Stromberg v SU

[Robin]

Just wondered if there's any advantage of changing my twin Stombergs for twin SUs on my Vitesse mk 2 - is there any noticeable difference in terms of performance?

[Clive]

No. and No.

[Pete Lewis]

if you put all the component parts of the two makes out on a clean sheet you can see one is engineered the other is a load of bits and peices,

 

both do a good job the stromberg is generally more efficient,there are if ever needed more needles available in SU than Stromberg.

 

    and apart from the air cleaner porting and fixing holes together with the manifold all being different I agree with Clive

 

     my  newly acquired  T2000 has SU  ( yes i hate the things) and getting air filters to suit the std. vertical air box is like rocking horse pooh

      and the  stromberg easy available ones do not fit due to the ports and hole centres are very different  

 

Pete

[Colonel H]

Robin, Clive, Pete,

I was going to ask a similar question to the question posed by Robin, but in my case (I am also a Robin... So this could get confusing!), I have a GT6 Mk3. I got some excellent advice on this forum a month or so ago after requesting advice on where to take my car for an engine overhaul, and after a fair amount of research the two companies that suit me Geographically are Triumph Spares Worcester (Dave Saunders) and Jigsaw Racing, Corby (Mark). Both companies (and individuals) seem to be highly regarded.

On the subject of Carbs, Dave's opinion was (I quote) "it would be a huge mistake to exchange Stroms for SU". Conversely, Mark's strong view is that I need to get rid of the troublesome Stroms, and fit modified twin SU (from a Dolomite).

I was interested how two experts could have such polarised views. Neither would accept central ground that each have their pros & cons,and perhaps it's a 'win on the swings, lose on the roundabout' type decision. Sadly, it was at least a month ago, and I cannot remember in detail what the pros & cons are, and I remain confused! I do recall Mark saying needles for Stromburg 150 are very rare, while at the same time Dave saying a Newley rebuilt pair of Stroms are superior to SU (perhaps Dave can get all the spare parts for effective overhaul?).

If any GT6 owners out there have a preference for one or the other, which a good reason, I am sure we would all love to hear. My interest is having a very good,well tuned road car engine, rather than a track car (which it is not). Which reminds me... On visiting two separate rolling road facilities a couple of moths ago, both places were definitely encouraging the use of SU over Stromburg. No doubt in their minds. Perhaps they are easier to tune up? Or perhaps they need regular re-tuning, which would be appealing to the rolling road place?! (Apologies for cynicism!)

Regards

Robin D

[KevinR]

The range of needles available for SU carbs is much bigger than the range available for Stromberg's.

 

The Stromberg carb is technically better than an SU, but an SU is easier to tune - which may be important if you want to play with your engine performance to get the best from it.

 

There are also many more people who understand how to tune an SU compared to those who know how to tune a Stromberg.

[Mike Crewes]

Robins

 

When we had our Triumph 2000 rally car we looked into this question ourselves and we couldn't find ANYONE who thought there was any advantage with swapping to SU carbs; EVERYONE told us that properly set us Strombergs would give better performance and economy than SUs.  We got all parts from Chris Witor (and a load of advice) and rebuilt the carbs.  That car is the fastest T2000 I have ever driven and got us well placed in several rallies.

 

Hope that helps.

 

Regards

Mike

[Pete Lewis]

my recently acquired  74    Mk2 T2000 has blasted SU on it   

 

    and whilst I have an inherant hate for the thing they perform resonably

 

      what is not clear is while they look the same  but if you retain the std air box the filters are very different in porting,and hole centres and they are pretty much unobtainable  you cant fit a stromberg  air box to su without a lot of modifications   so you are now down the route of an alternative at high cost and much needle twidling

 

           you could fit spitfire ones but far too small area to last long.

 

Pete   ....Strombergs   love em 

[Robin]

Robin, Clive, Pete,

I was going to ask a similar question to the question posed by Robin, but in my case (I am also a Robin... So this could get confusing!), I have a GT6 Mk3. I got some excellent advice on this forum a month or so ago after requesting advice on where to take my car for an engine overhaul, and after a fair amount of research the two companies that suit me Geographically are Triumph Spares Worcester (Dave Saunders) and Jigsaw Racing, Corby (Mark). Both companies (and individuals) seem to be highly regarded.

On the subject of Carbs, Dave's opinion was (I quote) "it would be a huge mistake to exchange Stroms for SU". Conversely, Mark's strong view is that I need to get rid of the troublesome Stroms, and fit modified twin SU (from a Dolomite).

I was interested how two experts could have such polarised views. Neither would accept central ground that each have their pros & cons,and perhaps it's a 'win on the swings, lose on the roundabout' type decision. Sadly, it was at least a month ago, and I cannot remember in detail what the pros & cons are, and I remain confused! I do recall Mark saying needles for Stromburg 150 are very rare, while at the same time Dave saying a Newley rebuilt pair of Stroms are superior to SU (perhaps Dave can get all the spare parts for effective overhaul?).

If any GT6 owners out there have a preference for one or the other, which a good reason, I am sure we would all love to hear. My interest is having a very good,well tuned road car engine, rather than a track car (which it is not). Which reminds me... On visiting two separate rolling road facilities a couple of moths ago, both places were definitely encouraging the use of SU over Stromburg. No doubt in their minds. Perhaps they are easier to tune up? Or perhaps they need regular re-tuning, which would be appealing to the rolling road place?! (Apologies for cynicism!)

Regards

Robin D

Hi Robin - I agree that the debate is confusing. I also spoke to Mark at Jigsaw who recommended swapping to SU carbs as did a rolling road facility I visited recently! Others seem to think it's better to stay with Strombergs. Think I'm going to make the switch so will let you know if I notice any improvements. Robin

[Peaks]

I wonder if the confusion comes from the fact that there are so many variables with carbs. In my experience a newly re-built and well set up set of Strombergs do give better economy and crisper performance than SU carbs in a similar state.

 

But add into the mix people’s experiences with worn carbs, or badly set up carbs making a car run poorly then understandably they will get the impression that ‘Those Strombergs are rubbish’, or conversely  ‘SU carbs don’t run as well as Stroms’

 

They both work on the same principle so theoretically the actual differences like for like will be very, very small.

[Alan C]

Hi everyone.

I've just joined the new Forum. I didn't realise it was up and running before now.

I changed the 150CD Strombergs in my GT6 Mk3 for a pair of HS6 SUs many years back during an engine transplant/upgrade. I would definitely cast a vote in favour of the SU's any day of the week. I had numerous occasions where the Strombergs suffered split diaphragms usually when I was trying to get to my work!

SUs are far more robust and have greater tuning potential due to the much greater range of needles available. This is especially useful, if like me you have them mated to a tuned 2.5l six. The only probems I had was altering the throttle linkage and building heatshields for the GT6 inlet manifold.

I also think the SUs look much better than the Strombergs, although this is just a bonus and not a reason for choosing them.

 

Cheers

 

Alan

[Clive]

I think (being cynical) you need to be careful if the "expert" offering advice has a vested interest....

 

fitting twin HS6 carbs looks good on paper. Bigger carbs = faster. But usually not the case as they can easily be too big and only of benefit at high rpm (not used that often by most) at the expense of lower down the rev range losing torque.

 

HS6 on a 2.5 yes, that is what was fitted at the factory. But on a 2L road car, no. Same as camshafts and many other potential modifications. they are not a good idea in isolation, and as a package you can end up with a car that is not as good to drive as a standard one.....

 

As an aside, many rolling roads no longer keep a selection of needles. However, when I took my car along, the tuner (very well respected mini racer and preps cars for many historic events etc) had 2 goes at reprofiling the needes which took about 10 mins or so to get a flat CO curve, which means an even mixture. Good improvement in driveability and economy too. 

[JohnD]

Do not forget that the "Stromberg" was designed at the behest of Standard Triumph, which did not want to pay royalties to SU.   By replacing the sliding fit damper piston with one with a rubber diaphragm, they got around the patents.  Otherwise, both are 'constant depression' carburettors (as is Ford's Zenith brand) with no particular advantage, except that SUs are available in a wider range of sizes, so that those who wish can fit a bigger one - whether that has any advantage or not.

 

John

[Robin]

Hi All

 

A quick update - I decided to swap to twin 1 3/4 SU's on my vitesse (actually running on a mk 2 2000 engine with overdrive) and I'm pretty sure there's virtually no difference in performance. However, when I had the strombergs, I got about 200 miles from the tank whereas now I'm getting about 100 miles. I think the SU's are set up correctly (though I think the smell of petrol is stronger but no leaks) so I'm not sure why the dramatic increase in fuel consumption. If SU's are generally thirstier then I think I may swap back to the strombergs

 

Any thoughts?

 

Thanks

 

 

Robin

[Clive]

Has it been on a rolling road and the needles swapped to give the correct fuelling across the rev range?

[Robin]

Hi Clive

 

Not had a chance to try the rolling road yet - is this best way to set up the carbs?

 

Robin

[Clive]

Yes, otherwise you are only setting them up at idle. You will undoubtidly need new or repfrolied needles.

However, unless it is a heavily modified engine aiming to produce 130bhp or more, I doubt you will benefit at all. The smaller carbs will also give better driving for normal road use etc etc etc and the larger carbs will use more fuel, as when you put your foot down they let in way more air, so fuel will need to be thrown in to stop the engine stalling.

[Robin]

Hi Clive

 

I think the carbs came off a TR6

 

As I'm not planning to modify my current engine do you think it's better to try and tune the SU's and change the needles to achieve better consumption or just swap back to my strombergs which we're working ok?

 

Thanks

 

 

Robin

[Pete Lewis]

On a std car sti k to the Triumph tried and tested specification,

they spent ££££ and many thousands of miles testing ans analysing results to make it

take you shoppin, tear down the road , and go on holiday , or show off to the girlfriend

 

so the design does what it says on the tin

 

we all like to meddle , but rarely admmit when its not worked,

Can be good expensive fun but we dont have a design and developement department to

measure the effects

 

pete

[Clive]

TR6 never had HS6. Probably from a 2.5 saloon (at some point!) or even TR7. 

As Pete says, best bet will be the strombergs. Overhaul them if needed, and they will give good service for a long time. Just carry a spare diaphragm.

[Robin]

Hi Clive &Pete

 

Ok - thanks for the advice. As Pete says, it's been an expensive experiment!

 

Do you know anyone who could service the strombergs before I re-fit them ?

 

 

Robin

[Robin]

Sorry - one more question

 

If I wanted to improve the mpg of the twin SU's, how would I know what needles to swop to - or would a rolling road set up provide the info? 

 

Also, is it worth investing in something like a colortune kit to set up either SU or stromberg  carbs?

[Clive]

I am sure people may know a rough spec for the needles (I don't but the info is out there somewhere) but a rolling road will either have a selection of needles, or will profile one to get a perfect setup across the whole rev range. This is very difficult to do at home unless you have a wideband lambda sensor and controller to check the CO levels when driving.

[Pete Lewis]

as your local to me why not pop over for a cuppa and a look see 

 

if they are ok its easy 

 

if a rebush is needed  ive used the carb exchange in leighton buzzard 

 

Pete

[Robin]

as your local to me why not pop over for a cuppa and a look see 

 

if they are ok its easy 

 

if a rebush is needed  ive used the carb exchange in leighton buzzard 

 

Pete

Hi Pete

 

Thanks for the kind offer. I'll drop you a line to arrange a suitable time to come over - maybe sometime later this month if the weather is OK?

[Robin]

I am sure people may know a rough spec for the needles (I don't but the info is out there somewhere) but a rolling road will either have a selection of needles, or will profile one to get a perfect setup across the whole rev range. This is very difficult to do at home unless you have a wideband lambda sensor and controller to check the CO levels when driving.

 

Thanks Clive