Big Turbo Decision time

[Diver944]

You may remember that my turbocharger finally wore its oil seals out last month and started smoking badly. I took it down to Jon Mitchell in Bournemouth to fit a new Lindsey Super 61 Turbocharger and a new headgasket at the same time as I was preparing to start running at 18psi boost and my headgasket was still original after 16 years and 120k miles.

Now that the head is off it turns out that I do have some scoring on cylinder number 1 (probably caused by the fine metallic dust found on the piston rings which has come from the turbo impeller or maybe a loose bolt in the airbox)

The options are a 2nd hand engine or a rebore. I have never liked the idea of a 2nd hand engine especially as its an unknown quantity so we are proceeding down the rebore route using Perfect Bore who know the 944 engine, its coatings and are trusted by Jon. This will give me a number of options:

1. Line the cylinders, bore out to standard size, coat and fit original pistons

2. Bore out to the first oversize, coat and fit oversized pistons

3. Bore out, coat and fit 2.8 pistons []

Option 1 is obviously the most economical and currently my favourite. Options 2 and 3 will be a similar price as they both require new pistons. 2 & 3 may be forced upon me if the liner route is not possible, in which case I would choose option 3 because there seems little point in taking the whole thing apart and having new pistons fitted which are still 2.5

Man I miss my car, I'm bored with the Turbo in my van already []

 

[Fen]

Paul, I wonder if much overbore is worth it. I have been looking at this myself recently as my 2.5 bottom end looks like being the next weak link in my engine in terms of more power - not that I think it's physically weak I have read that the properties of flame propagation in a petrol/air mixture are such that the flame can propagate about 2" in each direction the time between the spark firing and the piston reaching TDC thus optimum size for a combstion chamber is something like 60-100mm. I'm positive about the top figure but unsure about the bottom one (as I don't care about minima []) and outside of this range negatives start to outweigh positives. As our standard bore is already 100mm then I wonder if increasing the bore further is actually benfitting as much as we would think? It isn't a huge overbore but circa 10% of the entire optimum range all the same and the volume the flame needs to fill increases exponentially with diameter. On that basis I have started to wonder that a 2.8 stroker may be the best bottom end for a 944T? You still need pistons to do that, mind.

 

[Diver944]

Yeah I wasn't very clear [&:]

The 2.8 is a stroker increase by using 100mm pistons and needs an S2 crank.

It's one of the classic 'while I'm in there' scenarios, I might as well put things back together that are bigger and better []

 

[sawood12]

What's the feasibility of a 3 ltr S2/968 block with a 944 turbo 8v head and appropriately sized turbo? I'm sure i've read somewhere that the very limited edition 968 GT Turbo's had this configuration and that certainly wasn't lacking in performance!

 

[Fen]

The head doesn't fit, basically. You're into fabricating waterways and things that I know of, plus doubtless others I don't. Can be done but it's time and £. The 2.7 head is 8V and fits the 3.0 block direct so one of them can be ported, thermal coated in the exhaust ports and have sodium filled avlve fitted to be like the Turbo head. Thing is why? I believe the 968 Turbo S and RS had an 8v head because the class of racing they were developed for had a horsepower cap (350 or 375bhp) that could easily be met with an 8v head, so Porsche used 8 valves. If I were doing a 3.0 turbo I'd use the S2 head as well personally. Then again I'd be prepared to bet that's £20k to get running right.

 

[Diver944]

The Powerhaus 3 litre 16 valve engine was purported to be $30k US a few years ago. Expensive, but gives you over 450bhp at the wheels [] which will be well over 500bhp at the flywheel.

 

[Fen]

ORIGINAL: Diver944
gives you over 450bhp at the wheels [] which will be well over 500bhp at the flywheel.

Mildly tuned then. Seriously.

 

[TTM]

I personally would go for a 2.8 stroker set up, probably retaining the stock K26/8.
That would mostly be for fooling the knob at the MOT who last winced when he saw my strut brace.
You really have to hate French road legislation and its "no mod whatsoever" policy []

Good luck for your rebuild Paul, looking forward to reading which set up you will go for.

 

[Big Dave]

Nah.
Ditch the turbo + fit a Supercharger.....[][][]

 

[John Sims]

Go for the stroker, you know you want to.

 

[944Turbo]

Is there an update?
How about, buy a US car with big $$$$ spent on its engine bring it here (with a V8 in the back of the container) swap the engine into your car sell off the interior bits . Drop the V8 into the the stripped US shell to build a V8 track and drift toy.
Tony

 

[Fen]

Tony, you've given this some serious thought, haven't you?

 

[944Turbo]

Just warding off the inevitable, 160K miles and over 300BHP driven hard it is bound to fail eventually, still on the original HG even, so planning ahead!
I have a whole stack of air miles that would make the search relatively painless, especially if I could take in a rennlist or PCA meet before shipping.
Tony

 

[John Sims]

But the steering wheel would be on the wrong side. Would be good for trips to Le Mans and The Ring though.[8|]

I agree with Fen, there does seem to be a little more to this then just a jolly jape.

 

[Guest]

ORIGINAL: John Sims

But the steering wheel would be on the wrong side. Would be good for trips to Le Mans and The Ring though.[8|]

I agree with Fen, there does seem to be a little more to this then just a jolly jape.

There's nothing with having the wheel on the correct side you know! [] It makes overtaking tractors down B-roads an adventure rather than just an event! []

 

[944Turbo]

ORIGINAL: John Sims

But the steering wheel would be on the wrong side. Would be good for trips to Le Mans and The Ring though.[8|]

I agree with Fen, there does seem to be a little more to this then just a jolly jape.

Thats alright the turbo engine would be in my car and on track days we pass on the left, does mean I would need a pasenger for better weight distribution.

Mainly the price of 944t's in the US is the deciding factor plus there seem to be some very fanatical owners - also it has just occured to me if it is to be track only would I have to pay the same duty on import as a road car?

Tony

 

[Diver944]

ORIGINAL: 944Turbo

if it is to be track only would I have to pay the same duty on import as a road car?

Forget that idea and just buy the #1 968 Turbo RS. Surely that would not be eligible for the same duty, it's a race car [8D]

http://www.lindseyracing.com/car4sale.htm