BMC Mini race engine & the car it fits

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BMC Mini race engine & the car it fits

Post by SirYun » July 5th, 2006, 8:28 pm

hi all,

unlike most of you i don't drive a TC powered car ..

i drive a mini..well i drive a opel corsa now 'cause the mini is in parts due to the ever present progessive mass reduction system (aka rust). but it will rise again and then i will try to make it go really fast.

the mini in the pics is not mine but a car I work on from a friend who has even less time than me..and me ands a buddy have been doing the assembly of the car as well as the engine work.

i'm not an engineer (I'm a doc/MD) but study engine design and modification as a relief from work.

as a mini is powered by an engine that is asthmatic and full of design quirks ( 5 ports ..what the heck where they thinking) head modifications comprise of hacking away rather large amounts of cast iron in some parts. sadly theory does not really apply to 5 port heads and the big yellow vizard book is well over 20 years old now so as far as further progesssion goes i'm either building my own flow bench and start developing myself
or going 8 port ( BMW k 100 motorcycle heads can be made to fit, still it feels like cheating..but i have succumbed i have a 16v head on the shelf)

so far i have helped to build a few engines of which I did mostly head mods for most and fully drybuild and build one with a buddy. pictured below. 1310 cc swiftune racing sw5 road cam (255 isch timing), 1.5 ratio rockers, vernier adjustable belt cam drive system, stainless exhaust manifold,alloy inlet, CalverST rampipe and ITG filter.. oh and a 35.7x 29mm modified head i cut myself and gives a 10.3 CR.
judging from a very similar build with a less worked on head this one should produce around 90 to 95 BHP

the target that has to be beaten: this is the first dynoplot from a very similar, using a head that was made using one of my heads as a template but with less neurosis involved :wink:.


the power that time was 89.5 BHP (din) at the crank (computed by coasting in gear) and 110 NM max but 90% is available at 1800 rpm. a few thousand km later later the torque had gone up to 125NM and power was also up a smidgeon to 90.1HP.

lower trace was before the fueling was sorted. gains after the RR session where very noticable. the weird power spike only showed up once.. during this dyno pull the engine suddenly sounded just that bit happier. never figured out what happened.

we where pretty chuffed and the flat topped power curve and the very flat torque curve must mean that the head was pretty decent..

my own engine will have pretty much the same specs but is 1330cc and has a Graham Russel/Keith Calver RE13 profile cam (280ish duration). i have seen 120+ BHP claimed but as dyno's vary wildly and the one I use is manned by a guy who does not give a hoot about the absolute figure but the difference between the power you come in with and drive away with, i would be ultra happy with 110 HP.. which would equate to about 5.6kg per HP


after 30 km or running very well the timing belt failed stripping off a lot of teeth (I hate when this happens..) stripdown of the engine revealed NOT ONE CLUE why this happend.

I can only think that the belt was a dud..

All in all the failure cost one cam, all pushrods, all valves and new bearings.

the rebuild is allmost down and includes a gearbox rebuild for cleaning purposes and minor touching up of the valveseats as well a fitting a new Russell/Calver RE13 profile cam. a friend for which I modified a head just started his engine up fitted with one of these and even with the mixture pretty much unsorted it is very nippy..

Image [/img] :cry:
unmodified chamber and the weakspot of the a series engine ..leaky gasket between no2 and 3.
gasket..-leaky.jpg (66.35 KiB) Viewed 13557 times
this induction kit is supposed to give about 4 HP gain over a K&N cone filter.
Filterkit-single001.jpg (60.06 KiB) Viewed 13508 times
finished head
head-1310-peter.jpg (94.45 KiB) Viewed 12753 times
the car..basicly rebuild using LOTS of new parts
Peter-mini.jpg (203.23 KiB) Viewed 12988 times
ze mini.jpg
my own mini.. it is one piece now waiting for paint..and waiting..and waiting
ze mini.jpg (51.5 KiB) Viewed 12704 times
Last edited by SirYun on October 11th, 2007, 11:56 am, edited 7 times in total.
Joost M. Riphagen

Guy Croft
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Post by Guy Croft » July 6th, 2006, 8:39 am

Hello Joost,

that is a fun post, and what a relief to see a non Fiat! People thingk that's all I do here! But then most people don't come here because they think Lincoln is 'too far'.
Some component names there I recognise, Swiftune eg., and I love Minis as it happens, they seem so tiny and tough these days.
Well, that said I don't love cast iron heads..

I did a total bare-metal ground-up restoration on a Mini Cooper 998 1982-84 when I was still in the Army, good learning curve! It is probably still going, reg HDL998E


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Joined: June 22nd, 2006, 9:42 pm
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Post by SirYun » July 16th, 2006, 2:32 pm

GC language control is pretty stern (no problems with that), so i edited some substandard english out.

Here are some picstures of what is inside (the pictures of the actual head where lost so these are from similar projects).

The chamber of my own head which is pretty much the same basic shape but with a bit of deshrouding and a minimaly reduced squish area in the plug region.

This head is on a buddies engine now as his head needs a weld repair (during porting I might have hit a casting flaw or waterjacket..there should have been over 6mm of cast iron there :evil: ) which is a bit of a hassle to get done).



after rough porting :


inlets.. it looks a bit messy but that is mostly due to the picture.
the cast iron is so much more resilient to reshaping than aluminium. Alas aluminum 5 port heads are priced well outside budget.


center exhaust port. After some major surgery on the guide boss. I left more metal in than is common.

Unlike normal i did not fully grind out the guide boss because I wanted to keep the exhaust as small as possible. That part of the port sees little flow anyway and extra metal helps to keep the guide cool and my very very rudimetary testing shows less tubulence behind the guide and the flow is now much more across and on top (which could be good or bad.. hard to tell we'll see what it does on a dyno)

oh btw the final finish is a bit better than this.

thank you

Joost M. Riphagen

Guy Croft
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Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK

Post by Guy Croft » July 17th, 2006, 6:12 am

Some good work there Joost, thank you for sharing it with us. Yes, ports never photograph very well! Show us the tools you used if you get time, DIY'ers are always interested in that.


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porting tools

Post by SirYun » July 18th, 2006, 5:30 pm

thanx Guy for the kind words,

the tools i used are:

dremel clone (15 quid) with flex shaft. I would like to get a proper 6mm flex shaft but they are just rather expensive. It's not a Suhner so you can't lean into it as it will stall and burn out.

3/4 inch stones, tungsten carbide burr. flame shape with a very fine cut and small chip breakers. for cast iron this will cut well when the right (quite a lot) amount of pressure is applied. it will feel like trying to use a knife on very cold butter.

final finishing is a 80 grit roll for the inlets, 120 grit for the exhausts.

chambers are cut using a burr and the bottom is ground using a fine flat stone followed by sanding disks 60/80 grit which is suprisingly effective , when new, in removing metal. to match profiles i use a bit of plasticine clay to make small molds. for instance short side radii. but thin soldering wire is handy too, to compare shapes.

furthermore sanding cloth/tape for smoothing the dividers. the siamese port uses only one valve at a time so the divider needs to be rounded. very hard to get too. but treading the abrasive tape though both ports gets a nice radius.

marker pen. to avoid merryly cutting away i try to mark offending areas so that i get the shape I aim for, not one dictated by the shape of the stone or tool i use.

for the seats i use Neway cutters using 20/45/70 angles. slow but nicely controlable

so yes it can be done using a dremel/clone but the supplies are way overpriced.

UPDATE: I have since bought a proper grinder. It is rather large and is rated at 740 watts and has electronic variable rpm wich means it has LOTS of torque even at low RPM.
As per advice from a lot of porters who work with american cast iron i use it at the slowest speed (13.000). hold the end fixed against the shoulder and FIRMLY hold on while applying minimum of pressure and concentrating on guiding the burr along the intended path. Once you get the hang of it it is a tad less intimidating

I still use a dremel clone for detail work near the seats and in really hard to reach places.

UPDATE: for leveling chambers a ROUTER is ideal.. I borrowed a 1300w version with 1/10 mm adjustment from a friend and it is very effective in working onm the floor (this is of course a bit of an oddball engine wich uses a chamber which a ideal of this approach..even with newly cut seats.. no fear of damaging them. As for modifying chambers.. the carbide burr shown below in the same machine is very effective and reaaly smooth..)

for the short side radius i found of that a long (70cm) and narrow piece of cloth backed abrasive threaded through the port and pulled againmst the SSR is very effective in getting the right profile after initial coarse grinding.

for CC ing a chamber I use a slightly different approach.

I set up the head dead level. then use a miniscule amount of vaselin along the edge of the chamber. I use alcohol as fluid (no rust) and fill up using a Lab style hand burette with a balloon while looking along the surface . I compared volumes for the method using a plexi plate and for all practical purposes the volumes are within a .2cc and this is much easier and does not have the trouble with trapped bubbles
various burrs. the coarse ones (top 2) do not work well with cast iron nor aluminium.

that could be due to the underpowered drive , but it chatters too much.

the lower two do a good job.

i prefer the finer one as it gives better control
IMG_0026.JPG (143.17 KiB) Viewed 13789 times
burr.. it will make you go burr when it bites.
Burr.jpg (180.93 KiB) Viewed 12742 times
ccing the easy way
CC’‚­ng-the-easy-way.jpg (76.62 KiB) Viewed 12802 times
a large grinder..
Protool.jpg (190.8 KiB) Viewed 12746 times
Joost M. Riphagen

Posts: 81
Joined: June 22nd, 2006, 9:42 pm
Location: Maastricht, the Netherlands & Zyfflich, Germany


Post by SirYun » October 10th, 2007, 11:27 pm

some pics from the rebuild.

The gearbox (which is build into the sump) has been
fully stripped as well to make shure no metal was left behind.Hence the empty casing
(during the rebuild it turned out that the rod bolts where very effectively hobbed by the cam.
The hardening of the cam is good as it had only minimal damage even when half of four of the rodbolts was missing) .
the belt drive with shredded rubber
Belt-drive1s.jpg (213.9 KiB) Viewed 12728 times
just timed in (for all i tried i just could not get it spot on..still 0.25 degree off, but the chain stretch will add at least 0.5 degrees) using a Kent Cams chain drive untill the supplier of the belt drive sorts the belt issue out
rebuild.jpg (243.94 KiB) Viewed 12697 times
note bent valve
bent-exhaust-valve.jpg (166.57 KiB) Viewed 12705 times
valve to piston contact, close inspection revealed no further damage. the pushrods had served as a crumple zone during impact limiting damages tothe piston to a very light marking and
contact.jpg (169 KiB) Viewed 12714 times
belt.. minus important bits
stripped-belt-s.jpg (103.86 KiB) Viewed 12713 times
decent seats
interior.jpg (152.08 KiB) Viewed 12652 times
A full Safety Devices bolt in cage.
anti-crumple-thingies.jpg (150.46 KiB) Viewed 12659 times
the bent pushrods
pushrods.jpg (68.93 KiB) Viewed 12644 times
normaly there is no problem..but the cam can touch the connecting rod bolt if the cam drive is lost.
boink!.jpg (66.53 KiB) Viewed 12646 times
Joost M. Riphagen

Posts: 81
Joined: June 22nd, 2006, 9:42 pm
Location: Maastricht, the Netherlands & Zyfflich, Germany

Re: BMC Mini race engine & the car it fits

Post by SirYun » February 13th, 2008, 12:47 am

the first results.. not quite what i hoped for but as this is a bit a new cam (i had one of the first of these units..then it lingered on the shelf for 2 years) and build some teething problems where to be expected.

the fuelling was/is a huge headache. after 4500 rpm the mix goes lean regardless of the needle profile.

i had contact with the cam designer and i turns out the ignition advance is extremely different from what i had expected: nearly fixed: 7 degrees in at 3000 rpm. ergo the ignition is too advanced as it is

the fuel pump (a new mechanical unit..normally good for feeding about 95-100 bhp) seems to have a problem delivering enough fuel as well.

after a 200km drive on the motorway (wearing Peltor Optime II ear defenders..the induction system is a tad long and as a result a new plate still has to be made to close the rather large hole in the firewall).

Interestingly with a bit of choke the engine is reasonably quiet but when unthrottling the induction tract is VERY noisy and gives a very distinctive slightly metallic barking noise..and quite a stutter when the acellerator is returned to a lower level

as i had such a long drive i could investigate this behaviour, the sound reminds me quite a bit off a pulse jet engine.

using full choke makes a lot of the noise dissapears and the engine picks up and the noise stays down even when the choke is returned to normal.

i suspect it is a combination of heavy pulsing in the intake tract, too much ignition timing and a relatively lean mix. first point of action is to ensure the fuel flow is sufficient.

first dyno results...fueling is odd and a 200 km drive showed huge intake resonance issues..interesting
dyno_080208-re13ot.jpg (78.37 KiB) Viewed 12026 times
Joost M. Riphagen

Posts: 81
Joined: June 22nd, 2006, 9:42 pm
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Re: BMC Mini race engine & the car it fits

Post by SirYun » May 15th, 2008, 7:35 am

I have spend a few thousand km driving and tweaking.

pretty much convinced that the fuel system and fueling is in the ballpark. engine is extremely picky with regards to ignition timing. I used a fixed advance ditributor and that does function quite well actualy (for a competition car this would work fine as no time is spend under 3K anyway and the advance should be fully in by then )

i have opted for a mappable ignition in the form of a megajolt lite jr. (cost is about the same as having the mechnical distibutor altered one time) and Ford Motorcraft EDIS4 module.

installation is not trivial i must say and i have so far spend two full days fitting a crank sensor and sorting out the wiring ( i hate electics in cars..a lot)
IMG_0937.jpg (125.41 KiB) Viewed 11674 times
MJLt-Jr-needed-palaver-.jpg (107.64 KiB) Viewed 11675 times
rvs safetywire. every thing double locked. (136.57 KiB) Viewed 11674 times
Joost M. Riphagen

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