Over simplified, torque gives acceleration and horsepower gives speed. In general, more rpms mean more horsepower. However, as rpms increase the stresses on the engine increase and engine life decreases other factors equal. Street engines tend to have lower rpms and longer life than race engines. Street engines are more overbuilt for their "normal" use and are generally run at average lower percent of their potential capability.

You want to build your engine so that it can handle more rpms than you ever expect to place on it. Going to a higher gear is not normally a problem, expecially if you have a rev limiter. Shifting to a lower gear can be a problem: you can easily over rev when downshifting -- the rev limiter does not protect you here.

The higher the rpms that your engine is built to handle the higher you potential speeds in any gear, the greater the range between shift points, and the greater the margin of safety at a "normal" rpm.

Actual top end speed is a combination of horsepower, drivetrain, gearing, aerodynamics, and other factors. The build characteristics of your engine are dependent on its intended use. For street driving a very flat torque curve over most of the rpm range is normally preferred. Racing tends to keep the engine closer to its max rpm range. For flat-out racing, you generally want the torque and horsepower to peak near the top of the rpms. A dragster can use as much rpms as can be gotten out of an engine. Everything is a tradeoff. Every engine is custom for a specific set of needs.

Horsepower is most easily obtained by increasing cid. When race rules or other factors limit cid, engines are build to handle higher rpms in order to get more horsepower. That is why you hear of low cid engines with lots of hp, but it comes at a price. The cid is often cheaper. That is part of the reason the sb engines are stroked -- more displacement at about the same rpm limit at less cost than trying to increase rpms with the same cid.

Talk about enigne parts being a blur.....I heard this from a NASCAR enigne builder in an interview on one of the speed channels.....He said at 7,000 rpms,each valve opens and closes 53 times a SECOND,man that's fast.... When you get past 6000rpms you better have some high dollar premium parts in your valve train or the cheap stock parts will be in your oil pan quickly....

I have an old stock steel valve cover that I cut a slot across the top to adjust the rocker arms without spalshing hot oil on everything within three feet.. At idle the valves do not open and close that fast, but bring the rpms up to 2000 and things pick up real quick,amazing to watch....

One old engine builder described torque and hp this way to me;torque gets your car from 0 to 100 (or whatever speed),horsepower keeps it at that speed....

David

mr0077:

F1 engines turned 11,000 rpm over 20 years ago. Lets try 18,000 - 19,000 rpm today!

[quote] DAVID GAGNARD


One old engine builder described torque and hp this way to me;
torque gets your car from 0 to 100 (or whatever speed),horsepower keeps it at that speed....

Very good and very right, that's what the cobra is all about and nothing more......