Destroking 3SGTE

[mcjonesy]

I posted this on mr2oc.com already, but i thought i'd see what kind of response it gets here.

[Paste]
Ok, so i got ambitious and started doing a lot of math:

Let me preface this by saying that an engine with a rod/stroke ratio of 1.75:1 is said to be geometrically perfect. In other words, with that r/s ratio an engine is able to rev higher with minimal stress on the side walls of the combustion chamber.

So, here's the idea:

3SGTE Stock Engine Specs:
Rod: ~5.433in (~138mm)
Stroke: ~3.386in (~86mm)
Bore: ~3.386in (~86mm)
Displacement: 1998cc (2.0L, 121.87800in^3)

This gives the 3SGTE a r/s ratio of 1.6045:1 which, while impressive and very manageable isn't quite perfect. So, after thinking about it, I tried to figure out how to reach the "perfect" ratio.
If you decrease the stroke to ~3.105in (~78.867mm), the r/s ratio goes from the stock 1.6045:1 to a near perfect 1.7497:1. The only problem with this is that instead of displacing 1998cc of air/fuel, the displacement drops to ~1832cc, meaning we just lost .2L of displacement, and that just isn't acceptable. However, by over-boring the engine slightly to 87.5mm (~3.445in, .030 over) the displacement climbs back up to 1897cc.

Basically, you sacrifice .1L (.2L if you keep the stock bore) of displacement, but your engine will rev to close to 12k rpm safely which in turn means more boost which means more power.

This was the result of my being bored (no pun intended); please feel free to flame/comment all you want.

Matt