Stromberg Cd Carbs - Fuel Pressure

[PeteClan]

In order to run my original Clan in the HSCC 70's Roadsports race series I have to use twin Strmberg 15 CD carbs as opposed to the twin Webers I have used for years. I have a set I got from Jean-Claude a couple of years ago although I have had to modify them extensively to get rid of all the emissions attachments and use fixed needles. I am having trouble in finding out what fuel pressure I should run and I'm hoping that someone can come up with an answer. The engine is 998cc and should output approx 100 - 105 bhp.

 

Pete Richards

[GT6Steve]

I'd say the same as the Webers, 2.5 PSI.

 

Kas did a lot of good work with Stroms back in the day, why don't you give him a shout on his forum?

[GT]

Kas did a lot of good work with Stroms back in the day,

 

There are a zillion reasons why the figures from KK are plain wrong or utter fantasies.

After being suspicious for decades as to the behaviour of CD carbs at high revs, it's absolutely for sure now a SU or Stromberg is incapable of producing torque over 6000rpm.

 

You can add in the other problems which I can't go into,- cam period and lift on the IMP motor (both highly limited because of the simple problems of clearance and valve flow as well as reversion), why you won't even get 90bhp from a pair of strombergs on an IMP (unless you want to invent the horsepower figures....).

 

It's really all down to the WAY the CD carb works and the need to develop high specific torque from that short stroke/short rod Cov Climax engine.

 

This is why IMP engines only work properly on Weber carbs.

It's not something that is even worth debating.

[GT6Steve]

Since Kas is just plain wrong or utterly fantastic how come we can go to the SCCA records of the time and actually document his wins, successes and companies both in Triumph and Nissan circles when we can't find a single attribute for the GREAT GARETH?

 

Give it up GT, if you have nothing to contribute than shut the fuck up please!

 

You talk shit but supply nothing, Get lost!

Edited September 1, 2012 by GT6Steve

[GT6Steve]

OK ya know what, It's my birthday. I've been drinking. I should just shut up but the Great and Hollow Oz has pissed me off again with his ignorant attacks on Kas.

 

So while the great fatuous fuck will sit in his exile offering nothing I'll relate something Kas told me decades ago that may or may not help with Pete's efforts.

 

The Stroms will starve on long left handers???? because fuel surges and covers the bowl vent. I was instructed to bore a similar vent on the other side of the carb to eliminate this issue.

I never explored this cuz I went to Webers so I can't provide more specifics. Hey, just like the GREAT GT! Sorry, I would if I could.

 

Another tip, maybe well known, is that the rebuild kit comes with a pile of alloy Orings of various thicknesses that are precious for quick float bowl tweaks. I had knurled thumbs on my bowl screws to get it open in a hurry to try different things,

[PeteClan]

As I don't want to get into the usual slanging match with the expert on all engines ever produced I'll just say thanks Steve for the info and continue to enjoy your birthday.

 

Pete Richards

[GT]

So while the great fatuous fuck will sit in his exile offering nothing .....

 

The Stroms will starve on long left handers???? because fuel surges and covers the bowl vent.

 

ahum, my post wasn't to poison the thread.

You can thank Sergei in Moscow for his extremely interesting work on carbs, and as to why a Stromberg or SU will NEVER give power at high rpm as well as very high emissions & detonation if you attempt it.

 

I hadn't even gone into the Stromberg fuel surge issue, which is unsolvable on inline engines (rather than transverse engines).

This was an issue as long ago as 1982, and actually was the MAIN reason to move to fuel injection on the Vitesse.

Get back ON TOPIC.

 

I happen to know quite a bit about the Imp engine nowadays, having done a very large amount of work on the head 2yrs ago.

The bore/stroke ratio is such that you CANNOT get 100bhp/L unless you get the engine to produce power in the 7000-8000rpm range,- ie very little torque low down.

Adding to this, that the conrods are extremely short, and the bore size at 998cc is REALLY small.

 

Unless you get a really impressive head done for it, you CANNOT get the head to flow anything over 9mm lift, and they also employ lots of overlap to achieve anything like decent bhp/L.

 

Hillman/C Climax made a mistake making dished valves for this engine, so if you use them, you will lose a lot of flow.

If you want to use a CD type carb, you therefore have to BACK OFF the amount of overlap, and reduce the valve duration.

This will drop the top end power like a stone, and you will STILL get loads of reversion and stand off.

 

THEN:-

There is then NO SUCH THING as a decent exhaust manifold for it, as the Weber one with integral steel inlets (copied from TDC by Janspeed) is the ONLY one that is any good....

You probably know this, and I am very unlikely to want to make one specially for Stromberg carbs.

 

As I tried to point out, (My criticism of KK cannot be debated for the reason below..), the stromberg is INCAPABLE of producing power over 6000rpm, just like the SU.

WHY?

 

Well here it is:-

These "Best of British" carbs are incapable of producing the correct fuel droplet size.

 

This explains why no-one has ever made an engine using these carbs that produces good power above 6000rpm, and why you get dirty emissions and masses of standoff if you try.

 

The only way you could get something approaching a useable imp engine on CDs is by increasing the bore size to 1220cc, MAKING a new exhaust manifold, pusing the CR right up & living with a completely compromised motor.

[GT6Steve]

Sorry Pete, Steve

[PeteClan]

I don't think you should be sorry Steve. Thanks anyway.

 

Pete

[GT6MK3]

Gents,

 

Early warning - any personal attacks in this thread will be deleted. Feel free to debate the technicalities, but play the ball not the man please.

 

C.

[triumphlux]

As I tried to point out, (My criticism of KK cannot be debated for the reason below..), the stromberg is INCAPABLE of producing power over 6000rpm, just like the SU.

 

 

 

Doesn't this depend on the engine ?

 

Quote from Swiftune with their historic Mini's which have 2 SU's :

'Add Swiftune’s 42 years experience of building competition A series engines and you won't be surprised that the 1293cc engine is now producing over 120bhp at 8000rpm.'

 

And I saw those cars a few times in action and they are as fast as Lotus Cortinas and BMW 1800's !

[GT]

Quote from Swiftune with their historic Mini's which have 2 SU's :

'Add Swiftune’s 42 years experience of building competition A series engines and you won't be surprised that the 1293cc engine is now producing over 120bhp at 8000rpm.'

It remains to be proven that they are INDEED making 120bhp at all.

As you know, the A series is an almighty bodge-up of an engine.

 

I've seen all sorts of claims made for A series motors, and when it came to testing it on my old Bosch rolling road, it wasn't making anything like the power claimed.

 

If anything makes a difference to the behaviour of the SU carb as an inlet system it's the INLET manifold.

This is absolutely critical to the behaviour of the carb, and the "damping" factor, which of course is ever more critical on the A series because of the stupid firing order and robbing taking place at the ports.

Have you noticed on the photo above, it has the old TR4 type carburettor with the long body and fixed not biased jets.

These are much better than the Stromberg, despite the stromberg having phosphor bronze needles instead of brass ones.

Strombergs also have a miserable selection of needles available...more like non existent!

 

Are you also aware the 150CD zenith Stromberg does NOT flow enough for 55bhp from 1L per carb as we amply demonstrated on your own car? It literally maxes out completely at 5500rpm.

Your 2L STD engine needed 175CD carbs to make it work properly.

 

The imp engine would struggle to achieve even 80-85bhp on such a system, because of the severe limitations of the original IMP sport Stromberg inlet manifold, and the fact not a single decent exhaust manifold exists to work with that combination, contrary to the better developed mini LCB, where the engine is upright, not canted over 40 degrees to the right as it is on the Imp.

 

I once posted the results of a back>back test on the A series engine showing differences of up to 8bhp merely on the design of the LCB. That is 8bhp/L!

The inlet manifold also showed as much variability, and don't forget on a race car you don't need a SPEEDO!

[Merlinonline]

Hi Pete. Chris Davis here. Long time, no speak. How the devil are you? Good to see that you are still peddling a Clan. I bought a '73 G15 just before Christmas and am doing a nut and bolt restoration. On the subject of Stromberg fuel pressures; on Alison's G15 I used a Bendix silver top pump feeding a Filter King throttled down to about 2/3 without knowing the actual pressure. I found the best way to stop flooding and surge was to use float chamber valves from 175s (I think they were 2.0, but not sure) and to replace them regularly as the needle seats wear very quickly with high revs. Hope to hear from you soon. All the best. Chris