Building Chevy 4.3 liter V6 - 1994 with balance shaft
(→MACHINING AND PORTING) |
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The big question now is if to use aftermarket billet main caps and drill the engine block now for a 4 bolt cap pattern or save that money for the next build. The answer to this is "no", not at this time. The next build may include this modification but aiming at some 250 hp does not require such measures. | The big question now is if to use aftermarket billet main caps and drill the engine block now for a 4 bolt cap pattern or save that money for the next build. The answer to this is "no", not at this time. The next build may include this modification but aiming at some 250 hp does not require such measures. | ||
| − | + | === MACHINE THE HEADS - PORTING === | |
I will not port the heads as this would imply access to a flow-bench. What I will do is blend all sharp edges in the combustion chamber even if it will cost me a bit of CR (compression ratio) to avoid hot spots in the chamber. Then the blending will extend into the runners behind the valve-seats. Also the valve guide bosses will be blended to a blunt round shape inside the runner. Avoiding sharp edges there will help keep the flow laminar. | I will not port the heads as this would imply access to a flow-bench. What I will do is blend all sharp edges in the combustion chamber even if it will cost me a bit of CR (compression ratio) to avoid hot spots in the chamber. Then the blending will extend into the runners behind the valve-seats. Also the valve guide bosses will be blended to a blunt round shape inside the runner. Avoiding sharp edges there will help keep the flow laminar. | ||
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'''HEADS - MACHINE''' | '''HEADS - MACHINE''' | ||
I have removed all the studs and prepared for screw in studs. I'll go with 3/8" studs. The choice of rockers will also be decisive. Aiming at a nice steel roller rocker such as CompCams Magnum Pro Roller Rocker 1,6:1. The geometry defined I'll have the bosses machined for proper height of the studs then the centers bored according to proper alignment from the lifter bores to the valve stems. Came up some new information about valvetrain geometry which will be incorporated here. Most probably I will NOT need guide plates as the rocker arms have stem guides. | I have removed all the studs and prepared for screw in studs. I'll go with 3/8" studs. The choice of rockers will also be decisive. Aiming at a nice steel roller rocker such as CompCams Magnum Pro Roller Rocker 1,6:1. The geometry defined I'll have the bosses machined for proper height of the studs then the centers bored according to proper alignment from the lifter bores to the valve stems. Came up some new information about valvetrain geometry which will be incorporated here. Most probably I will NOT need guide plates as the rocker arms have stem guides. | ||
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| + | '''CAUTION:''' | ||
| + | The replacement studs proposed for this exact engine will not work! SUMMIT proposes ARP studs which are shorter than the V8 parts and feature a M10x1.5 thread for the base thread. This means the outer diameter of the screw in part is 10 mm. The original bosses on my heads have a diameter of 9.4 mm which leaves us with 0.6 mm diameter to cut the tap which is 0.3 mm on each thread. This is a mere 0.012"! | ||
| + | The diameter of 9.4 mm is a perfect center bore for a 7/16"-14 thread. | ||
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| + | Last week (OCT 2016) I had the stud bosses machined by 1 mm (0.04") and made a test assembly with some old TRW screw in studs and a new COMPCams 1.6 ratio rocker arm. | ||
| + | What we found was that the valve geometry is too far to the exhaust side and I need to lower the axle of the rocker arm. We modified 1 of the studs (on a lathe cut a smaller radius onto the shoulder above the hex to lower the assy by some 3.5 mm total. This just put it about right and withouth the 3/8" rocker arm nut it just barely clears the valve covers. | ||
| + | With this information we'll most probably cut the bosses down an additional 4 mm (0.16") for a total of 5 mm (0.20") to get enough clearance to adjust the valvetrain geometry on all valves. Maybe even a mm more. | ||
Machine the valve spring pockets and the valve guide bosses for clearance to accomodate the new lift and oil seals. | Machine the valve spring pockets and the valve guide bosses for clearance to accomodate the new lift and oil seals. | ||
| − | + | === PISTONS - ZERO DECK === | |
It turns out to be a problem and to solve this I will have to do a complete test-assembly including camshaft and rockers with valves. JE Pistons states that 1.585 CD (compression distance/height) pistons are a "zero deck" application while this is not entirely true. As my block is 9.025" deck height and I do not intend to machine .050" off that block I will have to go with custom pistons at a 1.600" CD. As I'm getting really close to the head now and using just the gasket to form the squish distance of some 0.030" - 0.040" (0.85 - 0.95 mm) in order to get good results, I will assemble it with the heads and valves and at the same time determine clearances. The pistons will need valve pockets to accommodate the greater valve lift. | It turns out to be a problem and to solve this I will have to do a complete test-assembly including camshaft and rockers with valves. JE Pistons states that 1.585 CD (compression distance/height) pistons are a "zero deck" application while this is not entirely true. As my block is 9.025" deck height and I do not intend to machine .050" off that block I will have to go with custom pistons at a 1.600" CD. As I'm getting really close to the head now and using just the gasket to form the squish distance of some 0.030" - 0.040" (0.85 - 0.95 mm) in order to get good results, I will assemble it with the heads and valves and at the same time determine clearances. The pistons will need valve pockets to accommodate the greater valve lift. | ||
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