BRN2RUN
Active Member
All of my past specifics is listed in my garage area, so i'll devote this to current and future modifications. I'd recently bought a used set of ported and polished heads off of another member here, to work on. Whoever had worked on these before, had did a pretty good job.....including bowl work. It looks like they had removed light casting from the combustion chambers, and I wanted to do a full job on them.
Bear in mind that i'm not an expert and these are my first heads that i've worked on, but i've spent many hours of research on various things--dry flow versus wet flow, intake versus exhaust bowls, compression, fuel atomization/ maximizing efficiency, air flow patterns, etc. It's time to put it into practice.
The great thing about these is that they were already put on someone's car, so it gives an indication of what could be improved. Having the fuel burn patterns and seeing what residues are left, gives a good idea of where flow design could be improved upon. The stock combustion chambers had built up a little bit of carbon in some of the smaller casting marks in the combustion chambers, which may likely be creating small hot spots and hot ridges that may lead to an increase in detonation.
I cc'd the original chamber, and it was 60 cc. It looks like there was only a light casting finish removed, but it's safe to say that if anything was hogged out, it still measured less than Ford's factory specs. My almost finished chamber measured 62 cc (with spark plug and valves in), and considering that Ford's official specs on their chambers are 61.5 to 64.5 cc's each, it's clear that even from the factory, there's no real strict measurement. I'm wondering that if, because these are even fire engines, if the two opposing banks aren't vastly different in combustion chamber size and costing some power. Also, i'm wondering if some of the cylinders aren't higher in compression than they should be, which may be causing some light detonation and some power as well. Detonation doesn't just ruin engines--it robs the engine of some power.
Analyzing the unburnt fuel residue that is pooled up around the valve seat in the bowl area, as well as on the back of the valve, it's evident that even a rougher finish (what looks to be about 80-100 grit or so), there is some fuel that isn't getting atomized, and isn't even making it into the combustion chamber. Whoever had worked on the heads that i'd bought, had left some rougher casting marks right by the injector, which is a good idea to break up the spray a bit, also because the angle that it's on is shrouded a bit from oncoming air and any air that hits it would experience turbulence pretty much right at the injector. But based on the fuel pattern, this isn't the problem area. The problem is where the air/ fuel mixture slams up against the far side of the bowl, when the far side of the bowl is basically at a 90 degree angle. Air travels at the top of the runners, and it makes sense that the full air wave/ pulse would smash against the back of the wall, along with the fuel. The air is slippery enough to make it through, but i'm thinking that putting some dimples in that area might break up the fuel enough so that it's a finer mist, so that any fuel droplets are much lighter, to make it out the valve.
Here's some rough work after a few hours--the middle chamber still needs some work, but it shows a bit of an evolution. The spark plug boss is almost finished on the left, the middle one needs to be ground down a bit more, and the almost stock right one is quite the hindrance in airflow/ fuel flow. I've still honoured the heart shaped pattern, but i've tweaked it and refined it a bit.
Here's after a bit more work and refinement. It may not be evident from the pictures, but there was an additional layer that was removed and smoothed out around the spark plug bosses and in that general area, to contour it more.
I'd taken the chambers almost out to the gasket (allowing for 1/16" of an inch for gasket expansion), and although these aren't yet polished and finished, these two combustion chambers are almost completely done. I'd grinded down the spark plug boss/ bung area to cut down on flame/ spark shrouding, and smoothed out any sharper edges (especially the one around the outer edges of the combustion chamber, and the angled line right by the quench/ squish area, so that it has more velocity in and out of the chamber. These had cc'd at 62 cc's, so that's well within Ford's factory rating of 61.5-64.5 cc's per chamber. I don't suspect there to be much, if any, compression hit, though the efficiency of these chambers seem like they would be more conducive to a better burn. My estimate is that the intake side will be more or less the same efficiency, but the flame will burn better and the exhaust valve will breathe better as well, considering that i'd de-shrouded it quite a bit.
On the area around the spark plug leading up to the quench/ squish zone, I think that i'll have a rougher, almost satin finish, around 80-100 grit. From what i've analyzed on other heads (as well as the carbon/ fuel patterns on these heads), that's where the majority of the make or break zone will be in terms of burn/ combustion quality. Fuel swirls across the spark plug area, towards the exhaust side, and fuel should atomize well in the burn as it swirls across a rougher texture. The eased ridge should promote an easier transition over and across and to and from the quench/ squish area, across the stroke/ cycle range. The chamber also goes just a little deeper around the intake and spark plug area, giving a slight advantage in cc area and overall shape.
I don't know what that weird indent was in the middle of the chamber, but I took it out. Does anyone know what this is? My guess (if it's not a casting flaw) is that it may have been for some sort of purposeful turbulence (intentional dimple?), but it was bugging me--most of the really high performance heads that i've seen, have these types of things taken out of them, or the heads never had them in the first place. The slightly roughened finish around that area should speed up flow and velocity (in both out of the intake valve, and into the exhaust valve--there's tons of shrouding around that whole middle area), but atomization should mostly be addressed already in the fuel bowl with dimples by slowing down the fuel just enough, and as the fuel sweeps across the 80-100 grit spark plug area as a failsafe to burn whatever fuel isn't atomized.
Judging on these dye patterns that HotRod Magazine had seen after they tested wet flow on some of their heads (they're not 3.8 heads, but have a similar heart shaped pattern), it's clear that fuel takes an outermost circular pattern, but it's also clear that if you leave the atomization until the combustion chamber, that it's going to have adverse effects--the concentration of blue dye is fuel, and quite a bit even gets up into both of the quench/ squish areas. That gives credence to the theory that the intake bowl work can be make or break, in terms of power.....and that a dry flow bench only tells part of the story. It gives an idea as to how air flows in the combustion chamber. The dimple appears to be effective in its general area, but if fuel isn't getting atomized well before that point, it looks like it's of little use, anyways, because a large portion of fuel is still getting past the spark gap and outside of the flame pattern.
Some guys dimple the combustion chamber, but I think that would be too turbulent and could cost some power and flow in and out of the chamber (though some strategic dimpling may be effective in the intake bowl). Plus, it may lower the compression ratio a fair bit. Other guy have cut lines into the chambers, and there's also Singh Grooves, to which i've never seen anyone try it and notice any difference (again, this would likely drop the compression level). Even on the back of valves, some people have noted that the only thing that they've noticed is that fuel pools up. I think that the more efficient way is to create swirl, to create light 80-100 grit sanding marks in the direction that the air/ fuel flow is headed, across the spark plug boss and towards the exhaust valve.
Here's a combustion chamber with a much better burn, where the blue dye is not concentrated anywhere
Of course, if anyone has anything to add on theory, or anything else, feel free to contribute.
Bear in mind that i'm not an expert and these are my first heads that i've worked on, but i've spent many hours of research on various things--dry flow versus wet flow, intake versus exhaust bowls, compression, fuel atomization/ maximizing efficiency, air flow patterns, etc. It's time to put it into practice.
The great thing about these is that they were already put on someone's car, so it gives an indication of what could be improved. Having the fuel burn patterns and seeing what residues are left, gives a good idea of where flow design could be improved upon. The stock combustion chambers had built up a little bit of carbon in some of the smaller casting marks in the combustion chambers, which may likely be creating small hot spots and hot ridges that may lead to an increase in detonation.
I cc'd the original chamber, and it was 60 cc. It looks like there was only a light casting finish removed, but it's safe to say that if anything was hogged out, it still measured less than Ford's factory specs. My almost finished chamber measured 62 cc (with spark plug and valves in), and considering that Ford's official specs on their chambers are 61.5 to 64.5 cc's each, it's clear that even from the factory, there's no real strict measurement. I'm wondering that if, because these are even fire engines, if the two opposing banks aren't vastly different in combustion chamber size and costing some power. Also, i'm wondering if some of the cylinders aren't higher in compression than they should be, which may be causing some light detonation and some power as well. Detonation doesn't just ruin engines--it robs the engine of some power.
Analyzing the unburnt fuel residue that is pooled up around the valve seat in the bowl area, as well as on the back of the valve, it's evident that even a rougher finish (what looks to be about 80-100 grit or so), there is some fuel that isn't getting atomized, and isn't even making it into the combustion chamber. Whoever had worked on the heads that i'd bought, had left some rougher casting marks right by the injector, which is a good idea to break up the spray a bit, also because the angle that it's on is shrouded a bit from oncoming air and any air that hits it would experience turbulence pretty much right at the injector. But based on the fuel pattern, this isn't the problem area. The problem is where the air/ fuel mixture slams up against the far side of the bowl, when the far side of the bowl is basically at a 90 degree angle. Air travels at the top of the runners, and it makes sense that the full air wave/ pulse would smash against the back of the wall, along with the fuel. The air is slippery enough to make it through, but i'm thinking that putting some dimples in that area might break up the fuel enough so that it's a finer mist, so that any fuel droplets are much lighter, to make it out the valve.
Here's some rough work after a few hours--the middle chamber still needs some work, but it shows a bit of an evolution. The spark plug boss is almost finished on the left, the middle one needs to be ground down a bit more, and the almost stock right one is quite the hindrance in airflow/ fuel flow. I've still honoured the heart shaped pattern, but i've tweaked it and refined it a bit.
Here's after a bit more work and refinement. It may not be evident from the pictures, but there was an additional layer that was removed and smoothed out around the spark plug bosses and in that general area, to contour it more.
I'd taken the chambers almost out to the gasket (allowing for 1/16" of an inch for gasket expansion), and although these aren't yet polished and finished, these two combustion chambers are almost completely done. I'd grinded down the spark plug boss/ bung area to cut down on flame/ spark shrouding, and smoothed out any sharper edges (especially the one around the outer edges of the combustion chamber, and the angled line right by the quench/ squish area, so that it has more velocity in and out of the chamber. These had cc'd at 62 cc's, so that's well within Ford's factory rating of 61.5-64.5 cc's per chamber. I don't suspect there to be much, if any, compression hit, though the efficiency of these chambers seem like they would be more conducive to a better burn. My estimate is that the intake side will be more or less the same efficiency, but the flame will burn better and the exhaust valve will breathe better as well, considering that i'd de-shrouded it quite a bit.
On the area around the spark plug leading up to the quench/ squish zone, I think that i'll have a rougher, almost satin finish, around 80-100 grit. From what i've analyzed on other heads (as well as the carbon/ fuel patterns on these heads), that's where the majority of the make or break zone will be in terms of burn/ combustion quality. Fuel swirls across the spark plug area, towards the exhaust side, and fuel should atomize well in the burn as it swirls across a rougher texture. The eased ridge should promote an easier transition over and across and to and from the quench/ squish area, across the stroke/ cycle range. The chamber also goes just a little deeper around the intake and spark plug area, giving a slight advantage in cc area and overall shape.
I don't know what that weird indent was in the middle of the chamber, but I took it out. Does anyone know what this is? My guess (if it's not a casting flaw) is that it may have been for some sort of purposeful turbulence (intentional dimple?), but it was bugging me--most of the really high performance heads that i've seen, have these types of things taken out of them, or the heads never had them in the first place. The slightly roughened finish around that area should speed up flow and velocity (in both out of the intake valve, and into the exhaust valve--there's tons of shrouding around that whole middle area), but atomization should mostly be addressed already in the fuel bowl with dimples by slowing down the fuel just enough, and as the fuel sweeps across the 80-100 grit spark plug area as a failsafe to burn whatever fuel isn't atomized.
Judging on these dye patterns that HotRod Magazine had seen after they tested wet flow on some of their heads (they're not 3.8 heads, but have a similar heart shaped pattern), it's clear that fuel takes an outermost circular pattern, but it's also clear that if you leave the atomization until the combustion chamber, that it's going to have adverse effects--the concentration of blue dye is fuel, and quite a bit even gets up into both of the quench/ squish areas. That gives credence to the theory that the intake bowl work can be make or break, in terms of power.....and that a dry flow bench only tells part of the story. It gives an idea as to how air flows in the combustion chamber. The dimple appears to be effective in its general area, but if fuel isn't getting atomized well before that point, it looks like it's of little use, anyways, because a large portion of fuel is still getting past the spark gap and outside of the flame pattern.
Some guys dimple the combustion chamber, but I think that would be too turbulent and could cost some power and flow in and out of the chamber (though some strategic dimpling may be effective in the intake bowl). Plus, it may lower the compression ratio a fair bit. Other guy have cut lines into the chambers, and there's also Singh Grooves, to which i've never seen anyone try it and notice any difference (again, this would likely drop the compression level). Even on the back of valves, some people have noted that the only thing that they've noticed is that fuel pools up. I think that the more efficient way is to create swirl, to create light 80-100 grit sanding marks in the direction that the air/ fuel flow is headed, across the spark plug boss and towards the exhaust valve.
Here's a combustion chamber with a much better burn, where the blue dye is not concentrated anywhere
Of course, if anyone has anything to add on theory, or anything else, feel free to contribute.
