(09-04-2023, 11:17 AM)Malcolm Parker Wrote: Belated Happy Returns on your big birthday, Ruairidh, I wouldn't mind being your age again.

On Friday I took the Pytchley out on my quite arduous test circuit up and down the edge of the North Yorkshire Moors.   Whilst it was running well, when I opened it up on the old drove road along the top of Sutton Bank, pictured, it was reluctant to pull much over a true 45mph in top, surprising given its light weight and 5.25 rear axle. 
I suspected that the cylinder head was holding it back.   It was fitted with a bronze 9E1 head that although it has been skimmed, does not appear to have a particularly good compression ratio.   I decided to change the head for a late Ruby type.  Having got the bronze head off I compared it with the Ruby head and it seemed clear that the bronze head had a much deeper combustion chamber.   The depth at the valves was 12mm with the bronze head compared to 9mm for the Ruby one.    I then looked at a new aluminium Ricardo head that I had in stock and this looked to have a better compression ratio than the Ruby head.    I am running my RL saloon on a Ricardo head and am very pleased with the performance.
The new Ricardo head was duly fitted to the Pytchley with a new 'early' gasket and the car was taken up the road on my 'test' hill, a steady climb of 951 yards with a couple of easy bends.   With the Ricardo head the Pytchley made the climb in 68 seconds on the first run, a full 4 seconds faster than the best I had been able to achieve previously.  The speed up the hill was altogether faster, cresting the summit at 38 mph whereas the best was 30 mph previously. 
Suffice to say I am a happy Easter Bunny!

(09-04-2023, 01:00 PM)Charles P Wrote:

(09-04-2023, 11:17 AM)Malcolm Parker Wrote: Belated Happy Returns on your big birthday, Ruairidh, I wouldn't mind being your age again.

On Friday I took the Pytchley out on my quite arduous test circuit up and down the edge of the North Yorkshire Moors.   Whilst it was running well, when I opened it up on the old drove road along the top of Sutton Bank, pictured, it was reluctant to pull much over a true 45mph in top, surprising given its light weight and 5.25 rear axle. 
I suspected that the cylinder head was holding it back.   It was fitted with a bronze 9E1 head that although it has been skimmed, does not appear to have a particularly good compression ratio.   I decided to change the head for a late Ruby type.  Having got the bronze head off I compared it with the Ruby head and it seemed clear that the bronze head had a much deeper combustion chamber.   The depth at the valves was 12mm with the bronze head compared to 9mm for the Ruby one.    I then looked at a new aluminium Ricardo head that I had in stock and this looked to have a better compression ratio than the Ruby head.    I am running my RL saloon on a Ricardo head and am very pleased with the performance.
The new Ricardo head was duly fitted to the Pytchley with a new 'early' gasket and the car was taken up the road on my 'test' hill, a steady climb of 951 yards with a couple of easy bends.   With the Ricardo head the Pytchley made the climb in 68 seconds on the first run, a full 4 seconds faster than the best I had been able to achieve previously.  The speed up the hill was altogether faster, cresting the summit at 38 mph whereas the best was 30 mph previously. 
Suffice to say I am a happy Easter Bunny!

Malcolm

Is there a science to the apparently different plug on no 4 or were just low on 18mm plugs?

Charles

Ps. That bronze head looks ideal for a blown car