GM BBC 990's questions

needforspeed66gt · Post by **needforspeed66gt** » Sat Dec 27, 2008 12:24 am

I thought it was much worse off than that before you posted pictures - look at the radius chamber wall cutters in your sunnen catalog - they work great for transitioning.

Do you use those Winona screw in liners? Don't see them too often anymore.

Post by **maxracesoftware** » Sat Dec 27, 2008 12:58 am

e-tach wrote:Thanks again Larry - all very very good infomation, well put - and greatly appreciated.

Any advice on deshrouding or chamber reliveing for the bigger valves?

this #990 head likes the valve unshrouded around the intake valve
at its nearest point right next to the cylinder wall side.

so sort of keep a good transition curve from the seat-to-chamber,
but you can "dig-out" around the valve in that area between
the chamber wall side and the intake valve,
its about 1-3 the circumference in that area needs some unshrouding,
but more important unshrouding just next to cylinder wall.
Maintain a nice radius transition around the intake valve
in those areas -to- the chamber

its not going to be like a modern SB2.2 Chamber type laid-back wall,
so it will like to be more dug-out if you know what i mean ?
just maintain the same chamber unshroud shape,
but more away from the valve's edge in that 1-3rd area

on the exhaust side...just the majority of unshrouding around
the exh valve will be at the deck-to-exh valve edge interface
...this is at the Quench or Squish area next to exhaust valve's edge
.....it will sort of turn the Chamber outline shape like a Heart-shape
when unshrouded .

the rest around the exh valve needs just minimal unshrouding with
larger radius transition from valve job top angle-to-chamber

e-tach · Post by **e-tach** » Sat Dec 27, 2008 2:38 am

Larry -

Thanks yet again for your very detailed reply - it is great to have you on here!

Needforspeed66gt-

Nope - I dont use those liners myself - these heads were ported, etc, many years ago, long before I got into the game, and have sort of been floating around the area, and have been on numerous local 4x4 pulling trucks. Now everyone likes to run the Darts.

I am doing these up for a "stock" pulling truck