2 or one is best?

[00/63484]

Ok - so this has been asked before but before was before and now is now and things just keep on getting more annoying. My blueprinted 1500 engined Herald 1360 convertible runs very well thank you. New, anti nasty-petrol hoses recently fitted plus a new cheap mechanical fuel pump which seems to be doing the business. Unfortunately, we live in a built-up area of West London and driving any distance in ANY direction means sticking to 20mph or risk points, or worse, a speed awareness test. In these new and ever more restricting circumstances, how does the team feel about my dropping one of the shiny HS4 SU's and running around with one only? The long branch exhaust manifold will stay, and I will need to source the right single carb manifold (advice please...?). Just a thought and a possible experiment - but am I being overly pessimistic? I use the car quite a lot just to spite old Ghengis Khan (sorry, Sadique) as my perfect and very useful 1996 Spacewagon had to go due to ULEZ charges and old Euro 3 ratings. Yes, the Herald won't accelerate as well, but will it save me fuel? I can always replace the second for holidays... 

 

[Pete Lewis]

fit the single stomberg CD150 and manifold as per the 13/60 was originally

certainly more economical may need some needle tweaks to run the 1500 through the range 

Pete

[Qu1ckn1ck]

Properly set up twin carbs are usually more efficient than a single carb set up and so should be more economical.  Perhaps you should consider some restraint on your right foot instead ?   😆  

[Pete Lewis]

[Pete Lewis]

wasnt there some tests done by John  Kipping about the pros and cons of 2 or 1  and the 1 came out best  ???

Pete

 

[johny]

Think youre right although not sure it was done on a 1500. Also I reckon the idea is to use one of the HS4 so will that be easy on a Stromberg manifold? 

[Colin Lindsay]

45 minutes ago, Pete Lewis said:

Isn't that a handbrake?

 

[NonMember]

1 hour ago, Qu1ckn1ck said:

Properly set up twin carbs are usually more efficient than a single carb

No, not on a four. They probably are on a six. They nominally breathe better but won't give as good mixture control.

A single carb on a 1500 - whether it be a Stromberg on a 13/60 manifold or an HS4 on a Toledo one - will work fine and give good economy, but will lack top-end power.

[PeteH]

There is always going to be an issue with carb`s. In that getting the right mixture across the range of demand is at best a compromise. Fuel consumption, assuming all else is well with the engine, relies largely on the atomising of the fuel, which unlike direct injection is under the control of induced swirl the finer the particles the better the flame propagation as the atomised fuel/gas ratio leading to a better burn and releases more energy. How many carburators is in my view largely academic?. Many look at the issue from a standpoint of "throw in more fuel, get more power". Which works, but the level of unburnt fuel in the exhaust gases is the measure of efficiency.

Pete

[JumpingFrog]

You have two main routes.
1) Fit a Stromberg CD150 on a Herald 13/60 manifold - easiest to find probably, but needle selection is more limited as the carb is generally less popular.
2) Fit a single SU HS4 or HS6 on a Toledo 1300 manifold - I've done this, the Toledo linkage is weird, I was missing some parts so used those from a Mini which fits well.

IIRC the article Kipping did (maybe you can find it in the TSSC archive) said that a Toledo 1300 manifold, modified (ported) to take a HS6 instead of a HS4 delivered almost the same performance as twin carbs. However, I still believe the Herald 13/60 manifold is much better than the restrictive Toledo one but fitting an SU on one would be difficult. FWIW, the Toledo manifold was also used on the late emissions controlled Spitfire 1500 in the US.

[johny]

Interesting, recently Ive been looking at the Canley info on the last US Spitfires (electric fan for radiator cooling etc) and it looks like at the end they used a single heavily emissions restricted Stromberg CD150 on this manifold:

[rlubikey]

John Thomason (Spit 1500 Sec) looked at this in the 90's. He decided that the single carb "log" manifold (see Johny's post above) was well designed by Triumph for efficiency during the 70's oil crises. He found you got slightly less power, slightly more torque, and slightly better economy compared to the Spit dual carb set up. He may well have referenced John Kipping's previous work, I don't remember. You can find his report in the Courier archive. Have they corrected the missing entry in the index for this article yet?

One thing he noted is that the manifold ports are smaller than the head inlets. He surmised this improved the mixture velocity and turbulence, hence the improved torque and economy. I also remember Vizard mentioning stepped diameters as an anti-reversal technique, though this may have been applied to exhausts, I don't recall. There was a subsequent article by another member who spent time grinding out the log manifold port diameter to match the head, and being very proud of his work. I don't remember him presenting before and after data, so we don't know how much he gained - or more likely lost!

Cheers, Richard

PS: Found it. John Thomason's article is "Economy Spitfire?" and is in Courier 216, June 1998, pages 8-14.

PPS: See also my post in "Single Carb Or More?"