DU6 information reqeust

[markmga]

Hello all,

I'm new to the forum  - I joined to try and learn a little about DU6 carbies, which I understand were used on some racing TRs.

I have a pair of these carbies and would like to find some information about their assembly and set up. No-one I've spoken to has any documentation so far. I noticed that a couple of DU6 equipped cars have been discussed on the forum and was hoping that someone could pass on some details about them. Contact details for any of the car owners would also be helpful.

Thanks for any suggestions,

Mark

[John Morrison]

Welcome Mark,

DU6 carbs were used of the 1962 le mans racing TRs's, 

there will be one or two folk here will have some info for you,

John.

[TwinCamJohn]

This may help.

Click on the 34 replies

[tr graham]

the triumph sabrina engines used in tr3s and trs cars in 1959-60-and 61 at le man did indeed use the twin DU6  not an easy carb to set up  the 1962 cars would have used DCOE carbs but alas it was not to be.

graham 

[Motorsport Mickey]

 There were only 85 x DU 6 carbs made from memory and were the original choice for the Cooper FPF F1 engine which was the development of the old Coventry Climax fire engine (where's Fireman Tom when you need him, he'd give further info) static pumping unit which ran lots of revs (about 11,000 from memory). The DU6s suited them for balls out power and flow without the complication of part throttle and quick switchs of revs. As posted above they were also fitted to the Le Mans racing TRs of 3 and 4 models (although the TR4S was called the TRS, much conversations about that) the DU6s sometimes come up for sale but now fetching very strong money well over £1k or £1500 for a pair.

After researching and some detective work back in 1987 we found 5 x DU 6 carbs in the Norfolk area and bought them for £80 a carb, 48 hours later we had made inlet manifolds to suit 2 of them of enormous length ( "11") to try and bring the torque peak lower down and after a 2 hour setup period on a rolling road with probably the best man in the UK for SUs, Peter Burgess at Alfreton had them running well enough to compete in the Birkett 6 Hour relay race at Donnington on the Saturday. They only gave 8 HP more than my very well developed and altered 2 x 1 3/4 SUs and were nothing like as nice to drive, with the torque coming in at 4000 revs, fitting Webers in contrast gave 15 hp more. In retrospect I think the Weber type shorter manifolds would have worked better for progression which is what Paul Hogan has fitted with them now running on his car.

When I asked around as to why these 5 x DU6s were available the owner said "they'd been taken off cars back in the early 1960s and put under benches and replaced by Webers which were easier to keep in tune and gave many options with variable chokes and the other changeable pieces ". When I asked some historic Cooper racers back in 2002 if they'd like a pair of DU6s they preferred to keep their Webers regarding the DU6s as "detuning" their cars.  They certainly look nice though in the engine bay.

Mick Richards

 

Edited November 28, 2019 by Motorsport Mickey

[boxofbits]

Interesting story Mick.

I think Burlen Fuel Systems started a project to re-introduce the DU6 in 2016 and the latest news is that it will happen and likely to be re-launched at a trade show next year. 

Kevin

[Peter Cobbold]

They look good but when we look into the fluid mechanics of the SU it is obvious where the snags lie compared with a twin SU arrangement.

A DU6 wont reduce the constant depression much at all as that is set at a minimum by the weight of the piston. If the piston is fitted without a spring the air velocity over the jet falls and that has a severely non-linear effect on fuel droplet size and combustibility. Big droplets lead to greater cyclic variaitons in combustion of the mixtur and sub optimal power generation. That means that even if a lighweight pistons were cast eg magnesium the depression could be minimsed but the air velocit over the  jet would fall and the droplet size increses impairing combusition and less power.  Much more here:

https://supertrarged.wordpress.com/2017/07/10/how-does-an-su-carburettor-work/

^^ slides 45 -47 show how reducing air velocity over the jet severely impairs atomisation of fuel.

https://supertrarged.wordpress.com/2015/02/25/combustion-basics/

^^ section on Vagaries of combustion

Fuel droplet size is paramount for power and economy hence the very high injection pressures used in moderns.

Peter

Edited November 28, 2019 by Peter Cobbold

[BlueTR3A-5EKT]

Arnott produced a carb for their supercharger and that did not have a spring over the piston

https://www.prewarcar.com/295163-arnott-supercharger-carburettor

[Peter Cobbold]

28 minutes ago, BlueTR3A-5EKT said:

Arnott produced a carb for their supercharger and that did not have a spring over the piston

https://www.prewarcar.com/295163-arnott-supercharger-carburettor

In a carb feeding a blower atomisation is not important as the blower will vapourise the fuel, both mechanically and with heat, so Arnott could remove the spring to minmise the constant depression

Most prewar SUs had brass pistons and no spring, the extra weight of the piston ensuring good air velocity hence good atomisation.

Peter

Edited November 28, 2019 by Peter Cobbold

[markmga]

Thanks for the comments everyone. I expect that a damper and weak spring would be needed for road use. The advent of oxygen sensors in exhausts might assist with tuning and needle selection. I'm still to find any literature on assembly or tuning, which is surprising if Burlen are planning on re-introducing them.

 

Mark