17 replies to this topic

[Bryan Du Rand]

My number one requirement when searching for my mini was a 1275 engine,I found one a bought it. Only to my shock and horror found out it was an 1100.

It's a south african big bore engine, apparently only south africa had this, where the bore size on the 1100 and 1275 is the same (as far as I understand) here is a link describing it
http://samini.co.za/...read.php?tid=73

Am I correct in thinking the that the only difference in these 2 engines is the pistons and crankshaft and that if I swap out these 2 parts I'll have a 1275?

This is probably a dumb question but Is this an engine out job?

Is there a cheaper and easier way to get similar performance gains?

[Spider]

Yes, that's the 2 major parts that needs swapping out for the 1100 to 1275 conversion.

 

Other items that will likely need changing are the needle in the carb and the distributor.

 

It will definitely be an engine out job and you'll need to strip the engine down. I have to add that you'd also likely need to recondition the engine while you were at it.

 

As to costs, it's so highly variable as you might be able to pick up a crank and pistons for a song or find other ways to get the performance you are seeking from your 1100, which are no slouch by the way.

[timmy850]

The SA1100 crankshafts are desirable pretty much everywhere but SA. They are a strong crank & good to make a revvy 1071 Cooper S type engine. With some higher spec parts like cam/pistons and flywheel they can be a really nice engine. 

 

When the 1100 engines were stock they had a very heavy flywheel and big heavy pistons so good for a normal engine, but less good for a fun engine

 

I have one of the SA1100 crankshafts hidden away for a future project!

[absx2]

Always something new and interesting to learn on this forum and the idea of a 1071 type screamer really does it for me, it`s a shame I chucked out a damaged 1275 block this year as it could have been decked.

[miniGTS]

I have a SA 1100 big bore that's had flywheel lightened, all balanced, head ported and gas flowed, etc.

I've not yet taken the car out on the roads other than around the block but since finally getting the timing sorted and carbs balanced, it seems to rev up quite happily.

I just need to get the final bodywork trim done and roadworthy sorted so I can start enjoying the car.

I have a build post up titled 'my gts build'

It's a SA GTS but currently has the 1100 engine in. I plan to have the GTS engine fully rebuilt next year.

[miniGTS]

Yes, that's the 2 major parts that needs swapping out for the 1100 to 1275 conversion.

Other items that will likely need changing are the needle in the carb and the distributor.

It will definitely be an engine out job and you'll need to strip the engine down. I have to add that you'd also likely need to recondition the engine while you were at it.

As to costs, it's so highly variable as you might be able to pick up a crank and pistons for a song or find other ways to get the performance you are seeking from your 1100, which are no slouch by the way.

Why change the distributor?

[timmy850]

You’ll need a different advance curve for the different engine configuration. The longer stroke piston moves faster through the stroke (for the same rpm) so it’ll potentially need a different amount of advance

Edited by timmy850, 25 November 2024 - 08:17 PM.

[Bryan Du Rand]

I thought Noone had responded to this and then found all this helpful info here. Thanks guys.

Just dropped my mini off at a specialist this morning. We are coverting it to 1275cc. Really looking forward to more power and torque.the price was reasonable although we'll see if we run into any snags along the way... he did not mention the distributor

[Lplus]

I thought Noone had responded to this and then found all this helpful info here. Thanks guys.

Just dropped my mini off at a specialist this morning. We are coverting it to 1275cc. Really looking forward to more power and torque.the price was reasonable although we'll see if we run into any snags along the way... he did not mention the distributor

The cooper S engine used the same distributor in all its sizes, so clearly changing capacity isn't likely to render the existing distributor useless.

[Cooperman]

The things which tend to mean a different distributor curve is recommended are a significantly increased compression ratio and a different camshaft profile.

[timmy850]

 

I thought Noone had responded to this and then found all this helpful info here. Thanks guys.

Just dropped my mini off at a specialist this morning. We are coverting it to 1275cc. Really looking forward to more power and torque.the price was reasonable although we'll see if we run into any snags along the way... he did not mention the distributor

The cooper S engine used the same distributor in all its sizes, so clearly changing capacity isn't likely to render the existing distributor useless.

 

 

They may have used the same distributor, but it was timed in very differently depending on the application. This was also a "race homologated" distributor, so not necessarily the best for road driving or today's fuels. 

 

 

[Lplus]

 

 

I thought Noone had responded to this and then found all this helpful info here. Thanks guys.

Just dropped my mini off at a specialist this morning. We are coverting it to 1275cc. Really looking forward to more power and torque.the price was reasonable although we'll see if we run into any snags along the way... he did not mention the distributor

The cooper S engine used the same distributor in all its sizes, so clearly changing capacity isn't likely to render the existing distributor useless.

 

 

They may have used the same distributor, but it was timed in very differently depending on the application. This was also a "race homologated" distributor, so not necessarily the best for road driving or today's fuels. 

 

 

You are quite correct the static timings are different, however the discussion is about changing from 1098 to 1275 and the change between 1071 and 1275 cooper s was just 1 degree. My point was that just changing the capacity from 1089 to 1275 using the same block and other parts is unlikely to require a major change in distributor. 

[Spider]

If you were to plot out the various Cooper S distributor curves;-

 

You'll quickly see they are not really ideal, especially for the street.

 

The 1098 can almost be looked at as a long stroke 998, same bore, almost the same valve sizes, almost the same cam profiles.

If you were to plot out the 998 and 1098 distributor curves;-

 

 

They are very different.

[nicklouse]

If you were to plot out the various Cooper S distributor curves;-
 

You'll quickly see they are not really ideal, especially for the street.
 
The 1098 can almost be looked at as a long stroke 998, same bore, almost the same valve sizes, almost the same cam profiles.

If you were to plot out the 998 and 1098 distributor curves;-
 

 
They are very different.

Don’t forget this is a short stroke 1275 not a long stroke 998.

Did not get the dizzy with mine to see what it’s setting were. But I think they did have the vac advance while the S ones did not.

[Lplus]

 

If you were to plot out the various Cooper S distributor curves;-
 

You'll quickly see they are not really ideal, especially for the street.
 
The 1098 can almost be looked at as a long stroke 998, same bore, almost the same valve sizes, almost the same cam profiles.

If you were to plot out the 998 and 1098 distributor curves;-
 

 
They are very different.

Don’t forget this is a short stroke 1275 not a long stroke 998.

Did not get the dizzy with mine to see what it’s setting were. But I think they did have the vac advance while the S ones did not.

 

Presumably S distributors and settings were designed for spirited driving whether on street or track, when the improvements in fuel economy at light throttle settings provided by increased advance at lower revs were not considered important.