DU6 SUs

[rcreweread]

At Southern Carburetters stand at Goodwood this weekend there was a very nice racing 3A in pride of place which I understand belongs to the boss!

 

Anyway, whilst I was there they took off the bonnet to start the car and I noticed a row of DU6's fitted to the car - one of the mechanics was covering the carb inlets with his hand to aid the starting proceedure and when it started, it sounded superb but with a very lumpy tickover.

 

Chatting to them, they told me they will shortly be producing new versions of these carbs - now this may be old hat to those in the know, but thought I would post this on here in case it wasn't - he also told me 85% of their production/manufacturing is done here in the UK so they can maintain proper quality control which is most reassuring!

 

I seem to recall posts on here indicating these were not very successful on our 4 pots, but clearly they think there must be potential demand for them to justify reproduction - I thinks Jags use them - has anyone ever tried them on a 5 or 6 engine as a matter of interest?

 

cheers

 

Rich

[Peter Cobbold]

Rich,

This thread describes the challenges you would face getting them to work for road driving:

http://www.tr-register.co.uk/forums/index.php?/topic/48988-du6-carbs/page-2

The same problems will arise on the 6 cylinder.

 

Peter

[Malcolm Tatton]

It will be very interesting to see what happens with these. I challenged the lads in the SU store at the Revival about the setup and their claim was that the carbs ran well on their test car (XHP 939). They have produced the prototypes by 3D printing and appear to be investing a lot of time and energy into the project so I assume that they believe that the problems can be overcome.

 

Guess it's wait and see whether they make it to production.......

Edited September 15, 2015 by Malcolm T

[Don H.]

The guys at the SU stand at Goodwood tell me that the DUs will be ready (essentially) in the next couple of months, but they're planning a 2016 introduction as they have some things to develop further. I believe one of their highest priorities is the DU4 (1½ inch) version for Minis and other smaller engines. (An owner of Burlen races a Mini, if I heard correctly). They know they're going to catch some grief over the pricing they'll need to get for these, but they're hoping those who have said they really want 'em will be able to dig deep enough.

 

My guess is that if the performance is there, the market will follow.

 

Here's the announcement they were distributing at the Goodwood Revival this year. (Click on it for a larger version.)

 

 

Here's a 3D-printed prototype body in their Revival High Street shop.

Edited October 3, 2015 by Don H.

[Peter Cobbold]

For high rpm circuit racing they may make for marginal gains, which are useful.

Even so they are going in the opposite direction from Hamill's suggestion for twin SUs of removing the piston spring and damper to gain responsiveness to sudden wots. But that trick makes for rought road running.

 

For road running I'm sceptical that metering can be made sufficiently flexible, with either mod.

Peter

[ianc]

Those who had a look at the current competition cars displayed in the top bay of Wye Hall at this year's IWE will have noticed that Richard Owen's TR2 was sporting a pair of ORIGINAL (not repro) dual-choke SUs. Richard had cleverly contrived a distance piece in order to mate the carbs to a Weber inlet manifold, and had, as a temporary measure, fitted modern SU (shiny!) piston chambers - but he has the originals at home.

He described the installation thus:

I am currently experimenting with a pair of “twin choke” SU carburettors bought on ebay. This set had previously been used on a Climax-engined Cooper Monaco in the USA with moderate success. Standard Triumph used twinned SUs on their Le Mans TRS cars in 1959 but there is no available set-up information, so this is very much a trial-and-error experiment. The SU Company had originally intended the twin choke SUs as a rival to the Weber DCOE but abandoned the project. Hence, these carburettors lack refinements such as a functioning choke. Apparently, only 50 sets were made.

 

Ian Cornish

[acaie]

Very interesting - how might they go on a TR7V8?

[Alec Pringle]

" how might they go on a TR7V8? "

 

Doubtless with considerable difficulty and expense, and then prove to be a grave disappointment . . . . .

 

Rather like having mad passionate sex, starkers, on the summit of Mt Everest . . . . . just because it's technically possible doesn't necessarily make it a good idea.

 

I'd suggest that it isn't coincidence that just about every manufacturer who ever tried DUs seems to have rapidly developed a more satisfactory fitment . . . . .

 

Cheers

 

Alec

[Peter Cobbold]

The all-important air pressure drop across an SU is unavoidably set by the weight of the piston plus spring downforce. This 'choke tube depression' has to be such that when acting on the area of the piston 'rim' it counteracts that downforce. So having one choke tube per cylinder makes b***r all improvement to that pressure loss. If you measure the weight of the piston and its effective area the pressure drop can be found and compared with Webers etc.To get an SU to work with less depression I would look to making the piston much lighter than standard and/or bigger in area.

DU6s look like they should swallow air better but they wont, the pressure drop is still there.

So in answer to the original query three DU6s on a 6-cylinder will still incur a pressure drop that should not be present in the PI manifold.

 

Peter

[roy53]

.

 

Rather like having mad passionate sex, starkers, on the summit of Mt Everest . . . .

 

Alec

 

I do wonder what goes on under that ponytail Alec ??

May be life is more exciting in the west country

 

ROY

[Paul Hogan]

Don H put me onto this rather negative thread about DU 6 carbs. He was saying that the word on the forum is that they don't work. Well I can tell you that's utter rubbish. They not only work very well but having taken before and after dyno tests with webers and the DU6 carrbs on my car they gave an immediate 8 bhp increase at the back wheels. Not only that but the performance/power curve reading were improved at the bottom end (1500 rpm on the SU as opposed to 2000 rpm with the weber ) and were equal to the weber further up the rev range.

 

SU Burlen who are working on re-introducing these carbs in du6 and du4 sizes, have made improvements over the original design by incorporating a cold start/choke control. Everyone who has driven my car remark on how good the response is but unlike Richard who has modified a manifold, I use a manifold specifically design for the TR/DU6. We have also tried a triple DU6 set up on a Jaguar 6 cyl engine - they were used on XK120 in period and again they work very well. I suspect they would look pretty good on a TR5/6 engine so I might try them out on my Dove.

 

hogie.

 

PS Edit I've never had sex on top of mount Everest and I suspect neither have you Alec!

Edited September 20, 2015 by Paul Hogan

[Peter Cobbold]

Hogie,

Interesting. The hp gain suggest the Webers are dropping more pressure than the SUs. I can calculate the SU pressure drop . But not the Webers. Cant find any data for the Weber venturis' "permanent pressure loss". Its not a figure Weber would broadcast !

Peter

Edited September 21, 2015 by Peter Cobbold

[Don H.]

For those who haven't seen under the bonnet of Paul's XHP939 TR3S tribute car, here it is on the SU stand at the 2015 Goodwood Revival:

 

 

 

 

 

Edited September 21, 2015 by Don H.

[McMuttley]

More nice pictures Don, good to see a company put effort into a display - its a shame we are nearly always away when the revival is on :-(

[Don H.]

Some of the companies -- like SU -- put a LOT of effort into those Revival High Street displays! Here's the Shell display, including their take on a vintage Triumph. The Shell licensee of their vintage image was promoting various nostalgia items from the corporate artwork collection and the relaunch of the Shell X-100 lines of oils for classics.

 

 

 

 

 

 

[Spit_2.5PI]

So that's where NTK246 the Blacksmith's Atlas pickup went!

 

 

Richard

[Don H.]

Burlen Fuel Systems appears to have a Facebook page on "DU6 carbs".

https://www.facebook.com/DU6-carbs-340230112803436/timeline/

 

These are presented as intake manifold drawings for a TR4 engine.

 

 

Hogie, the manifold in the second drawing looks a lot like what was on your car at the SU stand at the Goodwood Revival, yes?

Edited October 6, 2015 by Don H.

[Keith Jenkins]

The drawings for the manifolds and the Facebook page, with the other drawings and manifold patterns for DU6 applications, belong to KJ Engineering. We have developed the manifolds for Paul's car as well as a number of other engines.

[Don H.]

Welcome to the forum, Keith. Mutual friends have spoken about your background and your current work -- and I'm impressed. Good to have you here.

[Keith Jenkins]

Hi Don,

 

Thank you for your welcome, good to be here. With regard to my current works, we are just doing our best with our development side of things. Very nice to know that you hear of us and even nicer to see that you are impressed.

 

Keith