HS4 or HS6 - That is the question!

[chesney]

Evening all,
I suspect I know the answer but no harm in asking
I have a 950 engined Minor. This is soon to be uprated with 8 inch drums, LCB, exhaust, alloy manifold and a 12G202 head. I also have a choice of two carbs, a HS4 and a HS6. The HS6 is in very good condition, the HS4 needs rebuilding as the linkages are a little stiff, the spindle is worn, but inside it seems OK. Question is - will the HS6 'work' on the 948, as if so I can fit it, but if it's worse than a HS2 on an 1100 manifold there's no point! If not, it'll have to wait until I can get a rebuild kit for the HS4.
TIA..

[daveyl]

The HS6 is really too big. A HS4 or HIF38 should work, although some may disagree. Most 'mini' 998s run with a HS4 which has the small valve head. Is yours a standard spec 950?

[chesney]

It is, standard soon to receive a 12G202 head and 1098 cam. I thought it too big, seems a shame as it is in lovely condition inside and out.
Even more of a reason to get my 266 cammed 12G940 headed fire breathing 1100 rebuilt (especially since the low oil pressure light keeps coming on )..

[JOWETTJAVELIN]

If I were you I'd be careful with that 948 - even in the 'frogeye' Sprite they weren't special. It is a plodder. The 1100 has a relatively long stroke. The 1275 is a fairly durable engine.

Remember your own admission that the HS2 was fitted to the 1100...

[chesney]

It won't be getting any performance work done to it if I can't get the blasted oil lamp to stop coming on!
I disagree as it happens, I feel the 950 can be tuned just as much as an 1100 can, (as long as it has oil pressure )

[mike.perry]

Fit an oil pressure gauge, especially if you are going to tune it.

[JOWETTJAVELIN]

Do you have Vizard's book?

[chesney]

Got one, its ready to go, its an 80mm gauge though so got someone making up a panel for it
may connect it up to see exact pressure, but two switches later, must be less than 5 psi
I have got the 'yellow bible'

[bmcecosse]

The 948 is an excellent engine - do try to fit a crankshaft damper - I broke two 948 cranks before I got hold of a damper, and an oil cooler. You obviously need to rev it to get some power. Ideally the HS4 - but the good thing about SU carbs is that they are variable choke - and so the piston only opens as far as it needs to - and on a 948 the HS6 is unlikely to ever be full open. But no harm! It will work - so just use it.

[daveyl]

I very much like the 950. Mine has been bored to 998 and warmed up.
A tuned 1098 certainly has more torque, perhaps better acceleration. But, the 950 is 'sweet', it loves to rev, gives reasonable acceleration and can break the speed limit on the motorway! And most importantly, gives a very reasonable mpg urban.

I've had a couple of 1300s and tuned 1098 fitted before. So 950 = less power and acceleration! (slightly better mpg). It wouldn't be every ones cup of tea.
But the baby 'A' doesn't feel as stressed when revved and it just consistently puts a smile on my face.

[chesney]

The point in me even considering a HS6 is because I have all the bits (as before) and they need fitting. The HS4 is obviously the ideal carb, but it needs rebuilding, so I could get it all ready, know I have a working system (on the HS6) and simply swap carbs as and when. If it makes it undriveable, fair enough, I'll have to think again..
I won't be adding anything until I've solved the oil pressure conundrum though, I'm gonna have a look at the oil pickup and see if anything is amiss in there.
As for which is best, the only 1100 I have driven had compression well below 100psi in all cylinders and a 4.55 diff in it, so not a great comparison . Will have to decide soon whether I am going to have my spare 948 rebored to 998, or to use the 1100 Maybe I should start a poll

[bmcecosse]

998 is a good engine. Use the 1100 block and a 948 crank! Simples....... Withe Mini pistons and the 1100 rods of course.

[philthehill]

Yes the 948cc engine is an excellent engine to tune. My first tuned engine (a long time ago now) was a 948cc unit bored to 998cc, used 998 cooper flat topped pistons/rods, Cooper 998cc camshaft, a modified 12G295 head, lightened flywheel and competition clutch, twin SU HD4 carbs and not forgetting the all important damper and twin row timing chain. All was statically and dynamically balanced. The water pump and dynamo were fitted with larger BMC competition pulleys to stop the dynomo flying apart at high revs and the water pump cavitating. The car used to fly. Unfortunatly the hill climb class stucture changed from under 1000cc rear wheel drive to 1300cc (now 1400cc) front/rear drive (those dreaded Minis) so went straight to a modified 1275cc (now 1380cc) missing out on the modified 1098cc experience. I sold the 998cc which was eventually fitted to a racing Lenham Sprite.

[chesney]

That's a good suggestion BMC, the 'revyness' with the durability of the 1100 block (I understand the 1100's had a bearing for the camshaft where the 950 doesn't??). Only problem I can see is that the 1100 block I have needs a rebore, so will probably need sleeves to get the pistons right (or 998 oversised ones I suppose )..

[bmcecosse]

Exactly - unless you have a special need to stay under 1 litre, just bore it.

[philthehill]

As Chesney states the 948cc block in standard form only has the white metal bearing at the front. It is most important that if you are putting extra load on the camshaft/valve gear that all camshaft bearings are fitted with white metal bearings (& line bored) or there is good possibility of damage to the block/camshaft.

[bmcecosse]

Which is an impractical thing to do - hence use a 1098 block........

[philthehill]

The above comments refer to the tuning of 948cc blocks. Also it is not impractical to fit white metal camshaft bearings to a 948cc block. Any machine shop worth its salt should be able to carry out the procedure relativly easily. Admittedly it is horses for courses but any good engine tuner would not put a sports cam in a 948cc block without carrying out the above procedure.

[daveyl]

Just a question to put out there. When I re-built my 948, I did compare the mains end caps locating rings with a 1098 and noticed that they were different sizes. This may be of no consequence, as you'd simply use the 1098 caps (or not!?)

However, are the caps the same size/width? I can't remember. I'm aware that someone has done the '948 crank in the 1098 block' conversion but I notice that the mains bearings are listed as different part numbers at the distributors for both engines.

[bmcecosse]

Of course you need to have cam bearings - it's just not worth the considerable cost to do it to a 948 block when 1098 blocks are plentiful!! I believe there is a very slight difference in the main bearing width which can be sorted out with suitable thrust washers. Main bearing caps must always stay with the same block.