porting the exhuast manifold

[thehookeup]

so as i understand it you dont want to have a exhaust port and a wxhaust manifold that are gasket matched, you want to have a "step". with the exhaust port being smaller than the entry into exhaust manifold. i guess it helps with the the exhaust pulsation, making sure that the back pressure doesnt push back into the exhaust port.

im just wondering if this is a big deal, or if i can enlarge the ports to the same size without affecting the plusation of the exhaust gases its on a ej22t stock heads and stock exhaust manifold...

[206er]

I have heard about having a step into the manifold too. something about helping back pressure.
I ported my exhaust manifold about 2" in,mainly to get rid of some welds inside that were basically restrictors. I'm not sure if I actually picked up any power since I did it at the same time as a few other mods.
I used a grinding stone about 1" wide on a big old high speed drill motor.

[thehookeup]

yea im not really worried about picking up power, cause if it did i know it would be too small to notice. i am just worried about screwing up the back pressure. i would like to match the ports, but if a step is what i need a step is what i got.

[sammydafish]

it's called a reversion damn. It works well in turbo cars where the turbo is mounted close to the valves. It also works well when tuned headers are used. I'm not sure if it would have any effect or a measurable one on the Subaru since the length from the head to the collector or turbo is so long. You might want to see what turbo Porsches do. I didn't notice the last time I had one apart.

[evolutionmovement]

It must be using the reflection from the step to repel exhaust pulses from getting back to the valves, right?

[thehookeup]

you got it.

[sammydafish]

It must be using the reflection from the step to repel exhaust pulses from getting back to the valves, right?

yup