Single or twin carbs for economy on 1500 ?

[paulhumphries]

As I've already said I intend TRYING to fit a Dolomite HLS 1500 and BW65 autobox into the Herald I'm hopefully collecting later this comming week.
At present, being a HLS lump, the engine has twin SU's.
My (more than ample) gut says single 1.5 carb will probably give best economy but twins for performance. I don't have a problem keeping the twin carbs but only if they aren't much worse than a single carb for thirst.
I drive carefully and most of my journeys are in 30/40 limits with only occasional ventures on dual carriageways / motorways where even there I tend to do less than 60 mph in a modern car easilly capable of more than twice that speed.
I want economy rather then power and therefore what is going to be the best carb set up for me - existing twin carbs or a single SU / Stromberg ?

Thanks.

Paul Humphries

[piman]

Hello Paul,

there is nothing really inherently more thirsty with twin S.U.'s versus a single. If you want the best from them, tune the engine as best you can and perhaps even fit the 'weak' needles specified for that engine.
Economy is basically in driving style, as you know, so I would initially set up what you have as well as you can.

Alec

[paulhumphries]

Thanks for the reply.

As you say I'll stick with the twins to see how they perform.

Paul Humphries

[Clive]

John thomason (sp) did a proper comparison on his 1500 spitfire abiut 10 years ago, Ran a single 1 1/2" su during the week and twins for racing. He had both set up on a rolling road etc, and did LOADS of miles with them both to get a comparison. The twins gave a bit more power and a bit less economy, not as big a diffrence as expected on both counts.
I believe John Kipping did lots of work on different setups too, and in the end (I am happy to be corrected on this) a stromberg setup wqas the most economical, but he plumped for a single 1 3/4SU. Asl Dave Pearson at Canley Classics, he probably did all the work. I suspect the SU would give good power too, maybe better than the twins. And the late (metro type) carbs are well regarded, certainly in mini circles.
Clive

[Richard B]

cliftyhanger wrote:

Ask Dave Pearson at Canley Classics, he probably did all the work. I suspect the SU would give good power too, maybe better than the twins.

Yes I heard that too.

Supposed to have been the most economical setup witha proper 4-2-1.

[ferny]

I've seen CC say a single HS6 was the most economical.