...Do I really need to worry about valve to piston clearance with 8.25 compression?
454,
On a stock engine, I have never had the need to worry about these small changes. The risk is in whether one is sure that one's Vette engine is stock inside...
...Now, push rods and lifter change in wear pattern still is my concern, hense for the posting. Yes, it will change position a little. But at still only 0.486" lift at the valves is the spring tension still pretty stock for the lifters and push rods?
It is perhaps possible that you may have a spring not exerting the potential energy that it did when new, however, it is unlikely that you have one so weak that it will cause problems. Of course, one with a broken coil ring or jammed dampener could still be possible.
...Also, very interesting idea on changing the exhaust lift only. Don't know much about this, except most cams seems to have more lift on the exhaust side than the intake. Can you tell me more? Do they sell half sets of rockers, or do you have to buy them by piece?
This was the way how dual pattern cams came about. In the early 60's (perhaps) the entrepreneur racer did the rocker arm ratio changes which gave the exhaust valve a longer duration and lift, and then the cam manufacturers and some big manufacturers caught on with the practice to cut dual pattern cams (where the exhaust ramps had a bit more duration or lift or both). Typically, you have to buy a set of rockers as a complete set. Stay away from the stamped big manufacturer rockers of vintage 1974. Todays stamped rockers are more accurate and consistent and flex less under load.
I do not presume to know what JohnZ means by his statement, but I get the sense that what he means is that one change alone to the engine usually will not produce a measurable power increase. And I agree with this interpretation 99%.
THERE IS NO MIRACLE 1-CHANGE FORMULA THAT WILL YIELD GOBS OF HORSE POWER FOR AN ENGINE.
However, the 1% I am holding on is for the following: Many of the big-manufacturer's engines came pretty ready for performance. Many times the big manufacturers would produce an engine with a scheduled poor timing curve to make the engine fall within certain parameters. So within these small and narrow changes, one could make the engine perform crispier or more responsive. Granted, some of these poor tuning schedules were in the interest of emissions. Many of these engines are one change away from making that leap into big improvement (but I am not talking about the 305 that your aunt has in her Oldsmobile..:L).
So, if for example, you had determined that the engine needed to "breathe" better, then you are looking at opening-up the intake with an improved intake manifold, a higher flow carburetor (if needed), change the exhaust rockers to create that dual pattern effect (but if you are going that far, then might as well replace the cam with a dual pattern cam that will produce its most at the right engine rpm range), install some headers, and eliminate restrictions on your exhaust system, and tune the distributor curve to take advantage of these changes.
In this example, you would be looking at 4 different changes -new intake manifold, new rockers, new headers, and perhaps a new carburetor, and a new cat-back system.
I personally like the dyno reference to measure the horsepower output of a car or engine before and after changes have been made; however, this is pretty expensive, unless you have a connection at the local dyno shop. The only other way to find out how you well you did in improvements is to take it to the track (oval or 1/4 mile).
...Some day I really do want to pull the engine and completely rebuild. Then I would put a higher lift roller cam, lifter, push rod, and spring set. But would like to still use the 1.8 rockers to get a little more lift at a shorter duration to get more lower RPM power. Just don't have the money now.
or blue-print it and install a turbo or supercharger to take advantage of that 8.2:1 ratio...:dancenaughty
