boxerfan

I am looking at getting a nice set of custom pistons for my rebuild. They will be spec'd for using an MC block and will raise the CR significantly over the stock 7.8:1.

I am trying to get a design that will work for a 10V headwith a higher CR to get more umph off the line and probably max out at 14 to 15 PSI of boost on pump gas.

The kicker is that I am also trying to factor in the clearance and compression required to toss a 20V head on there in the future.

I know the volume of the 20V head is substantially larger than the 10V. The CR tossed about when a 20V head is bolted straight onto an MC1 bottom end is in the 'hood of 6:1. Way too low for a daily driver. Does anyone know the volume of the 10V head vs 20V head?

Clearance volume at 7.8:1 needs to be 65.382cc, at 8.4 (MC2) 60.08cc, and at 9:1 55.575cc for the 10V head. Now I need to know the difference in head volume to work out corresponding CR values when a head swap is done.

The design of the pistons will be modern and offer a superior flame-front action to the factory dish designs.

I am also going with a slight overbore to 81.5mm.

More to come...

redneck with an audi

i dont know the specs that u are asking but when u figure them i would be interested in the group buy if i can help in any way let me know.

boxerfan

All things being equal a double duty isn't possible with the stock 10V head. The volume of the 10V vs. 20V is too great. I am going to hog out the 10V head and then cc it to see how much larger it gets. It will most certainly remain smaller than the 20V but it is bound to get much closer.

There seems to be a significant amount of material that could be removed at the fire rings and from around the shrouded valves in the 10V head. I have also seen figures for a ported 10V head rising from 130 to 165 intake CFM and 85 to 130 CFM exhaust and that rivals the flow of a 20V head. This also means the pistons will be an 82mm diameter.

Once that is done I will revisit the calcs.

With a stock 10V head the resulting CR for a piston that would yeild 7.5:1 in the 20V would be 9.9:1. Somewhat high for boosting! lol.