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Somewhat Modified 500bhp 986

PopPopBangBang

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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:

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This is the engine:

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And this is the turbo:

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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.
 
Fabulous!
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.
 
Fabulous!
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:

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Process drawing example for the cross member modification:

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And what it looks like from under the car:

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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.🤔

Jeff
 
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.
 
There must be a retrofit market for a 'kit' like this with dead Boxster engines costing so much to rebuild?

Further to this there now is... as some who read the October issue of Porsche Post may be aware of as it was the cover car. Adam Towler drove and thoroughly enjoyed the car:

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I was absolutely chuffed with his summing up of the car and its capabilities.
Development and testing at north of 400bhp is now ticked off with several thousand miles completed and I'm pushing to validate it at 500bhp early next year which will involve a new spec gearbox and a couple of other bits to support that power output reliably. Given performance is already at GT car levels I'm very excited to see what it does when all the stops are taken off the engine!

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Productionising a kit out of it was a bit of effort but there's a few cars in build already based on the kit so I'm super excited to see how other people use the bits to build some seriously performance capable Boxsters.

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For those interested I've done a couple of narrated deck style videos. One on the development and ethos of the project available here:
and one on the end result weights and balances which is available here:

A big thank you to those on here and elsewhere who messaged and nudged to request this was turned into a kit and to Adam Towler for taking such an interest in the project and Dan Bathie for the amazing photography of the car in motion.
 
Matt,

Thanks for the interesting videos. It’s great to see that you’ve moved this on to a production footing to make it available as a kit, and wish you success with the project.

The cheapest 986 Boxster on AutoTrader ATM is just £3k, with lots of new stuff fitted but with an engine issue. Ripe for conversion, and would make a great - and affordable - track-day Q-car!😀

Jeff

PS: How do you handle the higher engine power and torque outputs you quote, given the torque limitation of the Getrag transmission which has always been a constraint on the more powerful 981 and 718-series Caymans and Boxsters?
 
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The availability of good Boxsters that have an engine issue requiring an expensive repair was a big driver in the decision to do this as a kit, there are just too many great cars being broken for parts due to a £10K M96 engine repair bill.... if for the same £10K you can have a car which is capable of hanging with GT cars in performance terms it gives a much more convincing case for someone to spend the money vs breaking the car for parts or selling it to someone who will.

With regards power and torque, it's important to first understand that power is just torque X RPM / 5252 - essentially its a made up (but very useful) thing that we use to measure the amount of work an engine can do. The gearbox doesn't care about power, what concerns it is RPM and Torque.

RPM is important because most production gearboxes are splash lubricated so the bearing systems inside them will have an upper lubricity limit based on the available oil supply. Torque is important because it is the actual twisting force provided at the gearbox input shaft which the box then multiplies accordingly through the ratios within it and the final drive.

The 5 Speed on the Boxster is actually an Audi 012 gearbox, which is made by Aisin. Only the 6 speed is Getrag. The 012 gearbox is a very strong gearbox for its size and has been used in various aftermarket GT40 builds and other mid engined performance cars as well as having sat behind a huge amount of VAG group applications. When doing this conversion you're actually reuniting the gearbox with the engine it was designed to be behind.

The 012 Gearbox has an upper torque limit of somewhere around 300ftlbs, it can do a little bit more than this in 3rd/4th/5th due to the lower torque multiplication. As such we cap the torque based on boost pressure and gear position to avoid excessively loading the gearbox. The ECU we recommend has excellent boost control so is more than capable of drawing a flat torque curve at exactly the desired figures. In practice this means at 400bhp spec we run 1bar boost in 1st, 1.35bar in 2nd gear and 1.75bar boost in 3rd and up. This both keeps the gearbox happy and optimises traction with peak torque at high boost circa 330ftlbs at 5500RPM. Here's our boost by car table for example:

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When we want more power than this we simply raise the RPM limit and change the cam profile to suit, the turbo charger on the validation car is massive so we have no issues filling the engine with air up to north of 500bhp an the engine is built to rev to 8250RPM with titanium retainers, double valve springs, supertech valves etc. What this means from the gearbox perspective is the input shaft turns faster but the load on the gearbox remains the same as it previously did, from our BHP perspective we've now done more "work" in the same period of time (as there's more cylinder firings in the same time period) so our power calculation gets bigger accordingly. Here's the math:

330(ftlbs) X 6500(RPM) / 5252 = 408bhp

330(ftlbs) X 8000(RPM) / 5252 = 502bhp

In both these scenarios the torque on the gearbox remains identical, we're just doing more work in a given period of time.

The other two things to consider in this application are clutch and driveshafts, both of which obviously see the engine torque in a related way. For clutch we designed a new flywheel for the 20V engine which carries the standard production clutch from the Audi RS4, this clutch is a larger diameter than the standard clutch and is rated at 350 ftlbs in the OEM application. Using this gives us an OEM/Production car pedal feel, great clutch life and all the torque holding we need.

The driveshafts are subject to very large torques due to the torque multiplication produced by the gearbox, the biggest multiplications are in first and second so limiting boost and therefore torque in 1st and 2nd gear keeps the driveshafts in a sensible loading window.

The really nice thing is how the car drives with this sort of setup. It's super linear with power rising across the rev range, it's not spikey or hard to manage and with a decent set of tyres on the car (Michelin Cup 2 in the VP cars case) it has fantastic traction and puts the power down without any issue at all. Here's a power plot at 400bhp:

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You can see how linear the car is, arriving nicely into boost in the mid 3000's with a linear rise in power across the rev range. This is one of the reasons it's so quick, there's no having to get out the throttle - in the dry it grips and goes :)

Hope that wall of text is of interest and explains a little more how we've tried to engineer reliability as well as performance into this.
 
You do yourself proud with these kinds of posts.
Love the detail in simplistic terms, all adds up to a competent well thought out conversion.

How do the insurance companies respond to this kind of mod?

You have a capacity reduction here, and usually people put bigger engines in cars, so maybe things are ok?

You have not mentioned turbo lag, have you mapped this out with boost control?
Sorry if I have missed this, but where is the turbo intercooler and pipework?
 
Many thanks for the comprehensive additional insight Matt, and didn’t appreciate that the 5-speed transmission was of Aisin manufacture. Clever use of sophisticated boost control to maintain transmission durability. As a mechanical engineer, thankfully I’m not - like many - confused by the distinction between power and torque and their corresponding relationship!😀

That’s a very neat solution for the compact air/coolant intercooler covered in your first video above, which I’ll leave you to explain for Graham’s benefit.

Jeff
 
You do yourself proud with these kinds of posts.
Love the detail in simplistic terms, all adds up to a competent well thought out conversion.

How do the insurance companies respond to this kind of mod?

You have a capacity reduction here, and usually people put bigger engines in cars, so maybe things are ok?

You have not mentioned turbo lag, have you mapped this out with boost control?
Sorry if I have missed this, but where is the turbo intercooler and pipework?

Thank you, it's nice to share some of the engineering and thought process - plus on Booster I can be quite open as it's "ours" rather than something subject to NDA etc.

Classic Line are aware of the conversion and happy to cover it with all the usual classic car / unique vehicle options they offer such as agreed value etc. Adrian Flux are also happy to extend cover. Putting decent cover on a repowered car which represents its new value etc. is not a problem.

With regards turbo lag it's important to differentiate between turbo lag and boost threshold as they are not the same thing. The boost threshold is the point at which the ICE is providing sufficient energy in the exhuast stream to drive the turbo compressor to the required speed. This is a physics limit as big turbo which requires lots of exhaust energy to drive it will not achieve a useful compressor speed for the desired boost if the engine can't provide that amount of exhaust energy.

Conversely turbo lag is a physics driven element which depends on the rotating assembly mass, bearing system, design of the turbine, optimisation of gas flow into the turbine etc. etc. in basic terms turbo lag is considered the time it takes for the compressor to accelerate to the required compressor speed for the desired boost pressure given all the energy into the turbine it could ever need to do so.

What this all means in practice is the Boost Threshold is the RPM point at which the engine can make full boost / torque whereas Turbo Lag is how long it takes the engine to make full torque if you plant the throttle at high RPM / an RPM which is above the Boost Threshold.

The validation prototype Booster has a GT3076R Turbo charger which is massive and quite old school, it's too much turbo for the power the car is currently making but gives great options in terms of always having enough airmass to explore what the correct turbo for the applicaiton actually is (that's a G25-550 if anyone is looking for the answer). With this massive turbo the boost threshold is around 3750RPM, the lag when above this is pretty low as the GT30 is a ball bearing CHRA design with a decent turbine design, maybe a second or so to reach full boost - this delay actually really helps driveablity as all the while it is ramping into boost the engine is making more and more torque so this effect softens the throttle response a little and in turn gives a bit of traction optimisation as well as an easier time for the gearbox and driveshafts.

With regards chargecooling this is acheived with a water/air intercooler (same type of system as Porsche use on the 718) located under the intake manifold. We've validated two different systems, one made by PWR specificially for the Booster which is suitable for up to 350bhp and is perfect for a standard or mildly modified engine and available as a kit with pump, front mounted water radiator and associated sundries. The second is a little more boutique and involves using the LH bank charge cooler from the Mclaren 570S / GT4 car, this unit is made by Hanon Systems and is extremely high quality and high performance with a turbulating core design, when using this option you essentially cut and paste the left hand bank setup from the GT4 car. This solution is suitable for up to 500bhp.

Water/Air intercoolers are nice because you can locate them all in the engine bay with super short pipe lengths which helps transient throttle response a little and also creates a neat package. It also means we can use some of the weight of the system to offset the inherient imbalance a 4 cylinder turbo engine has, by packaging the charge cooler and all the ancils on the inlet side we get a pretty well balanced power unit - the VP car is 1KG different across the rear axle for example.

Hope that's interesting :D
 
Many thanks for the comprehensive additional insight Matt, and didn’t appreciate that the 5-speed transmission was of Aisin manufacture. Clever use of sophisticated boost control to maintain transmission durability. As a mechanical engineer, thankfully I’m not - like many - confused by the distinction between power and torque and their corresponding relationship!😀

That’s a very neat solution for the compact air/coolant intercooler covered in your first video above, which I’ll leave you to explain for Graham’s benefit.

Jeff

The big driver in really looking into the 20V as a power unit option for the 986 was the gearbox. Being able to achieve the install in a very OEM way without bell housing adaptors or similar was key as having a bell housing pattern which is directly compatible with the engine gives you all the NVH and stiffness of assembly benefits you lose or have to try and engineer solutions for with an adapted setup. I essentially built the installation in CAD before commiting to the project which allowed for some basic FEA etc. and all the bits etc. for the VP car were machined and on the shelf before the M96 was removed from the car.

We also did a quick and dirty aero study to understand flow through the engine bay etc. to get a good idea on thermals and general ideal component positioning which also defined the choice of charge cooling and related component locations:

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The boost control sophistication is all enabled by the choice of ECU. The Ignitron unit we recommend isn't well known outside of VW / Audi circles but it is a hugely capable bit of kit running a VE based model of the engine for control. In short it is as close to an OEM ECU in strategy and capability as you'll ever find in the aftermarket and this is what allows for the excellent, OEM like, driveability and feel that has been achieved. It's really hard to do acheive this when you're calibrating off a raw MAP sensor signal as your load input!
 
Thank you for the details.
I ran a Subaru Impreza a few decades nearly ago to 370 bhp on a stock engine but a big crude turbo and a simple ecu (Apexi).
pit needed a huge air to air inter cooler, but the Legacy used a water to water inter cooler to great effect.
In the end, the car ran well, no lag and to 8K rpm, nice car.
 

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