webber carb conversion stromberg head

[CBUEB1771]

so theres nothing to be gained on fitting a webber carb ?

It all depends on what you are trying to accomplish. For competition I agree that Webers are the way to go, mainly because you have so many adjustments to work with in response to varying track and atmospheric conditions. For normal road use the Weber is a much less compelling choice. I put a Weber head on my +2 after the original Stromberg head was damaged by ingestion of a flat washer. I can attest that Strombergs (as would any constant depression type) clearly have smoother part-throttle response. I would just as soon use Strombergs on the road.

[rgh0]

Thanks for the info, Mike.

I'm sure John has his reasons, but it is interesting he stays with the 1.562' intakes with a long stroke motor. 6500 rpm is definitely at the upper range for that valve size.

If he had gone to the 1.625" valve size, with his cam, peak power might have gone up 4-500 rpm to give you maybe 165 hp.

But I bet you are quite happy with the performance you have now!

David
1968 36/7988

David
The stage 3 head stays with smaller valves and ports to keep port velocities up during part throttle driving. To big ports and valves and long cam durations dont help mid range torque which is critical for a road cars drivability. The stage 3 conversion head still breaths very well with its short duration high lift cam and is not really constricting top end power at a 6500 rpm limit even in a long stroke motor.

If you go to his stage 4 race head you get bigger ports and valves which are good for full throttle performance in the upper rev ranges you certainly get more power but this really requires a steel bottom end to take advantage of it and you loose some mid range flexibility as a trade off.

All these statements are relative and even his race head with high lift short duration cams works well on the road compared to traditional race spec twin cam engines with their relatively poor porting, long duration low lift cams and big holes in the torque curve around 4000 rpm

Looking at the Weber conversion manifold it looks a relatively good implementation. The longer inlet runners may help midrange torque a little and provided the flow passages inside have been done OK it should get around the same top end power as a well tuned set of 175 Strombergs or SU,s. It will feel stronger as well given the more instantaneous response of a fixed choke carb. However you will not get a major output power change with just the Weber carb as the head is the breathing limit not the carbs in setting power output. Without probperly matched set of other changes such as compression ratio, cams, porting, exhaust header etc you will not substantially change the output of standard stromberg engine just by bolting on this manifold and 45 DCOE. The current best technology for maximsing output siamesed port engines is to use whats called a scatter cam that adjusts the valve timing to advance one cylinder and retard the adjacent cyclinder timing to minimise the cylinder charge robbing effect of the siamesed port.

If i was serious about competing in a twin cam powered car i would get a Weber head or use a McCoy conversion if allowed by the race regulations. While it is an interesting technical challenge to see how much power you can get from a Stromberg head you will always be limited by its siamesed ports compared to what you can get from the equivlaent level of development in a non siamesed port engine.

cheers
Rohan

[del@ace]

well read your reply , quite frankly , you would never use the strombergs again , if you tried my conversion , very smooth, not one person who has responded to this topic , got it , , i am watching for some one to come up with the right answer, before this topic stops in 5 days time, i will or may release the right answer why this manifold works ,

[steveww]

so theres nothing to be gained on fitting a webber carb ? i can tell you its like calk and cheese, first of all strombergs are crap, , diaphrams that get pin holes , etc , and whats the point of putting a pic of four motor bike carbs on a webber head , on this topic , your not allowed to run the motor bike carbs in the classic sports and saloon car championship, , and further more i know my adapter manifold works , the end

There is no need to be quite so aggressive.

First of all if this thread is for racers only then it should be in the Racing section. Therefore bike carbs a very relevant.

Strombergs are not crap as t you so eloquently put it. Like any other carb if they are well maintained and correctly set up they work very well. I am sure in all your vast experience you must have come across a poorly set up Weber with flat spots and poor progession? Therefore by your sound reasoning all Webers must be crap as well?

I have never doubted that your manifold works however I fail to see how simply bolting on a Weber is going to significantly change the power output of a Stromberg head twinc.

I really must get around to putting my modified Stromberg equipped Elan on the rolling road.

[1964 S1]

Hello Del,
How many cc's is your 1000bhp Nissan and what IS it with your threats to end the thread and discussion? You started it, if you don't like the discussion you can always just get the heck outta here.
What right answer are you talking about? Is this a 5th grade pop quiz? Why so nasty?
Unless I'm mistaken, LotusElan.net is comprised of a bunch of friends.

Eric

ps; what is "calk?"

[worzel]

Hi

At the risk of "ruffling feathers" is this a car forum I've logged on to or are we talking about something REALLY REALLY important?

Keep it in perspective folks- if the conversion details are really as he stated I say bloody good luck to him. If they're not does it really matter?

John

[M.J.S]

Thanks for the info, Mike.

While it is an interesting technical challenge to see how much power you can get from a Stromberg head you will always be limited by its siamesed ports compared to what you can get from the equivlaent level of development in a non siamesed port engine.

cheers
Rohan

Without being drawn into a slanging match, as this discussion seems to be verging on at times, I have to agree with the power limitation issue of trying to get the air through a siamesed port.

Before being swallowed into the addictive monster that is Lotus, for more years than I remember I have been an enthusiast of the classic Mini Cooper. My 1967 1275 'S' race car sits nose to tail in the garage with my Elan +2.

After over 50 years of 'A' series tuning, the major problem has always been trying to squeeze power out of an engine with just 2 inlet ports.

After millions of hours of tuning what is evident is that fitting a large weber gives virtually no benefit on a road engine over single or twin SU's, and on a full race gives only marginal benefits over a large single HIF SU. If a 'swan neck' manifold is used then there is no difference at all through restricted flow, and only a long 6 or 7 inch manifold produces the goods at high revs (and on my own 1380 race engine There is no power difference noticable between my 45 Weber and single 44mm SU HIF below 6000 RPM. Only above those revs does the Weber come into its own.

What this means in relation to the Lotus? I cannot possibly see a Weber 45 on a swan neck manifold giving much if any improvement over a pair of well set up strombergs, and if it does it will be at revs seldom used. It may SOUND faster, but I doubt it is.

What about working on a much simpler conversion to run twin SU 44HIF's instead of the similar strombergs. They are bloody cracking carbs (originally from the MG Metro and Maestro engines), cheap, tunable, readily available and highly revered and tuned by Mini, Midget and Sprite racers across the world.

Just a suggestion.

Mark.

[CBUEB1771]

After over 50 years of 'A' series tuning, the major problem has always been trying to squeeze power out of an engine with just 2 inlet ports.

Pehaps memory is playing tricks with me but I recall something about Chapman and Mike Costin coming up with an inlet manifold with two "blades" that protruded into a cylinder head with siamesed inlet ports. I con't recall the engine. The blades effectively separated the inlet ports. This was one of the clever rule-benders like Costin's profiled cam followers that effectively increased valve lift with a standard camshaft. De-siamesing the ports of a Stromberg head would have no value unless two twin-choke carburettors are used.

[RotoFlexible]

After over 50 years of 'A' series tuning, the major problem has always been trying to squeeze power out of an engine with just 2 inlet ports.

Pehaps memory is playing tricks with me but I recall something about Chapman and Mike Costin coming up with an inlet manifold with two "blades" that protruded into a cylinder head with siamesed inlet ports. I con't recall the engine. The blades effectively separated the inlet ports. This was one of the clever rule-benders like Costin's profiled cam followers that effectively increased valve lift with a standard camshaft. De-siamesing the ports of a Stromberg head would have no value unless two twin-choke carburettors are used.

Just came across this in a magazine article elsewhere on LotusElan.net:

"For 1951 Colin decided to concentrate on a car to race in the popular 750 Formula.

"By this time he was working for a firm of construction engineers, and thus was able to devote most of his free evenings to his cars. The basis of the Mark Ill was once again a 1930 Austin Seven, with a divided Ford axle providing independent front suspension. This time, however, Chapman did not confine his work to chassis and suspension, for he thought up a means of de-siamesing the inlet ports of the side-valve Austin engine which eventually led to the 750 Formula being changed-just to give the others a chance."

[denicholls2]

To the degree the data collected is honest. I'm no dyno specialist, but discussion among the crowd at a dyno day awhile back suggested that treating dyno output as a certification of actual output is pure hooey. Participants who had run their cars at less conservative locales (This one was NE Dyno in or near Worcester, MA) reported getting numbers as different as 550 vs. 350 RWHP (I calculate 57 percent higher) for a spiffed-up Maserati Biturbo.

(I can represent that the owner's face suggested he thought his had actually shrunk.)

A dyno sheet is either a conversation piece or a tool. It's proper use is to compare it to prior and subsequent runs in an effort to make the numbers go as high as possible. Comparing a sheet from one dyno to one from another is not very informative, unless done with the same car under similar test conditions, in which case it will likely make my point well.

Many dyno owners know full well that there are people who want to treat their numbers as certified horsepower. It's in the best interest of these owners that their customers don't leave with a disappointing certificate. Caveat Emptor.

[cabc26b]

David Vizards tuning the A-series ( or modifing the mini I can't recall the exact title) delves into carb set ups for the five port head - for what its worth a expanation of the problems and solutions along with data for comparison sake not absolute numbers....

[M.J.S]

Vizard's book on the A series is a bible not only for that particular engine, but for tuning in general. It contains a great deal of common sense and dispels many myths lingering from the early days of tuning. For ?15 or so it should be on everyone's shelf. The flow and performance comparisons of carbs in relation to engine performance at given revs is something of an eye opener.

[rgh0]

[quote="CBUEB1771Pehaps memory is playing tricks with me but I recall something about Chapman and Mike Costin coming up with an inlet manifold with two "blades" that protruded into a cylinder head with siamesed inlet ports. I con't recall the engine. The blades effectively separated the inlet ports. This was one of the clever rule-benders like Costin's profiled cam followers that effectively increased valve lift with a standard camshaft. De-siamesing the ports of a Stromberg head would have no value unless two twin-choke carburettors are used.[/quote]

Desiamesing the ports on a 4 cylinder engine has value provided you have independent runners into each desiamesed port so you eliminate the cylinder robbbing affect. These can be connected to carbs in a variety of ways

eg
A large single carb and plenum,
A 2 choke carb or 2 single choke carbs with cross over manifold - one choke feeds cylinder 2 and 3 and one choke feeds cylinder 1 and 4
A pair of 2 choke carbs or 4 single choke carbs feending the 4 independent desiamesed runners

By the way the famous 750 formula engine that Lotus used and caused the rules to change to ban desiamesing was developed by a guy called Derek Jolly who built it in Australia, had a lot of success and then took his "secret" engine to the UK to race there. He ended up with Lotus as did many itinerant racers did and Chapman used the idea. Derek ended up having a long friendship with Chapman and was the Lotus importer in Australia for many years. Mike Bennet who has the first Lotsu formula car (a Lotus 12), plus a S3 7 and Elan in Adelaide has some fantanstic photos and film that Derek took while working and racing with Lotus in England in the early days

cheers
Rohan

[steveww]

David Vizards tuning the A-series ( or modifing the mini I can't recall the exact title) delves into carb set ups for the five port head - for what its worth a expanation of the problems and solutions along with data for comparison sake not absolute numbers....

There are details in this book of a special A series manifold developed for twin carbs. The cross over was specifically tuned for flow, very interesting.

I have looked at fitting a pair of SU HIF 44 to the twinc. The problem is that they are deeper below the centre line and the float bowls need to be positioned inside the footwell Having compared the Stromberg 175 and the HIF 44 side by side with a vernier I can not see that there would be much difference between them. I would be interested in putting them on a flow bench however the guy I used to use for this has now retried.

[Vince]

I know that this is an old thread but just thought that this link may hold some relevance, wanted to do something similar myself but I think in the name of economics I am just going to bite the bullet and go with my Strombergs. http://lotus-europa.com/manuals/misc/ca ... %20DGV.htm This guy goes through the whole process from conception, to prototype to final result with no claims are that too far out there to be unbelievable.

Vince
US
'70 elan +2