this weekend i got hold of 2x 45mm jaguar su carbs, was wondering if a single 1 of these carbs will work on a stock a14. at the moment it's got the standard hitachi carb on it.

It's not so much 'will it work' as much as it is 'can it work' . What I'm saying here is that _absolutely_ it can be done, and great potential results, BUT that is only going to be the case if:

The carb itself is in good shape - piston moves freely, float height set right (new needle and seat whilst you're at it) and no leaks around the throttle shaft (new ones are available, around 5 thou thicker, so you ream out the hole so they are a snug fit.)

The intake manifold arrangement is well enough designed to give good airflow, and gentle enough curves etc, to get good mixture distribution evenly to all cylinders.

The needle and spring combination is selected (often dyno or at least widebamd EGO sensor logging required to get it there) to produce the right air/fuel curve across the whole range from idle ( a touch richer than stoich), to part throttle cruise (practically as lean as you can get it without experiencing mssfires) and then the final section of the needle for higher rpm/full throttle work (where again you'd want to go richer than stoich - 12.5:1 or theeabouts, .

That the thickness of the oil in the daahpot is similarly experimented with (since it slows the rise of the piston, just enough to make the engine 'suck harder' on the jet until the piston has risen to it's full height for that much flow), providing a replacement for the accelerator pump on conventional carbs. Basically too thin and the piston rises too fast, and it leans out. So you need _some_ oil in there, just start with something like 30 weight engine oil, then try thinner, perhaps sewing machine oil, or a 50 50 mixture of both. Essentially run thinner and thinner oil, until it develops a flat spot when you floor it, then go back to the previous slightly thicker one. If any race setup out there actually has no flat-spot with no oil in the dashpots, it's a fairly good sign that the needle profile is deliberately thinner at the part throttle/cruise range, making it way richer and when you nail the throttle, it does lean out still, but since it started rich, it'll handle the leanout which doesn't get as lean as it would with 'ideal' needle. That's the only way they don't have a flat spot. You 'could' do that, but the drawback (not important for racing since they are at full throttle most of the time, except f behind a safety car) is of course it's runnign way too rich at part throttle. Which totally destroys any decent fuel economy.

So as long as you do these things (and it's mostly just a bit of trial and error, and I can elaborate on how to get the right needle and spring combo if you like)

And to answer the original question - 1 3/4" single SU isn't a bad match for the a14 at all. they have been used in certain racing classes years back in the UK where people have gotten over 200hp through a single SU. I'm not saying that they wouldn't have made more power with a bigger carb - no by that stage at 200bhp the carb was a restriction to say the least. But for an A14, you're likely not aiming for astronomical power - perhaps low-mid hundreds?? - It'd be more than adequate for that. Due to typical cam duration (and rememberng there's not a lot of flow until past about 50 thou valve lift) being what it is, although there is some overlap of intake opening periods (i.e. whilst #1 intake is about to close, #3 is opening) it's not massive/full overlap, as such, the end result is in fact that there isn't too much competition for the intake air, and a single central SU would get nearly identical peformance as twin 1 3/4 SUs would.

thanks for the explanation, helps a lot! will keep you updated as things move along

I thought most jag sus where 2 inches? I have a 2 inch su I want to use
for an A10 supercharged setup but its overkill with max size recommended
to be the 1.75 inch for 1 liter engines. I also have a HIF 6 and Stromberg
1.75 but dont have external fuel bowls like the older SUS have.
What do you think Jmac? single strommy or hif for the a10 with 10psi of boost.

Yes, exactly right. Put another way, a single carb flows 98% of what twin carbs do -- if the single carb is feeding all four cylinders via a plenum and the twin carbs are only feeding two cylinder each.

Not to say the driving characteristics will be equal, but peak power will be fine.

45 mm is large for a stock A14 (GX carbs are only 38mm). I would expect low-speed driveability to suffer, but who knows? Give it a try. Some guys have run the large 240Z Hitachis on the smaller engines, so definitely it can be done.