I know, different thread, but also different topic.

stock head on a 454 HO is with a 118cc combustion chamber,
they approach .540 lift exhaust side, assuming the valves
cleared the piston barely with full expansion during full
lift, would a switch to 121cc combustion chamber heads
allow for larger lift, or am I in the wrong ballpark here?

if so, would a switch from 118cc heads to 121cc heads accomidate
as much as .106 extra lift exhaust side and still clear?

 

Do not expect the chamber size to have any effect on valve position. As long as these larger chambered heads are of similar design/mfr., (IOW, don't compare LT1 valve position [height] to sb2.2 heads) the valve stem tip height will need to be similar to allow compatible assembly with oem valve train components and retain adequate rocker arm geometry.

 

I'd have to agree with the previous post. Even a canted valve
isn't enough insurance to clear piston faces.

Have you considered a piston with valve relief? I had a set of
TRW which allowed for high lift cams and also had a dome to offset
the relief.

 

Scuzzy,

Piston to valve clearance problems are only related to cam shaft specs that are not max lift. In fact at max lift the valve is so far away from the piston that it's never a factor. It's when the exhaust valve is opening and the intake valve is closing is when it gets bad. Low LSA's and big durations will cause more problems.

Valve reliefs are the way to fix this problem.

On the heads it's better to no mill the heads, because that will get the piston and valve closer together.

Bret

 

alright, well i'm going with high lift, and a decent sized duration..

236/244* with 112* LSA

but my real question is, on heads that have a larger-than-stock
chamber combustion size, are the valve seats further away from the piston
than in stock heads?

or are they at the same height.. and just other parts of the
head are larger?

 

The valve seat postion is relatively the same in all heads of similar design. In other words most 23 degree SBC wedge heads have the seats in the same location.
Chamber size is usually controlled by shaping, ie. larger chambers usually have a "D" shape while smaller one usually have a "kidney" shape.

 

We realize you are talking about the canted valve big block heads, but the relationship is similar whether you are comparing oem small block heads to heads, or big block oem heads to other oem similar big block heads.

...or are they at the same height.. and just other parts of the
head are larger?

Yes! The valve head (and stem in my reference) and seat will be at the same/similar height. Or stated another way, the valve head/seat will be at a similar depth in the chamber, if your perspective is looking directly into the combustion chamber.

I'm not convinced we are clearing the confusion.

 

Yes I did. I only picked that example because I thought it would be easier to visualize! Any way we tried.

 

Oh. I'm clear on what was said. not confused anymore, but I
was there for a while. seemed like I wasn't getting a direct
answer, or I wasn't smart enough to understand.

anyway, cleared up, no bigg.