My 904 replica build thread ...

[andyjboy]

A few members of this board have expressed interest in the 'New longer-term project' in my signature so I thought I'd start a new thread in this section - please tell me if you think it's inappropriate.

It all started in the summer of 2009 when I visited Barrie Martin (of Martin & Walker) at their Thruxton Circuit premises.

For those that don't know, Barrie Martin has been building replica 904's for the past 15 years or so (along with 550 Spyder, 356 Speedster & occasional 356 Coupe replicas) but keeps a low profile so not many people are aware of his 904.

Unlike all other 904 'replicas' produced (eg by the likes of Beck, Thunder Ranch, etc) M&W's version is very authentic, utilising a dimensionally-accurate grp body bonded to a pressed-steel welded box-section chassis & although this is already 95+% correct - the main difference being the area immediately behind the engine (which is quite a complicated pressing on the original) - I asked Barrie to incorporate some modifications in this area to make it even closer to the original.

Just a bit of background information - Porsche originally designed the 904 to accept the new (901) 6-cylinder engine but unfortunately at this early stage in the engine's development the power output meant that the 904 wouldn't have been competitive so Porsche installed the 4-cylinder 4-cam engine in 2 litre form (~ 180 bhp).

By the time the 6-cylinder engine had been sufficiently developed to make the 904 competitive (1966), Porsche was more or less ready to unveil the new 906 (which was a much lighter dedicated racecar as opposed to the 904 which was the last Porsche racer that could be realistically used on the road), hence only six 904's were Factory-built with the 6-cylinder engine. However, many of the original (110) 4-cylinder 904's were subsequently converted to 6-cylinder engines.

This is the configuration of 'my' car - the original 904 body style equipped with a 6-cylinder engine.

Apologies for the long-winded introduction !

[andyjboy]

.

So, whilst Barrie set about building the chassis (sorry - I don't have any earlier shots when it was being built up in the jig):







I started compiling a list of all the essential parts that I needed to research & source - like Mike (Moore) this is the element of a project that I enjoy the most.

Initially I came up with:

1) correct, dished Les Leston wooden steering wheel:

[andyjboy]

2) correct instruments:



including the all-important 'triple' guage:



3) correct dash switches:

- including the 904/906/908 washer/wiper swich:

[andyjboy]

- & column switches:



4) correct steel/alloy rivetted bimetallic wheels:



5) correct F&R lamps:

- including the correct chrome-rimmed front ind/sidelights (which few original cars seem to have retained) & Hella foglamps:



- & so the list went on ...

[andyjboy]

I have built/owned a number of replicas in the past (including C & D-Type Jaguars, Lancia Stratos, etc) &, in my opinion, the whole point of a replica is to make it visually as close as possible to the original - & to attempt to capture the original driving experience.

One of the giveaways of a replica when compared to an original is usually the fact that everything looks too 'perfect' so one of my challenges was going to be to avoid having everything looking too good/new ...

In the past I have owned lots of original 904 parts - including many from my 'wanted' list but my view is that these rare/unique parts deserve to be on the original cars.

Nowadays, with the internet, it's much easier to identify/research/source parts - but it's still taken me many months & hundreds of hours to find some of the relevant parts that I needed ! :shock:

While all this was going on Barrie was cracking on with the body. As I mentioned earlier M&W's 904 bodies are dimensionally correct & visually accurate (both inside & out), the moulds having been taken off a genuine original car by Barrie himself.

The (many) individual body parts don't make very interesting viewing on their own so here are a few shots showing some of the sub-assemblies coming together:

First the inner (cockpit) area & roof 'frame' are trial fitted :





- next the chassis is turned upside down & the assembly of the complex lower front underbody & inner sill structure begins:

[andyjboy]

- once the outer body panels get added it starts to take on a recognisable shape :







- resulting eventually in a complete body/chassis assembly - notice. even at this early stage, the fit of the doors (I'm sure many of you familiar with grp panels will appreciate just how many hours it takes Barrie to get this level of panel fit):





For those that are interested, a more detailed step-by-step account of how the body/chassis gets built up (not mine) can be seen here:

http://www.technic-motorsport.com/M&...lery/index.htm

In my next post I'l talk a little about the drive train ...

[andyjboy]

In the interests of longevity, the chassis is constructed from slightly thicker gauge steel & is painted both inside & out so ends up slightly heavier (at ~ 62kg) than the original - other than that the overall weight of the complete car is very close ... approx 680 kg/1500 lbs.

Here's a shot of a completed chassis:



- an early 'photoshop' attempt by the Factory to illustrate the lightness of the new 904 chassis (in 1965) :




& Barrie's amusing 2009 version ! :




The M&W 904 was regarded as sufficiently authentic to be allowed to participate in the gruelling 2000/2002/2003 Carrera PanAmerican events - not only finishing all 3 years but coming a very creditable 25th & 13th overall in 2002 & 2003 respectively.

A few images:









- that's Barrie in the blue overalls.

[andyjboy]

Many (most ?) of M&W's previous 904 customers (I don't know the exact number but I think less than 20 have been built in the past 15 years) have opted for 3 litre engines (probably due to relative ease of availablility & cost) but, to my mind, these would give totally the wrong driving characteristics - the car needs a smaller/more highly-tuned engine.

The relatively few 6-cylinder 904's that the Factory built were equipped with the Type 901/20 engine - 2.0 litre twin-plug on 46 IDA Webers producing 210 bhp @ 8000rpm so I wanted something that had similar specs ...

... now it just so happened that I had a twin-plug engine sitting at the back of my garage !

This engine was removed from my 911R-inspired car before I sold it (I already had this project in mind at that stage) & has the following spec:

7R crankcases which have been shuffle-pinned & time-serted
Custom-made JE 90mm pistons (c/r 10.5:1)
Rebuilt/modified 40IDA Webers (36 mm venturis) on 'tall' manifolds
Ported cylinder heads with stainless steel valves and hi-performance springs
High-lift custom hand-ground cams
Lightened/balanced 2.2 crank with cross-drilled & grooved centre bearing
3.0 SC oil pump
etc

In it's original configuration with crank-fire ignition this 2.5 litre engine produced 220 bhp @ 7800rpm but I have since swapped in a period-looking Marelli-style twin-plug distributor operating through twin MSD boxes (which will be hidden from view) - 2 (dummy) Bosch CDI boxes & twin Bosch black coils will be visible within the engine compartment - so I am hoping for a little more ...

As I mentioned previously, I don't want everything to look 'too new' so I avoided any polishing/replating etc on the engine - opting instead for just a 'clean' look:

[andyjboy]

To get the most out of this high-revving engine I decided to go for a 906-style lightened flywheel & '69S lightweight clutch so I tracked down a suitable early std flywheel :



& got Mike Bainbridge to turn it into the 906-style :







Std gearbox ratios wouldn't really suit this engine's power characteristics so I consulted various experts (including a number of Early S members) &, with the help of a gear ratio calculator/spreadsheet, I came up with a range of optimum ratios.

After putting out some 'feelers' I located a suitable transmission in Phoenix, AZ - it was a totally rebuilt side-shift 914 box with all the best upgrades (904 mainshaft, billet aluminium intermediate plate, etc) & an ideal set of ratios (A,E.J.Q,X) to keep the engine 'on the boil' ...... another one ticked off the list ! :cheers:



(not much to look at ) ...

[ghost1001]

This is shaping up to be an epic thread/build....thanks for sharing it with us.