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MG MGB Technical - Help: Big engine, which carbs?

Hi guys,

I'm not quite there with my 2.1L conversion (got the plugs though!). I am now in a quandry as to which carbs to fit....

I've got a fast road cam and ported head on the 2.1. I intend to drive the car hard on the road (caning aroud the curves of the country roads in Dorset), but not racing or on a track.

I've got a choice of twin 45 weber, twin 1.75" SUs and twin 2" SUs. I like the look of the SUs, kind of more "original" looking, but would the 2" be too big for the engine/head combination?

I've read Pete Burgess's book, and he doesn't mention the 2", only the 1.75".

Any thoughts guys?

Cheers,

Grant :-)
G Hudson

Twin 1 3/4 SU. Weber fine but pickier, costs more, and you don't get anything from it with the siamese head. And it's eyetalian. 2" SU bigger than you can begin to use. You can set them up to work fine, but there is no advantage and they are much bulkier - makes it hard to work on. In fact, per Vizard, two 1 1/2 HS or HIF are good for in excess of 150hp, and you likely already own them. Do a bit of cleanup work and use good air straighteners and filters and you're off.
FRM
FR Millmore

Grant,

HS 6 and HIF 6 will be OK if you do not want to race the car. I have fitted HIF 6 carbs from a V8 and changed springs to red ones. The needles aught to be changed. My engine is not that capacity, 1868 only, but i selected BDR needles at lest, as they work very well in this engine.
I started with the SD 1 needles and a simple gas analyser on the road, checed out the needle list from teglerizer.com and ordered to sets of that I thought they would work from Moss.

Just figure out at which reeves and load performance is missing and have a look upon the 'stations' of the needles you are testing and the alternatives.

In my case only one set of needles was wrong and it took one afternoon of testing.

Ralph
Ralph

Grant,

If thst an Oselli engine why not have a word with them they could tell you what will give the best results.

http://www.oselli.com/services_mgb

Kevin.
Kevin Jackson

Hi guys,

Thanks for your input.

I thought the 2" might be too big, but got them cheap so i thought I might see if I could use them. Oh well, back on to Ebay for them then!

It's not an Osselli engine, just one built to th 2.1L spec by a friend of my dad's, although I might give osselli a call all the same, to see what they say.

Cheers again,

Grant :-)
G Hudson

Sorry, I forgot.

Vizard? FR Millmore - do you have any references/ book titles?

Cheers,

Gran :-)
G Hudson

David Vizard, "Tuning BL's A-Series Engine".
An absolute classic, now up to about three or four editions. Specifically on the A-series, but he gives you lots of basic engine/performance data, and is one of the very best at uniting theory, experience, and real world facts of life on cost/benefit values.
**NO questions required reading for anybody modifying any engine for any purpose.**
He also has a bunch of other stuff, that can be hard to find, but some is on the net. Been writing his experiences down very well for about 30 years.
This is by far the best and cheapest mod you can do to your car - Fix the mechanic!
FRM
FR Millmore

I'd certainly go for the SUs over the Weber on a 2.1 as the longer stroke means the engine's going to be at its best and happiest lower down the rev range. The DCOE won't do you any favours there at all, whilst the SUs will be unbeatable. Also, you'll still have vacuum advance for better fuel consumption when stuck behind all those caravans.
Steve Postins

Caravans?! DON'T get me started on caravans! I'm with Jeremy Clarkson when it comes to caravans! ;-)


Guys,

thanks for the input and refernces. Looks like I'll have a busy time reading.

Thanks again,

Grant :-)
G Hudson

FRM,

Webers are now Spanish - not eyetalian!!!
Chris at Octarine Services

Chris -
?Que pasa? The bloody world pasa, quickly and before we notice, downward to sad oblivion. But I have no quarrel with Espana, and they always were good at metal bits!
FRM
FR Millmore

G Hudson-

A 2.1l implies a stroke increase. I've heard about these for years, but no one ever seems to be willing to talk about them. How much stroke increase and how do you get the rodsto clear the cam?
greg fast

Greg,

I'm not sure about the amount of strke increase, but the rods are off-set slightly (non-standard), to modify the stroke. I think all parts can be purchased.

I bought the engine off a friend of my dad's who built it, ran it for a while in his MG, but swapped it for a V8 and then retired and moved abroad to sunnier climes, so i don't know much more than that.

I do remember seeing a description somewhere in a book a while ago. If I come across it, I'll let you know.

Sorry for not being much more help,

Gran :-)
G Hudson

Thanks Gran-

When I first heard about this I tried to contact the MGOC about it and they were very closed lipped about details of it.

While parts may be available in the UK, not generally so here. I'd appreciate any information you can post.
greg fast

This thread was discussed between 17/04/2007 and 21/04/2007

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