deck height

aircrew · Post by **aircrew** » Fri Dec 05, 2003 12:53 pm

I'm trying to decide the correct deck height for my 1956. the chambers are smaller than i expected at 52cc and I need about a .060 deck height to get the compression down. will this be ok or should i make the chambers larger? thanks

Post by **Marc** » Fri Dec 05, 2003 1:09 pm

It'll certainly work at .060", but you may want to go tighter for more "squish". Say you go with .050", you'll need to come up with 1.63cc from somewhere to have the same C.R. - that's not hard to gain in the chamber just by unshrouding the valves a bit. Another option would be to have small dishes milled into the center of the piston tops - they'd only have to be a little over .030" deep at ~2" diameter to yield that much volume.

Guest · Post by **Guest** » Fri Dec 05, 2003 1:16 pm

Thanks for the reply. Would it really make a big difference going from .060 to .050? enough to worry about? and can you elaborate slightly on unshrouding the valves to be sure i know what you mean?

Post by **Marc** » Fri Dec 05, 2003 1:56 pm

Honestly? If this is a fairly mild engine (small ports & valves) I doubt that anyone could detect the difference between .060" and .050". Taking it to extremes (.040" is generally recognized as the minimum safe piston-to-head clearance with steel rods) might gain a bit, but if you're planning on running this engine for a long time it's smarter to have a little more clearance than that IMO. I don't have any good photos handy of a massaged VW chamber, hopefully somebody can post some for you - but basically you just open up around the valve a little by laying back the wall of the chamber with a Dremel or air grinder (protect the seats with some old valves, you may even want to make some guards for the cylinder seating surface "just in case" you slip - simple to snip out of some old coffee-can lids).
Here's a couple of Mopar heads...not a before-and-after, but one is untouched stock and the other has had the valves unshrouded some:
http://www.moparts.com/Tech/Archive/mot ... rting1.jpg
http://www.moparts.com/Tech/Archive/mot ... rting3.jpg

Deck height · Post by **Deck height** » Sat Dec 06, 2003 3:34 pm

Running the same compression ratio the tighter the squash, the better the performance but the better the fuel needed. By loosening up the squash you can run higher compression ratio with lower quality fuel. So it's your choice. We normally recommend lower compression ratios for street cars so the timing can be set a little higher. We feel we get better performance with the higher timing then with high compressions and lower timing figures. Have Fun. Vic.