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Somewhat Modified 500bhp 986


PCGB Member
It's been suggested that I share my Boxster here by one of the Region 9 guys. This is also my first post on the PCGB forum so hopefully it's not considered too blasphemous.

This is my 1999 2.5L Boxster:








This is the engine:



And this is the turbo:



The engine is a VAG 06A 20V built with bits generally considered good for north of 600bhp. The turbo is a GT3076R on a log type manifold to try and get the boost threshold down as low as possible. It operates and drives like a standard road car as it has DBW throttle, dual sensor knock control, wide band lambda etc. etc. The engine emits to the same standards as the original and has a single, large metalic catalyst in the rear wheel arch, as the vehicle is pre March 2001 the catalyst doesn't need to be homologated to remain road legal. Closed loop crank case breathing and tank EVAP are implemented and properly controlled and the emissions performance is actually slightly better than the M96 engine as the 06A runs in L1 for much more of the normal drive cycle.

I'm quite often at the R9 monthly meets in this or my 996 so if you see it and would like a closer look then do feel free to ask.
Love modified cars especially those that do not look silly.
Yours looks standard, very nice build.
Why did you do it though? (a positive question!)
That looks so neat. A massive amount of work and development must have done into it. Any updates / desscription eagerly awaited.
Love modified cars especially those that do not look silly.
Yours looks standard, very nice build.
Why did you do it though? (a positive question!)

I felt the Boxster chassis would be capable of dealing with a lot more power than the they came with as standard and I was fairly convinced for a number of reasons that some consideration had gone into the 06A as a powerunit for the Boxster back in 1995/1996..... afterall the "smaller" members of the product range had traditionally been four cylinder. I was also very aware that a lot of 986 are being broken for parts / scrapped due to engine issues and that proving this concept would provide a way to save those cars.

Plus I love a modified Porsche! :)
That looks so neat. A massive amount of work and development must have done into it. Any updates / desscription eagerly awaited.

The concept took a bit longer than the actual build as a lot of CAD and FEA went into it first to fully understand how best to do it. The chassis/monocoque is totally stanadard with no holes drilled or bits welded to it, the 06A goes in on a bespoke front mounting using the original Porsche front engine mount in inverted form. The only "hard" modifications are to bolt on bits like the gearbox mounts and crossmembers, the rest of the floor components go back on in unmodified form. This was important to retain easy road legality i.e. because the shell is unmodified this counts as a very simple repower rather than an extensively modified vehicle in the eyes of the VCA/DVLA.

The transmission and gear selection are all as per the original car but with the gear cable run relocated for package (standard shift cables retained). The gearbox mounts directly to the 06A as they share a common bell housing pattern. A bespoke flywheel is used to carry a 240mm single plate clutch which shares the same release bearing profile as the original Boxster and thus allows all the standard clutch actuation system to be retained.

Electronics integration is all achieved at the engine/ECU harness, the chassis harness is original and unmodified and the 06A engine loom plugs in to the original connectors in the corner of the rear boot. It was neccesary to retain the DBW throttle whereas the original Boxster is cable but usfully Porsche had already done the engineering for a DBW throttle pedal and the parts from the early DBW cars simply bolt in negating the need for a functional safety study on the pedal box as Porsche have already done it. The original check engine light etc. functionality is retained along with the operation of the rest of the dash pack.

This is the original CAD concept render:


Process drawing example for the cross member modification:


And what it looks like from under the car:


All the ground clearances, approach angles etc. are all as per the standard car.
Excellent! A properly engineered job … well done!

Surprisingly few mods required for the installation, and it appears to fit in the confined engine bay very nicely. I’m just wondering if you’ve had any heat management problems with the high-mounted turbo compared with that used on the 718 F-4 turbo cars?

As you’ve pointed out, it’s a very tunable engine … what sort of power are you running? I assume that the powertrain masses F-6 vs F-4T are fairly similar, although the four-pot will have a higher centre of gravity and different inertia characteristics which could have some bearing on handling characteristics.🤔

So few mods you'd almost believe it was meant to be in there!.... I remain convinced based on having done this and some annecdotal evidence that an amount of package protect was carried out to support this engine in the early days of Boxster design to supports M96 as the "S" variant and 06A as the base model. Afterall the base model was already running an Audi gearbox.

No heat issues, the turbo is essentially in line with the intake duct on the side of the car so has very good ambient airflow in that area when moving and there is quite a bit of thermal management going on around the turbo etc. with regards heat sheilding and thermal lagging to reduce the amount of radiated heat.

The 06A is lighter than the M96 by around 50KG, the front engine mount assembly is designed to provide some additional "balast" in this area to avoid moving the mass balance rearwards. The effect on CofG is pretty minimal as all the heavy components (block, crank etc.) is still at the same height as the M96 (crank centre line is actually 20MM lower than standard). In practice the mass balance etc. is within 1% of the standard car.

Edited To Add: Apologies I missed your power question, between 300bhp and 500bhp depending on use. 500bhp is available on "Push To Pass", torque is capped dependant on gear between 300ftlbs and 350ftlbs to save the gearbox. PTP allows another 50ftlbs in third and up.
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There must be a retrofit market for a 'kit' like this with dead Boxster engines costing so much to rebuild?

You're not the first (or the second) to mention this and I'm looking into it. With a decent 986 with an engine issue at less than £3K and most of the bits you need to convert to a circa 300bhp 06A available in an MOT failed Audi TT for sub £1K it does start to make a bit of sense and a very viable way of saving a Boxster that would otherwise be scrapped or broken.

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