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1989 B350 Maxivan RV: LA 318 rebuild, interior works and so on

Discussion in 'Projects, mods, restoration' started by r0bin, Jul 6, 2020.

  1. dana44

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    Here is something to really look at. The closed chamber portion of the chamber, in your picture, above the valves, there is a step, which shrouds the valve as it opens, both intake and exhaust. Round that sharp edge. What this does is allows the fuel/air entering the chamber to flow over it instead of restrict the flow, and when the sparkplug fires, instead of hitting that sharp edge over the closed valve, it curls over it vice making the flame shoot back into the burned area over the valves. I know that part of the head, when you pulled them off the engine, was black. Black is unburned fuel that sticks to the surface. Round that edge and it will remain clean, meaning the fuel being squished there will burn and stay clean, and a clean combustion chamber means it is more efficient. And the more fuel/air that is being burned against the face of the piston and head means more power and greater efficiency.
     
  2. r0bin

    r0bin Member

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    I guess you mean the sharp edge that defines the "heart"-shape within the chamber? I did put a chamfer of roughly 1 mm on there, and rounded the apex where the two half circles meet quite a bit. Also pulled the chamfer all the way around the edge of the chamber, as the burn marks indicate that the head-gasket diameter is about 1-2 mm larger than the bore.

    PXL_20200829_100236789-2.jpg

    Edit: Didn't have the valves at hand, because they were still at the engine shop. I guess putting them in and then pulling the edge flush to the bottom of the valve would be the most proper way of doing that mod.
     
  3. dana44

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    You have the right location and good start, but if you look and think about it, the intake and exhaust valves are shrouded halfway around the valve when it opens. Your green line is actually how far this section should be rounded from the valve seat to the green line in your picture. As the valve opens, that small gap to the surface of your green line is actually causing turbulence that is preventing fuel/air from exiting the pocket until the edge of the valve is above that quench area. This is a loss of power, flow, a disturbance that smooth fuel/air combustion cannot occur. Rolling this edge back, even with the material removed and lowering the compression by one tenth, increases the flow to more than make up for the loss of compression. Another way to look at it, other than only half the valve being able to exit the open valve, when the spark occurs and the explosion happens, when the flame travels across the face of the valve, all that quench area is dead space, meaning the force on the top of the piston stops at the curved walls, thus the force against piston area is at best 70 percent of the piston top. If that quench area has a radius so the flame can travel into that area you would then have explosion covering 92-95 percent of the piston top, thus more efficient and more torque. Since this is a low end power you need, the greater force higher up is what you are looking for, the more burn while the piston is up gives you more bottom end power every time.
    I've been doing this porting more than 42 years (showing my age) and have never had an issue or problem afterwards. You have a good start by getting rid of the sharp edges, but if you are looking for more, it's still there.
     
  4. r0bin

    r0bin Member

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    So the engine builder hadn't started yet on the heads ... Good for two reasons: I can give him the valve guide bushings before he puts the heads together again ... And I've got the heads in the trunk now :D

    I guess I'll put the grinder to them a bit more. Regarding the amount: would you actually remove the material up to the chamber in that area? So that there is no break between chamber and where it goes up again?
     
  5. dana44

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    What I do to my heads and any I rebuild or port, is put the valve in the head and then lift the valve to see if there is any restriction between the valve and the combustion chamber. As I open the valve, if the distance (it's where you made the green line in your picture) remains constant, so let's say it is .050 clearance, as I increase the valve lift, if it remains the same it is causing interference and flow restriction. By having that wall distance increase as the valve opens, more flow, thus power, thus torque, thus efficiency. This happens at low rpm just as well as high rpm, and you want the low power.
    There was an old article about porting the W2 head (small block Mopar performance head), that have this shrouding of the valve. The testing did all the normal bowl work, port matching, etc., and the numbers for flow were looking very good. The guy then took a plunge cut of this shrouded area and opened it up an extra .050 without angling it any and increased the flow by 50cfm (that's a lot of extra flow for such a small amount of work). By angling or rounding this area around the valve (between the green line you drew and the valve edge), it moves and allows the fuel/air to be sucked into the quench area of that green line area, and when the spark happens and the flame starts moving across the piston, it burns into that area much more efficiently and cleaner, and produces more power. When you pulled off the heads, that area was black and crusty, wasn't it? Pull the heads off 50,000 miles later and they will be much cleaner, thus fuel isn't coking there (unburned fuel sticking to the surface, slow burning after the piston is lower in the bore), because the flame will burn against that area more efficiently with this porting of the combustion chamber.
     
  6. r0bin

    r0bin Member

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    Thanks for the quick reply. I think now I know what you mean, and I will get to it tomorrow or monday. Probably make the intake ports and exhaust ports a bit nicer as well. After a day of grinding I didn't have the mind for super fine work anymore ...
     
  7. dana44

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    I know what you mean with the fine work after all the big stuff. It is amazing what all those little sharp edges and steps do to the combustion and flow. If you think about the expensive hand built engines that for some reason have twice the hp and barely half the cubic inches, if you look at the work they do to the heads, well, that's where you make the power, they clean and contour the combustion chambers and ports, removing all the casting and machining marks throughout the ports and combustion chambers. When I started porting heads I used to polish them, then, did some testing with leaving the carbide burr cut surface (I had rushed and missed a combustion chamber polish but ended up pulling the heads off for another issue and saw the difference, thus stick with it and love it) , which leaves little dimples in the metal. You might gain 3-5cfm in top flow numbers with a polished surface, but have found the little dimples left by the carbide burr cutters prevent any engine, stock (or otherwise), or built for track/racing of any sort, does a couple things. One, the surfaces remain clean and do not get gummed up even if the engine burns oil, or is a two stroke. Two, prevents loading up, as in idling long periods of time and having to rev the engine to clear it out, moreso an issue with carburetor(s). Three, pull the heads and look at the combustion chambers that have burr cut surfaces and they are literally spotless, and I mean literally, so that loss of 3-5 cfm, which you will never be able to tell the difference between the two is not missed at all.
     
  8. r0bin

    r0bin Member

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    Final cut.

    Went over the heads again today, for some fine trimming of the nasty edges around the seats and the discussed changes to the obstructions around the valves.

    Also gasket matched the intake port and got rid of the bumps for the air-pump-inlet in the exhaust ports.

    I am happy with the heads now ;)

    PXL_20200914_112159832.jpg PXL_20200914_115316877.jpg PXL_20200914_115337146.jpg PXL_20200914_115343884.jpg
     
  9. dana44

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    Well r0bin, you did a pretty good job overall. I won't complain or critique because you at least got rid of the majority of the really bad stuff, a positive improvement over stock. Well done.
     
    r0bin likes this.

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