304 valve rocker differences

Hey all, I think I have a quick and (I hope) easy question.
I recently replaced my '72 304 with an unknown 304. At least I "think" it was the origonal engine. Anyway, the new engine has a different valve rocker set up. While my old one had an individual stud for each rocker, the new one has an aluminum "bridge" for each cylinder. Does anyone know what years this design was used?
And does this mean that I now have different valves and/or combustion chamber dimensions? Is it worse or better? I still haven't seen 1/2 the power out of the new engine that I had with the old one despite the headers and cam.
Thanks!

 

Does your new engine still have the tag on the front of the passanger side valve cover? If it does you can tell what size engine it is plus,year of maufacture and if two or four barrel carb. My FSM for 1972 shows the V8, does not stipulate 304 or 360 but shows the valves on and indivdual stud, not on a bridge as its called. My FSM for 1975 shows the 304/360/401 again no stipulation on V8 size, with the bridge and a rocker arm shaft.
I think the shaft was used on the 401, but thats just speculation. But I have a spare 304, a 1975, and it uses the bridge. Hope this helps...If you have the tag numbers, post them and you may get more answers.

 

I ment to mention this in my reply....You mention you used a different cam and had low power..The 304 in question has a non adjustable valve train..to get more power out of a performance cam you would have to use the correct length push rods, otherwise the valve will not stay open the correct length of time and therefore a loss of power.

 

My 304 has the same aluminium bridge as yours. Some come in stamped steel bridges as well.

 

Length of push rods really should not affect how far the valve opens. How far the valve opens is based on the lift of the cam lobe and the ratio of the rocker. The push rod length will determine the geometry of the rocker to valve stem. It is important that this is correct. If it is off very far you will bend/break push rod and it will cause your valve guide to wear faster by pushing the valve stem in to the guide instead of straight down. If the push rod on a non-adjustable rocker set up is too long it could cause "valve float". That is when the oil pressure in the lifter causes the valve to float off the seat instead of sealing the cylinder pressure. This will kill performance by reducing compression and if it's bad enough, causing the valve to come in contact with the piston. Washers under the non-adjustable rocker stand is and old trick to keep the lifter from pumping up so far that it causes valve float. Hope this helps.