20 replies to this topic

[Zac]

G'day All.

Ive spent a bit of time rebuilding a set of MG sprite/midget twin HS2's, found a correct mini manifold, got the floats at the right angles, and all the linkages sorted. They've got H6 needles in them, and were previously running alright on an A+ 1275. I even went to the trouble of blasting all the linkages/screws/springs and getting them all re-electroplated (was getting some other stuff done at the same time), so they're like brand-new.

I'm putting my 1976 1100 clubman back together, and was wondering if I'd notice much of a performance difference between the factory (and in very good condition HS4) and these HS2's. The motor wont have any other mods, bar a set of LCB extractors and _maybe_ a slightly warmer cam. The reason I'm hesitant to go for the twin HS2's is that I could get a fair sum of money for them here in NZ, and it might be worth it to just sell them... One of the reasons I would consider using them is that I now have the right manifold for them, whereas I'll need to make or purchase another one to use the HS4 witth the LCB's.

What do all the folks out there in mini land think? Would I notice much difference using the HS2's over the HS4?

Cheers for your input

[Brams96]

Quick answer = Yes.

You will need to get it rolling road tuned though. The H6 (for a 1.75") needles might be too much for an 1100 but a proper RR will sort the fueling. Have you got the original head? You'll see a bigger increase in power if you change the head at the same time as the cam.

[minibarnerz]

Glad you asked this, im having exactly the same dilema at the moment, although i got a 1330 and wondering wether to use twin 1.1/4 or a HIF40 carb....

[Big_Adam]

I'm thowing mine in here,

Hs2's are lovely, as long as they are in good condition.

If you buy a el cheap second hand set of ebay or similar its going to give you issues unless you rebuild them. My pair worked fine but went out as the spindles where very worn and leaked badly so I could never get them juuuuuust right.

Now they are in a box in the garage.

So as long as they are good rebuilt either by you or a shop, they should be good.

[Zac]

I'm thowing mine in here,

Hs2's are lovely, as long as they are in good condition.

If you buy a el cheap second hand set of ebay or similar its going to give you issues unless you rebuild them. My pair worked fine but went out as the spindles where very worn and leaked badly so I could never get them juuuuuust right.

Now they are in a box in the garage.

So as long as they are good rebuilt either by you or a shop, they should be good.

Hmmmm, they might be the way to go then, I did put new spindles in them, and the housings were in pretty good nick, they feel really good now.

re: the H6 needles, what do you mean by 1.75"? that wouldnt be referring to the size of an old H6 carb would it? Because I'm refering to the marks on the actual needles themselves. I think they're listed as being for a cooper, and rich... Have it in a book somewhere...

No, don't have the head from the sprite/midget. I'm not really wanting to change to much about the 1100, as its such a sweet runner, and has done very low k's.

Cheers.

[Brams96]

re: the H6 needles, what do you mean by 1.75"? that wouldnt be referring to the size of an old H6 carb would it? Because I'm refering to the marks on the actual needles themselves. I think they're listed as being for a cooper, and rich... Have it in a book somewhere...

Yeah, sorry, I mis-read what you meant by H6. An H6 carb has 1.75" ports which would flow more air meaning if you put the standard needle from that in your H2's (1.25") the fueling would be all wrong. There is a little info on your needle HERE.

Refering to the head I meant are you still running the 1100 head or have you changed it to a larger size like the 1275 12G940, but after re-reading your previous posts I see I mis-read again, woops.

[MiniLandy]

Yeah, when they're well set up, they'll be nice. That's what i'm putting on my 1275, once i pull it for a rebuild.

Make sure you've got nicely breathing filters though, i went for a pair of genuine K&N cones.

[bmcecosse]

Sell them ! The single HS4 on a good alloy manifold is better - even BMC discovered that when the 1275GT was produced. And it didn't have the good alloy inlet manifold. Think about it - each cylinder breathes independently - so they can breathe more easily through the larger bore 1.5" carb (especially if you Vizardise it) than they can through the samller carb. There is no worthwhile flow from one carb to the other port through the 'balance pipe' - in fact it's a hinderance - the junction with the inlet stubs destroys the smooth flow from each carb in that area. Twin SUs work better if fitted to Weber like inlet manifolds - long anbd with NO balance pipe. Twin 1.5" SUs are pretty good though - and twin HS6 are even better............

[MiniMonty]

As above - but...
A series engine = shared ports = can only breathe through one carb at a time.
A series engine can NEVER breathe through both at once (so defeats the object of twins) and time lapse in swapping from one to the other as vacuum
will come and go to a degree. A small effect - but real and one which will always (necessarily) increase caused by the effect itself. (oooh a nice reverse catch 22...)
Hence you ALWAYS hear about people constantly re-balancing their twin carbs. Not rocket science and no surprise. You CANNOT balance twin carbs
on an engine where the ports are shared.

Therefore - One good carb (working constantly and efficiently) is better than two amazing, astonishing or even "built by the engineers on star trek" carbs.
An E-type is different... Even a TR5 or an old MkII Spitfire is different. But a Mini can never twin carbs.

BUT - they do sound grrrrrreaaaaat with a couple of pancake filters on !

Reap the rewards of your hard work on the twins, sell them to the owner of a 6, 8 or 12 cylinder engine
and spend the money on something else.

Best wishes
Monty

[Zac]

Cheers to everyone for their input. I've stuk them up on the local auction site, and will see how they go . Looks like a decent allot HS4 manifold will be part of my next minispares order .

[cooperrodeo]

MiniMonty. Why should an old Mk2 Spitfire be different? Two cylinders share one carb in the A series and the Spitfire engines. The only difference is that in the A series the division takes place in the head, whereas in the Spitfire it is in the manifold.

[MiniMonty]

MiniMonty. Why should an old Mk2 Spitfire be different? Two cylinders share one carb in the A series and the Spitfire engines. The only difference is that in the A series the division takes place in the head, whereas in the Spitfire it is in the manifold.

My mistake - was thinking that the MK2 spit was 6 cylinder but you are of course correct.

[MiniLandy]

My understanding is that twins won't give any extra top end power, but give a bit more low down grunt, and a slightly better throttle response. This is due to the better inlet tract shape, which is straight down through the carb and into the port, rather than round two sharp curves like a single carb split for the two ports.

Hell, having a pair of slightly smaller carbs instead of one HS4 might even cost you a bit of top end power. But when do you EVER use the top end power in a mini? I'd much rather have a nice beefy torque curve, so i'll be putting my twin HS2s on my mini soon.

[finch661]

i swapped my Hif44 for a set of twin hs2. best thing i ever did. i agree that can be a pain to set up, but the throttle response is great and the noise you get off them with some pancake filters...no regrets about doing it. my only advice would be to fully rebuild them

[Cooperman]

Personally I've always liked the twin SU set-up ever since the Mk 1 Cooper 997 and 998. Remember, the 998 Cooper with twin HS2's gave the same power as the 1275 GT with 1275 cc's and a single HS4. BLMC were just trying to save money with the 1275 GT. That's why they went to one carb and for no other reason.
The advantage of the twin SU's, or the twin spilt-Weber set-up as developed by BMC Comps, is that the inlet charge goes straight into the inlet tract without any more corners. The demon thing was to partly blank off the balance pipe in the inlet manifold to smooth out the inlet flow. In fact I have such a manifold called a 'Torquemaster' and it looks absolutely standard once the name is filed off - it fools the scrutineers!
If set-up properly SU's should not require a lot of fine tuning.
If a large single was better, it would have been homologated for competition, but never was and even when BMC Competitions used the Clubman GT they used an 'S' engine with twin HS4's.
I once had twin HS6's on a 1330 Cooper 'S' full-on rally car and with a 649 cam they were good, especially at over 6000 rpm and when climbing the Alps in competition where the air is really thin. We used to undo the carb piston damper to get more air in when doing those alpine passes.
The MGA, MGB, Sprite/Midget, etc, all had 'A' or 'B' series engines with shared inlet tracts and they all used twins. If a large single is better, why were they not so fitted.