Your write-ups and photos are very interesting and informative. Very helpful. Is there any way you can show photos with arrows to define some of the terms you are using? I understand "Bowl", "intake runners", valve guides, etc, but many of the terms you used in the first few posts are in need of arrows to point out which part of the heads you are describing.
Great work with the porting. Think I understand your discussion of atomization. The air has to mix well with the fuel mist entering to get complete burns which gives the best pop in the cylinder which translates to mpg and power. Happened to look at a set of Dart (I think) heads the other day and looked at the detail inside the intake side. Noticed hundreds of tiny horizontal lines cut into the aluminum on the intake side which would obviously create some turbulence or tumbling/bouncing of the air/fuel mix that rushes past. Is it that this air bouncing past the tiny ridges creates some turbulence which forces a better mix of air and fuel coming into the cylinder?
Then, on the exhaust side, am I correct in believing that this area should have a very smooth finish to not create turbulence which would help evacuate the gases without any (or very little) turbulence?
Thanks! That's a good compliment coming from you, since you've done a crazy amount of great work on your own build.
You are correct in that the air is bouncing past those tiny ridges to mix the air and fuel better. If a surface is polished, the air flows better, but the fuel falls out of suspension by sticking to the walls and is slower than the air and it pools up before it reaches the combustion chamber. Perosonally, I think that with fuel injection that this isn't as much of a problem as in carbed engines, since the injector already sprays a fairly fine mist of fuel. But it is nice to have some roughened surfaces, just in case. The exhaust does benefit from the smooth finish, since the air fuel is mostly burned and carbon also has less of a chance to stick to the surface.
Last night, I was wondering whether to continue on with these heads.....the guy that had done the work on them before me, had opened up the bowls to the extent that they likely aren't flowing well. That's my assumption as to why the fuel was pooling up in the bowl in the picture that I posted, that because he had ground down the first valve seat angle to be flush with the bowl diameter, in that I think that there was enough velocity lost where the air/ fuel mixture had slowed down enough so that it wasn't making it into the chamber to the extent that it should be. Apparently, bowls need a venturi effect to ease the transition of air in or out.
I'll have to build the ports up a little in the throat areas with JB Weld, if i'm going to continue. The bright side is that there are some pro guys that build up certain areas with JB Weld, on purpose, like the floors of the runners or exhaust ports, to create a ramp to accelerate flow to get the velocity up. I also think that the floor of the high end runner (the right hand side of the intake runner) is too deep and that the concave here could be costing some CFM.
It looks like these heads have a five angle valve job.....do these heads have a five angle job from the factory?