What's the purpose of those small "blind" exhaust port channels?

ginek

Excuse me perhaps an ignorant question.

Just having a stripped z22se head on my bench.

On the exhaust side I noticed there are some narrow channels that fork from the exhaust ports toward the manifold. And manifold actually blocks them.

There must be some purpose for such design, otherwise I imagine wouldn't they just introduce some turbulence in the exhaust flow?

evocarlos

its for the factory SAI (secondary air inlet) system required in some countries for emissions at startup

evocarlos

Secondary Air System
The secondary air system is designed to add oxygen to the exhaust gases to aid in the final "burn off" of the emissions. Fresh air is pumped into the exhaust by either an electrical/mechanical pump or a special one-way reed valve that utilizes the pulsing of the exhaust from the piston firings to suck the fresh air into the exhaust system. The secondary air is then injected into the exhaust manifolds, catalytic converters, or both.

Secondary air is used most commonly during the warmup cycle to help burn the rich air-to-fuel mixture needed to run a cold engine. Usually after two to three minutes, the catalytic converter is nearly at operational temperature, so the secondary air system shuts down. On some larger vehicles (e.g. trucks and SUVs), the secondary air system pumps air into exhaust manifolds during warmup and then directs the air into the catalytic converters during normal operation to help "burn off" the high fuel loads required to operate these heavy vehicles.

ginek

Evocarlos, thanks for explanation. Based on your hint, I'm able to find more information.

It seems something from the past - I think introducing air into exhaust was in the early days of >>emission industry<<, also this passages are entirely blocked by manifold I don't see a way where fresh air could enter at all. Nevertheless, I'm looking at Germany/UK sourced cylinder heads. Alternatively, if there is any country they actually made this system work on z22se (or close derivative), would be interested to see entire system.

In fact this thread suggests, it's a left over casting from the past:
http://www.cobaltss.net/forums/2-2l-l61-performance-tech-45/secondary-air-injection-late-production-2006-l61s-38488/

I'm thinking now whether just to fill the holes with some heat resistant metal epoxy and grind to finish the port wall, would have a positive effect to the exhaust flow. Can't believe nobody has tried something like this.

evocarlos

its still a requirement in sweden
not an old casting leftover
2012 turbo manifold with SAI pipework

nobody has tried filling them as its pointless once it fills with exhaust gas the rest of the gasses pass it by