How Much Horsepower Can You Hope To Get
 

There are some basic laws of physics at work in an engine, so we can quite accurately predict the potential horsepower an engine is capable of.

The bottom line is how much fuel mixture can you get in the cylinder, this is ultimately defined by the size of the inlet valve on a naturally aspirated engine.

A couple more hp can possibly be attained by further tuning of the exhaust and intake so that the exhaust is actively scavenging gasses at a certain RPM, and if the intake has increased air pressure, e.g. air to the carbs is ported from the front of the car so that at speed air is being forced in.

 

 

2 valve per cylinder, parallel valve, pushrod engine

Inlet valve size mm (inch)

Max hp (flywheel) 4 cylinder

Max hp (flywheel) 6 cylinder

33.172 (1.306)

103.71

155.54

35.052 (1.380)

115.79

173.68

35.433 (1.395)

118.33

177.49

36.322 (1.430)

124.34

186.49

36.600 (1.441)

126.25

189.38

36.830 (1.450)

127.84

191.76

37.465 (1.475)

132.29

198.43

37.750 (1.486)

134.31

201.46

38.100 (1.500)

136.81

205.22

  
  These figures represent the  most to expect from a highly developed and well built race engine. Don't expect this kind of power just by putting a sports exhaust and richer jets on. Check out David Vizards manual on tuning triumph engines. The most power he could get after much development work is similar to these figures. If someone tells you they have a naturally aspirated 170 horsepower  4 cylinder engine ask them what size there inlet valves are. if they are bigger than 1.5' let me know I would be interested to know what valves they used etc, if they state any of the above sizes you have a pretty good idea it was a case of "the fish I caught was THIS big."!!  
   
   
  My test car showing the difference a race spec cam makes, all other parts remained the same!