997S.2 DFI Cylinder Heads/ Valves Pics - 26k Miles

[Ian_UK1]

The OP in this thread is having the X-51 kit fitted to his car and has posted some piccies of the inlet valves / heads / pistons on the DFI motor to show the carbon build-up. Interesting result.

http://www.6speedonline.com/forums/997/275183-hear...

[Gibbo205]

Hi there

Looks interesting, but is that amount of buildup causing any power loss, have any owners moaned about loss of power or dyno'd one.

In fairness compared to VW/Audi they don't look to bad, but would be interesting to know if the build up looses horses on a Porsche.

[Ian_UK1]

The interesting thing for me is that there was no significant build-up of carbon on the valves at all. There are some deposits on the sides of the inlet port, but their effect will be minimal. This is VERY good news for the owners of flat-6 DFI Porsche cars. The potential for carbon build-up was the only complete unknown on what otherwise seems to be a very strong and very reliable engine.

I'm really intrigued as to why the Porsche engine remains unaffected by carbon build-up when every other DFI motor on earth doesn't. I had expected the inlet valves in a 26k mile engine to look just like they do in the Audi engines - choked with thick, black, immovable deposits. There will be a rational, technical explanation - any ideas?

Here's the detailed piccy:



I can only guess that the valves, when fully open, are partially in the path of the spray of fuel from the injector inside the combustion chamber. This would wash and cool the valve backs in a similar way to a port-injection engine.

Edited by Ian_UK1 on Wednesday 16th May 16:41

[itsybitsy]

this is more goodnews for the dfi engine which having been around for 4 years now and has so far has proven reliable across internet forums with cars both in regular use and on the track.maybe porsche have got it right with this engine and may prove to be good(reliable) as metzger based road cars albeit not as race focused(strengthend camshaft etc)?i still think the 991 gt3 will be 9A1 dfi engine based.

[UkRob]

Hi,

Could the DFI inlet valve problem for most engines be that the valves are vertical where the boxster valves are horizontal, this would mean less oil running down the valve stems through gravity, just a thought, pic of Subaru Boxer engine also, does this suffer inlet valve carbonizing.

[Ian_UK1]

The carbon build-up on the inlet valves in Diesel and DFI petrol motors is caused primarily by oil contamination from the crankcase breather system, not from oil seepage down the guides. In port injection petrol engines, any oil is washed off the valve backs by the incoming fuel during each induction stroke. In DFI engines (and Diesels) the fuel is injected directly into the combustion chamber, so it never passes over the valves to wash/cool them. Hence build-up occurs.

[Rockster]

Ian_UK1 said:

I'm really intrigued as to why the Porsche engine remains unaffected by carbon build-up when every other DFI motor on earth doesn't. I had expected the inlet valves in a 26k mile engine to look just like they do in the Audi engines - choked with thick, black, immovable deposits. There will be a rational, technical explanation - any ideas?

Edited by Ian_UK1 on Wednesday 16th May 16:41

How about Porsche really knows what it is doing? Or does that fly too strongly in the face of opinion Porsche doesn't know $#%& about cars?