I have all the tools and knowledge I need, prob more than the pros do lol. So on with the thread...
OK I will make this quick.....The long intake runners allow this manifold to achieve the great torque numbers at lower rpm. As air rushes towards the intake valve its builds up speed and its static pressure lowers as the result. Once the intake valve closes this rushing air hits the back of the valve, slows down and in turn its static pressure rises. This rise in pressure causes a higher static pressure than the rest of the manifold where air is moving around to the other cylinders. This pressure change causes shock waves that travel up and down the intake runners. Helmholtz frequency waves can in turn be used to push air down in the cylinder. As the valve gets ready to open up again, frequency waves can help push more air down the cylinder from it traveling from the plenum and back. The optimum frequency wave is usually known by looking at torque curves as the torque curve of an engine is tied directly to its volumetric efficiency.
What does this mean about our cars. The intake side is greatly influenced by the exhaust side and the cam overlap between the intake and exhaust side. The 04-05 years have smaller intake runners and smaller exhaust tubes. The 06-08 have bigger intake tubes and exhaust tubes, but Honda fixed the tourque peak problem by giving these years different camshafts that change the overlap between the intake and exhaust side. This way the low end torque didnt suffer and the engine gained more top end. What will I see on my 04 by changing to a bigger manifold and TB. Well, an increase in the top end for sure but also a shift on the torque peak RPM. It will take a few more RPM to make the same torque, but it the torque difference will be so minimal that I will only notice the top gains.
Things I noticed about the TSX intake manifold...... This manifold suffers from a few things and will never be a performer manifold, but it does its job ok for torque purposes.
1) Small plenum (the smaller the more throttle response and better part throttle engagement, also good for MPG's)
2) Thin casting ( makes shaping it tricky and blowing through is easy)
3) #4 and #1 runner openings are very oddly shaped ( totally different from the middle two runners, not good for high RPM)
4) Plenum ends short on #1 runner ( It almost hits the alternator so I can understand why they made it this way, but again not great for high RPM).
5) Runner openings are squarish ( not good for high RPM gains).
6) Casting imperfections ( although better then usual Honda manifolds)
Things to improve.....
1) The intake runner opening need to be reshaped. This is where most gains will be achieved.
2) Clean up casting imperfections (plenum and runners)
3) Match the two halfs. Where the manifold bolts together with the injector base I noticed that they didnt match 100%. This is due to cooling effects as parts will vary with shrinkage.
4) Match the manifold to the head
5) Make my own heat shield IM gasket. The Hondata one leaves way too much of an opening around the intake runners. This causes little pockets where vortexes can occur.
The intake runner opening and their squarish meet up. Hard to tell from this pic. I will take some more later on.
On with the tools to use for this project...
Since I will not be bolting up a bigger TB or greatly porting the plenum no CNC's will be used. Just great old hand work. My choice are carbide porting tools and flap wheels.
Flap wheels are great. They last long, they are cheap, come in almost every imaginable size and grit. My favorite thing about them is using them to reshape the runner openings. Also with the extension they can go up and down the intake runners to clean up casting imperfections. They also allow for even porting.