What determines the redline of an engine?

[rcdice]

I'm sure many factors go into this but what are the major determining factors that affect redline of an engine? A few observations:

Viper 6,000 rpms
C6 Zo6 7,000 rpms
Ferrari 430 8,000+ rpms

Just curious.

 

[SingleMalt]

Pretty much the weight of the individual valves and the type and rate of the springs are the most important factors. In the very high RPM range, oiling becomes a major factor (main bearings and such) as well as lifters.

Rev limit should always be lower than the point at which the valves begin to 'float.' Very easy to see on a dyno chart; HP drops.

Mike

 

[Mark Red GTS Cooper]

It is the point just before the pistons and valves collide

I know, SMART ASS,,

http://www.cartalk.com/content/columns/Archive/1999/November/03.html

Dear Tom and Ray:


How do engine manufacturers determine the "redline" for an engine? Is this a "self-destruct" limit? Would you recommend keeping the rpm to, say, half of the redline during routine driving? -- Cliff

Tom: Well, I don't know about engines these days, but back in the glory days of the American Motors Corp., the redline used to be determined by trial and error. When a guy came in with a blown engine, the service manager would ask him if he happened to notice the rpm just before the piston shot through the hood.

Ray: Actually, it's mostly determined in the laboratory and test track these days, using sophisticated engine monitoring equipment.

Tom: The redline, by definition, is the engine speed (in rpm) that you should not exceed. And if you do exceed it, you are in real danger of having your engine parts start to fly off.

Ray: Virtually all cars with computer-controlled engine management systems now have switches that shut off the fuel injectors or spark when you hit the redline. This is an attempt by manufacturers to make cars more and more idiotproof (although the idiots always seem to eventually regain the upper hand).

Tom: But in normal -- and even abnormal -- driving, you really shouldn't come anywhere near the redline. Not only are you putting significantly more wear and tear on the engine, but you're not even gaining much. Most cars produce their peak torque well below the redline -- usually in the 3,000 to 4,000 rpm range. So you should always be at that engine speed or well below.

Ray: I can only think of a few exceptions to that rule: when you're passing on a two-lane road, when you're accelerating to get on a highway ...

Tom: Or when you're driving a rental car!

 

[Tom F&L GoR]

Often modern engines are designed for low speeds (better driveability) so the ports aren't big enough to get to high speeds and hurt themselves.

While it could be the valve springs and subsequent valve float (resulting in piston to valve contact,) on larger engines which usually have a pretty large stroke, it becomes piston speed limited.

Mean Piston Speed is 2*(stroke/12)*RPM, so for the same piston speed, a short stroke engine is capable of a correspondingly higher engine speed. OEM engines are maxed out at about 4000 ft/min, F1 engines are around 9000 ft/min.

Overrevving a long stroke engine will pull the pin bores off the bottom of the piston. It's pretty spectacular.

 

[Chuck 98 RT/10]

http://www.cartalk.com/content/columns/Archive/1999/November/03.html

Could those two boneheads be any dumber? If I had a nationally published column and somebody asked me a question, I'd take the time to do some research before answering. I wouldn't trust those two knuckleheads to pump gas.

 

[GR8_ASP]

Maybe you should look at it another way. First specify what you want an engine to do and then spec out the components to achieve that end.

Interesting read though on what people think is in the minds of the engineers.

 

[acrdakota]

Redline is based on a huge number of factors that are almost too numerous to list here. But piston speed and acceleration rank very very high on the list. The very reason why you don't see vipers spinning much over 6k and why a 360 will turn 9k. The piston speed (in ft/sec) are actually very similar between the two. Reason being the longer stroke of the viper moves the piston a greater distance with each revolution, so on and so forth. It would take pages to full explain everything.

 

[Bill B]

You guys are all wrong! It determined by the little red line on the tach!

 

[Viper X]

So, if I rub the red line off of the tach, I can just keep going till the end of the gage?

 

[Dave's Big Brakes]

The real answer, is when the rods come flying out of the block

 

[AviP]

So, if I rub the red line off of the tach, I can just keep going till the end of the gage?

Yes, if the rev limiter setting is deleted. But given that peak horsepower is acheived at 5600 rpm in the 8.3L engine, your engine will be very inefficient and will require serious tuning in the mid to high rpm range to find useful horsepower up there.