SA1100 vs 1275 for a road engine

[timmy201]

I feel like I already know the answer to my question, but thought I'd check with those who have experienced both engines

I have an SA1100 crank & 1275 block and was planning on building a high rpm engine, big cam, head, 3.76 diff etc

However my recent experience with my high compression 1098 (small bore) has me reconsidering my SA1100 plan.

What I've come to realise I want is:
Something nicer on the highway at 100kph, so maybe a 3.1 diff. We have a few long trips throughout the year, with one about 1000km over a weekend so I want something that'll be reliable and a little more comfortable
Lower compression (under 10:1) so it's easier to start, doesn't need 98 octane, easier to tune, less chance of head gasket failure etc
Limit the RPM so that I can spec lower pound valve springs, rockers etc to prolong valvetrain life
I don't do any track days. The speed limit here on 95% of the roads near me is 100kph, so I want something to suit these speeds

So my initial plan turned out the opposite of what I think would be best now.

The real question is: is there any way to spec an SA1100 engine to be a smooth, grunty, reliable & long lasting road engine or should I just go for a 1275 instead?

[360gts]

First, there is never any substitute for cubic capacity.
The 1275 has way more torque than a 1097 SA engine. So, for normal road driving....IMO...a nicely tuned 1275 will be the best alternative.
I like a standard flywheel on a road engine.......helps smooth out the long stroke 1275 engine.

However, if you wanted a high revving engine....the SA 1097 unit is a good starting point. The SA 1097 crank is a very strong item...uses A+ rods in the 1300 block. (many track owners in the UK have used this crank...getting hard to find now) Short stroke.....very different to the regular 1098/1100 engine.
Sure there are lots of others on here with more thoughts on your question.
Cheers
D

[LarryLebel]

Off topic but Timmy you need to put the info your other post into a website.

[goff]

Timmy
I have a SA engine in my car , it is a lovely engine , but as Dermot says " no substitute for CC " .

My engine , SA Crank , 1300 rebored + 10 thou , it needed a rebore , Minispares Evo cam , MK3 cooper S head with 20 thou removed , twin 11/4 carbs , S distributer , standard flywheel ect , gearbox is 4 syncro remote , close ratio and 3.2 diff , i had a 3.6 diff in fisrt of all , but was going to Classic
Le-Man from UK so changed for the higher one , i have also fitted pot joints , its a lovely engine and will pick up from 1,000 rpm with the Evo cam , people ask why would you detroke a 1300 and i tell its a lot smoother than a 1300 and i love the engine , will rev to about 8,000 , but i never do that , again a few on this forum have SA engine including Mark and Rich@minispares & Andy B72 , they used to import the cranks from S.A. , i had never heard of the SA cranks until i found this forum and met the three i mentioned above , i got my crank from " The long beared Boss " Rich . ,
i would say go for it Timmy , the difference between 1100 small bore and big bore 1100 SA , at least you can rev it without worrying about the crank breaking on the SA engine

[Costafortune]

A good 1275 is fine. Make sure it's properly balanced, a good camshaft for torque, single carb, high compression, about 70 bhp and a 3.1 diff.

[timmy201]

First, there is never any substitute for cubic capacity.
The 1275 has way more torque than a 1097 SA engine. So, for normal road driving....IMO...a nicely tuned 1275 will be the best alternative.
I like a standard flywheel on a road engine.......helps smooth out the long stroke 1275 engine.

However, if you wanted a high revving engine....the SA 1097 unit is a good starting point. The SA 1097 crank is a very strong item...uses A+ rods in the 1300 block. (many track owners in the UK have used this crank...getting hard to find now) Short stroke.....very different to the regular 1098/1100 engine.
Sure there are lots of others on here with more thoughts on your question.
Cheers
D

Thanks, that all makes sense. I am still working through the dilemma of making a fun revvy engine that is good on weekends or something a bit smoother and easier to drive in traffic and generally a bit more tame. I have got the SA100 crank and some A+ rods already which ever way I go

Off topic but Timmy you need to put the info your other post into a website.

What exactly did you want me to write about?

Timmy
I have a SA engine in my car , it is a lovely engine , but as Dermot says " no substitute for CC " .

My engine , SA Crank , 1300 rebored + 10 thou , it needed a rebore , Minispares Evo cam , MK3 cooper S head with 20 thou removed , twin 11/4 carbs , S distributer , standard flywheel ect , gearbox is 4 syncro remote , close ratio and 3.2 diff , i had a 3.6 diff in fisrt of all , but was going to Classic
Le-Man from UK so changed for the higher one , i have also fitted pot joints , its a lovely engine and will pick up from 1,000 rpm with the Evo cam , people ask why would you detroke a 1300 and i tell its a lot smoother than a 1300 and i love the engine , will rev to about 8,000 , but i never do that , again a few on this forum have SA engine including Mark and Rich@minispares & Andy B72 , they used to import the cranks from S.A. , i had never heard of the SA cranks until i found this forum and met the three i mentioned above , i got my crank from " The long beared Boss " Rich . ,
i would say go for it Timmy , the difference between 1100 small bore and big bore 1100 SA , at least you can rev it without worrying about the crank breaking on the SA engine

Thanks for sharing. I also heard about these engines from this forum, it's interesting to hear that you've got a 3.2 diff and still fun to drive.

It would be an interesting comparison between my current 1098 small bore and the SA1100 big bore. The current 1098 small bore definitely has some low down grunt, but it starts to slow down above 6000rpm (and I don't want to push my luck with the crank)

A good 1275 is fine. Make sure it's properly balanced, a good camshaft for torque, single carb, high compression, about 70 bhp and a 3.1 diff.

I feel like this is the most sensible option, but then I struggle with wondering if my mini needs to be sensible - it is a mini after all and only gets driven once a week at best. I did like the idea of it being the same stroke as the original 850 engine, but with a bigger bore


Just for reference I have the following parts already planned:
SA1100 reground crank
1275 block on original bore
A+ rods and ARP bolts
Early 12G940 small valve head
I have got a pair of H4 carbs that need assembling.

I don't have a 1275 crank, but I'm sure I could easily swap for one

[mk1]

For what it's worth, the SA1100 makes a fantastic road engine which is far superior to any equivalent 1275.

The "nearly" square bore / stroke ratio makes it silky smooth & much less stressed than any 1275, but big GT size journals make it reliable too.

The spec that Goff describes above would do exactly what you are looking to do with less fuss than any 1275.

Personally, I'd say give it a try, I doubt you will regret it, but having said that, a close to standard 1275 / 1300 engine will do what you are looking for too.

If you decide to go the standard(ish) 1275 route, I am sure that there will be plenty of people who would be happy to buy your SA crank.

[goff]

Timmy , I had two miniJem cars , one with VDP 1100 engine, same as MG1100 , small bore and the other with the SA 1100 , you ask how they compare, like chalk and cheese , guess which one I sold , yes the small bore one , love the SA1100 engine car .

[Exminiman]

Despite its larger capacity, I have always thought the 1275 engine is a “rough” engine, ideally it would be closer to square like the 1071.

Ford,s pre crossflow engine is way over square for similar size and TBH always much preferred the way it drives.

Cant see any reason why right cam and head shouln’t give decent torque.

[CooperTune]

As I try to downsize my mini collection, having four Cooper S blocks and three Cooper S cranks only makes it tougher. One is a no brainer; it is the original 74 1071 block currently .030, crank .010/.010. Also have a 1275 block thin flange .020 bore with .010 /.010 crank. Another 1275 block bored 73mm but all I have left over is a SA 1100 crank and a 970 crank as well as a thick flange 1275 block bored .040 with steel caps, 4 bolt center. I have wanted to build a big bore short stroke for some time. I built a 1275GT engine to 74mm bore, crank .010/.010, Metro rods, SW5-07 cam, Calver ST cyl head, twin 1 1/2 SUs and LCB. It makes bags of torque and 3.44 CWP 5.5 /12-inch wheels and Yoko cheater slicks it spins the tires at will in most gears. I have a set of 6-inch rods but no desire to wack 1/8 off a block to build a 970. I've had the 970 crank 20 plus years looking for rods. I really want to build a 13 to 1 CR , ST643/544 cam, full race head 1360. Fuel will be an issue but they do sing. Steve (CTR)

[timmy201]

For what it's worth, the SA1100 makes a fantastic road engine which is far superior to any equivalent 1275.

The "nearly" square bore / stroke ratio makes it silky smooth & much less stressed than any 1275, but big GT size journals make it reliable too.

The spec that Goff describes above would do exactly what you are looking to do with less fuss than any 1275.

Personally, I'd say give it a try, I doubt you will regret it, but having said that, a close to standard 1275 / 1300 engine will do what you are looking for too.

If you decide to go the standard(ish) 1275 route, I am sure that there will be plenty of people who would be happy to buy your SA crank.

Thanks Mark. The smoothness & low stress sounds like it would be nice to drive.

I guess the risk is that the block gets a huge chop off it and it's a one way process if I don't like it. There's also not many SA1100 engines running out in Aus to test drive or get advice from.

Is there a particular piston that is more suitable than others (higher pin height etc)?

Timmy , I had two miniJem cars , one with VDP 1100 engine, same as MG1100 , small bore and the other with the SA 1100 , you ask how they compare, like chalk and cheese , guess which one I sold , yes the small bore one , love the SA1100 engine car .

Thanks Goff. I did expect the short stroke 1100 would be much better than the long stroke overall, especially given the bigger valves and better head of the big bore engine. I guess the main question I had was if it was worth going for SA1100 vs 1275 given the extra displacement etc

Despite its larger capacity, I have always thought the 1275 engine is a “rough” engine, ideally it would be closer to square like the 1071.

Ford,s pre crossflow engine is way over square for similar size and TBH always much preferred the way it drives.

Cant see any reason why right cam and head shouln’t give decent torque.

Thanks for your thoughts!

As I try to downsize my mini collection, having four Cooper S blocks and three Cooper S cranks only makes it tougher. One is a no brainer; it is the original 74 1071 block currently .030, crank .010/.010. Also have a 1275 block thin flange .020 bore with .010 /.010 crank. Another 1275 block bored 73mm but all I have left over is a SA 1100 crank and a 970 crank as well as a thick flange 1275 block bored .040 with steel caps, 4 bolt center. I have wanted to build a big bore short stroke for some time. I built a 1275GT engine to 74mm bore, crank .010/.010, Metro rods, SW5-07 cam, Calver ST cyl head, twin 1 1/2 SUs and LCB. It makes bags of torque and 3.44 CWP 5.5 /12-inch wheels and Yoko cheater slicks it spins the tires at will in most gears. I have a set of 6-inch rods but no desire to wack 1/8 off a block to build a 970. I've had the 970 crank 20 plus years looking for rods. I really want to build a 13 to 1 CR , ST643/544 cam, full race head 1360. Fuel will be an issue but they do sing. Steve (CTR)

You've got plenty of options there!

[Philsa]

Hi Gents

Here is my 2 cents as a South African Classic Mini Specialist for a number of years. I have owned all the variants of minis that SA has on offer and have now been running a 1071 Cooper S engine fitted with a SA 1098 crank for about 9000-9500 kms of all condition hard driving.

So a SA big bore engine with a STD, 10, 20, 30 up to 40 thou oversize on a 1098 is all great. I have rebuilt a number of these engines, even taken a block and bored it out to the 1098 piston size that I have and used the 1098 crank. Rings is not a problem generally here in SA for used 1098 pistons. For a performance increase I do recommend lightening the pre A+ flywheel and backplate for a start. Fitting a LCB with an alloy inlet manifold as most 1098 engines still have the one piece inlet/exhaust manifold. Lastly your choice of performance air filter. I have been on numerous Mini Owners Club of SA (MOCSA) runs with 1098 engined minis and stay on par with anything else that joined in the run. Just for info in the late 70's up to the mid 80's there was quite a few highly modified 1098 SA engined minis that ran extreamely well in our local racing scene (clubman series, castrol classics etc). These engines was naturally blue printed and out and out race items, but still.

I have also taken a whole bunch of 1098 SA big bore engines and converted them to 1275 engines using the 1275 crank with usually 40 thou or 60 thou 1275 pistons both std compression and high compression. So thus I have quite a few of said 1098 cranks on the shelf at my disposal ranging from std/std to 40/40.

The best option would be to find/source, strip and assess, rebuild and then use a complete SA big bore 1098 engine with its pistons still usable on new rings and whole engine reconditioned with the gearbox or simply use the 1098 power unit. I do also recommend buying a few spare oil filters for the SA block as the rest of the world it is not a common oil filter.

For any questions PM me.
Cheers