12 replies to this topic

[TrialsLife]

Right sometime soon I may get my engine bored out. Its a 1275 Mini Cooper SPI
I know a guy who can do this. What I need to know are the pros and cons to this. Obviously pros = power. So what cons are there, are there problems with the headgasket, cylinder head? Any other problems that may occour?

Will an insurer even notice an engine re-bore I'm going to declare almost everything, but if I can get away with it I will.

I want to keep it at the standard stroke which is 81.28mm but I'm not sure on how far to take the bore. 73.50mm would take it to 1379cc would this be too much? Or should I keep it to something more modest like 71.67mm 1312cc.

I know I'm going to have to replace the pistons to fit the new bore. Will anything else need to be replaced. Any mods need to be done to the cylinder head or gasket. I'm really not too sure if I should go ahead with this. This mini is running as standard atm, but will be reciving a stage 1 kit, induction kit and new suspension.

Can someone shed some light so I can just ask my mate to take it away and do it?

Cheers

Kyle

[Sprocket]

Dont over do it on the tuning as the SPI runs out of squirt around 90bhp

If your keeping the standard head, but fitting an uprated cam I'd say you'd be fine with 1380cc. If your considering a modified head and a fairly wild cam then you get to the limit fairly easily and if you are not carefull melt the engine. There is an option to increase the size of the injector, but this is still at the experimental stage. Best bet is a Rover 100 K8 or K16 1.4litre SPI injector, the whole thing apart from the manifold is a direct swap. But the results are unknown.

Cooper S packs consist of a modified head, 1.5:1 ratio rockers, lcb, modified inlet and takes it to 82bhp, to give you an idea

I'm doing this but to 1399cc with an MG Metro cam. I have already sourced a bigger injector and running this as we speak on a test baisis on the standard engine. Keeping the standard head is restrictive but with the extra cubes it should produce a lot more torque lower down the revs, the head strangling it higher up the revs. I t more of a test, research and development, to see what the results are, I'm not after every last bit of power, just cheep. Im just waiting on the piston rings being delivered.

Edited by Mini Sprocket, 30 January 2006 - 10:50 PM.

[TrialsLife]

Cheers for the advice mate.

I 'm not sure that I want to change the SPi, do you think 1330 would be alright with the standard SPi.
Planning on getting better fuel pump, regulator, SU throttle body and shiny radiator to keep things cool.

Questions still stand, anyone ever had problems other than the SPi not keeping up with over boring?

Will the insurer notice an over bore? All other mods are going to be declared.

So I've worked out the standard head should be fine for a 1330, but what about the head gasket? Should I invest in a quailty one while I'm there?

Shall I go for cheaper pistons around £250 for a set of 4, or should I go more expensive. Is it worth getting a good set? Or will £250 's worth be fine?

[TimS]

Insurance wise. up to +.60 is standard engineers overbore and does not affect your insurance as it is not done for power gains in their eyes as the engine is still a 1.3. Though you still need to inform them of this.
Headgasket wise, I use the Payen BK450 gaskets on my 1330 and have no problems at all.

Piston wise if going for 1330 or std overbore sie that the Hepolite 21253 pistons are great little pistons and are readily available!

[Bungle]

babybeks has just had a over bore and cam change on her spi

beks or tarks might be able to help :wink:

[icklemini]

unless you *need* a 1380, just go for the next size up as this will give the most life to the block (+20 then +40 then +60, then +120 (1380) - If you take it out to 1380 then there's no more rebores!!

just a thought: does it actually *need* a rebore??

TTFN,
Dave

[TrialsLife]

Cheers for the help guys, I think I'm going to go for it in the summer though. Bide my time first.

To be honest it dosn't actually need a rebore, but the thing is it seems to be an easy power gain. I can get the re-bore done on the cheap, so thats a bonus.

[AlexM]

While we are on the subject i hear the SW5 camshaft is especially good on an injection mini! Swiftune

[TrialsLife]

Hmmm temptation. Think I'll put that on the list.

Have a look around here, just seen this place in Mini World CLICKY HERE MUN

[icklemini]

getting it done cheap is one thing - but the work is a complete engine strip...

if you have bigger bores but you dont increase the volumetric efficiency of the head then you wont release the benefit of the bigger bores

Would suggest (as the bottom end is sound) get a decent cylinder head first as this will be cheaper than new (decent) pistons and the work involved in stripping it all down to actually do the rebore..

TTFN,
Dave

[eddyg]

but if you have the time and money and do both i.e new head and a rebore i am sure you will see quite good gains out of the engine.....yes??

[icklemini]

absolutley

my point above was based on whats been said by : basically - 'i can get the rebore done cheap' as its "easy power gain", etc

[Bigbudders]

To be fair mate its not going to be a easy cheap power gain when you consider the fact the engine has to come out, and you need to invest in new pistons. I don't think you'll get a very noticable pwergain just from a rebore. Ok so the camshaft would help, but i think the first improvement to make apart from a stage one kit would be a well modded head....just my opinion though