Moving Engine Bores, Partial Block Fill
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Moving Engine Bores, Partial Block Fill
I will soon be sending my 400 block to the machine shop soon and have a couple of questions.
Has anyone tried offsetting the bores in the direction of the thrust face? The rational behind this is to create greater leverage on the crankshaft immediately after TDC (At TDC in a normal situation the piston, pin, rod, and crank are all lying on a common centerline so no matter how much pressure there is on the piston, no torque is seen at the crank). The offset allows the crank to start delivering torque sooner in the cycle. I've read that 0.020" is as far as one can offset the bore because of gasket restraints. I sonic checked my block and the thinnest cylinder is 0.224 on the thrust face so I should have plenty of meat to cut into.
Has any one tried a 1/3 block fill on the street? Any over-heating concerns with a 400 block (I've got the BB rad)? I assume that the fill is done prior to boring and honing, right?
Has anyone tried offsetting the bores in the direction of the thrust face? The rational behind this is to create greater leverage on the crankshaft immediately after TDC (At TDC in a normal situation the piston, pin, rod, and crank are all lying on a common centerline so no matter how much pressure there is on the piston, no torque is seen at the crank). The offset allows the crank to start delivering torque sooner in the cycle. I've read that 0.020" is as far as one can offset the bore because of gasket restraints. I sonic checked my block and the thinnest cylinder is 0.224 on the thrust face so I should have plenty of meat to cut into.
Has any one tried a 1/3 block fill on the street? Any over-heating concerns with a 400 block (I've got the BB rad)? I assume that the fill is done prior to boring and honing, right?
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Re: Moving Engine Bores, Partial Block Fill (74vetteman)
I don't know about offsetting the bores to accomplish what you're wanting, to do, but I know of a couple of stroked 400's on the street that are partially filled. I know of one that is filled to the bottom of the freeze plugs, and he runs normal temps on the street. I adds to the rigidity of the bore. It's better so fill it before you bore/hone the block, but there are fillers out there that don't expand when they cure. I'd recommend filling beofer boring/honeing in any case though.
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Re: Moving Engine Bores, Partial Block Fill (74vetteman)
I have not heard of that before. My honda v-4 uses offset piston pins. Which might accomplish about the same thing. But heard somewhere that it was for even piston loading. So you didn't have a cylinder thrust face.
I really don't see how .020 would change anything enough to even matter.
Block filling in the very bottom is common in stroker motors. If you have the pan off of a motor you can see that the top of piston only comes down about half way in the bore. So almost all of the heat is in the top of cylinder.
I really don't see how .020 would change anything enough to even matter.
Block filling in the very bottom is common in stroker motors. If you have the pan off of a motor you can see that the top of piston only comes down about half way in the bore. So almost all of the heat is in the top of cylinder.
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Re: Moving Engine Bores, Partial Block Fill (gkull)
The reason I am inquiring about off-setting the bores to the thrust face is because of what I read in Vizard's "How to build max. performance small block Chevy's". In it he states that "on a high compression engine it is well worth the effort". He also states that the usual technique for doing this is to use offset pins in your pistons which can be offset up to 0.060" before encountering excessive bore wall friction. However these pistons are expensive.
The only reason I am considering this is because I am boring the block anyways, and if I can make some extra torque and hp, why not! Vizard states "When you go to .02 offset in the block (if the material is there to do it), there is no disadvantage".
I guess my biggest question would be setting up the block for this. Would it be more difficult then a normal set-up? Any machinists want to respond?
The only reason I am considering this is because I am boring the block anyways, and if I can make some extra torque and hp, why not! Vizard states "When you go to .02 offset in the block (if the material is there to do it), there is no disadvantage".
I guess my biggest question would be setting up the block for this. Would it be more difficult then a normal set-up? Any machinists want to respond?
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Re: Moving Engine Bores, Partial Block Fill (74vetteman)
I can sse the logic but in real life I question the merit. I do believe there would be some to offest boring the cylinders to move the bore further away from the intake valves. I believe you could measure that in terms of airflow if you were running large valves.
I've seen block filler to the bottom of the freeze plugs on the street. Bound to help a 400 hold things steady.
The offset piston thing is pretty common with the Mopar and Ford guys. They install pistons "backwards" so the piston pin is offest the opposite way. Makes for a little piston slap when cold , but nothing terrible. Kind of acts like installing a longer rod.
Jim
I've seen block filler to the bottom of the freeze plugs on the street. Bound to help a 400 hold things steady.
The offset piston thing is pretty common with the Mopar and Ford guys. They install pistons "backwards" so the piston pin is offest the opposite way. Makes for a little piston slap when cold , but nothing terrible. Kind of acts like installing a longer rod.
Jim
