3.4/3.6 Turbo upgrade kit

MisterCorn said:

A tuned 996 turbo is a thing of joy. More than that, if ever you waver and wonder why cars should be fuelled by petrol you should get in to one. A tuned 996 turbo at 500hp is fantastic. At 650hp it is an absolute weapon. After that it is all totally pointless, but we can, so we do.

That said I love my C2 and probably drive it more than my turbo.

MC

Click to expand...

Hence my thinking that a 400hp+ C2 could be a lot of fun!
Lighter weight, compact, fast, useable - that is until it goes bang!

Any thoughts from some of you engine builders out there, sheer madness or just an overly expensive project on an unsuitable base engine?
It's also possible to squeeze in a 400hp+ LS3 lump which would be more reliable but it wouldn't be a true porker then and despite being lighter weight the CoG would be wrong compared to a flat 6 I suspect.

I looked into ls3 conversion for my C2 that I'm slowly building (I've got a standard C4 also) so fancied trying something different.

I've still to decide on a power plant yet.

Regarding the turbo conversion, if bolting this on to say an engine that has been rebuilt by Hartech with there cylinder strengthening and other weak points addressed I wonder how it would fair.

Only real concern for me is boosting an engine that wasn't designed for forced induction, standard compression ratio really suitable ?

And I quote:
"The TPC Racing 996/997 Carrera Turbo was developed as a direct bolt on kit. This system requires absolutely no internal engine modifications necessary to maintain the engine's overall reliability or longevity."
(Should that be taken with a pinch or a bucket of salt?)

If you were rebuilding and engine to fit this turbo then I reckon you could reduce the CR so that you could I turn run more boost to up the power.
It would get expensive though.

However after more Googling this old PH post, from the very knowledgeable Mr Baz Hartech relating to Supercharging a 996, probably sums the turbo option up and puts this thread to bed:

[report][news]Monday 21st July 2008quotequote all
The supercharging problem is two fold.

(1) If you supercharge or turbocharge an engine you raise the true compression ratio (remember the compression ratio quoted is only the theoretical ratio if the cylinder filling was 100%). The performance of an engine varies mainly with the true compression ratio at any one moment and anything that increases it within useable limits will increase performance. Camshafts, induction, exhausts, etc can also increase true compression ratio in the power band they were intended to operate in and therefore increase output but rarely by more than 100%, while any induction charging system easily exceeds 100% in the operating range.

So fitting a supercharger usually increases charge efficiency and true compression ratio at lower revs while fitting a turbocharger usually increases it at higher revs. Both need changes to the theoretical (or static) compression ratio to operate safely (lower static compression) and changes to the ignition timing, cam timing and fuelling.

Also pistons are made oval and tapered so that when they are at running temperature - they expand and fit into the bore more closely. The more relative power an engine produces the more taper and ovality you need to put on the pistons (as they will run hotter and get bigger at the top). This makes the top of the piston smaller than a lower power piston would be in the same engine. Although the 996 pistons are if anything over tapered - and although the bores have probably gone oval to increase the clearances, the extra cylinder pressure will increase blow by if the pistons do not expand and could seize.

So when an engine is tuned by turbocharging or supercharging - if it still runs OK on many of the original parts and control systems - it is just luck that it wasn't built to closer tolerances - and enables you to still get away with it more by luck than design but it always brings it nearer to some design limits.

A mild supercharger can improve torque at low revs and probably get away without too many other changes and so is an easier option than a turbocharger (and needs less intercooling). However, the big ends on a 996 (in common with all modern engines that seem to be being fitted with progressively relatively narrower shells) are a known weak spot - not too bad but one of the first things that will need replacing in an otherwise good high mileage engine. We are told this is to reduce friction and improve ecconomy although it is also a neat way to control eventual life expectancy.

For me this factor alone would make supercharging with this engine a risk (as the extra power/torque developed cross refers to extra load on the shells and as they are supported by oil pressure - a wider shell provides more support for longer) and so I would expect a reduced lifespan unless the supercharger worked only at low pressures and revs - in which case it is a lot of money for little reward.

The 996 has big end shells that could be 20% wider and still fit inside the original con rod and the crankshaft and so the big ends are one of the weak spots in these engines that could have been improved upon (the mains could also be 10% wider).

The shells we are having manufactured to enable us to regrind the crankshafts are being made to accomodate the extra widths available (to eventually improve yet another aspect of the standard engine during a rebuild) and we have already prepared a lower compression engine to fit them to and to induction charge.

This winter we intend to fit the engine into a track car as a mobile test laboratory in which to test extreme engine conditions. This will enable us to remove this weak spot from our engine and find out what is the next weak spot to address as soon as possible to prepare a solution - hopefully - before it hits higher mileage standard engines (and hopefully we can have a bit of fun in the process).

Baz