18 Feb 2008

It’s here… a Honda 2.4 liter K24A1 and a K24A2 cylinder head! The engine will come apart, in preparation of getting oil squirters added and honing the cylinders for the new rings (and pistons). Compression will be lowered to 8.5-9.0, for running boost on our crummy 91 octane gas here in California. While lots of people say I don’t need to lower compression, I have a good buddy that built all sorts of crazy Honda engines, all the way up to 1200hp drag racing monsters. He said that all it takes is one long hill and being in the wrong gear to cause detonation (pinging) which will very quickly destroy the engine. The plan is to design every part of the engine for 400hp, but run it at a more “reasonable” 300hp.

A little more infomation about oil squirters, these are oil nozzles mounted in the block that squirt oil up at the bottom of the pistons. The idea is to keep the pistons cool to avoid detonation, yet there’s a lively debate on the forums regarding the need for them. Some people say that switching to forged pistons negates any need for them, while other’s say anything that keeps the pistons cool is a good idea, which I agree with. Factory stock pistons are cast aluminum. This means that as the engine gets hot, the coefficient of expansion for both the piston and cast aluminum block is similiar, so as the piston gets hot the piston-to-cylinder clearance is maintained.

In a boosted engine though it’s common to swap in forged pistons which are far stronger and more resistant to detonation. However, since they are made different, their coefficient of expansion is higher than cast pistons. This can be a very, very bad thing if the engine is run hard (like up a long hill or on a road racing track). The piston keeps getting hotter and hotter and expands faster than the block. Eventually it expands enough to start rubbing on the cylinder walls and once that happens, they get really hot and completely lock up the engine. Sooooo, oil squirters seem like a very good idea to me!

I’m not sure when the engine build will happen, probably in parallel with the chassis build. The goal is to have it done before the chassis is finished. In fact, I’d like to have it done before it’s time to put it on the chassis table, but that’s probably optimistic.