emissions & SVA

[hugh]

my crossflow engined caterham is finally built after a build period of 1 year and 2 months surely a record! problem is, engine emissions currently 9% at idle i,m told the idle jets i,ve got are far too big, what is the limit for these engines. the spec of my engine is as follows, lotus twin cam pistons 234 cam, shaft big valve head and twin weber 40,s my advisors tell me we could use smaller jets to get it through the test (but it will run like a pig) and then change it after the test all advice gratefully recieved regards hugh

[Roger King]

This may be nothing more than a need to adjust the idle mixture screws. It is quite possible to have oversize slow run jets and still adjust the tickover mixture to the correct figure. Obviously this is not the ideal situation, but it can be made to work.

 

What jets do you have?

 

The other rather more difficult problem could be if you have a flat cylinder head with your flat Twincam pistons. This effectively means that you would have no combustion chamber, which would lead to poor squish, long flame travel, etc. It is possible that this would require the engine to run rich in order to idle properly.