46 replies to this topic

[Retroman]

I suggest a cam change before putting the engine in...

It can be changed in car but is not recommended on a 1275 as you can't change the followers in car.

A 264 or 266 cam

http://www.retromini...roducts_id=1251

[Northernpower]

If in the future you're going to make changes to the head I agree now is the time to change the cam. It's a relatively easy job to do when the engine is out and almost impossible when its in. You'll certainly extract a lot of performance out of a modified head for a modest outlay. Just ask on here what type of cam you need. It should be fun

[Dusky]

Carbs on standard manifold CFM comparison;
Single HS2       84
Twin   HS2s    111
HS4  1 1/2       92
HIF 44           133
With Vizard mods to carbs and manifolds, good air filters and stub stacks expect a 25%+ cfm increase, effectively moving the power potential up to the next size of carb.
 
As a rough guide 1.98 to 2.2 cfm is needed per hp.
 
Notice the 84cfm from one HS2 and only 111 from two...the twin manifold is chronic.
 
The twin HS2's are 1950's tech and fine on a standard 998, or a historic Cooper or S.
They were designed at a time when both engine and carb performance was not fully understood.
The manifold was made to fit in the tight space of the back of a Mini engine, before the 1275 cc engine was even designed.
If the twin HS2 carbs were any real good, why did the MG Metro and late 1275 Coopers use an HIF44...?

There must be some nuance to those numbers. Would only make a hif44 good for 67bhp or 83 with a 25% increase ( using 1.98cfm/HP).

[Cooperman]

I have seen just over 80 bhp on twin HS2's with a better head and cam.

[Jase]

Never changed a cam, will give it a go, just need some recommmendations I guess? Is that a good or contentious question?

 

Thanks

[Northernpower]

Never changed a cam, will give it a go, just need some recommmendations I guess? Is that a good or contentious question?
 
Thanks

A great question. What about an SW5-07?

[carbon]

I'm sticking with the twins, did have them on a GT before and was plesed with the setup. I didn't have the finance at the time to make too many changes but keen to add some complimentary upgrades.

If you carry out the Vizard mods, fit K&Ns, and set up twin HS2s properly you will not be disappointed for fast road use with a 1275.

 

But getting the right inlet manifold will make an improvement.

[carbon]

I have seen just over 80 bhp on twin HS2's with a better head and cam.

And over 100bhp on twin HS2s from a well built 1380 with 286 cam in a Midget (not mine...)

[Cooperman]

 

I have seen just over 80 bhp on twin HS2's with a better head and cam.

And over 100bhp on twin HS2s from a well built 1380 with 286 cam in a Midget (not mine...)

 

That is fantastic.

I have always fitted either a Hif44, HS6 or twin H4's/HS4's on engines which are intended to give more serious power. It looks like twin HS2's can give a good result if the rest of the engine is well assembled even with a 'hot' cam and large capacity.

[Retroman]

 

I have seen just over 80 bhp on twin HS2's with a better head and cam.

And over 100bhp on twin HS2s from a well built 1380 with 286 cam in a Midget (not mine...)

 

With some better carburation how much more would you see? I suspect about another 6 or 7 horses and similar torque gains from about 3800 revs upwards.

Over about 60bhp standard twin HS2's are restrictive, not to say they won't make more.

I have had over 90bhp from a 999cc S running a Vizarded HS6, 16.45 second 1/4 mile on road rubber, with a near road weight car.(I think if you reverse engineer the figures its near to 95)

There is no way on earth that car would have done the giant killing it did with asthmatic twin hs2's.

It once won the 1300cc class and regularly had 2nd and 3rd.

It was less than 1.5 seconds slower than a Works Cosworth at Harewood Hillclimb,

You can't compete with a works 2 litre twin overhead cam 16valve turbo'ed motor with 1950's tech HS2's

   Relative to the butterfly area the side wall area is large, as are the spindles, any internal sharp edges and casting flows also detract greatly from efficient airflow and the manifold is chronic, which makes the whole twin standard HS2 issue inefficient at higher airflow volumes.

111cfm from 2 carbs is lousy.

Any cfm figures quoted are Vizards.

 

 

[Jase]

So basically :) I will see a reasonable increase if I upgrade the standard 1275 carb to twin 1^_1/4s or a Hif44 which sounds more reliable. I can upgrade to a mild cam, lighten the flywheel, add rollers, electronic ignition, new exhaust system and that should give me something that will be reliable and keep up with modern day traffic in the city?

[Cooperman]

The best answer is obviously the HIF44.

I have actually run an 'S' with twin HS6's on a rally car. It was being used in an alpine event in Europe and the ability to breathe more air did work well, but in normal use it was not really any better than twin H4's (it had to have twins to meet the homologation of the 'S' which was only available with twins).

For what the OP wants the best option would be to sell the twins which would more than cover the cost of an HIF44 and good manifold.

[Minigman]

As has been said previously, the twin 1.25 SUs are quite restrictive above 70bhp but will go on to 80bhp ok and do improve throttle response. Youd be far better off with a HIF44 or twin 1.5SUs. A good flowed head, 266 cam and slightly lightened flywheel will see a vast improvement and feel. The final drive ratio should be looked at too. Anything higher than a 3.2:1 will kill off the nippiness but does improve motorway driving. Minis should be nippy not mile eaters in my opinion. LCB and RC40 will finish it off nicely.

[Jase]

As has been said previously, the twin 1.25 SUs are quite restrictive above 70bhp but will go on to 80bhp ok and do improve throttle response. Youd be far better off with a HIF44 or twin 1.5SUs. A good flowed head, 266 cam and slightly lightened flywheel will see a vast improvement and feel. The final drive ratio should be looked at too. Anything higher than a 3.2:1 will kill off the nippiness but does improve motorway driving. Minis should be nippy not mile eaters in my opinion. LCB and RC40 will finish it off nicely.

 

Okay so are twin HS4s easier to manage or is HIF44 the best way to go?

[Minigman]

Theres no doubt a HIF44 is the way to go. I like twins personally. Theyre not as difficult to manage as people say and I find they dont go out of tune any more than a single carb. If youre looking to improve your engine on a £1k budget, you cant go wrong with the HIF. Get a HIF44, a good stage 1 kit, do the cam and get it set up on a rolling road! Then start saving for a decent stage 3 head.