Retarding the camshaft will give you added intake valve-to-piston clearance and tighter exhaust-valve clearance. However, without checking the clearance on your engine, we would only be giving you a guess. The camshaft profile will dictate how quickly the valve is opened per degree of crankshaft rotation. Four degrees of retard at the crankshaft only moves the camshaft 2 degrees back. Going back over some Cam Pro Plus data that I have for both a mechanical flat-tappet cam and a big-block roller cam, I came up with these measurements: With these cams I only saw around 0.012 inch of lift change for the flat-tappet, and around 0.016 inch for the roller. These numbers were generated at 10 degrees before and after top dead center (TDC), respectively. This lift change was over 4 degrees of crankshaft rotation, which simulated retarding the cam 4 degrees. This multiplied by the rocker ratio of 1.5 gives you approximately 0.018 inch for the flat, and 0.024 inch of additional valve-to-piston clearance from the roller. The normal intake piston-to-valve clearance you're looking for is 0.080 inch, with exhaust clearance coming in at 0.100 inch. We've run the clearance tighter on the engine dyno, but we were running in a controlled environment with rev limiters, and not shifting the engine though gear changes. You need to check piston-to-valve clearance at 10 degrees before TDC on the exhaust valve, and 10 degrees after TDC on the inlet. Cut your piston to achieve the above-listed clearances. Remember, when a valve loses its head, it's not a pretty sight.
Shake, Rattle & RollQ I own a '72 Chevelle with a big-block 454 engine and a Muncie transmission. This combination has a more-than-minor vibration beginning at 3,500 rpm and lasting to 4,500 rpm or more.I know this engine is externally balanced, so I have checked the flywheel part number and it is the correct Chevy part for this engine. Is the damper also different for this engine? Can the correct damper be identified by looking at it while mounted on the engine? Why are so many aftermarket dampers available? Do they offer an advantage over the stock damper? Thanks for any light you can shed on this subject.Don James
A There's nothing worse than driving down the freeway with your Muncie shifter buzzing and rattling at you. It's quite annoying, and if you have the incorrect balance it can damage your engine.
Yes, the 454 externally balanced dampers can be identified on the engine. From the back side of the damper you will need to look into the inside of the damper hub. This is the internal piece that is pressed onto the end of the crankshaft. You will find a cast-in lug that is about 1 inch thick and approximately 2 inches long cast to the inside of this hub. If the inter-damper hub is completely round with no lug, you have a 396/427 damper. This will cause your engine to shake itself apart. The factory GM damper for the 454 engine is sold under PN 10216339 and is the proper counterweighted damper for your engine.
Yes, there are a lot of aftermarket dampers on the market. Some use dry-friction clutches to control the harmonics. Some use thick, viscous fluid. Others use elastomer O-rings to tune the damper. And some even use steel balls (pendulum type) to dampen the harmonics! And we haven't even begun to talk about damper diameters, materials, and weights. This gives you quite a selection of dampers for a big-block Chevrolet. If you're building a racing engine to be used in sanctioned competition, you must run one of these SFI-certified dampers that have been tested to "Oh My God" rpm. Each manufacturer will state its benefits over another manufacturer. I prefer the ATI Super Dampers for my engines; they're great right out of the box for most performance engines. But in the world of NHRA Pro Stock and Nextel Cup, ATI is able to tune its dampers from 1.2 to 4.5 pounds of inertia weight, and has a 40-90 range of durometer hardness of the O-rings to tune the damper for the specific application. ATI claims that these can reduce the torsional twist to 0.2 degree or less. This gives you maximum power output and increased durability.
I sure hope that when you check it out you find a 427 neutral-balanced damper on your 454. That will be a very easy swap to eliminate the annoying vibes. Good luck.