Good morning everybody hey, I’ve got a 010 4 bolt main small block Chevy with a set of 041 heads fresh out of the machine shop hyeurtetic pistons double spring valves just kind of curious what kind of a redline I should consider. I’m hooked up to a tremec 6 speed with a fresh rebuild. And the rear end out of a 95 Trans Am any ideas on rpm limit? Im thinking ocassional 6500 with normal limit of 5800.

 

Much will depend on the valve train. Light springs can become a designed-in rev limiter. If the lobe profiles, valve train reciprocating mass, and springs/retainers will support higher RPM, head flow characteristics will have increasing effect. If the top end can perform at higher RPM, crank/rod/piston balance can become a limiting factor. Right around a sustained 6,000 RPM the materials are a significant part of durability.

If the goal is 5,800 RPM with an occasional flash to 6,500 on shifts, etc., even a stout stock rotating assembly can support that. That doesn't mean cast rods and a gray iron crank pulling cast pistons around, but a stout bottom end. With that, just verify that the lubrication and cooling are up to the task of sustaining that RPM, then plan the heads and valve train.

2¢

 

RPM depends on the cam grind. If the cam grind really starts dropping off power above 6000 rpm then there's no requirement to go higher.

Like Vader said, it also depends a lot on all the internal components. Generally stock components can handle brief moments around 6000 rpm. When I bought my car, it came with an old school 383 stroker. Cast 350 pistons, stock 400 rods and rod bolts. Had a really nice solid camshaft. I was spinning it to 7000 rpm doing 1/4 mile passes. At 200 passes, the stock rod bolts lot go. I pulled the intake and heads off and thrwe the rest in the scrap metal dumpster at work.

Current engine has internal components that can easily survive 8000 RPM and the camshaft makes power up to there but I only shift at 7400.

With factory OEM components, it's really a dice through. Too high an rpm can put a lot of stresses on parts not designed to go that high.

Rod bolts hold the con rod onto the crankshaft. During a power cycle, the piston is pushing down onto the crankshaft. Rod bolts are not doing a lot there however when the piston is moving back up into the cylinder, it has to stop at the top. The rod bolts are keeping the piston from trying to make contact with the head.

Valve float. High rpms can cause valve float. Old weak valve springs can cause float even on a stock camshaft. Valve float happens as the valves are closing. The camshaft opens the valve but the valve springs close the valve. If the valve springs are too weak, as the valve slams down onto the valve seat, it can bounce. This will cause a loss of cylinder pressure which will cause a loss of power and could also cause damage. The faster the engine spins, the faster the valves need to open and close.

So engine redline depends on so many factors it's hard to say what the limits should be. As for the "Red Line" on a tach, that should never be maximum rpm of the engine because you can easily go over it. Engine rpm limit should be controlled by a rev limiter. If a tach has an adjustable red line, that should be the WOT shift point, not the engines highest rev limit.

When racing, I don't even look at my tach. Shift light tells me when to shift and high end rev limiter keeps me from over reving the engine.

 

Both the above Posts were great!

When inquiring as to an Engine's Max safe or even Limit prior to failure...
One needs to specify as to which sub-section of the Engine is being discussed.

As already Posted, Valve-Springs/ the Valve-Train in it's entirety will limit power output and the ability of the Valve-Train to remain intact...
Valve float, Ejected locks, broken Valve Spings, bent Push-Rods, and Broken Lifters are all possibilities.
The engine can be spun past that point...
But will usually become mechanically locked by some degree of broken components.

Also Crankshaft speed and the Cylinder-Block are a factor...
Connecting Rod Bolts, Connecting Rods, and the Main Journals are also all at risk of Over-Speed...
Even if the Valve-Train is up to the task.

 

Are the flywheel bolts all tight?