From: Bruce White ([email protected])
Date: 23 Feb 2002
Time: 21:42:26
Remote Name: 129.96.230.135
John Sutton at http://www.motorsnippets.com has written the following article in his ‘Austin 7 Myths Dispelled’ section.
“Aluminium cylinder heads on unsupercharged Austin 7 engines reduce the horsepower output by about 15% compared with the equivalent iron head. This is because the side valve engine has a very large surface area to the combustion chamber and the faster conductivity of the aluminium allows the flame to go out too soon to give maximum efficiency. The works supercharged racers were giving an output of 50 to 70 horsepower depending on their state of tune and were running on alcohol fuel. In this state of tune an aluminium head was necessary to dissipate the additional heat. These works engines were fitted with 25 stud heads in 1931 subsequently increased to 32 studs in 1935. The additional studs were tightened to no more than 15 ft/lbs and were there to prevent movement rather than clamping pressure.”
The bit about reducing the horsepower by 15% on non supercharged sevens caught my eye, any other opinions out there?? I might have a Cambridge head going cheap..... but it looks pretty. For those who haven’t seen the site, check it out!
Bruce