Thread: Max Dynamic Compression Ratio?

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tcodi, I don't think you want to start fooling around with lead. I suspect there are some pretty hefty fines if the authorities find out you're using it on the street.

I don't know about you Eric, But I don't like "fly poop in my pepper". Yes, it is just a truck - but I figure while I'm at it I might as well try to make it as efficient as I can versus just tossing a bunch of stuff together, but that's just me. Coulda just bought a crate motor for that matter.

I intend to follow that plan Pat. Picked up my CC'ng stuff and die grinder's today. I was going to ask how many CC's is typically lost to polishing but I figured I'd find out soon enough. There is some flash to be removed around the perimeter and the chamber surface is like sandpaper. I intend to leave the ridge (but not the flash) around the intake valve to help dispurse any wet flow, will smooth out around the exhaust valve, and polish the chamber surface and exhaust port. I'll then CC and see where I'm at, balance them up, and go from there. Will also port match the intake.

I'll let you know what I end up with.

Originally posted by pat mccarthy
if you need more cc .work out the heads grind and polish them i would do this any ways scribe them to the block or head gaskets do not go right up to the edge keep back from it by0.030 or so and get all the junk out off the head and cc one and see were you are at

This is some good advice. Watch what you do to those L-31's though. They're pretty efficient with high swirl as cast, but as long as you only polish like Pat says you should be just fine. The valves are very unshrouded so only enough metal to polish it should be taken from there. If you enlarge the chamber to fit the bore a little bit better, make sure you don't change the shape of the chamber as it will hurt efficiency. If worse comes to worse and you can't get the CR where you need it with KB pistons, you can get custom pistons fairly easy. I got a set of custom Ross pistons exactly like I wanted them. I went through www.campbellenterprises.com They also have a nice CR calculator on their site.

Thanks for the help c_f68,

I don't intend to change the chamber shape for the reasons you mentioned - just going to remove the casting flash (thin jagged flanges that can't be contributing anything but hot spots) around the valves and chamber perimeter, and polish out the rough chamber surface.

I've read several articles regarding porting/polishing vortec heads and it seems there is little to be gained by messing with the pockets & runners, especially for low/mid range torque applications.

As an aside, I don't subscribe to the rough chamber surface (dimple) theory as being beneficial so long as there is an edge around the intake valve to re-launch potential wet flow. In this application the rough chamber surface just gives carbon a place to stick which smooths the surface back out and/or accumulates irregularities, so I figure polishing is a worthy endeavor to reduce carbon buildup, hotspots, and potential detonation. Rough intake runner surfaces is a different story and probably does aid in fluid suspension so long as there is sufficient velocity and the surface remains clean.

My background is aerodynamics. In aviation dimples and "trip strips" (hard edges) are used to re-attach/re-energize seperated laminar airflow boundary layers on airfoils to decrease wake drag. Works well, as long as the surface does not accumulate dirt or ice - which is more likely on rough surfaces. I've spent considerable time in wind tunnels messing with this kind of stuff.


For what it's worth?

Originally posted by MainCap
I don't know about you Eric, But I don't like "fly poop in my pepper". Yes, it is just a truck - but I figure while I'm at it I might as well try to make it as efficient as I can versus just tossing a bunch of stuff together, but that's just me. Coulda just bought a crate motor for that matter.

I intend to follow that plan Pat. Picked up my CC'ng stuff and die grinder's today. I was going to ask how many CC's is typically lost to polishing but I figured I'd find out soon enough. There is some flash to be removed around the perimeter and the chamber surface is like sandpaper. I intend to leave the ridge (but not the flash) around the intake valve to help dispurse any wet flow, will smooth out around the exhaust valve, and polish the chamber surface and exhaust port. I'll then CC and see where I'm at, balance them up, and go from there. Will also port match the intake.

I'll let you know what I end up with.

As long as you have the time.Do you own a magnetic deck checker and a dial indicator?