Many thanks to all guys! The links which you posted are very interesting! I had read that SPI was introduced in '91 for Cooper and in late '93 for non-Cooper version, and that they before had different type of carburettor...so, do you think that ECU/Injection System fo SPI versions were different and that for the non-Cooper SPI version it supplied less fuel? So, Janspeed reworked heads, probably he enlarged inlet valves, he put on an higher-ratio rocker and he increase the compression ratio...I didn't know this...very interesting! Do you think that Janspeed reworked the heads of all Mini sold in Cooper version? It seems strange because Cooper-S and S-Work were limited edition...more likely that they work only on those verion...but I don't know...all can be...who said that cooper ratings were optimistic? Did they do some test? How many hp they said were more realistic?

I think the Sprite 1275 had a HIF38 carb....... that may make up some of the difference in BHP

The non-Cooper SPis were rated at 50bhp, the Coopers at 63bhp, the Cooper S at 77bhp. Many say that Cooper's ratings were a bit on the optimistic side. As I just wrote, they had plenty of work done to the head and exhaust to boost power output as well as higher compression.

The MPi Cooper was the same as the regular model at 63bhp, but the Cooper S claimed 86bhp and the Cooper S works 90bhp. Again, according to some, "optimistic", especially because fuel limitations are the cap to peak power from an MPi and it's very difficult to get around them.

Janspeed reworked the heads for the John Cooper SPI models. This is where the bulk of the power increases come from. The compression was 10.0:1 for the standard Cooper and 10.5:1 for the "S" model. The head had higher-ratio rockers as well. I'm sure it would have had larger valves, but I don't know that for a fact. 

If you look up Janspeed you may be able to get more of the specific details you're looking for. A bit more information here: https://www.minicooper.org/rover-cooper-register/

There should be no power difference in any injected motor ('91+ Cooper or '93+ non Cooper) be it SPI or MPI as all were rated at 63HP, perhaps for the Japanese market restrictions.  The difference was in the 1275 carbed engines reintroduced in 1990, the Cooper got the better MG Metro type version with HIF44, better manifolds, cam, pistons and electronic ign. was rated around the 63HP, but was only one year before injection.  The non Cooper models could have a more basic 1275 (998's being gone before '93) using a single HIF4 on a cast iron intake/exhaust manifold, smaller dia. exhaust, mild cam, lower compression.

A Lot of information is available on this website under "Articles" section. But it is so horribly and inefficiently laid out now it is difficult to find.

Most of the same articles are found here in a much easier to find format. Written by the same person but on his own website now because I think the service agreement between Mania and He has changed over the years.

https://www.calverst.com/technical-info/


Here is a quote from one of the links about 1275 Engine Transplants and engine selection:

By far and away the easiest way to identify what you are likely to be getting. Economy variants of Metros mainly had the lower spec engines (8.8:1 CR), the HLE/plusher types better ones (9.4:1 CR), and MG the best (10.3:1 CR) and most popular. Don’t discount the Turbo engine just because you don’t want to get involved with all the turbo paraphernalia - it’s essentially a high compression engine (9.4:1) with superior grade pistons and a turbo bolted on. Unfortunately the camshaft is just the standard, run of the mill 1275 A+ type. The only point to bear in mind if going for the turbo unit is that many suffered gearbox failures, so it may be prudent to use just the engine fitted to your Minis gearbox. Power outputs are a bit variable, but generally go from 50-odd hp on the lower performance jobs to 74hp for the MG. That’s why it’s the popular choice!! The extra power comes from a special cam, Cooper S-size inlet valves, careful profiling of inlet throats, high CR, and efficient manifolding.

No it not offer other specs... reading around I found that (if I have not misunderstood) A plus 1275cc heads (940 casting) uses as standard the 33mm diameter inlet valves and the 29,3 mm diameter exhaust valve, both of lenght 3.57". Perhaps, the valves between the 2 versions with 50 hp and 63 hp doesn't change...very likely instead of being different camshafts. Do you know were I can find "camshaft, ignition timing, as well as compression ratio, intake and exhaust manifolds, accuracy of fuel atomization" information? Many thanks.

Since the article you mention lists the valve diameters, does it offer any other specs that could use for comparison?

As Alex said, camshaft, ignition timing, as well as compression ratio, intake and exhaust manifolds, accuracy of fuel atomization-- all of that comes into play.

And let's not forget the accuracy of the testing equipment at the time those motors were tested and the accuracy on the press release/journalist touting the news. The latest and greatest always seems to have better hp numbers than their predecessors...

Thanks Alex. Do you think that cylinder head is the same? Between the articles I read that the Inlet Diameter and Exhaust Dia. are respectively 33.33 and 29.2 for all late A+ models...so I think is the same. Any other differences? On the Inlet or Exhaust manifolds? On the ECU's? Thank a lot.

Cam mainly, and possibly slightly larger valves.

Hello guys. What are the differences between the 1275cc with 50 bhp of Mini Sprite Spi and the 1275cc with 63 bhp of Mini Cooper? How many and which components differ between the two engine? Many thanks.