Hi there,

I am thinking about building a new turbo engine for my 968. I currently have a 2.8 stroker turbo engine in it. Markus at the 951 forum built a nice engine with stock 968 pistons and 3.2 mm head gasket.
How about if I use my 4.5mm shorter stroker rods?? I guess the compression might get a little too low? Does anyone have numbers for the cc's of the 16 V head and piston bowls? Surely it would be possible to machine the block a little to compensate?
Has this been done before? (I would think so) Or is there something awfully wrong with the idea?
Please let me know!

Thanks,
Jarmo

 

You have a PM.
Raj

 

Hi Jarmo. Small world. Just saw this thread while looking for other stuff in archives. Have been doing some research on CC numbers lately. Since 928 S4 and later heads are basically same as 16V 944 heads these numbers should be valid in four bangers too.

https://rennlist.com/forums/928-forum/344250-head-and-piston-top-cc-numbers.html

Using "wrong" lenght rods isn't best possible idea even though it can work ok. My main main concern would be what happens to cylinder walls if there is even slight detonation. There is one SC'd 928 engine running which has 951 pistons in it. Since their compression height is about 2mm smaller than all 928 pistons except GTS this will result piston top which is 2mm below deck level in TDC. Engine stays together with 22 psi boost but I'm not sure if it has steel support rings around cylinder towers or not. If it has this could make a difference.

In any case I think its better to have pistons come little above deck level than below it. Few days ago I spoke with local machinist who installed valves into GTS heads. He had done two NA Ford 5.0 V8 engines for his Thunderbird. Just about only difference was that on one engine pistons came little above deck while on another they were at deck level. Compression chamber shape and ratio, valves, cams etc all remained same and still result was 20 more hp in dyno. He attributed this to less blowby into crank chamber. There could be some other explanation to hp increase but its not at sloppy engine build based on how well GTS heads were done.

 

Hello Erkka,

Thanks for your comments!
I have pretty much ditched the idea of using shorter rods.. along with the 16V head.
I will most likely go with factory like set up, 8V head with Mahle pistons. (well if I ever do it anyway!) Since I am not looking for ultimate power output I guess that might be the best solution for me.
Hehe.. I should have bought the s2 block you had back then when you bought my wheels.. I'll have to invest a bit more in to it now..

Jarmo