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MG MGB Technical - SD1 Carbs On a B??

Hi all, just had a thought but it's probably been done a million times before. does anyone know if it's possible to fit the 1.3/4 SU carbs from an SD1 onto a B series engine? would they be much better than the standard 1.1/2's? i've got a pair and they're pretty cheap from ebay too so it wouldnt be an expensive addition, or would it?

cheers
J P Connor

Common mod in the 60s - you need a suitable manifold.

Full benefit from Stage 2 head, K&Ns etc.
RMW

Not much benefit on a stock engine. Some overbore, a modified cam, ported head, etc are needed to take advantage of the gain. Focus on getting that body ready.
R. L Carleen

sorry, i know i should only be asking questions about bodywork.

J P Connor

RL has the right answer. Without significant changes to the head and porting, they may actually reduce the power of the engine. The SD1 engine is twice the capacity, so needs all the extra air the bigger carbs can provide. On the 1800, the standard engine doesn't suck hard enough to keep the air flowing at a decent speed through those big venturis.

Why should you only be asking questions about bodywork???

Mike
Mike Howlett

mike,

if you read my other thread titled "need help getting back on track..." you'll understand.

RL, you'll be glad to hear that the only thing i did to the engine was put it away and label up all the parts. i'm going to look at a pair of rear wings tonight hopefully and then get going on the real stuff.

nice.
J P Connor

I fitted a pair of 1.75in SU's to my 67 GT. I had a stage 3 head, fast road cam, 43D lucas dizzy, full exhaust etc. I really didn't notice any noticeable difference at any point in the rev range, even at the top end. Afterwards I spoke to someone at MG Motorsport(UK) who build race engines for the MGOC race series (so know what they're talking about!) and he still uses the standard 1.5in HS4 carbs on 1950 fast road engines.

I eventually changed to a Weber 45 DCOE (after listening to many contrasting views). It did made some difference, although it did take quite a lot of playing around with different jets etc. I would say that it gave a little more power at the top end, but possibly a little less torque at low revs. It's quite hard to say due to the car running a little lumpy for a while until I got the jets right!

Basically, for the cost of a brand new Weber kit, and for the most benefit a rolling road tune to get it running at it's best, it is a LOT of money for not a particularly big gain. The main difference with the Weber is the induction roar - I was running mine with open ram pipes, sounded great! Did make you want to red-line it everywhere though!

Performance wise I would only consider the Weber after getting the head gas flowed with bigger valves etc, a hotter cam, modified dizzy, exhaust etc. My engine was an 1860, you may achieve greater gains with a 1950 or larger.

A lightened flywheel is cheaper and would give you more of a power / performance gain as the engine is not having to rotate as much wieght, therefore giving more power at the wheels.

Just a little advice from my days of spending LOTS of money on a B-series, and sometimes not really getting much more power for my money (carbs)!

Hope I haven't confused you even more, just trying to help!

Paul
Paul Grundy

nah, still with you. i thought that webers would make quite a difference but i guess from your experience my thoughts were wrong. thanks for the info!

joe
J P Connor

As Webers are known as excellent carburettors, and generally give quite decent performance gains, there is an assumption that this is true in every case. 'Most' 4 pot engines have an 8 port head. 4 inlets and 4 outlets. In such cases, when a pair of SU's are fitted, there is no direct air inlow into each of the 4 inlet ports, as the SU's are only single choke. By changing to a pair of Webers overcomes this and makes a considerable difference.

BUT....The MGB has only a 5 port head with just 2 inlet ports. The SU's provide a direct air inlake into each port so are pretty efficient. The weber setup is a single twin choke carb, so does not offer a huge benefit frm the point of view of air flow. There are several types of manifold available for use with the weber, some have quite a short 'swan neck' type to give maximum clearance with the inner wing for a decent sized air filter, you can also get a longer straight manfold, but this can restrict the fitting of an air filter. I was using this type and the Weber was quite close to the inner wing, even before adding a filter / ram pipes.

I think you're best bet is to have your HS4's rebuilt if they are worn (MGOC etc do them on exchange for around 120) and add the deep K&N air filter kit. Then go for exhaust, head, cam etc.

If you wanted to go for a complete package, the Oselli 1995cc fast road engine is quite reasonably priced, and from what they say on their web site makes quite a difference in performance. I was thinking about this a while back, but then also saw a 1950 cfrossflow engine with 185bhp at one of the MG shows, but that was silly money - about 5k+!!

Having spent quite enough money on the B-series engine, and wanting to be a little different, rather going down the traditional V8 route, I decided to go for a standard 160bhp 1.8VVC k-series, with the potential to tune it in the future. I've finally made it fit but it took me quite lot of long head scratching hours, and welding! I hope to have it up and running by the summer.

Paul
Paul Grundy

Just out of interest and to bring another head type into the thread, Webcon UK Ltd do a crossflow alloy head with four inlet ports for twin weber set ups and a selection of intake manifold kits to suit Weber DCOE / DGV and SU carburettors. www.webcon.co.uk if anybody is interested. I have absolutely no experience with these heads, but they look good.
Brynmor LLoyd-Griffiths

This thread was discussed between 01/11/2004 and 04/11/2004

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