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Supercharged Single Seater
Having had so much fun with our other single seater special at the Simola Hillclimb in Knysna, South Africa, we decided to build another weapon for attacking the hill....

Rest assured that no living Sevens were harmed in the process, 95% of the stuff came out of boxes Dad collected in the '60's. Recently we were able to purchase a job lot of bits from someone who had plans to build an Ulsteroid and amongst them was a new Phoenix crank, re-metalled rods, Honda 57.7mm pistons and a set of close ratio gears for a 4 speed box. As we already have a '33 Type "65" as well as a '26 Chummy & '28 Top Hat Type R plus sundry other marques we have the open 2 seater thing covered already, so the Phoenix crank gave us the 'unburstable' bottom end to take the little supercharger Dad bought more than 40 years ago. A Rootes type triple lobe MAG blower made by Motosaccoche in Switzerland circa 1952, originally for a VW 1100 or 1200 flat 4.

With a SWB chassis that's been hanging on the wall for 40 years, we set to work - first straighten and weld up the cracks in the chassis, then look at the internet for inspiration. Both of us were really taken with the shape of the Kaye Petre replica, so the basic idea was formed and we decided to go with an offset driveline. One of the  spare diffs was modified and the half shafts modded to suit. The basic offset of the engine was decided on and I welded up new mounts. We decided to drive the little MAG Blower off the nose of the crank using a Yamaha 650 shaft drive with universal - the jury is still out on this idea...

A suitable front axle was turned upside down and new spring mounts welded on, the leaf spring was reset to suit. I fabricated a suitable steel mounting bracket for the blower and the front shock absorbers. This plate is sandwiched between the spring and the chassis for stability and there is a brace back from the top of the blower to the chassis. New radius arms were fabricated along with all their fixing points and trimmed sections of angle iron with a suitable tapered hole were welded to the chassis to take the tie rod ends at the end of the new radius arms.

Basic chassis and driveline sorted, we turned out attention to the body frame. various spare rims yielded suitable jigs for body hoops, from 21" Model A Ford , 19", 17", 16" A7 wheels, 15" Alfa Giulietta & 13" Opel formed the basis for the slighly tapering tubular steel frame. Superleggera Coachwork in the making.

From here is was a case of bending duplicate pipes to suit the left and right sides of the frame as closely as possible. With this done I approached someone about wheeling out a body. This was a little disappointing as for the (rather high) agreed price, I was supposed to get a body completed ready for paint, instead I got a body half roughed out with no side panels that still needed a lot of work and he now wanted a lot more money Long story short, we agreed to disagree and went our separate ways. Needless to say my aluminium working skills are rapidly's just welding the darn stuff....

So this is where we are with the body thus far, I'll post some detailed mechanical pictures later. 80% completed and 80% still to go....


Port Elizabeth
Sunny South Africa


Hmmm I notice that my careful re-orienting of all the pictures in my files came to nothing and it certainly didn't load them in the sequence I intended.... sorry about that, they were supposed to be in a chronological build sequence.

More of the body in progress....


A few more, we have developed our own Bowdenex conversion off the one that was fitted to our Type "65". Basically copying the fittings but using modern cable inners and outers and it's made a huge difference to our other Green special. You can see the front axle details a bit here, similar to our green car which was converted into a single seater circa 1949. There is at least a bit of Alfa here as the extensions off the axle to hold the spring shackles are two litre Alfa conrod little ends, the Green Job uses parts of a second front axle, but we didn't want to cut up another axle.

We've raided Dad's 60+ year old stash of bits for all the brake fittings and things like the hand brake lever etc. The steering box, steering wheel and the brake pedal actually come from the Green Job, when dad rebuilt it there was a box of bits he couldn't find and so he raided his stash. Several years later that box emerged when he moved closer to me, so the new Job has a physical connection with the Green Job. Also many years ago an Uncle had a single seater out here called the Consul Special, that ended up getting crunched and was scrapped, but Dad saved the throttle pedal, so that's going in there as well.

My wife Lucie in the Green Job - see the other thread about re-metalling the rods.....sigh Angel


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That looks like hours of work which I hope will be followed by hours of fun. I'm most impressed, crack on!
Love the way the blower is stuck out front, lovely job.

Not sure about the upside down front axle.

But it does stick to the ceiling well though Big Grin

Yes Tony I agree about the axle, I would have thought replicating a Duck type set up would have been a good way to go, but maybe Grieg has it all worked out, it is certainly novel and unless people experiment with these things we won't know if they work. Looking good though Grieg I will watch this thread with interest, you could use aircraft rivets instead of welding the Aluminium panels together, just a thought.
Black Art Enthusiast
Apologies for the pictures that are sideways and of course the Australian view of Lucie in the Green Job.....

I'll see if I can correct that, if not perhaps one of the moderators would be kind enough to do so ?

Agree on the Duck type axle, however there were quite a few of these little single seaters built out here and both our green one and the sister car, the Blue Job have this upside down front axle and both were built circa 1949-1952, so we replicated it.

In retrospect I'd probably have gone with the Duck type given that we didn't make Simola last year due to the delay in the body and I shelved it from May to December. But I have lots of other things to finish first..... It's taken about 5 months cumulatively to get this far, so another 3 months should see us ready for Classic Friday at Simola on the 4th May.

I'll post more pictures later

It is unusual to pair consecutive exhausts. Is there a basis? Possibly of less consequence with a blown engine.
Were traditonal supercharger drives cushioned in any way? Especialaly following a hookes joint running at an angle.
(31-01-2018, 05:44 AM)Greig Smith Wrote: Apologies for the pictures that are sideways and of course the Australian view of Lucie in the Green Job.....

I'll see if I can correct that, if not perhaps one of the moderators would be kind enough to do so ?

Agree on the Duck type axle, however there were quite a few of these little single seaters built out here and both our green one and the sister car, the Blue Job have this upside down front axle and both were built circa 1949-1952, so we replicated it.

In retrospect I'd probably have gone with the Duck type given that we didn't make Simola last year due to the delay in the body and I shelved it from May to December. But I have lots of other things to finish first..... It's taken about 5 months cumulatively to get this far, so another 3 months should see us ready for Classic Friday at Simola on the 4th May.

I'll post more pictures later


Hi Greig, as a metal shaper myself, I can really appreciate the quality of the panels that you've formed. A great bit of work; well done. You've done a fantastic job of the frame which underpin a really beautiful body.

Regards John
Thanks John and everyone else for the encouragement, it’s been a lot of fun to get to this point, I’ve been fortunate to grow up with a Father who encouraged me to join in his hobby and I actually learned how to drive on a 1930 A7 in 1979 aged 9…

Bob - the exhaust was modelled on the sister car to our Green Job, in retrospect consecutive firing order may not be the ideal exhaust manifold configuration, but I like the way it came out, I think it looks rather good and I’ll see how it performs when we fire it up, I’m not after any land speed records here, but I would like to trounce that 1100cc Riley TT Sprite up the hill…. The other stiff competition in my Pre War class is a very nice Type 35B, hence me targeting the Riley… Tongue

Something I should have done earlier was to give credit to Steven Murphy of SBM Engineering, a supremely talented friend who has managed to turn my ideas into reality with amazing skill and attention to detail. Steven cut and welded the offset diff & side shafts, he also cut and welded the spring hangars onto the front axle which he made from cut down Alfa Romeo con rod little ends. He also manufactured the shaft drive for the supercharger. It’s driven directly off the nose of the crank via a 650cc Yamaha motorcycle shaft drive with a universal – this was entirely Steven’s idea and he not only sourced the shaft, but fabricated the entire drive. The blower is mounted on a purpose made steel plate, welded and gusseted, sandwiched between the nose of the chassis and the front spring & also carries the mounting points for the big friction disc ends of the A7 shocks. It required some quite precision measurements to ensure that the blower and the drive would all fit together. Steven fabricated a special coupler with a threaded end that screws into the nose of the Phoenix crank, the Yamaha universal joint is bolted to this and then it angles forward to the blower in the nose. He also fabricated a special pair of circular plates at the blower end. These are located via a spigot in the centre and the drive is taken via 4 high tensile shoulder bolts. A 1mm tolerance was allowed and is taken up by 4 little ‘O’ rings to stop things rattling, so we should be good to go unless the whole caboodle grows by several inches in flight like Concorde, in which case some rapid re-engineering will be called for. Steven also took 2.5 lbs off the flywheel and pressure plate. New linings were fitted and double clutch springs. This is what the competition handbook recommended and it worked a treat in the Green Job.

A word on the actual supercharger, it’s an MAG triple lobe Rootes type blower made by Motosaccoche in Switzerland circa 1952. Originally sold as a kit for flat 4 VW 1100 and 1200cc Beetles which would bump them up from 24 horsepower to 42 horsepower. We are driving it at crank speed which according to folks much brighter than me will give between 5 & 6lbs boost which should bump the horsepower up from around 29 Bhp at normally aspirated to north of 45 Bhp, bearing in mind that these are small English ponies. Dad took the blower into a turbo charger shop and all they succeeded in doing was to strip it and lose all the special fasteners. Enter Steven to the rescue and he actually machined up new thin 18mm nuts with a metric fine thread for us – even more impressive is when you consider that 18mm metric fine taps are not readily available anywhere and we looked hard… Yes he worked out how to cut new fine threads inside an 18mm nut using an 8mm metric fine tap…. Incredible chap !!

A large source of inspiration and information are the 750 bulletins and the compilation of all the technical info which is basically the competition handbook, from here came the Mike Forrest double oiler conversion and the over-bore on the oil pump. Also the increase in block to crank case stud size to 3/8ths or in our case 10mm as we’re a metric country and finding high tensile Imperial bolts is not easy, so 10mm HT cap screws were machined down to bolt the block down from the underside. To do this involved drilling through the crank case where possible and then tapping to 10mm. With this done we made up a surfacing jig consisting of a router blade which mounted into a threaded mandrel to locate it centrally, (Dad machined this up on his Myford lathe in a jiffy), this was then threaded into the block, the router bit was installed from underneath and I clamped the shaft into my battery drill and I ran it at high speed in reverse to effectively shave the underside of the block to provide a suitable flat seating surface for the cap screw heads. Worked a treat. For fixing nuts we decided that ordinary nuts just didn’t look the part, plus the cap screws had a reasonable thread length, so Dad machined down some 10mm thread couplers – basically long nuts for joining threaded rod, so we now effectively have a double height nut securing the block, plus two additional hold down studs at either end of the valve chest, these are threaded into the block as well as the crank case. In all instances the holes for these little extra hold downs don’t actually penetrate the block so no chance of an oil leak. The front hold down stud replaces the square camshaft bush locating bolt.

The Doug Woodrow Manual has been absolutely invaluable in assembling the 4 speed box, the pile of bits we bought came with a new set of close ratio gears, but little else and so raiding the parts boxes produced 3 passable selector forks and a steel selector plate, which turned out to be incorrect, so another one was scratched out of another box. The forks were mismatched as was the selector plate and it took quite a few goes at them to fiddle and file and fettle things to a point where the gear lever would select the cogs and then it was up and down the adjusters until all the gears selected cleanly – without the Woodrow book, I’d have been up the creek with a leaky canoe and no paddle. On the plus side we can now build 4 speed boxes blindfolded. I’ve had the box on and off plenty times…… what was Sir Herbert thinking with that silly oversized tooth on the driven plate and the matching groove on the inside of the input shaft ???

The steering box is a Lavine steering gear which turns on a set of seriously long needle rollers; it has a nice feel to it. This is actually the original box from the Green Job, when Dad restored it, (resurrected it from the dead is more like it), he couldn’t find this box, so used the spare one he had found. Several years later a move closer to me unearthed the original box with the rusted out portion of the wheel. When building this car I knew I wanted that steering wheel – a look at the pic above of the dashboard mock-up will show you why. Two more items which have found their way into the build are the original drilled brake pedal from the Green Job and the throttle pedal from a late Uncle’s written off single seater “Consul Special”. Dad saved the pedal for posterity and 50+ years later it’s back in a race car again – I like that !!

I repaired and strengthened the SWB chassis; it was a banana shape with notable cracks through the engine mounting holes extending down the sides and in one instance right through the lip at the bottom. There were several additional holes drilled into the chassis as well… the poor donor car must have been owned by a rather rotund chap with an electric drill and an itchy trigger finger. I used a 38x38x2mm length of steel square tubing which I cut to length to fit into the channel from the edge of the nose piece to just where the additional lip starts on the chassis. The chassis had been sand blasted and primered, so I drilled the damaged mounting holes larger to clean out the edges, I cut all the cracks open with a thin angle grinder disc. I then sprayed a very thick coat of Wurth Zinc rich primer into the channel and also onto 3 sides of a length of the tubing and basically slid and hammered it into the underside of the chassis while the Zinc primer was still wet. I used clamps and pieces of wood to keep it in position which when tightened up, totally removed the banana curve of the chassis. Once the square tube was fully seated home; I welded it to the underside of the lip with a large MIG welder in 1 inch lengths skipping an inch between welds. I also welded close the engine mounting holes by rosette welding them to the top of the square tube underneath, also all the cracks by welding through them to the tube below, ditto the old steering box holes and the additional holes. As I was making new offset engine mounts and fitting the Lavine steering box this wasn’t an issue.

The block was ported, I spent quite a lot of time here making sure that I flowed it as best I could; the picture is part way through the process. I also opened up and radiused the oil feed holes in the new Phoenix crank quite a bit. I also weighed and balanced the rods by grinding and filing the flashing under the cap to get all the rods to weight the same. I shaved the underside of the pistons to equalise the weight although there was virtually nothing between them.

Talking of pistons, these are 57.7mm Honda pistons with the block bored to suit, reading in the old forum they are just over 1mm shorter than the originals…… research on blown motors suggests that a slightly lower compression ratio is better for the burn under forced induction. Does anyone on this forum have experience with these 57.7mm Honda pistons  ?? As they are just under the top of the block at TDC, the only way to bump up the compression ratio is to shave the top of the block and then re-cut the valve seats. I consider the underside of the block too thin to even consider shaving and then there are those pockets for the cam follower guides……  I’d hate to put the whole thing together only to pull it all down again to shave the block – Input on this with the blower feeding them would be appreciated as this whole blower thing is a very new minefield for all of us out here in the Colonies.

Well I’ve rambled enough, here are some pictures

Port Elizabeth
Sunny South Africa

More oily bits

Some more body progress, following up on the collective wisdom and figuring that aluminium isn't that hard to whack out of shape, I filed a louvre jig out of some hard wood pieces - these were supposed to be a trial run before actually going the whole hog and filing them out of steel - turns out that the few test pieces I did looked so nice that I went ahead & did both sides of the body. The gap behind the steering arm on the RHS is for a bulge to accommodate the throttle as things are tight down there, this is the next bit to be made

I measured the thickness of the wood, added 1mm to it for the thickness of the steel cutting blade on my small grinder - the Dremel took ages and ate the heavy duty cutting discs at a ferocious rate, so I did a test run on some scrap with the small grinder and walloped it hard with the jig. I think the secret here was to leave a 10mm flat section at the back of the jig, so that while the actual louvre was being shaped, this flat bit held the rest of the panel firmly and helped keep the panel straight & flat.

De-burring with a small half round file and some emery cloth, a few light taps with a nice Sykes Pickavant panel hammer and job done. Oh yes, we added a reinforcing piece under the top lip to keep the strength where I had to cut away the lip to accommodate the exhaust manifold. Some soft aluminium rivets make it look the part.

This is Mum and me in early 1970 in the '30 Special I learned to drive in 9 years later and one of Lucie in the '57 Spider after a quick trip to Knysna where the Hillclimb will be held - visiting other Giulietta friends on holiday from London. The Plus 8 belongs to another friend. (I needed 2 more pictures to get up to the allowable 8 in one post...)


Another hard day in Africa

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.jpg   Tapping the crank case to 10mm with a Jig.JPG (Size: 215.43 KB / Downloads: 1,113)
.jpg   seating the 10mm cap screws from underneath.JPG (Size: 90.82 KB / Downloads: 1,108)
.jpg   Close up 3.JPG (Size: 57.96 KB / Downloads: 1,102)
.jpg   Seat cutting fixture.JPG (Size: 109.27 KB / Downloads: 1,106)
.jpg   Rod Smith machining cap screws.JPG (Size: 54.34 KB / Downloads: 1,102)
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.jpg   double oiler jets.JPG (Size: 43.14 KB / Downloads: 1,093)
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.jpg   Modified cap screws 1.JPG (Size: 114.71 KB / Downloads: 1,096)
.jpg   Double oiler pipe.JPG (Size: 69.77 KB / Downloads: 1,086)
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Greig I would suggest that with your motor being blown the reduction in compression ratio is not an issue, however the loss of squish may have some impact on overall performance.
Black Art Enthusiast
Seven owners over here have been using the Honda pistons for the last 20 years or so,and I believe they are as good or better than anything else available.Problem now is Honda have stopped manufacturing them in oversizes.
I know of one car,blown, that has been raced and hillclimbed certainly for 15 years.My own trials car we uprated it to blown and the engine had already been together 9 years on Honda pistons and ran well.
I wouldn't worry about the slightly lower comp running supercharged,old theory was it raised the effective comp by 2 ratios,ie 7 to 9:1.
Nice work on the car.

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