Small vs mild vs large streetport

[NoDOHC]

If you go too big with the street port, your intake manifold will become your primary restriction. If you go too small, the engine can't breathe. From what I am told, you want the intake tract on the engine to remain the same cross-sectional area throughout. If anything, the port should be slightly smaller than the intake runner.

Basically street manners are completely determined by port timing. If you extend the port downwards too much, it will not idle well. Upwards hurts your starting and low-end torque.

The minimal street port that I have on my 4-port was designed to leave port timing completely stock, but to close the port more abruptly (better dynamic tuning) and allow for additional cross-sectional area to support my 1.42" primary and 1.68" secondary intake runners.

It idles rock-solid and does not stall at launch (110 Wlb-ft at 1000 rpm by g-tech). It really doesn't start to pull until 3500 (pulls the tires loose) and it comes alive at 5500 (weeee).

I will post power numbers when I get a chance to go to the dyno.

[RETed]

Porting isn't just about taking a die grinder and changing the port shape...
I think it was Judge Ito said it best when he called it a 3D process.
Good porters can actually keep the stock intake port shape and get it to flow better just by redoing the contour within the passage!
Think about it!
If the entire intake path was straight, then changing the port shape will change airflow dramatically.
Because the intake path takes a very abrupt bends to get into the combustion chamber, there's a lot more voodoo that just grinding metal away here and there...
It'll take tons of fluid dynamics theory to hash all this out...

In general, a smaller port will give you better (port) velocity.
Velocity is GOOD, especially for low end.


-Ted