remanufactured by an SU carb specialist. When completed a pair are to be fitted to my TR4A. I would be very surprised if any are available on Ebay, if so they would be of fifties manufacture! As they are being made to order they may supply a body only. Quote Link to post Share on other sites
Peter Cobbold Posted October 3, 2014 Report Share Posted October 3, 2014 They are unfinished casting having just been remanufactured by an SU carb specialist. Who? Quote Link to post Share on other sites
Chris59 Posted October 3, 2014 Report Share Posted October 3, 2014 Andrew Turner, may be ? Some of these DU6 were for sale at the Beaulieu Autojumble : they were originals (not repro), and hugely expensive..... Quote Link to post Share on other sites
Peter Cobbold Posted October 3, 2014 Report Share Posted October 3, 2014 Glen Hewitt of Protek made a pair to feed a Marshall blower many years ago. Quote Link to post Share on other sites
Motorsport Mickey Posted October 3, 2014 Report Share Posted October 3, 2014 (edited) As probably the last person (as far as I know) to race DU6s on a TR I can confirm Stuarts comment regarding their characteristics. As fitted on a Coventry Climax FPF F1 engine where the engine performs very well at high revs and the DU6s gave a large hole which worked well at top revs is not necessarily what a road engine needs. The reason I was able to track down these DU6s was because when Webers came in vogue with their flexibility and power delivery, the much more difficult to set accurately DU6s were taken off and put under workshop benches. When I approached some classic Cooper racers and offered the DU6s to them their opinion was "no thanks why would I want to put inferior equipment on my car " ? The power delivery came in at 4000 revs (even with longer special length inlet manifolds made to lower the revs it came in) and was very much of the switch on/off characteristic, not nice and only gave about 8hp more than well developed 1 3/4 SUs. Driving the car was slower by dint of it's more difficult power delivery preventing earlier application of the throttle until further through the corner. Admittedly the car had only had 2 hours on a rolling road and would have benefited from further work and in my opinion the fitment of shorter standard length inlet manifolds to reduce the instantaneous power and torque application and make it a smoother drive. Given that it was at 4000 revs where all the action happened and a shorter manifold would have increased the revs for power feed in but in a smoother manner in my opinion the carbs would not make the cars a joy to drive on roads but they certainly offer the" bling" effect. Mick Richards Edited October 4, 2014 by Motorsport Mickey Quote Link to post Share on other sites
Chris59 Posted October 4, 2014 Report Share Posted October 4, 2014 Very interesting comments, based on your experience : thanks for sharing, Mick. Quote Link to post Share on other sites
Peter Cobbold Posted October 4, 2014 Report Share Posted October 4, 2014 The reason why overcarburation doesnt work at low horse powers is because the air flow cannot lift the piston reliably. Even with no spring fitted the weight of the piston could prevent it opening correctly. Also, the pulsing air flow as the inlet valve opens then closes gives a rich mixture, possibly too rich and power suffers. Look at it another way. If the air flow is too low , which depends upon horse power, the depression lifts the piston less than in a normally sized SU. Either you need a smaller SU with lighter piston, or more air flow such as two cylinders fed by one carb. We can revisit this when FinP attempts to get the DS6s to work!! Reducing piston weight would be high on my list. It is possible to calculate the depression needed to lift the piston's weight (plus spring if fitted). We need the lowest possible piston mass. But good damping too to prevent flutter with those single inlet valve openings. One DU6 would be really good to feed a blower, for up to 250+ hp. But two on a four pot.... challenging. Peter Quote Link to post Share on other sites
ctc77965o Posted October 5, 2014 Report Share Posted October 5, 2014 I would be very surprised if any are available on Ebay, if so they would be of fifties manufacture! As they are being made to order they may supply a body only. SURPRISE! http://www.ebay.co.uk/itm/SU-Twin-Choke-DU6-Carburettor-Pair-Triumph-TRS-Climax-Formula-Lotus-Cooper-/290682169786 Quote Link to post Share on other sites
stuart Posted October 5, 2014 Report Share Posted October 5, 2014 SURPRISE! http://www.ebay.co.uk/itm/SU-Twin-Choke-DU6-Carburettor-Pair-Triumph-TRS-Climax-Formula-Lotus-Cooper-/290682169786 Yes that was an original set, they do appear very occasionally but its still a case of why bother to my mind Im afraid. Stuart. Quote Link to post Share on other sites
Peter Cobbold Posted October 5, 2014 Report Share Posted October 5, 2014 Yes, getting them to work could be a lot of botheration for FinP. Here's the usual applications of SUs, note how the SU size and number relates to max horsepower, and hence to air flow:http://www.sw-em.com/SU_vs_disp.jpg So two HS6s ( = two 1 3/4 inch) are suitable for 100-150hp. Two DU6s would therefore be suitable for 200-300hp. So for say 120hp they are definitely oversized: piston lift will be lucky to be at max more than halfway up the choketube. There's little scope to lighten the piston by removing metal. FinP will need to experiment with springs that reduces piston downforce, using tension springs suspended from the apex of the dome. I have not seen it done before. The inlet valve surges will need the pisiton lift damping in both directions to reduce flutter. And the easy bit, the needle will need complete refiguring to cope with the lower depression. The TRS Evocation with the Alfa twincam engine runs DU6s. How'd he do it?? Peter Quote Link to post Share on other sites
stuart Posted October 5, 2014 Report Share Posted October 5, 2014 The TRS Evocation with the Alfa twincam engine runs DU6s. How'd he do it?? Peter You would have to ask Phil Tucker about that but IIRC not very easily! Stuart. Quote Link to post Share on other sites
Motorsport Mickey Posted October 5, 2014 Report Share Posted October 5, 2014 Lot more difficult on a TR 4 cylinder engine, with it's much different Torque delivery, as the Cooper guys said why choose to have inferior equipment on my car. I was tempted to keep them for bragging rights and bonnet lifted pint sipping sucking of gums with admiring onlookers and then I thought...nahh. Let those that want them buy them or their cloned alternatives, I'm sure they will be happy and good luck to them, I'm for 1 3/4 HS6s or Dellortos (probably 40s for the better torque) or even Mikunis which Mr Burgess gives a gold star and a tick to. Mick Richards Quote Link to post Share on other sites
stuart Posted October 6, 2014 Report Share Posted October 6, 2014 FWIW the hardest parts to find or restore for them is the special floats made of plastic covered cork. Stuart. Quote Link to post Share on other sites
Don H. Posted October 6, 2014 Report Share Posted October 6, 2014 With the new "Stay Up" floats made, as far as I can tell, of syntactic foam, maybe it's a do-able project to whittle them out of another float? If one were so inclinded, that is -- not for me! Quote Link to post Share on other sites
FinP Posted October 19, 2014 Author Report Share Posted October 19, 2014 TR4A is going in for fitment of the DU6's in the next few weeks. I will entrust the car to them to make it function by their development work. Not only are they manufacturing the DU6's but they also manufacture bespoke needles to the characteristics of the engine on their rolling road. most of the work being racing Jaguars. Will report back on the outcome. Quote Link to post Share on other sites
stuart Posted October 19, 2014 Report Share Posted October 19, 2014 Good luck with that, be interested to know the cost of it all as well. Stuart. Quote Link to post Share on other sites
Peter Cobbold Posted October 19, 2014 Report Share Posted October 19, 2014 TR4A is going in for fitment of the DU6's in the next few weeks. I will entrust the car to them to make it function by their development work. Not only are they manufacturing the DU6's but they also manufacture bespoke needles to the characteristics of the engine on their rolling road. most of the work being racing Jaguars. Will report back on the outcome. Go along when its on the RR and check that the pistons really do lift the full diameter of the choke tube at full chat (ie max rpm +wot). I very much doubt they will - in which case they restrict the air flow more than they should, and probably about the same as twin SUs.. Fettling needles is trivial, getting the air to lift those pistons is not. Keep us posted !! Peter Quote Link to post Share on other sites
Motorsport Mickey Posted October 19, 2014 Report Share Posted October 19, 2014 (edited) Similar sort of problem with HS8 carbs, look good but the standard 1 3/4 HS6 perform better. Prior to tracking down buying and fitting the DU6s we experimented with the HS8 carbs and could not get enough vacuam to lift the piston the full amount. We tried cable lifts attached directly to the pistons which worked and got the flow but everytime the car went onto tickover the pistons would stick resolutely to the bridge and required Schwartzeneger like right leg application to break the suction and get the pistons moving which then flew to the top and the car took off like Billy Whizz ! It allowed excellent starts (but with very little control because of having to overcome the bridge suction) and the idea of trying to race it and convert the sticking piston into something usable in corners filled me with horror ! The carbs needed an air bleed to weaken the mix on the bridge, hours of research and a couple of dozen books (hardly any internet info on carbs available in 1986) later trying to find a carb which would give the 2" choke size with an air bleed and therefore be allowable under TR Register regs narrowed it down to the fabled DU6s, after that it was merely down to finding a couple still remaining out of the original 70-80 made. In the event we found and bought 5. The detail of how we did it has already been posted and is available under the search facility, look for "Twin cam posting" and there's another different posting with photos of the DU6s fitted. Mick Richards Edited October 20, 2014 by Motorsport Mickey Quote Link to post Share on other sites
vivdownunder Posted October 26, 2014 Report Share Posted October 26, 2014 At one stage I had 4 of the last series DU6 carbies ex Covenrty Climax. I'd thought of fabricating a manifold and fitting a set to the 3A until I was told they needed a long branch manifold for road use. That entailed a cutout to the inner guard for the carbies, so the idea went out the window. Another problem was lack of a choke, although I was confident a Mk2 Jag choke used for HD SU's could be adapted. In the end I was persuaded to part with all 4 which found their way back to the UK. Viv Quote Link to post Share on other sites
wspohn Posted December 16, 2014 Report Share Posted December 16, 2014 I noticed this when googling on the DU6s in regard to a question that came up in another forum, and thought I'd post to add some info here. I've owned quiet a few TRs - TR-2, TR-3, TR-4, TR-4A, Swallow Doretti, but don't currently own any. I had a set of DU6 carbs along with a rebuild gasket set and had them fitted to a 2.2 TR-3 I was running - still have the fabricated intake manifolds about somewhere. I think I may also have some DU6 intake trumpets around somewhere as I converted them to more modern staggered Weber intakes when I had them on the TR3. I also experimented with running 4 of the H4 1 1/2" SUs on a Triumph engine (it got a bit tight for clamps between the carbs with that set up). They were indeed too much carb for the engine size and I eventually sold them to the owner of a TRS to be used for restoration of that car. As it happens I also had the opportunity to not only follow the local restoration of another TRS in Vancouver, but also to race with it (it was heavy and not up to sprint racing, nor as fast as my MGA, but was no doubt a durable endurance car). The British had a tendency to go overboard on SU carb size. The Rover 2000TC never needed twin 2" cabs, nor did any of the racing MGs, which almost universally do far better on a pair of HS6 carbs. The factory even experimented with the DU6 carbs on their MGA Twin Cams, for track use, but wisely ended up speccing either H6 or Webers. Even Lotus switched from the DU6 on their FPF Climax engines (an engine that could actually get those pistons to rise!) after the first season and went with Webers. They are neat period pieces and in demand by Cooper Monaco owners for use in vintage racing, even if using Webers would be better and faster. Nice to see people still talking about them. Closest I've come to anything like that since is the triple 1 3/4" SU set up I created for my MGC back in the 1980s. Sorry I don't have any pics of the DU6s I had, but here's one of one of my race engines - an MGA Twin Cam, but in 1950 cc displacement and running 12:1 and Cosworth L1 cams. The Webers on it are 45 DCOE. Quote Link to post Share on other sites
GT6M Posted December 16, 2014 Report Share Posted December 16, 2014 Peter, wanting moer carb for your blower engine,!!! there is a 3" inch singl SU too. fitted to some Jags, cos a bloke brought a one off manifold, and .another 3" carb. to fit onto it, thus makin it a 3 3" set up, instead of 3 2" inchers it did,nt work v well on a 4.2 engine Also goto the SU site, there some info there aboot the DU6,s http://sucarb.co.uk/technical-su-carburetters M Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.