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30 Years of Modifications and it's Finished (Supercharged 4.3, 440hp)

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    30 Years of Modifications and it's Finished (Supercharged 4.3, 440hp)

    This is the history of my 1973 Stag which has evolved many times in 30 years of ownership and inevitable modifications due to an owner that cannot stop fiddling, but I think I'm finally done!
    I had always wanted a Stag after travelling in my Uncles in the early 70's as a young boy, that V8 sound and performance was just amazing back then when most families like mine were driving around in Austin Maxi's and Allegros!
    So In 1992 I bought a totally standard White Mk1/2 from a friend for my wife to use as her daily driver and various holidays including a trip to Nice via Switzerland over the Alps. The car was an Auto so did rev fairly high on the Autoroutes but was a pleasure to drive.

    After a few years the fiddling bug was calling and being in my mid 20's a plan was hatched to deliver more power in an otherwise standard looking car (no bonnet bulge) by fitting a Rover based petrol injected engine and manual gearbox. At the time vey few had done this, so a lot of research was needed. In my search someone put me in contact with David Carter in Sussex who was going down a similar direction.
    The Stag Engine was sold to an English couple living in Tenerife, palletised and dispatched from my work in Guildford and then set about purchasing an old Rover SD1 3500 Vitesse and stripped all the necessary parts, looms, ECU, trip computer, Cruise control and the Engine went to TVR for an an upgrade to 4.3 with gas flowed head, enlarged valves and throttle, fully ported inlet performance camshaft, whilst Mark Adams (a local specialist on the Rover ECU) made an adjustable ECU.
    To make use of the SD1 radiator and allow more room the engine bay was adapted to make this fit, moving it further forward than the standard radiator. The Battery was moved to the Hood stowage area.

    A BMW differential was also recommended by Brighton Stag Specialist and he made a cradle using the existing Stag subframe, which turned out to be horrible with all sorts of vibration and mounting issues.
    The front brakes were upgraded to Jaguar 4 pots and vented discs.
    Anyway the Engine gave 296 Hp and the car looked standard, but due to the relatively soft springs and lack of Anti squat in the rear suspension the car bonnet would rise like a speedboat under acceleration
    which was dangerous! Stiffer springs helped but this compromised the ride so something had to be done!

    With The BMW differential in mind a plentiful supplies of BMW parts David Carter and scoured the local scrap yards and found the BMW E30 subframe appeared to be about the right size to fit the Stag, in theory allowing the brakes and suspension. We bought two sets and to see how it might fit but the track was still wider than the Stag which would mean the hubs on the rear wheel would sick out relative to the rim, so knowing the BMW parts are very interchangeable the track can be narrowed by using BMW 5 series wheel bearings and Hubs and shortened 5 series (E28) driveshafts which have the benefit of two CV joints instead of splines. This also meant using Discs from 5 series and calipers with a cable connection for the handbrake (there is no room for the drum).
    We added fixing points to the chassis, measured it all up with plum bobs and tape measures and when the wheel alignment was checked it was better than most production cars at the time..very lucky!

    The car still looked great, if a little tatty around the edges so in 1997 David Carter and friend Johnathon Finnis encouraged me to do a full body restoration with a change of colour to MG pearlescent Tahiti Blue.

    I've run out of space for the next section covering the restoration and final spec on the car, so this will follow in Part 2
    1972 Stag 4.3 Serpentine RV8 Injection, Rotrex SuperCharger, ZF4HP24 Auto, BMW 2.65 LSD

    Part 2

    The Stag was stripped which as usual exposed some poor previous repairs and rust, but structurally the car was solid. Martin Thaddeus, currently working for David did the panel work and made in metal a custom front spoiler to cover the previous very ugly SD1 radiator enclosure I had made .This was later featured in Martins body restoration book!
    Other body modifications included fog lamps in the front spoiler and Twin Exhausts recessed into the boot floor, whilst the Stag very faded rear lights were changed for Fiat Coupe round ones.New Stag units were not made at the time.

    Recessed Exhausts
    Front Spoiler with fog lights
    The car went on to win the best modified at National day in 1999 and sat garaged for 8 years after children arrived, when finally it came out to head to Le Mans which was great. but led me down the tinkering path again towards Supercharging the RV8.
    Initially I thought an Eaton style charger would be the easiest route because it fits in the engine V so I found one including water/water intercoolers on Ebay, but my fabrication skills were beaten with the inlet manifold.

    2008-03-16 090.JPG

    This led me toward using a Rotrex charger which is really like a turbo charger but driven by a belt instead of the exhaust. This would mean converting the engine from V belt pulleys to the later serpentine belt but again due to the height restrictions in the Stag engine bay I read it wouldn't fit, however after making a backing plate allowing assembly to be lowered it just clears the standard bonnet together as well as the Rotrex (on the far right, like a large alternator)

    20170422_105047 (2).jpg
    The Supercharger is fed cold air from an airbox behind the headlights and blows the air down to a huge Intercooler sat in front of the radiator, then comes out on the drivers side and into the inlet plenum chamber. The Rotrex needs its own oil cooler and that sits next to the engine oil cooler under the car (near the rollbar). The fuel and ignition are all controlled by an ECU (no distributor) an it runs up to around 12psi boost , giving 440 hp and 440lbsft torque on a very docile tractable engine (we saw 500hp on the Dyno but this was dialled back to preserve the engine)
    The standard TVR clutch would slip over 4000rpm so a dual plate version for uprated American V8's was fitted and all was well except for horrible slow gearchange on the Rover sourced gearbox.

    That lead me to what I hope was the final phase of modifications which I'll go into on part 3 if you're still awake!
    Attached Files
    1972 Stag 4.3 Serpentine RV8 Injection, Rotrex SuperCharger, ZF4HP24 Auto, BMW 2.65 LSD


      Part 3

      I have come to the conclusion that for the majority of my driving I enjoy a car that rides and corners smoothly, isn't too noisy, but has the ability when you want t to press on quickly with some excitement and I'm now able to do that.
      Through all the modifications I did the R380 gearbox was always slow to change, first gear was unusable and didn't really suit the character of my Stag.
      This led me to change back to an Automatic last year, the 4 speed ZF4 other Stag users are enjoying, to but due to the power of my engine I've had a hybrid strengthened version based on the ZF4HP24 made that also used the largest Range Rover 4.6 torque converter to reduce slip. Couple this with my 2.65 ratio Limited Slip differential and 80mph is just over 2000 Rpm in 4th lockup which makes a really nice cruise and it's good for economy.


      The rear suspension uses BMW Z4 springs and 320 dampers which are probably softer than the standard Stag, but a rear roll bar is fitted , the front runs Chris Witor variable rate red springs with adjustable Koni dampers together with an uprated 1" rollbar. I added some extra caster and Camber with adjustable trailing and swing arms which I found really helps with stability and the way it enters corners.
      Tyres are 225/50/15. I have alloy front hubs with stronger Stub axles (these were pre-production Monarch) and also incorporate larger wheel bearings and Lancia vented discs with BMW 7 series callipers.

      Inside the car I have digital temperature controllers for Transmission oil and engine temperature with twin fans on the engine. Surprisingly even though the radiator is almost completely covered by a 100mm thick intercooler the radiator temperature rarely goes over 70 degrees!

      So in summary the car has a split personality, it's very comfortable and happy to cruise with a supple ride as it was intended, but if you want to press on 60mph comes up in just over 3 seconds!

      I hope this hasn't dragged of for too long!
      1972 Stag 4.3 Serpentine RV8 Injection, Rotrex SuperCharger, ZF4HP24 Auto, BMW 2.65 LSD


        Superb! Thanks for sharing. A terrific Q-car.
        1974 Mk2, ZF Auto, 3.45 Diff, Datsun Driveshafts. Stag owner/maintainer since 1989.


          What a fantastic piece of kit, beautifully put together - you must feel rather chuffed!




            Thank you for the kind comments, not every ones cup of tea I know, but I'm really pleased with how it's turned out. To be honest had the original tail lights been available new when I did the body restoration I would have stayed with those!
            Cheers, Dorian
            1972 Stag 4.3 Serpentine RV8 Injection, Rotrex SuperCharger, ZF4HP24 Auto, BMW 2.65 LSD


              The spec and looks are fantastic, all credit to you. Which ECU are you using for engine management?


                I'm using Megasquirt, its the MS3X for both Fuel and ignition. Putting the supercharger to one side I think the ignition mapping makes a huge difference to the economy and torque in the lower rev range on the Rover engine. I have an Android based touchscreen built into the Stereo and the ECU connects to this showing the speed fueling and ignition advance which is interesting and makes for easy fault finding.
                1972 Stag 4.3 Serpentine RV8 Injection, Rotrex SuperCharger, ZF4HP24 Auto, BMW 2.65 LSD


                  Which stereo are you using please . Nice looking car and mods.


                    Thanks Dorian.
                    A number of us are successfullyt using MS2 or 3 on our TV8’s.


                      Hi, I have a single Din Xtrons Android unit, which has the touch screen pivoting out. It works well but is about 15mm too deep for the hole, hence has a spacer fitted and sits proud. My centre console is different from standard, the ash tray is gone and the heater controls for the centre dash and foot vent moved to the outside of the radio, whilst the cabin has a digital controller in the main dash. The SD1 trip computer sits below, but I have wondered if this could be exchanged for a double din allowing the screen to sit at a better angle (45 degrees). Has anyone tried?

                      I've been really impressed with the Mega squirt. I'm sure it makes a big difference to the TV8 engines too...
                      1972 Stag 4.3 Serpentine RV8 Injection, Rotrex SuperCharger, ZF4HP24 Auto, BMW 2.65 LSD



                        nice write up,David Carter always had a good eye for what parts could fit a Stag,like brake up grades

                        73 mk 1/2 now gone to the dark side BLUE


                          He did have a talent and he wasn't scared to try new things. Mostly they worked but I do remember that when searching for an alternative steering rack for the Stag, also from BMW, he proudly fitted one, got in reversed it out of the garage only to find when he turned the wheel to the left it went right and vice versa! The rack was designed to fit behind the subframe unlike the Stag which is in front....
                          He subsequently found another which worked, you only learn by making mistakes as I have found out too over the years!
                          How did you know David?

                          Thanks Dorian
                          1972 Stag 4.3 Serpentine RV8 Injection, Rotrex SuperCharger, ZF4HP24 Auto, BMW 2.65 LSD


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