964 RS Cylinder head question - Page 1 - Porsche General - PistonHeads UK

The advantage is that a machined cylinder head stands a chance of achieving the factory design compression ratio of 11.2:1, whereas all the unmachined heads that we have measured struggle to make much more than 10.5:1 The knock on effect is that the piston also runs closer to the head, but since the squish clearance is absolutely lousy on a standard engine, closing this down will also aid combustion and reduce the likelyhood of detonation. Very often, we will take up to 1.0mm off a set of heads on a race engine in order to achieve good squish and high compression.

Translation please? Melv

I thought so. Of course the downside is that the valves are that bit closer to the pistons. So if you mis shift, as i did they colide a little bit easier. I suppose the answer their is NOT to mis shift. A bit of logical progrssion here. If an RS makes 260 with the lower cr what does it make after? It's quite reassuring to know you can skim off that much

Lets face it, if you miss a shift whilst racing in brogues, the valves and pistons are going to have a party anyway, so this is not an issue in the real world. More compression = more power, more torque as a result of higher cylinder pressures. Squish = clearance of head to piston, if correct it stops combustion in the immediate area and forces at high speed all the gas into the centre of the chamber, causing turbulence to stir up the mixture and improve burning. Generally 0.75 to 1.0mm is perfect but most 964's are around 1.25 to 1.5 at edges and over 2mm further in. This transitional gap between 1.0 and 2.0mm CAUSES detonation. We got 100bhp per litre with standard pistons and mild cams from adequate squish control.......

"racing in brogues" Now I need a translation! >> Edited by lemon yella rs on Monday 9th December 21:51

Thanx Colin -I am now older, but wiser!! Melv

"racing in brogues" can be roughly translated to: "Should one decide to drive your RS in a spirited manner whilst wearing inappropriate footwear, do not be surprised when a slip of the clutch inadvertantly causes the engine to momentarily exceed its design rpm limit and causes contact between the piston and the exhaust valve" Or: "I buzzed it". OK?

Ah, that explaisns why I buzzed mine then...and there I was thinking it was something to do with changing from 3rd to 2nd rather than 3rd to 4th whilst at the red line....I have a valve with an elegant S shape in the stem as a souvenir from that incident :-)

Isn't that guy in the RUF Nurburgring Fazination video wearing brogues? Foot must have got caught on the loud pedal... Melv

I thought they were Mush uppies.

Ah now I see. Yes that must have been it inapropriate footware! I Like that one . Have not used that one as an excuse before, must try it. Now where do I buy some brogues? BTW Ninemeister I liked Your little snipit in GT Purely Porsche very informative . Shame the same can't be said about the article on the RTS-2 at SPA.It must have been the worst desciption of a lap there I have ever read! Rubystone I have Six reminders of my "brogue" incident. I never seem to throw anything away!

Lemon Yella, I kept the best one...have to show you one of the pistons from the 2.4 I also lunched sometime

On my previous RS When doing a top end strip down I noticed my heads were stamped -.30. From the Tech spec books it says you may only do a .10 pass twice i.e.-.20 has anyone seen this before. seems strange a,make this cut in the first place b, to mark it up.Perhaps their is an update that shows this? I made some enquiries at the time but drew a blank.I wondered at the time wether there was any advantage in it.