46 replies to this topic

[Jase]

I have a brand new 1275 Spi engine sitting in my garage for my GT build. I don't want to for any serious internal work but I'm open to modifying it.

 

I want to fit 1^_1/4" twin carbs, there is no injection with the engine as it was one of the last brand new ones to leave Longbridge. I'm going to have to replace the distributor but pretty much open to anything else such as new flywheel etc etc.

 

In terms of use I just want something that will be reliable, will be able to keep up with modern traffic and if possible have a bit of a boost when needed.

 

Budget - up to £1k

 

Thanks

 

[Jase]

Link to images of engine:

 

http://www.theminifo...d-thread/page-7

[carbon]

Would suggest spending most of the money on a decent cylinder head job, but speak first to someone like Turbo Phil or AC Dodd for guidance on what to get done.

 

And the rest on a set of the Keith Calver's 1.4 rockers.

[Turbo Phil]

A decent stage one kit is your first port of call. I'd fit a single HIF44 & save the money you'll spend on twin carbs towards a decent head and rockers as suggested above, or a cam change.

Phil.

Edited by Turbo Phil, 05 March 2018 - 07:24 PM.

[ukcooper]

id do a 266 or 276 cam while its out then what Phil said when its in and if Phil has a booking free in the next 5 years id get one of his heads

[cradley-heathen]

ill also back a single hif44carb. easier to set up, less messing around, and it isn't going to be restrictive on the type of engine you are looking at running here.

 

try to get the inlet manifold matched to the head if you can. 276 cam if you like to drive in a more sporting fashion from time to time.

 

get a good electronic distributer, when you buy it tell them the engine spec and they should be able to give you one with a suitable advance curve.

 

when you have all that done get it rolling roaded.

[Cooperman]

My recommendations are:

 

Single HIF44 (or even an HS6) on a decent alloy manifold.

A fully gas-flowed head with 35.6 mm inlet valves and 29.5 mm exhausts and a comp ratio of 10:1.

Kent 266 cam timed in accurately with offset woodruff keys to suit.

Slightly lighter flywheel with a pre-Verto clutch.

LCB exhaust mainfold and a Maniflow twin-box exhaust system.

Aldon 'Yellow' distributor.

 

Final drive ratio is best at 3.2:1 or 3.44:1 with a cross-pin diff.

 

That would drive well and be a 'not quite so slow' road Mini.

[Jase]

A decent stage one kit is your first port of call. I'd fit a single HIF44 & save the money you'll spend on twin carbs towards a decent head and rockers as suggested above, or a cam change.

Phil.

 

Thanks to everyone for the recommendations, fortunately or unfortunately I already have the carbs, used to working with these having run a Spitfire for the past 30 years so sort of stuck on the idea.

 

Any recommendations for suppliers? (Phil, I'm guessing you are flat out although I am not in a rush).

 

Thanks

[Retroman]

Its unfortunate that you are stuck on the idea of the asthmatic twin 1 1/4s 

 

The standard 44 HIF is a much better option, yes they don't look as good,

 

but with a mild cam, a nice head and exhaust, the standard 1 1/4s are a weak link.

 

Have you considered a Vizarded HS4 1 1/2 ? As its a GT you would keep more of a standard look with better performance than the old HS2's.

[Jase]

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.

[nicklouse]

then put the twins on and then there is no point doing anything else to the engine.

 

like just about everyone on here would not do that.

 

been there done that and would not do it again.

[Cooperman]

The original Cooper 'S' 1275 had twin HS2's as standard. With the larger valve head, the 510 cam (a lovely road cam IMHO) and a better exhaust system it gave c.75 bhp which made it very fine to drive.

However, a single HIF44 or HS6 is better for more than around 80 bhp and at over about 85 bhp twin HS4's are also good, although not really better than an HIF44.

The key to better power is the cylinder head.

[Retroman]

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.

The only way you will see any real benefits of a modified 1275 engine and twin HS2s is to Vizard them and the manifold properly and fully.

 

Jase if you don't make carb changes you are pretty much wasting your brass on engine mods...

Standard twin HS2 are 60 year old fueling tech.

 

Once at about 60 hp, standard twin HS2's are a restriction, for several reasons.

 

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...?

[Spider]

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.

 

Sell the twins and that will give you enough money for a HIF44, a Manifold, an Airfilter and go half way to covering the rest of the wothwhile mods.

 

Twins look great, there's no denying that, however they can be harder to live with than a wife and at 2 x 1-1/4", they aren't going to do much.

[Jase]

Thanks for the advice, I'll have a good think about this. I may well go with a lightened flywheel, rockers, the manifold nd try the twins but I'll also pick up a HIF44 to refurb and fall back on. I'll run the car for a while (if I ever finish it) and make adjustments to the head etc as I get used to it.

 

Appreciate the quick responses.