The boy done good

[924nutter]

Well there you go. I have just got another tremendous bargain. As hen's teeth go this is cheap. A set of 0.5mm oversize pistons (second rebore) for a series two 924 turbo. Brand new with rings, plug standard big ends and mains, and according to the seller the main bearings are unobtainable, for the less than princely sum of £346.50 including deilivery. The 0.5 oversize will increase engine capacity to 2007 cc, from 1984 cc. All I need to do now is wait for the warmer weather to come around again.

 

[Bertroex]

Hello 924nutter,

Congrats on the purchase but please allow me to get my head straight on this....
I have bought a while ago a 924 turbo series one. Story being told here:
http://www.ddk-online.com/phpBB2/viewtopic.php?t=17028

Now, I also came about a really interesting write up by Colin Belton from I think 1998-ish on how to extract more power from the 932. http://www.356-911.com/post1974/moderntuning/porsche924turbo.htm

So therefore, what will these overbores do to your engine with regards to power, torque etc instead of going down the bigger turbo /intercooler set up?

Best regards,

Bert

 

[924nutter]

I now have the service manuals in front of me.

Power outputs (R.O.W. figures) as we are not that bothered about the US specific power outputs as follows

170bhp running 7.5:1 c.r and 0.7 bar boost

177 bhp running 8.5:1 c.r. and 0.64 bar boost

I may experience some pinking (detonation) as I do not know if the bowl in the piston is designed to maintain the same combustion chamber volume of arond 59 c.c.
It will give a modest increase in power perhaps, maybe one or two bhp. The most interesting thing is that I have a trick cam available which was bought for a 924 n/a and was alleged to offer between sixteen and twenty horse power, but if used on the turbo I would only expect to gain the lower figure as cam changes on turbo engines are not as significant using the same profiles as normally aspirated engines. Its use depends on whether there will be any valve clash, due to the continuous rim of the bowl-in-piston design of the turbo item as opposed to the valve-head-recessed crown of the normal piston. If I can use it I would expect the engine to make 190 brake.

Three things ensure the greater specific output of the carrera.

Higher boost pressure, intercooling and a hybrid turbo charger, actually built up around a 930 turbo housing, to deliver the boost in sufficient volumes.

 

[Bertroex]

Hello 924Nutter,

Thanks for your reply. What I am trying to establish is that quite a lot of work and information is available from reputable companies or racing stables on the 931 since the 1980-ties and 1990-ties.

However, due to the relative low value of these cars, the early watercooled porsches are falling immensely below the "porsche development" radar and its "magic circle of trick engine/suspension/gearbox guru's" etc. I think there are only a handfull of people available who are still investing money in those cars...

Hence, we find ourselves on an online forum trying to assemble snippets of knowledge of what might have been known for years but it simply not available to us (anymore) or because perhaps we try to do it ourselves. Possibly you come to a point of trying to re-invent mathematics.

So therefore, the only "hot cams" that I know of were usually put in the 924 lodge sports cars: Piper cams. Your 0.5 overbore would be really usefull for an engine that was driven to the moon and back and is already rebuild with an 0.25 overbore and now is due for a 0.5 overbore? Is that right?

Could I, for example, consider a piper cam in a stock series 1 turbo engine and gain perhaps some flexibility?

Am I thinking along the same lines here?

Best regards,

Bert

 

[924nutter]

My 924 turbo is just coming up to 80,000 miles and is (according to our resident 928 gt driver) still properly quick. It doesn't need a rebore but the cam belt did go and one valve dinged a piston. My cam was bought back in 1992 from a now defunct company called P.M.C. Going from +0 to plus 0.5 in one go is not an issue, it just reduces the number of rebores by one. By the time the engine is ready to be rebored again I wont be bothered about it as I will be the other side of the grass. You ought to gain some mid range torque with the piper cam feartured about a year ago in one of the mags, but, as I have said, do not expect the same incremental chages by re-camming a turbo charged engine. Then there is the questoin of overdoing it and creating a recipe for pinking. I am ok down here, I can, for the moment at least, continue to run my 924 on leaded petrol which despite its 99 octane rating is infinitely superior to leading brands of 99 octane unleaded in terms of knock resitance.
The 924 turbo is never going to pull hard from low down because of the nature of the turbocharger, the engine is always going to be sucking past the compressor vanes below say 2,500 because the turbine has not got a sufficient supply of hot exhaust gas to get it spooled up, so there is always going to be a point at which the compressor starts to move a greater volume of air than the engine can suck, which is of course the point where we say the engine goes on boost. Without the boost you are effectively driving a two litre normally aspirated engine with a c.r.of 7.5 :1 in the case of the 170 horsepower engine. It is not going to be that flexible.
An idea for me is to try to obtain a series one turbo and wastegate and increase my boost pressure to 0.7 bar from 0.64, an increase of about 0.8 psi, but that again may necessitate the intercooler to prevent pinking. When you boil it all down you would probably spend less, wedging a 3.0 litre S2 into a 924s. 2 more brake than a carerra GT. Now that would be flexible. Hmmmmm, now where did I put my shoehorn?

 

[Bertroex]

Thanks for your reply. Strangely enough, I am not at all excited by shoehorning a later engine into a 924.
I am on a similar line with the 911 btw: I'd rather sell a kidney in order to have a 3.0 litre twin plug with 280 bhp instead of shoehorning a 3.6 pre-varioram into it, for example.
So, my 932 is a 1980MY affair, so I would like to explore a bit what it can do....

Exciting times!

Best regards,


Bert

 

[924nutter]

My other 924 turbo (1980) came to me as a series one, 170 bhp but although it had early heater controls (i.e. the three sliders) it has series two pistons, and the series two throttle body which consists of just one large butterfly, and the pressure duct is a push fit over the throttle body. The two sets of pistons differ slightly in that the 7.5:1 pistons have an offset bowl, maybe and experiment for better gas flow, the 8.5:1 pistons have a central bowl. What is really needed on the 924 is the technology of twin turbos like the Japanese use. Twin turbo sounds mighty grand but in fact on things like the Toyota Supra, one turbo is smaller than the other, delivering boost low down then the second one takes over higher up the rev range, or so it was explained to me at work, by Toyota petrol-head. I will say this though. Pound for pound, off boost, the 924 is has more get up and go, low down than my 944 turbo cab.

 

[Bertroex]

924 nutter,

Interesting point you make about the S1/S2 crossover. May I possibly email you my vin/engine numbers to have your opinion on this? I have a MY1980 car as well, I understand.

Its currently at Mike Bainbridges in Kendall, about ready to be scrutinised. I also just bought the 924turbo factory manual. Not cheap, but rather handy.

All the best,


Bert

 

[924nutter]

Should be able to get the type from the engine number as thePET cd should show which pistons to use up to or from which engine or chassis number. Doesn't the manual tell you which engine type is what?
The pistons have arrived and they are not Kolbenschmidt , but Mahle, which I am almost happier about, except that I think KS only made the forged pistons for the CGT as O.E.M.
Did you get the manual from ebay? We were nearly bidding against each other until the pistons came up.

 

[Bertroex]

Hello 924 nutter,

[&:] I did get the manual from Ebay- sorry to hear that we were bidding against each other. The manual does have an awfull lot of info on the US/canadian/ Japanese market 931 so I suspect it wasn't a proper UK version anyway.

I'll have a look to see what I can find...thanks for the pointers.


best regards,


Bert

 

[geoff Ives]

When are you two going to get married? [][][][8D]

 

[Bertroex]

When he doesn't get into a fit when he sees/hears my 911 [][]

[]

Bert

 

[924nutter]

ORIGINAL: geoff ives

When are you two going to get married? [][][][8D]

Don't hold your breath....no, then again do[]

 

[Bertroex]

ORIGINAL: 924nutter

Don't hold your breath....no, then again do[]

[][][][][]

You guys.....

Bert

 

[geoff Ives]

Be gentle with him Bert.
He doesn't know the joy of 911 2.7/ Carrera 3 ownership.

 

[924nutter]

I do , that's why I spent 13,000 on a 944.

 

[geoff Ives]

ORIGINAL: 924nutter

I do , that's why I spent 13,000 on a 944.

How many 944's did you get for that? []

 

[924nutter]

One less than the equivalent rusty 911 models[][]

 

[Bertroex]

ORIGINAL: geoff ives
He doesn't know the joy of 911 2.7/ Carrera 3 ownership.

I understand that it is quite an exclusive group[]

[]

Bert

 

[Bertroex]

ORIGINAL: 924nutter

I do , that's why I spent 13,000 on a 944.

Was that, incidentally, a record?[8D]
Or was circa 1987?[]

Bert