I am trying to get more info on this. Are all 1380cc displacement mini engines bored out 1275's? And what is the process for doing this? What other parts have to be replaced? Any info or links on the subject would be appreciated.

 

In a word... Yes. I'm sure others that have gone through it will chime in but it is not an uncommon rebuild. You will likely need new pistons etc but again I differ to those with more knowledge on the process

 

Big-Bore Power Units from MINI MANIA for the Classic Mini Cooper & Mini Cooper S The "Ultimate Street Performance Engine" from Mini Mania is the result of 30+ years of building and racing our own Mini Coopers. Because drivability and reliability are of utmost importance in any Mini Cooper, only components from well-established suppliers are utilized to build our Mini motors. While the standard configuration is described here, power-units can be customized to meet your particular needs for your Mini Cooper. Just ask your friendly Mini Mania Sales Technician for a custom power-unit quote.




Specifications:

• 73.5mm squeeze-cast pistons
• 10:1 Compression
• 10/10 Crank
• Elgin CAM003 carefully timed in at 108º for best horsepower
• HIF6 SU Carburetor with BDK needle or downdraft 2 barrel carburetor
• Dyno results: 113 horsepower at the flywheel at 6500 R.P.M., 102 ft/lbs of torque at 4700 R.P.M.
• +/- 120hp with optional 1.5 ratio rockers

These power-units are hand built with care, stand tested and tuned (final tuning, of course, is always done in the Mini). Shipped palletized and protected, the power-units are ready to bolt in and run.

 

to answer shortly, yes they are made from 1275's the main part you have to replace is the pistons (73.5mm) go with the omega pistons as these are best.

 

Thanks for the replies. I'm not interested in buying a 1380cc engine, I'm looking to increase the bore on my 1275cc with SPi. I want to add this stage 3 kit:

http://www.minisport.com/mini-spare-...T-KMST100.html

But before I do I was interested in going to 1380cc. This is probably a stupid question (I am just learning about this stuff) but is it possible to use the stock 1275cc pistons with larger rings? Also I see that the above website sells 1275cc pistons in standard or high compression, and in multiple sizes including standard, + 020, +040, and + 060. Would any of these larger sizes equate to fitting a 1380cc Bore?

Thanks again.

 

No you can't use bigger rings, there will be to big of a gap and the pistons will just "slap" around inside ruining your engine. +60 pistons = 1380cc, I would use high compression pistons, unless you were going to do a supercharger, but in order to do a 1380, you will have to get your ecu reprogram to get it to run properly or you can convert to a carb setup.

 

Great help once again miniroll. Okay, so 1275 +60 pistons equals 1380cc (73.5mm) so is it safe to assume that standard 1275cc pistons are 67.9mm and the stroke is something like 59.76mm?

So this begs the question, why do they sell "1275cc +60" but also "1380cc 73.5 pistons" and the later are significantly more expensive?

I am assuming the engine will need to come out of the car in order to do the drilling process. So as long as it is comming out are there other parts that fall in the "might as well replace while it's out"?

One final thing that comes to mind, I have heard it is difficult to find the equipment to do the tuning/ ECU reprogram in the US. I am assuming a 1994 engine would have OBD 1 but does that only allow reading of error codes but not detailed info from the ECU. What would be the name of the product or system that is required to do a tune on an SPi ECU controlled mini?

Thanks once again for all the help.

 

You need to pull your engine and send it to a reputable machine shop for this work, it is much too complicated for a beginner to do. The questions you're asking indicate that you have no experience with this type of work, for a good result you need to let the pro's handle this for you.

You can either have your engine done, or exchange your engine for one already built.

Mini Mania is a great place to do this, I'd call them and talk to them.

Any competant machine shop could do the work, but going to someone like Mini Mania who knows all the tricks and all the pitfalls means you'll be driving your car instead of frustrated and chasing problems. Just my 2c

 

Thanks for the reply. As I stated above and as you can tell, I have no experience in this but I certainly plan to learn as I go along. I no doubt would have a machine shop do the work but I would like to do as much of the tear down and rebuild as possible myself. I don't think I would be interested in shipping my engine to Mini Mania, I'm in SoCal right off route 66 and there are more restored classic cars per square mile here than almost anywhere else I can think of. I don't think finding a good local machine shop will be a problem and I'm not afraid of a little or even a lot of frustration. If the car never ran for 6 months or a year even that's something I could deal with. I've got the garage space and other cars.

Here's what I'm thinking. Start with the Haynes Manual (which I just recently received in the mail) and read as much as possible. Get a good working area for clean careful storage and lable everything and check it all twice. Take a ton of pictures to help remember what it all looked like before I started taking things apart. Hopefully find someone local who can help out when things get tough or I reach what seems to be an impassible barrier. I would be glad to pay someone for their time and I don't think it would necessarily have to be someone with experience directly related to mini's, although that would obviously be preferred.

I'm pretty sure I'll get it done in the end and learn a boatload along the way

 

The 1380cc engine has a bore size of 2.9, stock bore of a 1275cc is 2.78. The 13800cc piston is thus +.120 from a stock bore. The 1380 piston is often called a 73.5mm. Most 1275cc blocks can be over-bored to accept the 73.5mm pistons. Factory 1275cc engines including all the 1.3i version have a stock bore size of 2.78

 

I have been trying to find a company in the uk that can redo your ecu, but no luck yet, but I will post when Ifind something. If you do order the stage 3 kit, I would also get the performance cam they offer for the SPI as well and a adjustable duplex chain to get the most out of your engine.

 

Good luck and let us know how it goes!

I've always planned to drive Fiona (my 1275) until something gives out on the motor - then I planned to by one of Don's 1380's as a replacement. I've got over 85K on my 1275, but whoknows how much longer it'll run... hopefully for years to come.

 

I had a 1275 that lasted 130k, I was just going to rebuild it, but the wear on the block was excessive so i built myself a sweet 1380 (dynoed 120hp at the flywheel)

 

You my friend are an awesome member Thanks for all the info and even researching for me. When you said trying to find a company in UK I am sure you meant US correct? Because I am in Southern California and I would suppose it would be easy to find a tuner in the UK. Are you in GB btw?

Anyway, here's what I'm thing now. Try the stage 3 kit I linked above and see how that goes. That should be a pretty challenging project for a beginning DIY Mechanic like me and probably as much as I should bite off as a first step, and I could enjoy the car a bit sooner. Then when I'm getting antsy for more punch I could look into doing the Big Bore and new new cam, etc.

But even with just the upgraded Cylinder head, rockers, and exhaust I would likely need, or at least benefit from a rolling road (Dyno) session and a tune. What I'm unclear on is what is it exactly that you are so kindly trying to help find to redo the ECU? Obviously it is the ability to interface with, and read and write to the ecu. But in order to do that is it a piece of hardware specific to the mini ECU or is it just havng the correct plug and software? I know custom tuning is always best but it would seem it migth be possible to predict what adjustments to make to timing, fuel, etc based on the knowledge of going from standard 1275 cc SPi to polished/ported head with with 35mm inlet valves and Sport 1.5:1 ratio billet alloy roller tip rockers plus a free flow exhaust setup. For instance a tuner in the UK, possibly the one I buy the kit from, who has done several of these installs must see the range of changes having been made on previous customers cars and could adjust my ecu in the middle of that range as a compromise to an actual rolling road session I would think.

Let me know your thoughts, Thanks again

 

The stock ecu can't handle the increased demand of significant engine changes like the big valve head and the 285 cam, and it's not programmable (as of yet) like say a honda ecu is. Plus, the intake manifold and throttle body will be a big choking point limiting the power. Burlen makes larger throttle bodies for the spi, and megasquirt is the name banded about for ecu stuff. You really need to go the UK sites that are injection specific (for the mini) and you'll get lots of feedback there. There are specific SPI upgrade kits and there's an upgraded cam that's also cut for the spi engines that will still work with the stock ecu parameters, but not that stage 3 kit.

I too am in So Cal (Escondido) and am having a swap meet at my place on this coming Sunday and will be happy to chat with you then and introduce you to some other mini fanatics in our club who may be able to help you. I know one guy had an spi and heavily researched all the mods he would have to make, then opted to convert his spi to carbed, and then ultimately just sold it and bought another car to do all the fancy go-fast stuff to as the spi was a great little car as-is.

RE: 1380 engines period-- You're sucking 3 or 4 rebuilds out of the car in one foul swoop. The displacement change alone isn't significant enough to warrant that huge overbore-- usually you bore an engine to the next size only when needed. Cut it all out at once and your left with only being able to resleeve the block in order to use it again. Also, if you don't offset bore it, you end up with a mighty thin wall between cyls 2 & 3 and an area prone to headgasket burning.

 

Damn, I just spent 10 minutes writing a reply and it got deleted and now I have to run. Thanks Spank, I have more questions for you and thanks for the invite. I saw the thread about your meet/parts exchange but I cant make it down.

 

Thanks for the insightful reply. Okay, trying to bottom line it here, If I simply add a polished/ported head with bigger inlet valves and a free(er) flowing exhaust, but leave the cam, throttle body, bore, everything else stock will the ECU be able to adjust to be able to:

1. Start, idle, and run smoothly
2. Make more (safe) power? I don't care about passing our version of MOT since the car will be exempt.

 

Well, I appreciate your attitude, everyone has to start someplace, but I still say this is more than you should do on your first attempt.

I think were I you I'd simply rebuild the engine back to stock, so you can gain the basic knowledge you need, then if you want to upgrade it later, the Mini is very easy to work on in the car (as long as you're on your knees! ) or to remove and upgrade. This way you'll have a solid engine to run while you learn the next steps.

You have to know how to walk before you can run....

Good luck, and if you do pull it out and rebuild it, post up some pics along the way so we can watch over your shoulder.

I'd recommend a Bentley Manual too....

Oh, and definitely get involved with a group of other Mini fanatics, their experience and knowledge will be a huge advantage, not to mention you stand to make some great friends!

 

If you go from 1275 to 1380 you have to realize that if any problems with the cylinder walls crop up in the future there won't be any more metal left if you need to fix the bores

 

Thanks, yeah, I've abandoned the idea for now. Going with a Stage 3 head and exhaust mod instead.

 

The 1275 engine is offset overbored ...this is so... to keep the centre of the con rods inline with the crank bigends...........