22 replies to this topic

[redhot-mini]

Hi guys help me chose what to do, basicaly I have a 1380 engine with twin carbs to go in my mini or a micra 1.3 engine I fancyed somthing like a micra engine as more relyable than a mini in my experience and I will be using it for long distance driving what do you recon also what are the top speeds of each engine in a mini? As 1380 will have more bhp but will a micra pull better as made for a heavier car ?

[Broomer]

Those micra engines can be nippy in standard form.
Micra engine any day of the week. And you would have cash spare after building it when compared to the 1380 that will fall apart a couple years later.

[l_jonez]

Well you can only do 70mph in the UK but it all depends on the spec bhp and gear ratios of the 1380. I'm sure in one of the other threads someone posted the micra gearbox ratios and speeds.
You could compare ratios etc and work it out.
For long distance I'd take the Micra engine every time mine crusies at 70 all day long and gets 45-50mpg. The gear ratios are just right using the 1.3 box and 12" wheels.
Actually scrap that I'd take the Micra engine in all situations.

[ibrooks]

The Micra engine comes with a 5th gear so it'll wipe the floor with the 1380 as a cruiser. The CG13 with a decent intake filter and exhaust without the cats makes 100BHP in bog standard, do 100,000 without more than oil changes, your granny can drive it to the shops form. It's an impressive A-Series that'll really make 100BHP, it won't have the longevity, refinement, economy or general all round useability of the CG13.

 

I'm not biased against the A-Series I really like them as a solid simple little engine but I'm realistic enough to account for the fact that they were designed as a sub 1litre engine in the '50's. The capacity increases were all modifications on modifications and there's only so far you can push an engine beyond it's design specification. There's also been a lot of additional knowledge gained about the internal combustion engine in the 40 years between the designs, not to mention in the materials used. I've got a CG13 in the rear of my GTM at the moment and with the body off I can lift the rear of the car (just) that's engine, box, subframe and the chassis itself - I wouldn't be able to do that with an A-Series in there.

 

If it's a straight choice between the engines with their attached gearboxes then it's no contest. There would have to be other reasons for me to stick with an A-Series.

 

Iain

[Ethel]

I don't think there's any weakness in the design of the A because of its age. You'd be able to make that argument better against its gearbox and mechanical fuel & ignition systems. Not that the gearbox has much to do with cruising ability, that's all down to final drive ratio. No one has mentioned resale value, keep it A Series if it's in good condition & that matters to you.

[Midas Mk1]

100bhp a series is so much fun. Says it all really.

[l_jonez]

I have no intention to sell my mini so resale value is not an issue and let's be honest it does not devalue a mini, it just limits the market to people looking to buy non A series.

100bhp in a cg13 is more fun as your not counting the miles to the next rebuild/breakdown. Also you get better power to weight ratio with the cg13.


A huge point for me was cost I did my whole conversion for sub £500. to build a equivalent A series it would cost a couple of thousand.


But each to their own, if you like the A series then happy days if you fancy something different the Micra ( or swift gti) are good options.

[ibrooks]

I don't think there's any weakness in the design of the A because of its age. You'd be able to make that argument better against its gearbox and mechanical fuel & ignition systems. Not that the gearbox has much to do with cruising ability, that's all down to final drive ratio. No one has mentioned resale value, keep it A Series if it's in good condition & that matters to you.

 

The A-Series does have weaknesses. It's only got a 3-bearing crank - hence centre main straps to try and keep the things together. The rotating assemblies are heavy so they won't rev that high without lots of work. Plus lots of other little things that were perfectly fine in it's time but nowadays are simply out-dated. Then there's the fundamental limitations with things like the 5-port head and it's non-crossflow design - different heads are available but they are all extra modifications and the extra money involved to get you to a standard CG13 equivalent. Once you've bored the block as far as 73.5mm there is so little bore thickness that they all suffer from bore flex - and if you're about to tell me yours doesn't then you are deluding no-one but yourself.

 

Increasing the final drive is all very well but it's at the expense of the rest of the ratios. If you could keep the standard 4 with a 3.44 or 3.1 diff and add an overdrive then yes it could be a cruiser.

 

Fuel and ignition - again the A-Series can be converted to injection with fancy ignition but all that comes as standard with the Micra engine if you get a complete running setup.

 

Value. One of the big advantages of the CG conversion over the bigger engines is that there is very little modification if any required to the body so if you've got an A-Series then mothball it and keep a standard subframe so that it can go back in easily at a later date if it worries you.

 

Iain

[Ethel]

I'm not suggesting the A is a match for a more modern engine on that engine's terms out of the box, I just think people are sometimes too ready to slate it just because it's got a long history. You can certainly make one rev well enough, even with its 3 mains, at a price. I guess it depends on whether your hobby extends to car building as well as driving.  Personally, I'd play to its strengths as a tough old boot that's a great burner with low down torque and put a blower on it. Admittedly, this still won't be as cheap as an engine where breaker's yard supply outstrips demand.

 

I agree smaller & lighter engines are better suited to converting a Mini and keeping the Mini feel, but as far as I know only the bike engines avoid major subby modification.  I haven't seen a conversion that leaves the inner wings unscathed either, but I'm happy to be corrected by anyone who knows better. There's also the gear selector and driveshafts to fettle. I'll be very surprised if you can find a final drive from a higher revving engine, for turning wheels bigger than the Mini's, that will give you a good cruising ratio while not making first so high as to be next to useless.

[l_jonez]

Dont get me wrong i love the A series and have built a few in different sizes and tune and the other 2 minis still have them but a more modern engine is just better all round.

Read the 40 odd page long Micra transplant thread there's a fair few people that have left the inner wings intact. Both gear selector and shafts are a simple cut to length and weld back together job or you can buy them from all speed.

With mine I can cruse at 60mph which is 3k rpm and first is no different to any other car I've driven

[ibrooks]

I'm not suggesting the A is a match for a more modern engine on that engine's terms out of the box, I just think people are sometimes too ready to slate it just because it's got a long history. You can certainly make one rev well enough, even with its 3 mains, at a price. I guess it depends on whether your hobby extends to car building as well as driving.  Personally, I'd play to its strengths as a tough old boot that's a great burner with low down torque and put a blower on it. Admittedly, this still won't be as cheap as an engine where breaker's yard supply outstrips demand.

 

I agree smaller & lighter engines are better suited to converting a Mini and keeping the Mini feel, but as far as I know only the bike engines avoid major subby modification.  I haven't seen a conversion that leaves the inner wings unscathed either, but I'm happy to be corrected by anyone who knows better. There's also the gear selector and driveshafts to fettle. I'll be very surprised if you can find a final drive from a higher revving engine, for turning wheels bigger than the Mini's, that will give you a good cruising ratio while not making first so high as to be next to useless.

 

The Micra conversion does involve fairly major mods to a subframe - but a spare subframe isn't the end of the world and it's easy enough to put a standard one back in later if you want to retro fit an A-Series back in the hole. You don't touch the inner wings for a Micra lump (or at least you don't need to - slight alterations can make things easier but are by no means necessary). You need a slight bulge in the bulkhead crossmember to fit the standard Micra intake manifold - it's quite possible though to use a different manifold so you don't even need to do this.

 

It would be perfectly possible to fit a Micra lump to your concourse 60's Cooper S with all matching numbers and run it for several years before then sticking the A-Series back in there and no-one would know it had ever happened.

 

The gear-linkage - you shorten the Micra one and it even bolts into the same holes as the Mini selector did. Driveshafts - OK you've got to cut and shut a set but they are a bolt-on item so can be switched back to standard later with no evidence like the subframe

 

Final drives - yes they can be a problem with the bigger engines from cars designed for 17" wheels but a Micra had 13" or 14" wheels so even in a Mini with 10" wheels it's not a huge difference and certainly not enough to cause any noticeable problem.

 

Iain

[Ethel]

You're looking at  10% give or take a couple of couple of points, or about half to three quarters of your fifth gear overdrive. I must concede the first gear isn't an issue, being  a lower ratio than a Mini's - if Google speaks the truth.

 

Micra 5-Speed Manual Transmission

1st - 3.727
2nd - 2.048
3rd - 1.393
4th - 1.029
5th - 0.821

Reverse - 3.545

Final drive - 4.055

 

( I appreciate you can get a lower final drive ratio and interesting that there's no 1:1 ratio)

 

 

 

3.647 2.185 1.425 1.000 MKV/VI/VII Mini, ERA Turbo & Metro (A+ >'84)
4.004 2.307 1.435 1.000 Metro 1.0 HLE 

 

My conclusion is you might get a 5 speed box, but it's not likely to get as good a cruising/economy ratio as an A Series with a 2.7 or 2.9, and certainly not without doing some mixing and matching of boxes & final drives.

 

[ibrooks]

Not sure I believe that there isn't a 1:1 - why put a pair of cogs in rather than just locking the input and output shafts together for one of the ratios.

 

As for cruising - don't be so sure. Bear in mind that this is an engine designed to spin faster so it's never going to sound as harsh as an older engine at higher revs. It's also optimised for higher gas speeds and running closed loop management so it will be more fuel efficient than an A-Series revs for revs under the same load. It's also a huge amount lighter than an A-Series so the same speed is not going to be them same load in an otherwise identical car.

 

The 998 and 1275 boxes have different ratios if I remember correctly and the early 998 has a completely different box. There's also been talk about it being possible to fit an Almera diesel final drive if it really worries you that much.

 

Iain

[l_jonez]

Yep apparently the almera box will fit but to me the FD ratio is spot on with the 1.3 box. I can't see the need for anything longer

[redhot-mini]

cheers for all the advice ive just sold my 1380 for £500 so time to buy a micra :) a mate at work banger races them he told me 2 put a 1L gear box on a 1.3 he said the do about 60 in 5 seconds but max speed is about 70mph haha