Finding the redline range of an engine

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Delirious

Delirious

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Metroider17
I've always been fascinated with how when a company builds an engine, how they figure out where to put the redline on it at. Also I am interested on how they decide to stop engine RPMs (like my engine wont go over 7000 RPMS and redlines at 5500 RPMS)

Can someone enlighten me as to how they figure this all out?? :)
 
but could anyone here explain that testing as to how it's done and how they can tell it's in the redline range, and how they know when to cut off the RPM range
 
They make lots of engines. Then they rev them until they blow. They see how long the engine lasts after prolonged periods at certain rpm. Then calculate how high the car can rev whilst still prolonging engine life.
 
What I would do is figure out how much stress there is at critical points in the engine... sometimes the critical points are pretty obvious, other times you have to check a whole bunch of points to figure out what is going to be the most critical. Figuring out what the stresses are will be difficult, mainly because of the combustion going on in the cylinder. Anyway, the stress will vary with RPM, you figure out how many RPMs you can run before the stress is great enough to break the part. If it were me, I would get as close an estimate as I could for a good redline, then test some engines.

As far as having a different redline and fuel cutoff... well, I can't say for sure without talking to the people who built the engine, I would guess it has to do with failure due to fatigue.

In engineering calculations are done, but then prototypes are tested to validate the calculations. The most difficult thing about calculating the forces in an engine would be the combustion process... but that has been very heavily studied, I'm sure Ford or any other motor company could get a pretty good estimate for a redline before testing any motors.
 
I think the development engineers usually start out with a range in mind. In fact, I'm pretty sure of it. Before they begin, they already know what characteristics the engine needs to have... whether it's a low-reving stump puller that gushes torque and is easy to produce or a peaky screamer that is all top end and made of unobtainium.

They've already chosen an speed range at which the motor will work. They know how much power they want the engine to make. They know the basic shape of the torque and power curve they want to acheive. But most importantly, they already know how much it will cost to produce it at a factory.

That's because street cars are primarily designed around economic considerations. Therefore, the engine redline (and indeed the entire performance range of the engine) is a compromise between cost, durability and performance.

The testing (as it's already been pointed out) is done to verify the engineer's decisions and the quality of the production process.

Engines for race cars, on the other hand, are designed mostly around rules, with cost usually taking a back seat... though this depends on the team. Lots of sanctioning bodies impose rev limits to cap performance and cost.


M
 
Yeah, an engine would be designed with goals in mind, such as power output, redline, etc. So they don't just slap together an engine then try to figure out what the redline is on it.
 
diagrams/pictures or maybe even videos of testing and graphs of explanations work wonders with me, can anyone find any of these as far as this engine testing?
 
I saw a show on the discovery channel once where they were developing the motor for the new 05 mustang gt. And they had it on an engine dyno just doing run after run pushing the revs continuously higher. I think they got around 7250 or something.
 
I've seen some of the video through GM, basically they have an engine on a stand and they beat the hell out of it. They run them at a bunch of different rpm and just look at how they react. They blow many engines up getting them to the way they want. Watching an engine go boom is always entertaining.
 
I'm not saying this is how they do it, but this is what would make sense to me. The engines peak power and how high it can rev are controlled by two different things. The power peak is more determined by the valve timing and such, where as how high the engine can rev is determined by the internal components. obviously the entire bottom end, but also stuf like the rates on the valve springs, which determines how fast it can rev before the valves start to float. To me it would make sense that the redline (or better siuted would be a red zone) should indicate the place where the engine makes most of it's power. thats not always the case though. Where as the fuel cutoff/rev limiter, should be as it is currently used. That is, to keep the engine from reving past it's safe range of operation.
 
M spec pretty much nailed it. they know what the engine is gonna be used for, what components it will be made of, the tolerances for said components, approximately what power it will make etc.

and becaue they have been making engines for years already, their calcualtions and projections tend to be very close to actual results.

then, to quote someone, testing, testing, testing. a batch of engines will be tested, sometimes with variations in the components (cams, valves, pistons etc) some will be tested in cold conditions, others will be pretty much overheating all the time, some will be under load, others not so much, they use different fuel quality, timing, oils even, until they get a compromise between the performance they want and the cost.

then there is even more testing with the engine in the vehicle; hot weather, cold weather, high speed durability testing, first gear only, second gear only, third gear only etc, fans disengaged, fans permanently on, low electrical output from alternator, low coolant, low oil etc etc etc.

they try to account for every single thing that the engine could encounter in its life after they sell the car. mostly, they test to make sure that the engine will hold up for at least the duration of the warranty period.

some manufaturers, toyota and honda come to mind, test individual parts and engines till failure, and if a small, preferably cheap, modification will yeild a longer lasting part/ engine, they will employ it. and they have reaped the harvest of percieved quality/ good engineering as a result.

yeah it goes beyond just figuring out what the redline should be.

unless youre mclaren and you employ things like pure gold heat conductors/ deflectors.
 
To make it very simple, If you put an engine on a dyno, and graph it's horsepower and torque at progressively higher R.P.M.'s. You will notice that H.P.,torque and R.P.M. will ramp up the scale. When torque and H.P. flatten out and start to fall off, that is redline. I thought I had a picture of a dyno graph in my paper files, but alas, I can't find it. If I come across it, I'll scan it and post it .
 

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