Streetporting (Sp) is an internal intake/exhaust modification that can only be performed while the engine is disassembled. It is similar to swapping cams on a piston engine, it affects airflow (think lift) and timing (think duration). SP’ing is to be regarded as any other airflow mod (like air filter or exhaust mod) as far as power increases go. A large Sp on a stock car, for instance, might not be as noticeable as a small Sp on a modified car. Sp’ing doesn’t really change your idle ability or rpm, though a large SP can change idle tone a bit and perhaps even make the idle lumpy. IT does affect your driveability, mainly your low end pull. Especially, for instance, pulling out on a steep hill from a dead stop.  The gains on top end are definitely worth the risk, however. Gains from an Sp on a nonturbo are not large, but still worthwhile, around 5-15% depending on mods. Do not plan on passing emissions sniff tests with a port, though it still may be possible with effective emissions tuning.

I generally keep my ports fairly conservative, which is good for a street car. Exhaust ports are opened slightly earlier but kept mild for low noise and emissions. Intake ports are opened, within reason, as much as other ports, boundaries, and water jackets allow.

For the 6 port engines, I now offer 2 styles of port work. These are the “6th port only” streetport, and the “full intake/exhaust” streetport.

For those wanting a little bit of extra top end increase with no sacrifice in emissions, idle, low end driveability, or noise, I offer the 6th port SP. This mod basically opens up the auxiliaries (5th and 6th ports) only, while leaving the other intake ports responsible for idle and low/midrange power stock. I also leave the stock exhaust port alone, however the exhaust diffuser found in 86-91 rotorhousings is removed for better flow (this does not affect emissions or idle, and does not dramatically increase noise). The diffuser is cut out with a torch, and though this leaves a slightly rough cut edge, flow is greatly improved from before and this rough edge in no way affects port flow.

For those wanting the best all around performace available from 6 port engines, I port all the intake and exhaust ports to their practical limits, including primaries, secondaries, auxiliary 6 ports, and exhaust ports. Auxiliaries are ported as described above, secondaries are ported up to the very edge of the divider from the auxiliaries leaving a knife edge divider to keep functioning 6 ports effective, and the primaries are ported mildly since the 6 port irons leave little room for large port work here. Exhaust port diffusers are removed as described above and the port itself is reshaped and ported like a turbo engine streetport. The result is an engine with a mildly affected idle that may or may not pass emissions tests, but should offer good all around performance without significant sacrifice in driveability anywhere in the powerband. This is the best choice for most people IMO.