I know that redline is the max RPM's of a car, or at least the suggested max, but what I mean by the question is what exactly determines redline to be a particular RPM? I've always been under the impression that it had to do with how fast the engine can be turning before it shakes itself apart. If this is true then why would say a formula 1 car have such higher redline? Is it because the pistons are much smaller/lighter weight that there isn't as much mass to cause the engine damage at that high of RPM's? If you heavily modded a car's engine how would you or could you determine if the redline had changed?

the engine is not always the determining factor for redline. corvettes for instance, the engine can handle much more than the shown redline, but the components (air conditioning compressor, alternator) come apart if you take it any faster. redline is the rpm at which damage can begin, IIRC

Safir is right there are several things that can limit the top safe speed of an engine.

The most common I think is "valve float". The valves are pushed down into the cylinder by the cams, but they rely on springs to pull them back out. At super high revs, the springs may not pull back fast enough, and the valve will be in the wrong place at the wrong time. Worst case, the piston will bump into the valve (in some engines).

In higher performance engines the problem can be the accessories, for example the water pump would spin too fast and cavitate. Supposedly the 4AGE from the 80's MR2's is good for 11k rpm's or so if you underdrive the accessories.

I think these two cover most of engines. Some engines suffer mechanical breakdown at high revs (conrods breaking, wristpins snapping, bearings burning out).

F1 engines have stronger parts with better materials, stiffer valve springs to prevent float, etc, etc. Plus they only have to live a couple hours. On a street car the redline is set so conservative that you probably could run the car at redline for 1000 hours straight with no problem.

I don't think there is much of a science to knowing the new safe redline of a built engine. Stuff like stiffer valve springs, forged & shot peened parts, etc definitely increase the safe revs for the engine and a UD pulley can lower the speed on the accessories. However without lots and lots of engineering resources it's trial and (expensive) error.

cheers
mbs

F1 engines don't use typical valve springs as they simply can't close the valves quick enough. They use a hydraulic pressure actuator to close the valves. Camless engines are in development, in which the valves will be opened AND closed by hydraulic actuators, controlled electronically. The result will be infinitely adjustable valve timing, and engine speeds limited only by breathing capacity and strength of engine internals.

Another major factor in engine speed limits is the stroke length. If the piston and conrod have to move 4" each revolution the amount of force applied to the piston and conrod during each near-instant deceleration and acceleration in the opposite direction is MUCH greater than if the stroke were say 2". This is why high-revving race engines typically use a large cylinder bore and a very short stroke. It's also (partly) why a typical truck engine engineered for low end grunt with a long stroke can handle far lower engine speeds.

[This message has been edited by donjuan (edited May 09, 2001).]

What's the redline on newer Mustangs? I saw one the other day and I could swear it was 6k or lower. i was surprised it was lower than ours.

More so than mechanical limitations of an engine is its powerband. An engine is designed to make power is a certain rev range based on various factors (cam timing events... intake runner size, length and design... list goes on and on). While mechanical limitations do play a part, it's not the only factor. I've heard a 2.5 bottom end will hold together until valve float(6500+)... Subaru keeps the redline well under that because the torque curve has dropped off at 5500.

A phase II eg25 supposedly is good to about 6800 before valve float, and once that's fixed with better springs, even higher. Im *really* curious about Trey's stage II heads that promise to hold together to 8k. With managment to cut the rev limiter, that'd be a fun car. 40mph in first, 69 in second gear... HMmmmmmmmm

donjuan,
I thought F-1 engines use pneumatics (air) rather than hydraulics (oil) to close the valves.

Fred

Where can you buy these better springs, and will they help even if you don't rev past 6K?? And how do you install them or should I get pros to do that??

Thanks,
Stefan

It seems to me then that if you put better springs on the valves that you could have a higher redline. Also what about boring out the engine? How would this effect redline. It seems that if the stroke was increased that would lower the redline since the mass of the pistons are traveling out further from the longer rods, and and also boring out the cylinders would require bigger pistons, thus more mass at the end of the rods, making redline lower alson. Or is this just totally wrong and the mass of the pistons have no real effect on redline? I guess I always though the reason for using V12 engines was to have the same overall displacement, but be able to have shalower stroke and less mass on each piston to increase the redline, and thus HP, of an engine. Is this right? I'm sure there are aslo other reasons for using the V12 too though.

The great Cobb Tuning (http://www.cobbtuning.com/) sells stiffened springs. I'd say you'd need a pretty darned well-stocked toolset to do it. Proper torque wrenches, etc. The engine would have to be dropped, I'd say, as well.

The best time would be if you were getting head work done anyway (cams, etc).

Since you have asked this question, I think its safe to assume that you've never pulled an engine apart (neither have I, I'm just saying). And by that assumption, I'd say that you'd be best serverd by having a shop do it.

dirk

just to clarify, here's a list of what you need to install new valvesprings:

8, 10, 12, 14, 22mm sockets (14mm 12 sided)
OHC valvespring compressor
2, 5mm hex wrenches
Torx Plus 40 bit (this is what the 8mm socket is for)
feeler gauges
small inch-pound torque wrench
large foot-pound torque wrench
FACTORY SERVICE MANUAL

consumables:
head gaskets
intake manifold gaskets
exhaust manifold gaskets
cam seals (assuming you're installing cams too-- why do springs if not?)
liquid gasket (subaru OE or yamabond)

ColinL: And bandaids. Don't forget bandaids

You hit the nail on the head. Not many people have spring compressors just laying around. http://www.i-club.com/ubb-files/smilies/smile.gif

Was I correct, in my laymans understanding, that it'd be pretty trivial to do the springs when you do the cams?

dirk

cams alone do not necessitate removing the heads, so those are easy.

to replace the valvesprings though, you gotta have the heads off. once you've got the heads off yes the valvesprings are relatively easy, except the retainers are a bit of a bitch... two small half-moon shaped chamfered clips, it was a pain to get them in place with the stock springs.

So is it worth doing to a rather non modified engine. Ganz-style intake and exhaust. Even if I don't hit the rev limiter all the time, will it make things easier on my engine.

Thanks,
Stefan

P.S. dirk.gecko: You are right I am completely useless when it comes to mechanics and stuff. I would be the guy buying some sort of "engines for dummies" kind of books http://www.i-club.com/ubb-files/smilies/smile.gif