Lotus Elan

Dellorto DHLA 40 vs DHLA 40E

PostPost by: andyelan » Sun Jan 16, 2011 9:19 pm

Hi Everyone

A question

As some people here may realise, I own a '73 Elan 130S/5 and a '74 Europa Special. Now, both these cars have identical the engines with the exception of the carburettors which are Dellorto DHLA40 on the Plus 2 and DHLA40E on the Europa. As far as I'm aware the difference between these carburettors is that the DHLA40 has 4 progression holes while the 40E has 5 so, what I would like to know is, how would this difference affect how the engine performs and also can anyone suggest why Lotus would find it necessary to make this change (I am assuming this was an age related change rather than anything related to the different car models). Thanks very much

Regards
Andy
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PostPost by: paddy » Sun Jan 16, 2011 9:34 pm

I found (in several places) this text online, attributed originally to the "sideways technology" forum, but I didn't find the orignal message.

Type 1 the first DHLA40 (no letter after) if you like the DCOE of the DHLA family, but boasts superior atomisation and tuning ability to the extra research at Dellorto?This carb has an idle jet (which also runs the progression and adds mixture at cruising) that is not connected to the main jet stack, the idle jet operates on its own from the float bowl. Also the idle jet air feed for the emulsion tube is ot fixed at a set size like later models?The main jets run on their own from the float bowl like the idle?s?This gives two seperate circuits that must be tuned for perfect overlap to get good cruise and pickup?.This has the benefit on small engines and racing engines and hard tuned engines of giving the ability to make the idle jet progress long or short, you can bring the mains in early and cut back the progression on the idle jet air feed with differing jet holders with differing sized air holes, more air, bigger hole less progression?.So you can tune this carb a million ways for million application, Fewsters just got a pair of these. They are the ulimate in tuneablity, they are also as a downside extremely hard to tune without a massive jet box or rolling road, cause they need to be bang on the money. This type of carb uses a .1 venturi which has a bigger pilot hole that the .2 and .3 (ill cover later), this means a bigger signal is generated in the venturi tube which gives a bigger signal (pulsing) to the main jet stack - the venturi feeds the main power circuit into the engine, the big jets. So the .1 vent can tuned to get on the mains right away from very low rpm and are super responsive to tuning, you can delay the vent by adjusting the tubes and air correctors on the main jet stack, so it needs more signal to start the stack feeding the vent or less setup the opposite way, so they can be tuned many ways also.
Type 2 DHLA40E - These are the same as the DHLA40 with seperate circuits and use either 1 or 2 venturi, they have extra progression holes for the idle jet, so the progression phase can be increased in length (over more plate angle) to suit production cars, and aid economy, real smooth runners when setup with lengthy progression. The 2 vent is just like a 1 with tiny bit smaller bore size to the signal tube, so they have fitted .2 often in the E model as they have extended the progression phase and using the .2 vent means they don?t have to delay the mains as much as fitting the .1 vent, so making jetting easier and more responsive. The Elan +2 used these with the 1 vent as its punchy sports car, the Alfa?s used 2 vent and fitted the E model to flagship models with lazyier owners, who like crisp but relaxed power delivery. Power is equal on both types and they can both delivery the same results.
...


Also, according to this post:

viewtopic.php?t=1887

the DHLA40E was also fitted to some later Sprints and Plus 2s.

Hope this helps.

Paddy
1963 Elan S1
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PostPost by: elancoupe » Sun Jan 16, 2011 11:18 pm

Also, the E version has idle bypass screws, which enable precision balancing of the carb throats. On a normal (non suffix) version, you can only balance from carb to carb. On the E version, the bypass screws let you achieve optimum balance within the individual carb.

It's a nice feature, and is one of the reasons I obtained a set of E's for mine.
Mike
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PostPost by: andyelan » Tue Jan 18, 2011 8:17 am

Hi Guys

Thanks very much for that

Andy
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