12-01-2005, 11:36 PM
mpg9999 Wrote:There is less stress (and they can rev sky high) because they use very short strokes. The shorter the stroke the lower the piston speeds. Rod stroke ratio also has alot to do with it.
That reminds me...I've always wondered about Subarus, and why they don't rev to the ceiling.
Let's look at Jack's motor -- A lowly EJ25:
Bore: 99.6 mm
Stroke: 79mm
Redline: 7000rpm
Bore to stroke ratio: 1.2
Now, let's look at a HoMoCo K24:
Bore: 92mm
Stroke: 90mm (!!!)
Redline: 8000rpm
Bore to stroke ratio: 1.02
or a Nissan QR25
Bore: 88.9mm
Stroke: 100.1mm
Redline: 6000rpm
bore to stroke ratio: .888
On top of that, the H4 is naturally balanced!!! So what gives? Why aren't EJ25's (or NA EJ20's, for that matter) 9000rpm screamers from the factory? I mean, it has a better bore to stroke ratio than either of the two engines I gave examples of yet has the middle redline and the least horsepower!?! What gives?
(and don't even get me started on the st00ks. Undersquare what? No sense at all.)
1987 Oldsmobile Cutlass 442