906 cylinders

[tadd]

Does anyone know why the 906 used chromal cylinders?

Porsche used biral all the way up to there ill-fated 2.5 long stroke motor - which was cranking out 275 hp on 86.5 mm bores. The 906 was 220 or so on 80 mm. So for a 25% increase in power there was a rough 7% increase in fin area (I assumed 80 and 86.5 mm bores with a 10 mm fin diameter).

If the 2.5 was ok heat wise with biral, why did the 906 need chromal?

I'm trying to figure on if I need to budget for nickkies in my 2.0L clone project or if I can use a set of S birals with some JE 906 copy pistons.

Thanks in advance,
tadd

[Henry Schmidt]

Chromal was the predecessor to Nikasil and 2.5 engines used both chromal and Nikasil not Biral cylinders.
Most two liter engines built for racing these days are running 81 mm Biral barrels. We will soon have a custom 81 mm Nikasil barrels with full fins and a 2.2 sealing surface available for 2 liter race cars.
Here are some 2.5 pistons and cylinders to look over.

[Henry Schmidt]

Chromal was the predecessor to Nikasil and 2.5 engines used both chromal and Nikasil not Biral cylinders.
Most two liter engines built for racing these days are running 81 mm Biral barrels. We will soon have a custom 81 mm Nikasil barrels with full fins and a 2.2 sealing surface available for 2 liter race cars.
Here are some 2.5 pistons and cylinders to look over.

87.5mm



906 81mm

[tadd]

Henry:
Thanks for the shots! You got some cool stuff stacked away in boxes... Can chromal be 'honed' or do you pick (or make) the piston to match? Do you even need to run a 'grape type' hone before running new pistons and rings?

It's good to know when the reference books don't get it right.

tadd

[davidppp]

Hello, Tadd.

Its been a shock to me to carefully measure some birals after use..

They are very very oval in many cases..

I'm sure that using a solid barrel, either cast iron or, better, aluminium like Henry's or Nickies will give better shape stability..

The very latest technology for this is a German Plasma coating, which has been the solution to the serious problems with Nikasil experienced by Jaguar and BMW recently.

It is also now the choice for most if not all Formula 1 engines..

It seems that in the BMW and Jagual road engines (at least), Nikasil does not like the most modern fuels in use in Europe..and sometimes breaks down prematurely.

I have not yet heard of similar problems with Porsche cylinders coated with nikasil...but guess it may happen.

Does anyone know ?

Bottom line: I am proposing to commission a run of plama coated cylinders, with matching light weight F1-quality pistons, for some high-end 2L motors.

If this works out well, they may be a useful alternative.

Kind regards
David

[tadd]

Solving a problem that you don't know if it exists or not! Yee haw.

Seriously though, are you considering some sets beyond what you require? Who would be your piston supplier? Currently, all I know of for 906 'spec' P&Cs are LN engineering and a gentleman by the handle of OliveR in France(?) - I can't remember the company name right now. I have heard good things about both. Then there is using original chromal cylinders with new pistions. I had assumed when I started this little endevor that they would be non-existant but it seems you just need to contact the right persons .

I originally bored and TPed a set of 2.2 heads to use henrys special 2.0 pistons, but I decided to drop back an punt using a set of bored (37.5/36.5) and TPed 68 911T heads after reading about the early STs - and I already had a set in hand.

A choice of rods has been made, so now it is on to P&C choices and finding out what is out there...

tadd

[davidppp]

Yee haw indeed, Tadd.

My motivation to use the Plasma process for the bore surfaces is the same as that of the F1 teams..and for the same reason they use our piston supplier......Speed!

As far as I know Porsche have had no problems at all with Nikasil.

It seems however that we will be hearing more of this plasma coat process now that jaguar etc are using it in road engines..

Yes I will be able to sell some cylinders, and pistons too..in fact, ..the upfront investment is substantial..this stuff is not exactly plasma cheap...at all...
As to timing, well, as always its expected Real Soon Now..but anyone who has dealt with the German manufacturers will know, they are puntilious about all the little details, so am I, but once they get going, I am sure they will deliver very quickly..


Kind regards
david

[tadd]

I do a lot of small scale plasma sputtering for work. Argon sputtering is a pretty simple and cheap process (considering what you are sputtering - i.e. five 9s gold vs say TiO2) but you get really nice adhearing films thanks to the kinetic energy in the argon plasma. I've never done 'inside' anything... That would be interesting. I would guess that you have to 'stroke' the barrel up and down around the magnetron to get good even coverage. Then there is getting the part clean, but a few hours with Alkanox in an ultrasonic followed by a vapor degreasing with a halogenated solvent should do the trick. Rinse with acetone, then pump down for a while and backfill with a few 10s of torr of argon and away you go.

Nickasil is just SiC, right? Hmmm, I wonder.... Nah, that's going overboard.

I would like to hear a few more details, should I pm you my email or is it way too soon?

tadd