1380 engine question
Discussion
All the 1380 engines I have ever come across have been offset bored. Now I have been called by someone who has a newly built 1380 which is giving problems and which has been parallel bored. The problem he is having (pressurisation of the crankcase causing oil to blow out of all the breathers - maybe a broken ring at build time) is not connected, but I have always thought that parallel boring was only OK up to +0.060" oversize.
Anyone care to comment or advise please?
Anyone care to comment or advise please?
Peter, my book learnt knowledge says...
If you're going to a 73.5mm bore (which gives 1380cc I think), it is better to offset bore this then gives you one more possible boring at 74mm.
If you parallel bore at 73.5mm, an offset bore at 74mm (which you would have to do) wouldn't clean up all the bore wear from the 73.5mm.
Does this ring true with your thoughts?
If you're going to a 73.5mm bore (which gives 1380cc I think), it is better to offset bore this then gives you one more possible boring at 74mm.
If you parallel bore at 73.5mm, an offset bore at 74mm (which you would have to do) wouldn't clean up all the bore wear from the 73.5mm.
Does this ring true with your thoughts?
Peter, you've got me thinking now - would it be possible to build a 1380 that revs safely to, say, 7500/8000rpm for a reasonable amount of money? I'm not talking about building an engine cheaply, just not going down the steel crank/titanium rod/carbon fibre pushrod money no object route. Not that I'm planning on building one of these, just wondering...
I wouldn't like to do that with a cast crank. I think you would need a billet crank or an EN40B Cooper 'S' crank with everything well-balanced.
I'm not sure that a really high-revving 1380 would gain you much as the benefits of going to that large a size are that the mid-range torque improves. To effectively 'breathe' a 1380 at those revs you would need a very special head or you just won't get enough mixture into the combustion area. The inlet tracts and valve sizes are the restriction. The cam would need to be a wide-overlap and high lift - probably at least a Kent 296 or the old 649. I guess you would need a 48 DCOE Weber or twin 1.75" SU's too.
It would be interesting to build it though!
One question, why do you need 8000 rpm from such a large engine? A 998 or a 970 'S' is understandable at 8000, but a 1380??
I'm not sure that a really high-revving 1380 would gain you much as the benefits of going to that large a size are that the mid-range torque improves. To effectively 'breathe' a 1380 at those revs you would need a very special head or you just won't get enough mixture into the combustion area. The inlet tracts and valve sizes are the restriction. The cam would need to be a wide-overlap and high lift - probably at least a Kent 296 or the old 649. I guess you would need a 48 DCOE Weber or twin 1.75" SU's too.
It would be interesting to build it though!
One question, why do you need 8000 rpm from such a large engine? A 998 or a 970 'S' is understandable at 8000, but a 1380??
Just for reference - A race Miglia 1293cc motor runs to 8K using a 5-port head/649 cam and 45DCOE.
Is 8K possible with a cast crank? - I think the BMW K-headed conversions boys are seeing that kind of rpm due to the nature of the Bike cams and many are using cast crank bottom ends with either a 4-bolt main cap or a strap. Production rods will live to 8k if they are properly prepared - Especially the really tough ones (Innocenti rods).
Is 8K possible with a cast crank? - I think the BMW K-headed conversions boys are seeing that kind of rpm due to the nature of the Bike cams and many are using cast crank bottom ends with either a 4-bolt main cap or a strap. Production rods will live to 8k if they are properly prepared - Especially the really tough ones (Innocenti rods).
Edited by FWDRacer on Friday 29th May 11:09
I used to have a really sweet 1380 - fully worked rods n crank etc with a torquey cam ran really well to 6.5-7k . I wouldn't like to run a rubber crank for long at revs above that , so you go on to steel crank and rods and main caps in which case stroke it to 1460cc which is also nice - just a differant beast of an engine, just depends what you want to use it for , I actually prefered the 1380 for the torque but the 1460 did what it said on the tin , its amazing how smooth a full steel unit feels when the revs rise.
FWDracer, you're right on the mark - on an EFi forum, a guy is building a mini marcos (which I like) and putting in a K head conversion. Most of the conversions I've read about have been 1380cc, and also riding a bike I realise that they tend to produce their power further up the rev range.
So this got me thinking, would the head be compatible with the bored bottom end? (Obviously it is, or people wouldn't do it, but at what cost for the bottom end!)
I realise that BMW bikes aren't generally as high revving as Jap bikes, but even so they don't possess the torque of car engines (as they don't have the weight to cart around), so do they still need to be revved hard?
Questions, questions...
So this got me thinking, would the head be compatible with the bored bottom end? (Obviously it is, or people wouldn't do it, but at what cost for the bottom end!)
I realise that BMW bikes aren't generally as high revving as Jap bikes, but even so they don't possess the torque of car engines (as they don't have the weight to cart around), so do they still need to be revved hard?
Questions, questions...
Quick question for Cooperman, Guru, FWDR et al - is going to 1380cc 'just' a case of using the larger pistons, albeit offset bored? What I mean is, you don't need longer stroke crank?
I'm more inclined to go the 1330 route (+60 thou) but this thread has had me thinking! I'd be looking to use an MPi bottom end I think because I want to stick with fuel injection and this has all the necessary sensors for triggering etc. But I would be looking to change the ECU which would give me the option to raise the rev limit/control fuel supply etc, and who knows I might go down the bike throttle body route or even K series head at some stage (getting ambitious now!)
But what can I expect from an MPi crank in terms of revs/durability etc?
I'm just thinking of ideas at the moment, but hey - you never know what the future holds!
I'm more inclined to go the 1330 route (+60 thou) but this thread has had me thinking! I'd be looking to use an MPi bottom end I think because I want to stick with fuel injection and this has all the necessary sensors for triggering etc. But I would be looking to change the ECU which would give me the option to raise the rev limit/control fuel supply etc, and who knows I might go down the bike throttle body route or even K series head at some stage (getting ambitious now!)
But what can I expect from an MPi crank in terms of revs/durability etc?
I'm just thinking of ideas at the moment, but hey - you never know what the future holds!
as far as i know the mpi crank was virtually identical to the cranks used in the mg metro and the spi minis! the engine angle sensors were on the cam and the engine speed sensor is on the flywheel! if you are hell bent on using the rover stuff it CAN be a headache to keep everything going as it shud!
id fit a crank sensor and triger wheel to the pulley end of the crank,(go visit trigger-wheels.com) ditch the mpi cam and flywheel for much upgraded items that can produce and withstand the rpm u require, fit arp or similar bolts to anything and balance everything, fit a 4 bolt main cap and have a standalone ecu do the ignotion (and/or fuel) a single 1 3/4" carb is good for about 140bhp, so is a 45 webber.
bear in mind rover had trouble correctly fuelling the a-series with the twin point system, it may be worth fitting a single large throttle body! as was done to this a-series - http://www.emeraldm3d.com/em_projects_Aseries.html
id fit a crank sensor and triger wheel to the pulley end of the crank,(go visit trigger-wheels.com) ditch the mpi cam and flywheel for much upgraded items that can produce and withstand the rpm u require, fit arp or similar bolts to anything and balance everything, fit a 4 bolt main cap and have a standalone ecu do the ignotion (and/or fuel) a single 1 3/4" carb is good for about 140bhp, so is a 45 webber.
bear in mind rover had trouble correctly fuelling the a-series with the twin point system, it may be worth fitting a single large throttle body! as was done to this a-series - http://www.emeraldm3d.com/em_projects_Aseries.html
fikus, I've heard of the emerald ecu before (and met Dave Walker once, many, many moons ago) and I've looked at the canems ecu, which has maps for the MPi system. I probably will look to change the ecu at some point in the future (I want to get more experience with fuel injection), but want to build a suitable bottom end for my self ported head to go on. I have an MPi at present, and will probably modify an MPi engine, thereby keeping all the Rover sensors. As I've said, I hadn't really contemplated a 1380cc bottom end, this is all just 'what if' type theoretical questions (I must have too much time on my hands!)
I'm sure the MPi crank was a specific item (not too sure why though), and the choice of cam you can fit to the MPi is effectively limited by the Rover MEMs ecu - I believe all the cams for the injection minis are regrinds, because the cam has the sensors integral. Changing the ecu will allow control over fuelling/ignition etc so a wider range of cam timing could be used (providing the cam is fitted with suitable sensors, of course).
I just wondered (that word again) what was possible with the MPi crank? The same as is possible with any other 'standard' mini 1275 crank I guess!
I'm sure the MPi crank was a specific item (not too sure why though), and the choice of cam you can fit to the MPi is effectively limited by the Rover MEMs ecu - I believe all the cams for the injection minis are regrinds, because the cam has the sensors integral. Changing the ecu will allow control over fuelling/ignition etc so a wider range of cam timing could be used (providing the cam is fitted with suitable sensors, of course).
I just wondered (that word again) what was possible with the MPi crank? The same as is possible with any other 'standard' mini 1275 crank I guess!
The crank is common with all other 1275 A+ units. Mpi Flywheel is different.
As for capacity - if you are just refreshing a tired MPi unit - then torque is the only reason to go to 1380cc with offset boring. Personally I'd go +60 and settle on the cheaper pistons if it was purely a sub 6K rpm engine. I think the 50cc difference in terms of torque output between 1330 and 1380 you couldn't even pick up on dyno. Always happy to be proved wrong
As for capacity - if you are just refreshing a tired MPi unit - then torque is the only reason to go to 1380cc with offset boring. Personally I'd go +60 and settle on the cheaper pistons if it was purely a sub 6K rpm engine. I think the 50cc difference in terms of torque output between 1330 and 1380 you couldn't even pick up on dyno. Always happy to be proved wrong
Agree entirely.
In fact, my favourite capacity is 1330, i.e. +0.060". My reasons are;
1. It's cheaper to bore and does not require offset boring
2. The pistons are relatively inexpensive for really good ones (Hepolite 21253 @ c.£145 per set)
3. If necessary the block can either be subsequently re-bored to 1380, or sleeved back to 1275. A 380 block really does not have enough metal between 2 & 3 cylinders to allow for sleeving. Blocks will get harder to find as time passes and this is important for keeping our little cars on the road.
4. A 1380 will give a nominal 4 bhp improvement over a 1330, everything else being equal.
5. A 1275 block will always go out to 1330, but sometimes, very seldom, it is said to be a problem due to casting tolerances being off (although I've never seen it).
In fact, my favourite capacity is 1330, i.e. +0.060". My reasons are;
1. It's cheaper to bore and does not require offset boring
2. The pistons are relatively inexpensive for really good ones (Hepolite 21253 @ c.£145 per set)
3. If necessary the block can either be subsequently re-bored to 1380, or sleeved back to 1275. A 380 block really does not have enough metal between 2 & 3 cylinders to allow for sleeving. Blocks will get harder to find as time passes and this is important for keeping our little cars on the road.
4. A 1380 will give a nominal 4 bhp improvement over a 1330, everything else being equal.
5. A 1275 block will always go out to 1330, but sometimes, very seldom, it is said to be a problem due to casting tolerances being off (although I've never seen it).
rawky said:
I have a 1380cc, that blows oil out of the breathers...
Is this bad?
Pressure test needed. Block porosity isn't unknown. Is this bad?
When it does happen, it blows things out of things.....
My old girlfriends did this and we changed everything, apart from the block. Hole was obvious....
cooper199, i had kinda fallen of the meaning of that last post of yours half way through writing mine, sorry about that! tho i know spi cams are identical (profile aside) to std carb cams its only the mpi that had the angle sensor and i honestly swear the cranks are the same for all a+, if any differences it will be material or coating, nothing too physical that an mpi crank couldnt go in a early a+ or vice versa.
std mpi bottom end shud be fine for 1380, jsut use arp or similar bolts to hold it all together, it shudnt pull its self apart if you are using the mpi cams anyway. at worst id suggest a balancing of the crank and flywheel assemblies and a decent vibration damper balanced in there as well but material wise it shud be fine!
i have a friend (im sure every1 has 1 of these) that pushes the a-series to its limits, reliably runs 140bhp on a std 1275 bottom end jsut boosting the living daylights out of it, and when that blows up (he runs it a little too lean on high boost so cracks pistons quite often) he puts a std 998 in and that copes hapily with 100bhp , similar boost and those are wheels bhp figures from a reliable dyno!
std mpi bottom end shud be fine for 1380, jsut use arp or similar bolts to hold it all together, it shudnt pull its self apart if you are using the mpi cams anyway. at worst id suggest a balancing of the crank and flywheel assemblies and a decent vibration damper balanced in there as well but material wise it shud be fine!
i have a friend (im sure every1 has 1 of these) that pushes the a-series to its limits, reliably runs 140bhp on a std 1275 bottom end jsut boosting the living daylights out of it, and when that blows up (he runs it a little too lean on high boost so cracks pistons quite often) he puts a std 998 in and that copes hapily with 100bhp , similar boost and those are wheels bhp figures from a reliable dyno!
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