Overporting Smog Heads

Doug, how does the polishing of the chamber surfaces affect the performance, what have you noticed?

In theory, at least, it should allow you to run a slightly higher CR because it eliminates any hot spots. If you think about applying a torch to both chambers, you should be able to visualize how the unpolished head would have little red glowing bumps while the polished head would dissipate and reflect the heat more effectively.
It should help delay the build-up of carbon, (which will also causes pre-ignition) and flow air a little better.

Kool, I can see in-cylinder flow improving somewhat by polishing for sure. I am sure those bumps in the chamber surface from the factory casting act as a heat-sink since they protrude. I noticed you angled the intake valve-guide "tail", if you will, on the outside radius of the port towards the spark plug and exhaust valve. What is your theory on that?

I think it will help pull some of the air from the shrouded part of the valve and swirl it into the center of the chamber.
The runners have some minor details that go along with what I'm trying to do. Immediately after the port is gasket matched the runner is distorted slightly with opposing corners ported more deeply so that both the floor and roof are slightly angled.
The side of the port away from the exhaust valves has a lower floor. The short turn radius has more material removed on the exhaust valve side and the floor is higher.
In theory, this gives the air 2 distinct paths around the valve stem. If I ever set up a flow bench, I could find out if this helps or hurts flow. IDK.But what I'm trying to do is twist the air as it moves down the runners and create 2 streams of air that will cross and hopefully swirl around in the chamber. I would like to see what happens if I hook up a vacuum to a clear tube and run some smoke through the runners.

David Vizard did an article about building cheap flow bench Doug. Here is the link for it Porting School #4 - Budget Bench Electronics - GoFastNews.com - All Racing News All the Time! Your theory is interesting, could this tail directed in the way you have done, promote a slightly better in-cylinder mixing efficiency n the center of the chamber?possibly? for a street mill maybe. I know diesel engines are designed with a runner characterisitic that promotes swirl. Athough, they rarely ever go above 2500rpms, if that, if they are used properly. I will say I have never seen a tachometer in a pull-truck or tractor though while during a run.

I have plans for 2 different flowbenches an have purchased some of the parts to build one. Instead of a shopvac, I have a dust collector that I plan on using. What I don't seem to have enough of is time and space.
Most likely these heads will go on before I build the flowbench. I may have them flowed, IDK yet.

Yeah, I have an area I want to set a bench up in. Although I haven't decided on what to use for a vacuum source etc. But that will not be started for a while since all the money is going into mine and my sisters race cars. The flow bench is nice to see how much of an improvement anyone has made after a porting job or just seeing what you are dealing with if you can not alter the heads for a particular racing class. I am curious on how those heads will perform from what you have done thus far!

Originally Posted by 385serieshemi

Yeah, I have an area I want to set a bench up in. Although I haven't decided on what to use for a vacuum source etc. But that will not be started for a while since all the money is going into mine and my sisters race cars. The flow bench is nice to see how much of an improvement anyone has made after a porting job or just seeing what you are dealing with if you can not alter the heads for a particular racing class. I am curious on how those heads will perform from what you have done thus far!

I ported my 65 heads and put in 1.94 and 1.60 valves. I used a shop vacuum and a smoke source to judge flow with. It doesn't measure flow as on a flow bench but you can see the results. Based on my tests I believe that the air can actually be refracted. I look for high velocity and a flow that bends..no turbulence for the exhaust. On a ford small block I raise and widen the top of the port slightly. I remove and blen the smog port if late model. I haven't heard of anyone doing it, put I put a coarse grit on the inside bends and polish the outside. This seems to bend the flow..anyway it makes power. I like to CC and polish the combustion chamber to get as much reflected heat as possible. For the ford small block I slightly straighten the shot in ( particularly where the head bolt comes through) and cut out the imperfections. If you do nothing more than smooth the casting imperfections down and clean up the valve pocket you will feel it.

Talaposa, what size is the shop vac you are using?? I have two actually, one on the small side and a large one which we barely use.

Originally Posted by talaposa

I ported my 65 heads and put in 1.94 and 1.60 valves. I used a shop vacuum and a smoke source to judge flow with. It doesn't measure flow as on a flow bench but you can see the results. Based on my tests I believe that the air can actually be refracted. I look for high velocity and a flow that bends..no turbulence for the exhaust. On a ford small block I raise and widen the top of the port slightly. I remove and blen the smog port if late model. I haven't heard of anyone doing it, put I put a coarse grit on the inside bends and polish the outside. This seems to bend the flow..anyway it makes power. I like to CC and polish the combustion chamber to get as much reflected heat as possible. For the ford small block I slightly straighten the shot in ( particularly where the head bolt comes through) and cut out the imperfections. If you do nothing more than smooth the casting imperfections down and clean up the valve pocket you will feel it.

Wow... I realize this is raising the dead as this is an old post, but for some reason I never got an email notice on these last 2 posts. It appears that we think alike on quite a few things on porting, and it is nice to hear from someone who has seen and felt the results of some similar theories put into practice. My thought (and hope) on polishing the combustion chambers is to possibly get a little grace for running higher compression by slightly limiting the chance of detonation by eliminating any possible hot spots.
Putting a coarser finish on the inside bends than the outside makes sense to me, and while a different tact than I attempting, in a way is similar to my thinking. Having a rougher surface on the inside bends should slow the flow while the slicker finish on the outside would speed it up. Considering that there is less distance for the air to travel around the short turns, that air would be travelling faster than the air on the wider turns. The difference in the two streams would create a turbulence in the middle as each one created mini whirlpools, the slow air slowing down the fast and vise versa.
By creating 2 different speed surfaces, you would help to equalize the speed of the flow, allowing the entire charge to move more simultaneously down the port, and effectively, straightening it. Pretty cool.
My idea is a little different, I'm trying to redirect those streams of air that are travelling at different speeds into specific paths to twist the streams so that part of each one crosses the port from one side to the other, (straightening the turn), while also (in theory) creating a swirl effect to help atomize the fuel charge and possibly allow more air to occupy the same space by increasing velocity. Kinda like a rifled barrel. After reading that you have done the shop vac smoke thing I was considering trying, I may have to do that if I ever find the time to get back to working on those heads.