Just some things I've found out about the Si's engine compared to other Hondas/Acuras.
From k20a.org:
"The head is 100% TSX
the block is a tsx 2.0L version with dual oil balance shafts and oil jets with a type s oil pan.
oil jets, and the little oil pump cover signifies the dual shafts..
The oil pan is not from the K20a2 though. It uses a different casting so that the rear motor mount can attach to it.
The type s style single pump has a longer cover
see the tsx water oulet on the right side
looks like stock k20a2 clutch
As far as the cams, they have different part numbers so we are not going to know till we test them
'06 Si Cams
Intake 14110-RRB-A00
Exhaust 14120-PRB-A01
'05 Type S Cams
Intake 14110-PRC-030
Exhaust 14120-PRC-030"
All of this is actually pretty surprising since the engine designation is K20z3 and the 06 RSX-S engine designation is K20z1. Although the Si shares some similarities, it seems to actually be closer to that of a TSX, including the Drive-By-Wire throttle. Another example, is the transmission. The Si tranny uses 1st-5th gears from the RSX, but the 6th gear is from a TSX. The LSD is from a JDM DC5R. The syncros on gears 4-5 are carbon, not brass like the 02-04 RSXs. This should reduce the problems that tranny had with gear grinding.
The Si uses the RBC Intake Manifold from the JDM Accord Euro R. The TSX uses an RBB Intake Manifold. The difference between the two is the RBC uses shorter fatter runners optimized for high rpm breathing and the RBB uses a long narrow runner which is good for torque. This is part of the reason the Si loves to rev, because it was given the intake manifold do so. It's trade-off is torque. We all know the Si's torque is low compared to it's competitors. Theoretically, you could swap the RBB Manifold onto the Si and pick up better torque, at the slight sacrifice of top-end. How much sacrifice and how much gain is unclear. The RBB Manifold is also used on the 2.4L 160hp Accord.
The Si uses raised dome pistons.
picture of the balance shafts and oil pan
The balance shaft smooths out the engine, reducing vibration, which is why there's a difference in horsepower rating between the RSX-S and the Si. These are the reason for the 4 horsepower difference after the new SAE ratings.
Air Intake
Notice the MAF sensor on top of the Air Filter. For those that don't know the MAF (Mass Airflow) sensor converts the amount of air drawn into the engine into a voltage signal. The ECM needs intake volume to calculate engine load. This is necessary to determine how much fuel to inject and when to ignite the cylinder.
Honda advertises the Si as having a cold air intake. The snorkel runs under the battery tray to another box and from that box another snorkel runs to the fender. With it's length and all the bends it probably does drawn in cooler air but at the expense of throttle response.
Here's the Head, from Fgcoupe.com
Opening the block, from Fgcoupe.com:
I woulda just posted links but I figured it made more sense to paraphrase some of the people and post pics. Knowledge is free anyway.
Most of this info is on point, but I'm still trying to iron out some of the details. I'll keep this thread updated as I find more information. Still working on you R18 guys and gals but info is pretty scarce. I can tell you, though, it has the potential to be one helluvan engine.
