1NZ port & polish

[ChinoCharles]

10.75:1 at worst, 11.5:1 66% of the powerband.

9.5 was a hypothetical.

2000-5000 RPM: about 11.5:1 AFR
5000-5800 RPM: descends to 10.75:1
5800 on: stays around 10.75:1, horsepower flattens out, torque decreases 10%.

[largeorangefont]

Originally Posted by ChinoCharles

10.75:1 at worst, 11.5:1 66% of the powerband.

9.5 was a hypothetical.

2000-5000 RPM: about 11.5:1 AFR
5000-5800 RPM: descends to 10.75:1
5800 on: stays around 10.75:1, horsepower flattens out, torque decreases 10%.

Taking AFR through through the tailpipe on a dyno through OEM cats will give you invlalid results. You need a wideband with a bung installed pre cat.

Your mileage will improve after a tune. That is if you aren't flooring it more than you were to begin with.

If you are gonna get a PnP done free by a reputable shop in your area, yes It may be worth it. If some toolbox shop does it, it will most likely do more harm than good. I wouldn't pay to have it done to this motor. The funds are better spent elsewhere, either an engine swap, or a turbo\supercharger.

I used to work at a shop porting cylinder heads for many championship race teams in various forms of racing, so I know all the processes and methodologies pretty well. Moose is correct, although I doubt you would see 15 Hp on this particular engine without cams or other component upgrades.

[Moose]

Originally Posted by largeorangefont

Taking AFR through through the tailpipe on a dyno through OEM cats will give you invlalid results. You need a wideband with a bung installed pre cat.

Yeah, I was wondering what was up with your AFR.......that's not even close to what it should be! I mean, 11.5:1 is acceptable, but when you start dipping into the 10.X:1 area, that's not good. You could start having problems long term- excessive carbon buildup, detonation, premature O2 sensor failure, etc.....

[acrbill]

The thing about porting and polishing is that every head design requires different work. A lot of the time there is a long trial and error process before every bit of power is extracted.

There are basic things that every head port & polish should include.

Port match intake ports to the manifold.
have a slightly rough texture to the intake ports to help the fuel mix with the air.
open up the exhaust ports and get them as smooth as possible.
unshroud the valves if needed and polish the combustion chambers.

A bad port job can cost you power all over the place too. Keep in mind that it takes 8-12 hours to port and polish a head (for someone who does it often) so if some guy is offering it for free I would be suspect.

Porting heads traditionally offers huge gains. The problem with the Yaris is that it has a relatively low rev limit so much of the potential gains will be beyond the stock rev limiter.

If the guy is just going to clean up the ports I wouldn't bother. Once you open the motor up you are opening the proverbial can of worms.