How are RPMs defined?

[georryan]

This may be a silly question to some of you, but I consider myself somewhat car savvy, but how is the redline in the rpm range determined. I've heard it said that our heads limit our rpm range, and I think Kelly mentioned that his headers he was using added an extra 500 rpms to his redline. How do you know when you've reached red line or added more rpm potential to your car?

-Ryan

[Legacy777]

rotating mass and all the associated componants.....probably the biggest limiters on our engines are lifters/valves/springs, etc. Mainly valve train.

Put lighter components and/or stiffer springs, and solid lifters, you can probably safely bump your redline up.

[legacy92ej22t]

The Manufacturer sets the redline...

Our cars have an ECU controlled rev limiter that kicks in at 6500 rpm. Take it up to redline sometime and you'll see what I mean I'm pretty sure Kelly is running some kind of engine management. So if you replace your header and are still running stock engine management you wont see that extra 500 rpm anyways.

Some cars have a redline on the tac but no rev limiter. The manufacturer put it there (the redline) as a warning of the point at which you are running into the danger area for that engine. On one of these you could just keep pushing on through the redline unlit you kill the engine.

As far as I know with most stand alone engine management you can set up a rev limiter function yourself. So if you're breaking in a new engine you can set it at 4k rpm so that you cannot go too high in the rpms and damage the engine. Then once broke in you can set it higher.

[georryan]

hmm, ok, so would the point of floating your valves the the area of a redline limit? For instance, you get stiffere springs which then decreases the chance of floating your valves so your redline goes up.

Is that usually how they judge the safe limits of rpms?

[legacy92ej22t]

I had to stop halfway through posting to give my daughter a bath and didn't see Joshs' responce I think he understood and answered your question a lot better then I did.

[evolutionmovement]

Valvetrain is one determinating factor, but there are many. Sometimes its the bottom end (not on our engines). Other times the engine runs out of breath before an actual mechanical overstress situation may be present and they figure they might as well redline it for durability sake as there'd be no point in further revs anyway. There are also the accessories to think of and the higher the rpms the greater range they need to operate reliably at. I would think the main factor in our particular cars is that it runs out of breath anyway, then the next weakest link would likely be the hydraulic lifters before the valve springs. I believe I read that some EJ20s in Japan redline at 8 or 8.5k - these are all DOHC, so that point at a lack of breathing as the reason for the rpm setting on our engines. But this is just my best guess.

Steve

[entirelyturbo]

Our bottom ends are certainly capable of handling more than 6500 rpm. Our heads, on the other hand, aren't good for much more. Everything from valvetrain design to the airflow characteristics limit it...

I still am quite curious as to why my car will go past redline! I have only done it enough times to count on one hand, but I have hit 7000 RPM before. Once was in a good race , the other was at the time I was considering selling it when I was really pissed at it.

But a stock EJ22 has the redline at just the right place. It's really unnecessary to go for it, as our power drops off dramatically after about 6000 rpm.

[georryan]

I actually hit 7000 rpms once, but I think the fuel cut was just delayed in kicking in, because when I changed gears and shifted real fast and tryed to gas it, there was nothing for a second. It probably went off just as I was putting in the clutch.

I've hit the fuel cut on my car enough times to know were it kicks in, but I was just curious how manufacturers define were it should be located. On top of that, how someone with a good engine management system would know were the line would need to be in order keep there modded engine safe.

I saw a video the other day on modern sports cars. It had all the old imprezas and lancers up to last year's model. The video was showing them all race and did some detail analasys of them. It also showed some supras and skylines racing. I was noticing that one supra had a redline near 10 grand. I was shocked, and started thinking that the owner probably upped that redline by modifying it. The questions started flowing in my head at that point. Thanks for the answers guys, I guess the answer really isn't a simple one.

[ciper]

Just to add a quick note to the thread, one of my legacy has an alternator with bad bearings because of too much time spent at high RPM. Still charges just fine but you can hear noises. I would take it in the dirt and hold 5500+ for minutes at a time (left foot braking, automatic).

Ive seen a subaru engine spin up above 8k before, sounded pretty cool. Stand alone engine management and a misshift.

[georryan]

haha, I bet that would sound crazy cool.

[camshaftprelube]

Pistons are only designed to go a certain speed, and after that, their life is reduced dramatically. Con-rods are the same way, but usually their bolts are the weak link. Cranks tend to flex at real high rpm, especially if they aren't forged.