Real Fiero Tech

I am pretty sure I'm going to do some port work on the 20v engine included with the Corolla project I just bought. I found a cross section of the 20v head online, and I'm trying to decide how to approach this. Since I don't have a lot of experience porting heads (and no measurement tools, though I could make a crude flowbench), I usually just clean up the casting marks in the head, and focus on the valve pocket, or the area immediately behind the valves. I'll make sure there are no significant steps left from when the factory installed the valve guides, and I'm careful not to mess with the short-side radius. On my Quad4 head, the only changes to the actual port shape that I made were to raise the roof of the exhaust port and to clean up behind the valve seats.

My first reaction to the 20v head is to smooth the roof of the exhaust, but after reading through a lot of the information on this site, as well as others, I don't know if that would be beneficial. Someone recently posted a document where gains were made by deviating from the typical idea of a 4-valve intake port. Also, how should I deal with the divot on the exhaust port floor?

I've also heard that attempting to even the flow around the valve (creating a more efficient airflow "cone" into the cylinder) can help. I was considering either adding material to the floor of the intake to flatten it out and make it more D-shaped, and also possibly cutting the bottom "corners" of the exhaust to achieve a more D-shaped port, since adding material in the exhaust isn't something I want to deal with. I have some concern about losing velocity as well. I have seen builders shape the intake runners in such a way that the bottom of the runner is slightly longer -- the entry to the runner is curved. I don't know how much this would help either, unless the runner was a straight shot into the head.

Basically, what are some opinions on this head? I don't plan on doing much to the intake other than cleaning up the casting and matching to the throttles (not the gasket). I need opinions on the exhaust, however. The engine will be naturally aspirated for awhile so that I can get the car together and setup without rebuilding the engine, but it will eventually be rebuilt and turbocharged, so I am keeping that in mind with all of my modifications.

I've got a book on building motors, and it goes into a little detail about porting heads.

But it basically tells you that unless you know what you're doing, changing the overall shape of the ports isn't a good thing, but it had a similar cross-section with some notes on areas to concentrate on...

Just from memory, things like this:

For those with more experience: Thoughts?

If you don't have experience porting heads and you don't wanna mess up this head with trial and error with a flowbench try not to reshape the port.
Knock down sharp edges, focus most of your work on the bowl area behind the valves and that should be enough.
Unless you know what your doing, have access to an accurate flow bench and have more than one head to mess with, you won't pick up any significant flow numbers.

Correct.

A cutaway is very helpful, but you NEED a head with which to experiment if you want to go crazy. If that's not available, don't go crazy.

I would like to note just how awesome that head is already!! There seems no room to enlarge the valves though. If you have not thought to do it I urge you to consider getting a 3 or 5 angle job on the valves. To me the head looks VERY efficient.

White84SE wrote:I would like to note just how awesome that head is already!! There seems no room to enlarge the valves though. If you have not thought to do it I urge you to consider getting a 3 or 5 angle job on the valves. To me the head looks VERY efficient.

hey bud, this thread is eight years old...

Bryson hasn't posted here in a few years, but maybe he still gets the topic reply notifications...