26 replies to this topic

[mattso118]

Hi there.

Im currently running a very lightly breathed on 998, as much as I love my dear mini it is a bit gutless! I have been toying with the idea of an engine transplant for some time, and the funds should shortly allow for some lavishing on the lil Dorris.
So...
What is the simplest way of achieving 100hp ish, several people have suggested turboing a large bore motor whilst others have suggested trying to achieve the magic number an overbored N/A?

There are so many options out there and im a bit overwhelmed with the options. Not to mention the fact that I get quite excited reading peoples build threads !

SOOOOO any ideas ?

Thanks

[mk3cortina]

bike engine, light and at least 125hp straight away from any 1000cc you can find.

[minidream94]

toyota starlet glanza turbo - 1.3 and around 130/140ish brake (i think) Big conversion in australia where theres plenty of info, check out ausmini

nissan micra 1.3 - been done a couple of times over here, so quite abit of help and info, these are around 60/80 brake and will go on forever

suzuki swift 1.3 - 100brake (there abouts) and again been done loads over here so info is easily found

All fit under standard front ends with minimum mods

Or you could stay A series and run a 1330/1380 with all the mods, bike carbs etc etc

Nick

Edited by minidream94, 29 December 2010 - 01:21 PM.

[mattso118]

What sort of costs would you expect for the swift conversion in comparison to modification of an A series? And I take it a modified subframe is required to mount the engine to? Also with the swift I assume you have to go with the 5 speed box?

Sorry for all the questions, but im very curious very keen to learn and utterly desperate to have some power on tap !

Thanks

[Cooperman]

If you want to keep it as what might be called an 'original' Mini, i.e. with a BMC A-series engine, then the following would get you to 100 bhp N/A:

Bore to 1330 cc
A really good gas-flowed head with 37 mm inlet valves and 30.5 mm exhausts
A comp ratio of around 10.7 to 11:1
A 286 cam accurately timed in
LCB exhaust
Twin 1.5" HS4 carbs on a really good inlet manifold
An LCB exhaust with a 1.75" int dia exhaust system, RC40 or Maniflow
Re-curved distributor (or mappable one)
Lightened flywheel
All carefully assembled with good attention to detail

With this you might need close ratio SC gears to keep it on the cam which would also probably require a lower final drive ratio to keep 1st gear low enough for traffic driving. But it should give just over 100 bhp when set up correctly and the tank filled with super unleaded petrol.
Of course, a good turbo-charger or supercharger would also achieve this with a broader power and torque band, but probably for the same overall sort of cost. I built a turbo'ed 1310cc lump a while back with 7 psi max. boost and it gave about 112 bhp at around 5600 rpm and is a very smooth car to drive. I've always liked superchargers, although I've never ownd a Mini with one fitted. I did some work on a 1275 MG Midget with a Shorrock blower a while back and it is, apparently, excellent to drive with smooth power all the way and no 'turbo-lag', although I don't think lag is such a problem these days.

[minidream94]

the swift conversion (depending on whether you get a complete donor car, usually around £600 -£1000 for a decent donor) will reguire a modded subframe but there not too hard to make depending on yor welding skill. allspeed do the subframes for the engine aswell but there in the region of a good £650 for the frame and mounts. Another good thing with the engine conversion is you will be guarenteed alot more reliablility then the A series and ALOT moe torques http://www.allspeede...m/subframes.htm

All modern engines have atleast 5 speed boxes

I also am thinking on doing an engine conversion sometime with my estate as to be honest im not a big A series fan :S

[mattso118]

If you want to keep it as what might be called an 'original' Mini, i.e. with a BMC A-series engine, then the following would get you to 100 bhp N/A:

Bore to 1330 cc
A really good gas-flowed head with 37 mm inlet valves and 30.5 mm exhausts
A comp ratio of around 10.7 to 11:1
A 286 cam accurately timed in
LCB exhaust
Twin 1.5" HS4 carbs on a really good inlet manifold
An LCB exhaust with a 1.75" int dia exhaust system, RC40 or Maniflow
Re-curved distributor (or mappable one)
Lightened flywheel
All carefully assembled with good attention to detail

With this you might need close ratio SC gears to keep it on the cam which would also probably require a lower final drive ratio to keep 1st gear low enough for traffic driving. But it should give just over 100 bhp when set up correctly and the tank filled with super unleaded petrol.
Of course, a good turbo-charger or supercharger would also achieve this with a broader power and torque band, but probably for the same overall sort of cost. I built a turbo'ed 1310cc lump a while back with 7 psi max. boost and it gave about 112 bhp at around 5600 rpm and is a very smooth car to drive. I've always liked superchargers, although I've never ownd a Mini with one fitted. I did some work on a 1275 MG Midget with a Shorrock blower a while back and it is, apparently, excellent to drive with smooth power all the way and no 'turbo-lag', although I don't think lag is such a problem these days.

Thanks for the insightful reply.

That N/a build you suggest looks good. The thing that worries me about the forced induction route is the required bulkhead mods. I have read somewhere that you can usa a mirage manifold? That alleviate this but not sure how true that is, or if I have plucked that from nowhere.

What was the bottom end spec on the turbo you built, and will a forced induction motor producing that sort of power be more prone to mishaps than a similar power producing N/A?

Edited by mattso118, 29 December 2010 - 01:41 PM.

[Turbo Phil]

Yes the Mirage manifolds eliminate the need for a bulkhead box.
I'd say a Turbo engine with 100hp would be just as reliable as a 100hp NA, if not more so as a NA engine will need to be revved quite high to produce this kind of power, the Turbo motor on the other hand can produce this kind of power at much lower revs.

Edited by Turbo Phil, 29 December 2010 - 01:43 PM.

[Cooperman]

If you want to keep it as what might be called an 'original' Mini, i.e. with a BMC A-series engine, then the following would get you to 100 bhp N/A:

Bore to 1330 cc
A really good gas-flowed head with 37 mm inlet valves and 30.5 mm exhausts
A comp ratio of around 10.7 to 11:1
A 286 cam accurately timed in
LCB exhaust
Twin 1.5" HS4 carbs on a really good inlet manifold
An LCB exhaust with a 1.75" int dia exhaust system, RC40 or Maniflow
Re-curved distributor (or mappable one)
Lightened flywheel
All carefully assembled with good attention to detail

With this you might need close ratio SC gears to keep it on the cam which would also probably require a lower final drive ratio to keep 1st gear low enough for traffic driving. But it should give just over 100 bhp when set up correctly and the tank filled with super unleaded petrol.
Of course, a good turbo-charger or supercharger would also achieve this with a broader power and torque band, but probably for the same overall sort of cost. I built a turbo'ed 1310cc lump a while back with 7 psi max. boost and it gave about 112 bhp at around 5600 rpm and is a very smooth car to drive. I've always liked superchargers, although I've never ownd a Mini with one fitted. I did some work on a 1275 MG Midget with a Shorrock blower a while back and it is, apparently, excellent to drive with smooth power all the way and no 'turbo-lag', although I don't think lag is such a problem these days.

Thanks for the insightful reply.

That N/a build you suggest looks good. The thing that worries me about the forced induction route is the required bulkhead mods. I have read somewhere that you can mirage manifolds? That alleviate this but not sure how true that is, or if I have plucked that from nowhere.

What was the bottom end spec on the turbo you built and will a forced induction motor producing that sort of power be more prone to mishaps than a similar power producing N/A?

The bottom end on the turbo I built was standard. It was a bit of an unfortunate job which I was asked to sort out. The owner had paid something like £2000 for an 'expert' to build the turbo lump. When it was all finished the guy drove it down the road and after 4 miles, yes 4 miles, from new it 'blew up'. The engine builder said it was due to incorrect installation (oh, yeah!). I stripped it and all the pistons were broken. It turned out they were ordinary Hepolites and the geometric comp ratio 10.3:1. So at 7 psi boost, this gave just over 15:1 effective CR. Also the standard distributor was used, so when he accelerated, there was too much advance and monumental CR. Result, detonation and broken pistons. I fitted Omega pistons which are the correct ones for a turbo, opened out the combustion chambers to bring the CR to a sensible figure, fitted a specially curved custom-built distributor, had the turbo checked and calibrated at a max of 7 psi with a certificate confirming this and did a careful re-build. It gave 112 bhp at around 5600 and has proved reliable and driveable in traffic. In fact it's a great Mini now. The low revs at max power mean the bottom end is not too highly loaded.
I just felt so sorry for the owner as the original builder just didn't know how to build a forced-induction engine and had done no calculations at all and refused to refund any money as it was a 'cash-deal'.

[danrock101]

Belive it or not it's actually easier to make a 100bhp a-series than do a engine conversion and it will be reliable if built properly.
Coopermans spec will well clear you 100bhp
It depends what you're after, you would get away with a SW5 or 276 cam but if you're wanting 100bhp then 9 times out of 10 you're going to be wanting to go fast, therefor a 286 would be more fun.

my current a-series build I'm hoping for over 120bhp at the flywheel, then going to try and tweak it to aim for 135bhp or what ever the most I can get out of the MD 296 SP cam.

[mattso118]

Right thanks for all of the fantastic replies. This is what I love about owning a mini, evryone is so helpfull. Ive always been apprehensive about engine swaps and hear horror stories of massive costs. Plus I quite like those childsize looking a series lumps.

Driving fast had even crossed my mind. I stick vehemenstly to a sensible driving speed.....
I assume the cheapest way will be to source as many parts second hand and maybe get a good short engine with turbo pistons etc ?
Cooperman can you tell me what head that turbo build was running ?

Again, thanks everyone. I will now be daydreaming all night at work!

Edited by mattso118, 29 December 2010 - 01:55 PM.

[Cooperman]

Belive it or not it's actually easier to make a 100bhp a-series than do a engine conversion and it will be reliable if built properly.
Coopermans spec will well clear you 100bhp
It depends what you're after, you would get away with a SW5 or 276 cam but if you're wanting 100bhp then 9 times out of 10 you're going to be wanting to go fast, therefor a 286 would be more fun.

my current a-series build I'm hoping for over 120bhp at the flywheel, then going to try and tweak it to aim for 135bhp or what ever the most I can get out of the MD 296 SP cam.

Yes, the 296SP is a really good cam for high top-end power. I always work with Kent Cams as i've found them to do exactly 'what it says on the box'.
My 'S' has a 286, a 'demon' head done by a guy who worked for Longman, 11.2:1 CR, Karl Schmidt pistons, 1310 cc, twin H4's on a 'special' standard-looking manifold, an LCB, twin box RC40 at 1,75" ID, 1.5:1 roller-tip rockers, an Aldon 'Custom' distributor, light flywheel, etc, etc. It gives 117 bhp at 6400 rpm and mid-range torque is good, but there really is not a lot at the bottom end, made worse I believe by the 1.5 rockers which gaioned me only 2 bhp at over 5700 rpm.
Transmission is SC CR gears with SC drops (earplugs from Boots-the-Chemist), 3.9:1 FD, X-pin diff, comp drive shafts and central oil pick up.

[mattso118]

From this I'm assuming that a turbo engine is the way to produce good power cheaply, and reliably provided a strong bottom end setup is used. How much would people expect to pay from a reputable engine builder?

Thanks
Matt

[AVV IT]

If you want to keep it as what might be called an 'original' Mini, i.e. with a BMC A-series engine, then the following would get you to 100 bhp N/A:

Bore to 1330 cc
A really good gas-flowed head with 37 mm inlet valves and 30.5 mm exhausts
A comp ratio of around 10.7 to 11:1
A 286 cam accurately timed in
LCB exhaust
Twin 1.5" HS4 carbs on a really good inlet manifold
An LCB exhaust with a 1.75" int dia exhaust system, RC40 or Maniflow
Re-curved distributor (or mappable one)
Lightened flywheel
All carefully assembled with good attention to detail

Sorry to hijack this thread, but what sort of BHP could you expect from a 1275 or 1293 with these sort of mods, (without going as far as a 1330/1380 bore?).... Don't worry, I wont hold any body to any particular number quoted , I'm just looking at a rough ball park figure

[davejf]

If you want to keep it as what might be called an 'original' Mini, i.e. with a BMC A-series engine, then the following would get you to 100 bhp N/A:

Bore to 1330 cc
A really good gas-flowed head with 37 mm inlet valves and 30.5 mm exhausts
A comp ratio of around 10.7 to 11:1
A 286 cam accurately timed in
LCB exhaust
Twin 1.5" HS4 carbs on a really good inlet manifold
An LCB exhaust with a 1.75" int dia exhaust system, RC40 or Maniflow
Re-curved distributor (or mappable one)
Lightened flywheel
All carefully assembled with good attention to detail

Sorry to hijack this thread, but what sort of BHP could you expect from a 1275 or 1293 with these sort of mods, (without going as far as a 1330/1380 bore?).... Don't worry, I wont hold any body to any particular number quoted , I'm just looking at a rough ball park figure

My 1293 with;
MG Metro head, ported and polished
10.5:1 CR
286 timed in to 105 deg when new
Twin HS4's
Maniflow Stg 2 LCB and 1.75" twin box system
123 dizzy
standard verto flywheel (just changed it for pre verto lightened!!)
Bottom end professionally built, rest done by me.

When just run in and setup properly on an RR 4 years ago, it got 97bhp and the wheels.
It made 94bhp at the wheels last march, but after taking the whole lot apart a few weeks back and cleaning alot of rubbish out of the head, re-grinding the valves as compression was down by about 30psi and the fact the head gasket went last may i'm hoping it will be back to 97 ish again as it feels alot better to drive again and the amount of carbon build up on the valves must have had a big effect on flow!