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Discussion Starter · #1 ·
if a put in a cam, hd valve springs, balance the whole thing, how do i find that max point? Is there a science to this or just "feeling whats right"..
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Re: finding the redline..... (VWXTC)

redline isn't the point that mechanical problems occur(like the valves floating or engine blowing) its the point where the engine nolonger breaths properly and HP and Torque starts to drop off..
the best way to find out would be on a dyno.
 

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Re: finding the redline..... (dj age one)

I realize that, I was just being sarcastic! Yes, putting the car on a dyno would be best. Then you can see where your power starts to drop beyond usable.
Jay
 

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Re: finding the redline..... (VWXTC)

Technically, you guys are both right.
But, the redline is where your valves start to float (due to the valve springs not being able to control them), in turn the valves will bend. Being bent, the valve will be stuck open and the piston will come up and lay the smackdown
on it. It will either bend the head of the valve into the head (which would probably save the bottom end) or, break off the valve head, (which would bounce around and score up the cylinder wall, possibly eat through the piston and dammage the rod and crank)
So, if you were asking about peak power, the dyno is the way to find out where your motor makes it. There really is no advantage to rev your motor past that point. Most valve springs are usually designed to handle an over rev, miss shift, etc. And usually, that is at a much higher rpm than your peak power.
 

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Re: finding the redline..... (Scirocco53)

quote:[HR][/HR]
So, if you were asking about peak power, the dyno is the way to find out where your motor makes it. There really is no advantage to rev your motor past that point. Most valve springs are usually designed to handle an over rev, miss shift, etc. And usually, that is at a much higher rpm than your peak power.
[HR][/HR]​
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[Modified by gearhead455, 2:20 PM 4-10-2002]
 

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Re: finding the redline..... (Scirocco53)

quote:[HR][/HR]But, the redline is where your valves start to float (due to the valve springs not being able to control them), in turn the valves will bend. Being bent, the valve will be stuck open and the piston will come up and lay the smackdown
on it. It will either bend the head of the valve into the head (which would probably save the bottom end) or, break off the valve head, (which would bounce around and score up the cylinder wall, possibly eat through the piston and dammage the rod and crank)[HR][/HR]​
Not quite. You're assuming that the valve springs won't close the valves at all and cause the damage. They do close, but not all the way. The piston won't hit them, but you lose power because the valve isn't closing and you start to "leak" compression. This has nothing to do with any other mechanical limits of the engine. Running the RPMs up until the valves float may destroy something else. Redline may or may not have anything to do with valve float. You'd have to ask a VW engineer why they picked their redline at 7200 and then go from there.
 

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Re: finding the redline..... (Scirocco53)

Hmmm, well, if your engine isn't balanced, it may start coming apart almost anywhere. Factory specs (tolerances in manufacture) allow out-of-balance conditions throughout the rotating mass. The maximum build-up of these tolerances is one of the things the engineers use as the basis for redline. If you exceed their comfort margin, the engine will come apart.
If you start having valves hitting pistons at 8500-9500 RPM, its probably because you're breaking springs or some other valve train parts that were never designed for operation at that RPM. If float were the problem, the engine would simply stop accelerating.
 

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Re: finding the redline..... (VWhombre)

VWhombre, I am not interested in a brawl. It seems like everyone has or has heard different theories on this, that, or the other. The title of the post was "finding the redline" to which I replied. You on the other hand decided not to reply to the quiry, but to offer a rebut to my reply. What is up with that?
quote:[HR][/HR]If float were the problem, the engine would simply stop accelerating.[HR][/HR]​
The valves will not just float and everything will go back to normal. Dammage like the kind I described earlier will happen.
Maybe, we have two different takes on what the redline of a motor is?
 

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Re: finding the redline..... (DVS-VW24)

Another wise comment, but no reply to the title of the post.
I have an idea for a new Vortex forum. Let's call it "irrelevant reply forum" This way the people can deviate from the topic and claim that a particular topic had been covered in the archives if you just searched.
 

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Re: finding the redline..... (Scirocco53)

quote:[HR][/HR]Maybe, we have two different takes on what the redline of a motor is?[HR][/HR]​
"Maximum safe operating RPM" has always been my interpretation. I've never singled out the valves as the single factor in establishing a redline. I've run many an old four-banger to valve float with no damage. They simply stop accelerating.
If tomk1 has balanced everything, then I'm sure he has effectively raised the redline of the engine, but I don't know how far without knowing the specifications of every part in the engine.
I'm not looking for a brawl either. I just think there are other factors besides the valve train involved.
 

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Re: finding the redline..... (VWhombre)

makes sense....,
and as far as replies, all are apreciated, weather they are replying to my original post or stating different opinions and clerifying what others have said within the post...
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Re: finding the redline..... (tomk1)

There are bottom end issues. Notice that the 2L has a lower redline than the 1.8L. This is due to the longer stroke. Th episton has to move farther, therefore move faster, at any given RPM. To move faster it must accelerate more quickly, and as Newton said F=ma. Increase a (acceleration) and the forces on the crank/rod/piston/etc go up. Increase the force enough and something breaks. But that is not the point wherre redline is set, IOW you will not explode your stock 1.8 at 7201 rpm. A more important factor is fatigue life. Notice that most tachs have a "yellow zone" or some such (my tach is cross-hatched from 6800-7200.) If you read the manual carefully, this range is not for continuous operation, reason being that the stresses on the bottom end are high enough to be causing significant fatigue (for steel that's about 50% of UTS (ultimate tensile strength, the point at which it fails from a single loading) Any cyclically loaded part made of steel is designed to be loaded at less than 50% of UTS if it is to last indefinitely. Interestingly, aluminum always fatigues to failure in cyclic service no matter how low the stress, it just takes longer.
So, theoretically, if you assume the "yellow line" to be the point where fatigue loading begins, your bottom end could turn 1.414 (square root of two) times as fast as that before it flies apart instantly. This neglects balance considerations and probably some others that you lot will kindly point out.
And Scirocco 53, don't be so touchy. You are correct that valve float is an issue, but you are a bit off on the mechanism.
 

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Re: finding the redline..... (Dubai Vol)

Has what I described happened to you? Because that is exactly what has happened to myself, and two other friends of mines motors. I am not touchy. I stated what has actually happened on two 16 valve VW motors, and to a BMW M3 16 valve motor. The intake valves will bend when valve float occures on a 16 valver. I shift at 8000rpm, and the only problem I gave ever had is when I mis shifted and did not shut it down instantly. Like VWhombre stated; I felt a loss in power right away, kept my foot in it until the piston did drive the stuck open intake valve into the head. If you need proof, I can take some pictures of the carniage.
Obviously all moving parts in the engine (including the bottom end) have to be considered when you are talking about redline, but, the crank, rods and pistons will outlast the valves every time.
 

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Re: finding the redline..... (tomk1)

Guys, what the heL are you trying to prove here?!
Are you trying to define "redline" by when the engine stops making power or when will it explode!?!
The valve float guys are saying redline on the basis of when engine stops making power or the valves hit the pistons. The reciprocating mass people are taking redline to mean "the engine explodes"

So what is it going to be?


[Modified by gearhead455, 6:32 PM 4-12-2002]
 
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