45 DCOE Weber on BN1

[DerekJ]

Hi guys

Im enjoying my search for a new Healey. Its centred on finding a suitable 100/6 or 3000 with hard top and other rally related mods.

I've been distracted however by an interesting 1954 BN1 which has been subject to a body off restoration and now sports virtually an entire alloy body. Im not sure about the doors. It has 100S seats, louvred bonnet etc. but most intriguing is its carburation.

It has been fitted with a Denis Welch alloy head and high compression pistons but for some reason it is rumming a single 45 DCOE Weber on a modified manifold.

I wonder if some of the engine experts out there can give me an idea of what that is likely to mean in terms, of performance, drivability and fuel consumption, etc.

thanks

 

[Randy Forbes]

I would think that a single 45DCOE is under-carburating that engine. Throttle response should be very good, but will probably run out of breath as the revs go up; that long stroke will suck in quite a gulp of air.

I believe the maximum choke size for the 45 is 40mm (minimum is 28mm!).

There's a couple of readily available formulas for sizing Webers to an engine, but I'm too lazy to look it all up and post it...

For comparison, I'm running 36mm chokes in a one (1) bore per cylinder setup with three (3) 45 DCOEs on my 3-litre.

The racing Mini Coopers used to run a single 45 DCOE (sometimes a "disected" pair of 48s) and that engine is around 1 litre.

My 100/6 with a 3000 engine:

 

[glemon]

I don't know enough about the Weber to comment on whether the size/capacity is appropriate, but I do know that single carb applications (vs. a dual carb setup) on Sprites, such as a 1.75" SU, has been used successfully in highly modified engines.

I would also add that if you are seriously looking a a restored 100 that the carb set up should not play very big into your purchase decision, given the price of entry, and the relative ease at which the carbs can be swapped out I would focus on the bodywork, orginality and state of the interior, instruments, and trim, and condition of the major mechanicals, if they are all good and you want the car you can swap out back to dual SUs, or 1.75" SUs as used in the M for a very small fraction of the purchase price if it doesn't perform up to snuff with the single Weber, I believe SUs generally do a little better on gas mileage if that is a concern.

Lastly, hope I don't sound like a snob, but with the chance to get a 100 vs. a 6 cylinder car I would jump on the 100. They are older, rarer, and the original and purest form of the Healey design for the Austin engine big Healeys.

An instant conversation starter at any brit car meet, and a hoot to drive with a better balanced chassis than the big sixes.

Don't get me wrong, I love them all, but to me the 100 is a very special beast indeed.

 

[Genos2]

A 45 DCOE Weber works great on 11 0r 1200 cc spriget,I've even got a cannon manifold off one.It worked super on my 59 bugeye that I had. I had 2 40's on my BMW 2002(1998 cc).I agree w/Randy that a single would be so under carbed, it wouldn't be able to get out of its own way. A '100 is almost 2.7 liters. 2 45's maybe. cheers Genos2

 

[DerekJ]

Thanks Randy. It sounded like it would be a bit undercarbed to me too. Love your carbs. How are they for 'normal' driving? I'm assuming your car is also driven on the road as well as raced. Ive heard that most of the power with that set up comes in near the top end - Is that correct?

Greg, good point about the carb v car. Its a bit of a non -issue really as you say. The car seems good, Im still getting more info on it and there is a photographic record of a the recent rebuild. It has all alloy panels, which makes it an interesting proposition. The cars in finished in 100S colours. Might be nice to fit it with the 100M carb and cold air box set up etc.

Certainly dont consider you a snob and I agree that they are the purest Healeys out there. I'm a fan of the older models myself. I never really considered a 100 when I got my 100-Six, not really sure why? I do really like the whole late 50s early sixties Rally era though, so its going to be a tough decision as this 100 has whetted my appetite for the model.

 

[DerekJ]

Randy

I'm going to show my ignorance of carbs and engines here but just had a thought.
If the Weber runs with twin 40mm chokes and 40mm is just under 2 inches wouldn't that make it a bit like running 2 SU's - Somewhere between the 1 3/4 and 2 inch models.

Does that makes sense? Probably not as I'm sure there are numerous other factors to take account of. Would appreciate your thoughts though just out of interest and for my further education.

 

[GregW]

Hi Derek,
If that Weber is running 40mm chokes, that comes out to about 1 9/16". Bore size isn't the whole story though. For instance, my Mikunis are 42mm but they don't have butterfly valves to cause turbulence in the airflow.

 

[DerekJ]

Thanks Randy. My math was off there, For some reason I did my calc based on 50mm. Anyway it seems the restorer got the car without carbs and just fitted the Weber because he had one. Probably figured it roughly equalled two 1 1/2 SUs. I'm being told the car goes very well with the set up but I haven't had chance to test it.

 

[DerekJ]

Oops sorry - I meant Greg not Randy.

 

[busybrit]

This type of set-up on a 100-4 is likely to call for two 2" S.U's. Find out what type of DW head is on the car, DW should be able to tell you what carb set-up it will run best with.
Johnb

 

[Randy Forbes]

Does the 100 head have siamesed intake and exhaust ports, like an MGB/Spridget?

If so, that only leaves two (2) ports to shove the mixture in (and three__3__to get it out), so I guess a single DCOE would be the correct application.

If it were me (here we go...), I'd be watching Ebay to try to find a 48 DCOE. A 50 DCO (sand-cast) would cost as much as your car! As an alternative, verify what size main chokes the car's running, and make a determination whether or not you' benefit from going larger. The "calibrated parts are still available, if not cheap.

To get the most out of your application, you want it set up properly; Moss Motors has the recently released & combined works of John Passini, and I highly recommend it for a thorough understanding.

Look at the brightside, at least you don't have to synchronize a trio of them: