26 replies to this topic

[adam26y]

Im going to get another mini soon but I'm looking to get a metro 1275 engine and in the confinement of my shed take it to bits and assemble a engine around 90-100bhp ready for the minis arrival.
In the past i know that using a 1.3/4 carb is a great carb for this spec? I've heard that a 12g295 head is one of the best standard heads you can find?

And is a turbo worth it for the amount of work needed?

I'll be using this car for road use but with enough to wham to wipe a few boy racers smiles off.

I know there's a lot of diversity on specs but if someone could chuck a few ideas my way I would be greatly appreciated. I've read that David Vizzards book is very good but does it tell/show you how to do everything. I am very mechanical minded so don't quite need a dummy's guide to tuning.


Just to re iterate I don't really want to buy off the shelf things that will cost me an arm and a leg and will just sit there all shiny.

Any help will be greatly appreciated.

[KernowCooper]

Yes the Vizrads yellow book is a good read and shows exactly how to do exactly what you want to do, the 12G295 head is a small bore head fitted standard on the 998 Cooper, there are better heads out there now for the 1275cc+ engines. The book is a few years old but still current as there have been nothing drastically new in tuning the A series since. Recommended.

[Cooperman]

As above, a 12G295 is not a head for a 1275, it's a 998 Cooper head.

With regard to power, it's relatively easy to get 90 bhp at the flywheel and still have a nice road driveable engine. However, 100 bhp requires a lot more modification and will make the engine very 'lumpy' as well as needing a lot of revs which in turn means a fully balanced engine with a centre-main bearing strap, an expensive gas-flowed head, top quality pistons, etc.. The cam to get to 100 will have a narrow power band and a close ratio gear set will also be needed if the optimum performance is to be used and a lower final drive ratio.

However, 90 bhp can be achieved with a more moderate cam and more-or-less standard gearing. That would be nice to drive on the road too. The Kent 276 cam with a gas-flowed MG Metro head and a compression ratio of c.10.5:1 works well. You also need the HIF44 carb, or a pair of HS4's. The ignition system must be re-curved for the new specification and a better exhaust system fitted such as a twin box Maniflow system.

You can gain a bit by boring it to +0.060" which gives 1330 cc and doesn't scrap the block when it next needs a re-bore. For pistons at 90 bhp the 21253 as sold by Mini Spares are very good and will take up to 6500 rpm without any problems.

 

I hope this helps.

[adam26y]

Ah, thankyou both about the 295 confirmation, my father loved playing with 998s so that's were it came from. He got 100 mph out of a 998 but went through head gaskets like cups of tea.

Thankyou very much cooper man, are metro heads standardly gas flowed or is this an upgrade?

Will the standard metro bottom end put up with the power with the centre strap addition? No profiling or anything? Or would this be a possible extra? I have in my head something about adding a splash guard near the crank to splash the oil back up ? May be nothing.

Similarly will the springs and valves be adequate at this level?

[welshdan]

You wont be wiping the smile from many boy racers faces with a mild ish road cam and a standard ish head. A 'fast road' mini engine will never be fast in real world terms

[minimadles]

Mg metro heads are good but can stand some gas flowing and porting with special attention to the valve seat area as always build the engine to a high standard make sure you do a dry build to check and adjust tolerances there is a great thread in the projects section on engine building .

[Cooperman]

The poor aspects of the basic Mini head, i.e. the 12G940 casting as used on the MG Metro (and about every other 1275 Mini) are the intrusion of the valve guide bosses into the inlet & exhaust tracts, the shrouding around the outer edges of the valves and the profile of the 'short side radius' which is the curve the inlet tract takes into the valve seat.

The advantage of the MG Metro head as a basis is that it already has the 35.6 mm inlet valves rather than the 33.5 mm as fitt4d to most 1275 Minis & Metros. But be careful, some MG Metros had the 33.5 mm inlets with unleaded seats.

With a 276 cam a centre main strap is not really needed as peak power will be at around 5700 rpm so you won't be using more than about 6100 rpm.

To go for more power is then seriously expensive as the engine becomes very 'cammy' and an expensive gear set is needed. You don't want to be driving around at over 5000 rpm all the time unless it's a race or rally car. I know my 1310 cc rally Cooper 'S' with a 286 cam and all the 'bells & whistles' in not very pleasant to drive on the roads.

The 'splash guard' is, I think, a 'windage tray'. They can be fitted, but are not really any benefit unless you are racing. What is a good idea is a centre oil pick-up to avoid oil surge causing fluctuating oil pressure on long right hand bends.

However, as above, a Classic Mini is still a 55 year-old design and a fast Mini is still slow compared to fairly ordinary modern road cars. For example, I had a Rover 214 rally car which had a standard engine *as required by the regulations) and despite my 'S' having around 10 bhp more and weighing in at 250 kg more, the Rover was still quicker on any sort of average twisty road or on a bumpy surface. That's the difference about 40 years of design technology makes. 

There is no such thing as a 'fast road Mini', just a 'less slow road Mini'. But then, that's what classic car driving is all about. I mean, even an E-Type, another iconic classic, is slower than my modern BMW diesel saloon road car. Such is progress. Just enjoy driving your classic car, whatever make & model it is. 

[adam26y]

Thankyou Cooperman, ill get hunting out the parts I need, I've just spent half hour reading through AndyMiniMads step by step engine rebuild as madles suggested, wow what a read that was. The shopping list has been wrote. Just wish parts were as cheap as they were 5 years ago, brought a whole metro for £50 back then off a local and a mini for £100 of a drunk in the local pub.

[Cooperman]

IMHO the key to building a really good A-Series is in the detail and the care taken in building it.

I had to build an engine for a 1990 Cooper 1275 Endurance Rally car. This mandates no engine or transmission modifications.

I used an MG Metro cam, 'cleaned up' the head a little, but not so much that the scrutineers would know, cleaned out the ally manifold to remove the casting imperfections, matched everything, bored it out to the allowable limit, +0.060" and built it very, very carefully and accurately. In fact I 'blueprinted' it, raised the CR to 10.5:1, gas-flowed the HIF44 carb, fitted Aldon ignition, slightly lightened the flywheel (not strictly allowed under the regs!).

It gave 84 bhp at 5700 rpm and with a 3.44:1 FDR was very nippy and quite competitive, although trying to keep up with the more modern cars at up to 1400 cc was really hard work, which is why I sold it and bought a Rover 214.

[adam26y]

Yeah attention to detail can make or break anything. My father built a road mini with 100bhp at the wheels and 0-60 in 4.3 seconds, but my knowledge of what he did is faded. I know he modified the head himself and using a fluid made sure every port was identical, he needle balanced the conrods, lightened and balanced the crank, used a rally cam( for fuel economy) and used a metro lump. But I'm not exactly on talking terms with him so getting him to build it or advise me isn't really an option. It's done about 20k since then and hasn't blown up but I think it's sitting there needing a new clutch.

[Cooperman]

Are you sure it did 0 - 60 in such a short time. My Cooper 'S' has about 110 bhp, is a rally car with very low gearing and a kerb weight of c.715 kg and the best 0 - 60 I've ever got, using proper measuring equipment, was 7.3 seconds using 6800 rpm. The limiting factor is the wheel spin off the line. Maybe with a limited slip diff it might have been about 1 second quicker, but certainly no more.

The hotter the cam the more you need close ratio gears and these in turn mean you need a low ratio final drive in order to work with the consequence of a high first gear. It's all a 'trade off'.

With the performance of any average modern car, my own thoughts are that if you have a Mini you need to be a true classic car enthusiast and just enjoy the car for what it used to be - a true motoring icon with, in its day, fantastic performance. Build a nice engine with 85 to 90 bhp and just enjoy driving it on twisty roads.

[mk1leg]

Get yourself this DVD............ http://www.minisport...es-engines.html

its a great watch ...has full strip down and evaluation and a total rebuild..........

[adam26y]

Yeah we took it to a rolling road. And got all the print outs, bit of fine tuning on the his44 needed, he used a straight through exhaust with just a back box. I love minis so enjoying them is not a problem. Ill start sourcing the parts and have a good read of that book when I get it. Thanks for the help. Ill probably be lurking about in the future when I get round to doing the engine and encounter various problems

[welshdan]

I dont think the migs even do a genuine sub 5 second 0-60

My 160 bhp turbo 1380 definately doesnt, though it does 60 in just one gear change, and it has much more torque than any na motor...

[adam26y]

All I know is he and his mate did the engine. He used to build race engines and together they spent days working on the head. It was amazing sitting in the passenger seat! It was a rocket upto about 80mph then it started to round off upto 120. We've beat 3.0 vauxhalls in drag races ( not on a track either ) and any boy racer in the local 20 mile radius haha. Many people haven't believed it but i can assure you we dyno'd it. I find many people will doubt what you say, a lot of people said you couldn't get 100mph out of a 998 but I've been in one defying that lol. I'm looking forward to doing this engine myself though and although I'm not expecting to replicate that engine maybe after a few engines under my chest I'll try my hand at a more serious challenge.