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Well I Got The Header...

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the stock 7th gen manifold is such a hunk of junk, theres not much you can do to the lump of cast iron. the runners are VERY short and just dump into a chamber then down the pipe. you could port it out alot and youd have a decent turbo manifold. but for an NA engine you want equal length matched runners that are paired to the firing order to scavenge the exhaust pulses.

Does increasing the size of the exhaust openings do anything to improve performance over stock??

you mean porting the head or larger exhaust runners? i think my powerband has changed some, i feel like it pulls all the way to the end of the gear better.

I meant something as simple as filing the exhaust ports to smooth out the airflow into the exhaust.

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im not sure how much of a difference it'd make. you'd have to take off the head and take it all apart to do that.

What about smoothing out the openings in the exhaust manifold (versus changing to headers)?

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Be real tough to port a cast iron manifold on the 4A-FE/7A-FE vs the steel manifold on the 1ZZ-FE/2ZZ-GE engined Corollas. Not sure there is enough "meat" on the casting to do a decent job without weaking it too badly. Not the old Mopar cast manifold from the 60s and 70s - which returned impressive numbers for a cast OEM piece and had enough meat to port effectively.

 

Still - every little bit might help with making some more power. Old school techniques like gasket/port matching and contouring the entry and lengths of pipe for enhanced flow. Though in the end - probably cheaper to buy a header from the beginning compared to the cost of the abrasives kit and die grinder (dremel will not cut it here - barely makes it with mild steel).

 

Be real tough to port a cast iron manifold on the 4A-FE/7A-FE vs the steel manifold on the 1ZZ-FE/2ZZ-GE engined Corollas. Not sure there is enough "meat" on the casting to do a decent job without weaking it too badly. Not the old Mopar cast manifold from the 60s and 70s - which returned impressive numbers for a cast OEM piece and had enough meat to port effectively.

 

Still - every little bit might help with making some more power. Old school techniques like gasket/port matching and contouring the entry and lengths of pipe for enhanced flow. Though in the end - probably cheaper to buy a header from the beginning compared to the cost of the abrasives kit and die grinder (dremel will not cut it here - barely makes it with mild steel).

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