Lotus Elan and Lotus Elan Plus 2 Forums

Good afternoon all,

Every now and again, I think of a really obscure anorak style question...here goes!

The Weber 45 DCOE was presented with a number of references after this denomination. One previous post cited 45DCOE9 or 45DCOE13. The same references for a Renault Alpine 1600 are 62/63 and I think 38 for a MGB. I understand that these references might have facilitated identification on the jetting or venturi type (but I am guessing, do not take this as the gospel).

Does anyone with a genuine S1.5 / S2 26R car able to enlighten me on this subject by any chance?

The references (according to my 1974 WSM for the standard car) were 40 DCOE 18 and 40 DCOE 31) and the "S1 Racing Elan" documentation refers to a 40 DCOE 2 but this does not help for the S2 that used the 45 DCOE...

Many thanks

Andrew

I'm going to reply to my own post (!) with some extra information but I have yet to find the correct answer with acknowledgement of the source (no affiliation): (https://www.pegasusautoracing.com/)

"Optional suffixes take the form of numbers or numbers and letters. This usually indicates a "variant", generally a carburetor that was set up for a specific application. The factory jetting may be different, or a linkage might be swapped from one side to the other. (The Alfa Romeo Sprint Veloce came with a pair of "40 DCOE 2" model carburetors, but the Spider Veloce had two "40 DCOE 32" model carbs. The difference in this case is in the factory jetting.)"

Frogelan ,
Difference between the designator numbers on DCOE 40’s is far more nuance than just the selectable jets chokes etc,
Problem being the fixed machining to the body, with particular interest in the transition between jet systems ie progression, I have spent, although many years ago now, probably 100’s of hours in road testing T/C carburation, in consequence made measurements on 40’s bodies I had refurbished.
Not only is the progression hole position varied but the size as well the 1st hole usually slightly larger, couple of examples. Calculated throttle plate angle at the 1st progression hole.
DCOE 40 2 76.7 deg. 2nd hole 73.3 deg 3rd hole 68.9 deg
DCOE 40 18 77.6 deg 2nd hole 74.1 deg 3rd hole 69.4 deg
DCOE 40 31 79.5 deg 2nd hole 76.5 deg 3rd hole 72.5 deg
FWIW.

Back in the day it wasn’t the car manufacturers that set up the webers. Typically they’d send a sample engine to Weber in Italy where they’d be trial fitted and tuned on a dyno. Once Weber optimized the calibration the production carburettors for that particular engine with their unique settings would be stamped with a designated typo number indicating the calibration. Everything from Fiat 500’s to Ferrari V12’s were sent to that factory. Here in Australia Chrysler in the 1970’s sent their 4.3L Hemi 6 cylinder to Weber in Italy for calibration of 3 Weber 45’s which were standard fitment on E37’s, E38’s, E48’s and E49 high performance variants

Gentlemen,

Both your replies are fascinating. Thank you! I was aware of the setting up by the factory for the TC (the Anglia driven to Bologna by Steve Sanville if I recall rightly) but unaware that the number typing might be more complicated that a particular combination of otherwise easily changed brass parts!

The throttle plate angle point however is not one that I was expecting especially as various tuning firms add additional progression holes (rightly or wrongly) but in the excellent John Passini bible on the subject, there is mention of the extraordinary accuracy and repeatability of the Weber factory (so this point is very relevant).

What we know is that a pair of 45 DCOE Webers were fitted to the Series 2 26R, what is less clear is what the additional reference should be.

Obviously, the combination of the "brass parts" can also be worked on partly with a dyno and partly on the road so that adjustment can be made firstly for fuel quality and secondly for the climate (when I raced an MGB I had a dry and wet setting for 95 unleaded without using a booster).

I’ll check tomorrow and confirm the 45’s fitted to my S2. Worth noting that the weber models may vary according to engine supplier as customers could choose between BRM and Cosworth. Mine was supplied with Cosworth unit.
I’ll update this post with details.
Cheers
Vaughan

Thank you very much indeed Vaughan.

This would be very precious information as the small original production run means that even the Carburettor specialists are unable to help.

I have many engine bay photos...but cannot read the details of what are in any case GTS cars.

I think most of us have scoured the FIA's 127 document. The information on the auxiliary venturis is useful, but it is the model number of the 45 DCOE in 26R format that we are looking for (and it may be different for BRM and Cosworth sourced engines).

I did apologise in advance for this obscure and not very important request!

My 26R webers are 45DCOE13
Cheers
Vaughan

Thanks Vaughan!
I am very grateful!

I have spec documented 13’s are regularly on sites like eBay in period for after market tuners the 45 DCOE of choice were 9’s and 13’’s for smaller capacities or siamese inlet rac engines like MGB’s etc.
I’ve had 9’s on F2 twin cam engines and Hart BVBH spec non injection spec using tapered extensions and DCOE 48’s.
Cheers
Vaughan

Thanks for the extra note Vaughan.

For the time-being, I have "Spanish 45DCOE Webers" which are absolutely fine (only dyno tested so far). This is a "could be done" change that I may do in due course (have to finish the project first) and the question popped into my head after looking for a different car.

I am a surprised that Weber did not have a single 45DCOE simply with variable "brass / changeable" pieces and that despite looking, the "Tipo number" changes are not obviously identifiable (other than coincidentally for a certain manufacturer, market or engine type).

I will see if I can find additional explanations from Weber specialists (as I also have an additional nerdy question).

My understanding is that the Typo number reflected a factory set up including the normally interchangeable jetting parts but also the normally non changeble parts such as the progression hole location drilling and butterfly closed angle.

cheers
Rohan

Thanks Rohan for the concise résumé. I will see if I can find out any other details from the Weber specialists.

I have seen cases of carbs receiving additional progression holes (both back street tuning and Weber themselves) but I am not sure of the fluid dynamics reasons for the butterfly closed angle to be different but I'm sure there probably are some!