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1275 A+ Build Advise - PLEASE
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Author:  Minimadmarty [ Sat Dec 28, 2013 10:19 pm ]
Post subject:  1275 A+ Build Advise - PLEASE
G'day to all, this is my first post as a new member!

I'm looking to build a 1275 A+ engine for my 78 Mini which currently has a highly modified 1100 engine (it blows blue smoke if I use any oil less than 25W so due for replacement).

I want a good strong reliable bulletproof motor rather than outright performance. It's my first mini engine build (I have built Ducati engines in the past, well twice now!) so looking for advise please. Is an aluminium cylinder heads worth the extra money? What tips could anyone give for building a 'strong as possible' motor? Is it worth giving it a shot myself or leaving it to the pros? If so, any recommendation on the best engine builder in Australia?

All and any information greatly received

P.S. Just read Phat Kat's thread on "How to Assemble an A Series Engine" Brilliant reading
Author:  Kennomini [ Sat Dec 28, 2013 10:53 pm ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
I personally wouldn't bother with a 5 port alloy head, but if your looking at a 7 port alloy head they are proably worth a go depending on the port work.
Author:  mickmini [ Mon Dec 30, 2013 7:44 am ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
Reliability and performance for cost, you cannot beat a well worked iron 5 port head and large capacity - 1380cc +. You will easily get 80-100ftlb torque with the right cam which is a lot, and still be driveable - i.e. you don't need to rev it like crazy. You can use a lot of standard parts as long as you carefully check them - e.g. standard rods. Don't chase power, chase torque across the rev range for driveability.

If you have rebuilt ducati motors, a mini won't be a problem. There are a few tricky bits, but plenty of knowledge available on forum, in your local club and with your local mini specialist.

Make sure you check and rebuild the gearbox at the same time as the motor. No point in doing the motor and not the gearbox while they are apart.

cheers
michael

ps there are a few good engine builders on the east coast, but the Perth guys will tell you who your best local guy is if you don't want the freight.
Author:  Babes [ Mon Dec 30, 2013 10:12 am ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
Welcome to the forum mate, are you nor or sor? Im in Wanneroo and quite happy to give you the low down on whats what in the Perth mini scene.

If you want strong reliable then go stock with a few extra tweaks, as soon as you start chasing hp you will spend a stupid amount of money (i have an engine which has had over $15k spent on it and im still not happy!)

Have you got a 1275 as a starting point yet or still on the hunt for one?
Author:  Minimadmarty [ Tue Dec 31, 2013 8:33 am ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
Cheers Michael,

Great advise, it's hard not the chase the horsepower but you're correct it torque and drive-ability I'm after (the speed-demon in me I can save for track days on the bike!).

I've always been hesitant to over bore an engine - Does the extra 105 cc of a 1380 make much of a difference? Or would say 1310cc make for a longer lasting engine? (i.e. It can be re-bored to 1380 on it's next rebuild (in another 20 years hopefully!)).

If cost isn't an issue, what would be the most durable/strongest cam, rods, pistons, etc?
Author:  Minimadmarty [ Tue Dec 31, 2013 8:47 am ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
Hi Babes,

I'm North of the river not too far from the city. It's the extra tweaks I'm interested in knowing about. I don't have an engine yet, a guy down South has a 1275 A+ on offer for $1800 but I haven't made a decision yet as I'm still looking at a professionally built engine from a mob in Melbourne!

More information on the local scene would be great.
Author:  Kennomini [ Tue Dec 31, 2013 11:10 am ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
Minimadmarty wrote:
Cheers Michael,

I've always been hesitant to over bore an engine - Does the extra 105 cc of a 1380 make much of a difference? Or would say 1310cc make for a longer lasting engine? (i.e. It can be re-bored to 1380 on it's next rebuild (in another 20 years hopefully!)).

If cost isn't an issue, what would be the most durable/strongest cam, rods, pistons, etc?

Yes the extra cc of the big bores are worth it for "lazy power" you can have a 1380 make 100bhp or you can make a 1310 put out 100bhp, the difference is the 1380 possiably will have more torque and the engine components aren't working as hard to produce the 100bhp.
Also your idea of going for less of an over bore is a good idea to get a longer life span out of the block.
Cams are generally a durable part, it comes down to the correct profile choice for your engine/head and what power and drivablity you want out of the engine.
Rods are also fairly easy, so long as they are a matched set all weighing and balanced the same. Their are different std rods out there like S rods, A+ rods, large journal 1100S rods etc they all work well but proably the best std form rod is the A+ rod. On the other hand if money isn't an issue then their are plenty of race spec, after market rods on the market which are stronger and lighter but "bang for your buck" for a mild road engine, it's just not worth the cost. (Same with cranks).
Author:  drmini in aust [ Tue Dec 31, 2013 1:49 pm ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
If you are boring a motor to 1380cc (73.5mm) I'd use an A series block, not an A+. A series is a better casting, many A+ blocks had porosity and core shift (uneven cylinder wall thickness). Also, A series 1275s are way more common over here than A+.
And, I would offset bore it to 1360cc (73.0mm) first, and save the 1380 bore for next time. You will not measure a power difference between a 1360 and a 1380 to the same build specs.

If you offset bore it to begin with, after 1380cc you can bore out to 1400cc (74.0mm) in the future if you need to.
Author:  slide [ Tue Dec 31, 2013 3:35 pm ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
I'd go 1360 too, nice torquey cam (Wade or GR are better than Kent 266 or BL 731 IMO), maybe a bit of 5 port head work, bigger valves, 10:1 CR and 1.5 rockers, decent LCB exhaust and HIF44 carby on decent manifold should make for a good, tractable and very reliable drive. Don't forget the distributor, have it regraphed if possible to match your engine specs. If it's on 10 inch wheels then a 3.4 diff is great around town.
Author:  Minimadmarty [ Wed Jan 01, 2014 11:29 am ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
Wow, cheers guys this stuff is gold I'm feeling more confident about building this engine myself knowing the wealth of knowledge on this forum. (Expect loads of question once the build starts!).

Kennomini love the explanation
Kennomini wrote:

you can have a 1380 make 100bhp or you can make a 1310 put out 100bhp, the difference is the 1380 possiably will have more torque and the engine components aren't working as hard to produce the 100bhp.


Plus all the other advise - I'm gonna lock it in and go for a 1360 bore.

Drmini in aust - I'll definitely look more into the A series verve the A+

Slide - I'll definitely research the Wade and GR cams (I'm a bit annoyed with myself for recently selling a HIF44 on eBay, I knew I should have kept it!). Would twin 1.5 SU's be ok? (It's more for the grin factor and look of twins I like!).

Once again guys thanks for the advise and keep it coming.

P.S. HAPPY 2014 TO ALL
Author:  Kennomini [ Wed Jan 01, 2014 11:53 am ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
Twin 1 1/2 carbies will be fine so long as your happy with the extra carby tuning/matching that will be required. A single 1 3/4 carby would be fine but you'll get the same results from the twins, just a little more setting up.
Author:  Minimadmarty [ Wed Jan 01, 2014 12:06 pm ]
Post subject:  Re: 1275 A+ Build Advise - PLEASE
Any excuse to fine tune - isn't that why we all love Mini's so much?
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