I've tried google and the search function, and this question remains:

What is the "redline" of a chevy 350 engine?

What components (as in modified engines) will change the "stock" redline, and what the hell is a redline for anyway? Is there a calculator or formula for finding the safe redline? Any and everything pertaining to this redline and safe engine speed question is gladly welcome!

 

The actual redline of any engine will be different based on the components used. In stock form, the biggest limiting factor on redline in a 350 is the valvetrain. Over a certain speed, the valves will "float". A high performance valvetrain can move the powerband into a much higher RPM.

Another thing to consider is the length of the stroke. A lengthening or shortening of the stroke in a 350 (as in the 327 and 383) will change its maximum possible RPM.

Higher flowing parts, such as the intake and cylinder heads, will allow the engine to continue "breathing" at higher RPM's as well.

 

Just varies by what you have done to it. Also with a stock engine, you can safely spin it higher but after "x" amount of rpm it accelerates way slower than if you just shift. I shift my 305 at 5500 which is more than was ever originally recommended for it. I've acccidentally had it as high as almost 6500, only damage was it caused the harmonic balancer to slip.

Dan

 

I understand powerbands, this isn't the concern I have. My particular engine peaks it's torque and hp at 5500-6000 rpm, so that is my shift point. I'm asking this question to determine any hard and fast rules to find a maximum safe revolutions per minute.

If it's needed, I have AFR #1095 heads with the springs the "upgraded springs" whatever that means. I'm really not knowledgable about the components that are needed to determine this.

I'm also interested in any engine damage that can occur by "over revving" if that's possible.

 

Maximum rpm reliability depends on a lot of engine components. Stock components like rod bolts with heavy pistons don't survive for very long if spun over 6500 on a regular basis. I had an old school 383. Stock 400 rods and rod bolts and cast 350 pistons. It had good heads and a cam and I spun it to 7000 for a couple of years before destroying the engine when either a piston disintegrated or a rod bolt let go.

As for how high you "should" spin the engine, providing the internal components can take the rpms, depends on the powerband.

Most people think the red line is the shift point. Red line of the engine is a couple of hundred rpm below where the valves will float. You can have a camshaft that makes power to 7000 rpm but if the valves float because of weak valve springs at 6000 rpm, you'll never get the full potential of the camshaft. Using the red adjustable pointer on a tach is not the engine's red line. It's set as a shift point.

Shift point is usually just before where the HP curve starts to drop off. Reving it higher than that and your acceleration will actually start to decrease. You shift to a higher gear, it drops the rpm down to the start of the HP high end curve and you build up rpm again until HP starts to drop off and you shift again or cross the finish line and let off the throttle. A properly geared car should cross the finish line at or slightly after the shift point rpm.

My shift point is 7400 rpm. My rev limiter is set to 7800 mainly because by that time, my HP curve is really dropping off. With triple valve springs, my valves probably won't float until 8500+ rpm.

A typical SBC usually peaks in the 5400-5800 range. If your camshaft builds power to 6000, that shouldn't be a problem with the bottom end components.

 

Back in '82 one of the gearhead magazines took a new
'82 z28 and started bolting speed parts onto the 305
-got it up to about 400 hp(only the short block was
stock at that point)After several runs at 6800+rpm,
a stock cast piston blew,trashing the block,rest of
bottom end was still ok after the abuse.

 

This is good info thanks

I understand shift points and shifting to keep the engine in it's powerband, but that was a good refresher course

I have high quality components throughout my engine so I was curious as to the "limit" of the rpms, and it seems the simple answer is valve float. If you can upgrade the springs enough then your engine can rev higher, it seems.

I heard something about your ignition not being able to handle rpms above 6500, is that a myth or some truth to it?

Now the question pops into my head, what happens if you floor the pedal and spin your engine to valve float for a consistent period of time, say thirty seconds. What would happen to the engine? Let's just assume stock 350 that floats at 6500 rpm.

 

I ran a stock large cap HEI and ignition module to 7000 rpm so there's no ignition problems.

You should always run the recommended springs for the camshaft and have them installed at the correct height. The camshaft won't allow the engine to make power at the higher rpms where the valves will start to float as long as the proper springs are installed. Too weak of a spring and the valves can float before the engine reaches it's peak power. You can't install too heavy of a spring on a cast cam or they will literally break the camshaft. A billet cam can use a heavier spring than recommended.

Valve float normally is just a loss of power at high rpms because it's so brief but can also cause engine damage.

There are 2 spring pressures. Open and closed. Valve float is concerned with the closed pressure. As the lifter is coming down off the cam lobe, the valve spring is closing the valve. When the lifter hits the base circle, the valve is slamming onto the valve seat. If the closed spring pressure isn't great enough, the valve can bounce on the seat.

It's unlikely this bouncing will ever cause a piston to valve clearance issue but there's always a possibility. The bouncing has potential for other damage such as breaking the head off the valve which can cause a lot of engine damage. If there ever is a piston to valve clearance issue, the valves will get bent if not broken as well.

The bouncing actually vents compression pressure causing the lack of power.

If you stuck the transmission in neutral and put the throttle to the floor for 30 seconds, there's a good chance you'll have valve train problems before the bottom end decides to lets get. With no load on the engine, the bottom end isn't seeing any high stresses.