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Location:
Edmonton, Alberta, Canada
Registered:
October 2002
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How do you figure out redline?
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Sun, 09 November 2003 07:32
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I need to pick your brains about the elusive redline. How do you calculate the redline for a particular modified engine. Is there some magic number for specific engine designs or for combinations of parts like forged pistons, balanced rotating assembly, etc? I'm planning an 4AGTE for my '73 Celica project with modified stock internals (polished rods, balanced rotating assembly, pocket ported head, 3 angle valve job, adjustable cam gears, and homebuilt custom turbo) and I want to figure out the redline to avoid the self-destruction of my blood, sweat and tears.
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Location:
Adelaide
Registered:
June 2003
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Re: How do you figure out redline?
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Sun, 09 November 2003 07:48
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allthough not entirely technical, you should be able to feel/hear when the engine starts not loving it any more.
ie my rotor redlines at 7, i usually change at around 7250 if im dragging, or about 6500 normally, if you take it above that (ive had it to 8 to see what it felt like) it just starts running out of puff, cant get enough air or fuel.
otherwise when you get it tuned the dyno readout should give you a good idea of where then engines running sweet, and when it starts to run outa revs 
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: How do you figure out redline?
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Sun, 09 November 2003 09:45
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exactly as said. as long as it's tuned properly (ie, not pinging it's titties off), just keep going till the power starts to drop off, then change.
mine for example keeps going till about 7300rpm - so I change around then (of course not having a tacho, I do it by ear/feel)
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Location:
Montrose, VIC
Registered:
May 2002
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Re: How do you figure out redline?
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Sun, 09 November 2003 09:56
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From what I've learnt on my own engines, the sort of combination you've got should be safe to at least 8500rpm - I give my still-factory-assembled turbo 4agze regular 8200 excursions, and it hasn't shown any signs of trouble. That said, I did break one engine from excessive revs - this was due to disabling the rev limiter and a stuck throttle... It didn't break right away, rather it stretched the rod bolts and broke down over 600km from home. When I pulled the engine down, I noticed every rod bolt wasn't even finger tight, that's why a rod broke. However, my (highly educated!) lucky guess is that was the result of 12,000+rpm, so make sure you assemble the engine with ARP or similiar bolts and you shouldn't have any issues. 
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Location:
Lost in the K hole
Registered:
May 2002
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Re: How do you figure out redline?
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Sun, 09 November 2003 10:39
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rev until the engine stops making power??
ahhh, so if i push nos through my 5me, and its still making power at 9000rpm, this is ok????
redline is based on the mechanical and harmonic tolerances of the engine, not on its power characteristics. if i wanted to, i could fiddle the cam timing on my 7m to make 15hp extra at 200rpm past present redline, but i chose not to... why? cause the engine cant take it! piston velocities go through the roof, rod and crank forces the same, valves start to float etc etc
redline is what the manufcturer says, not what you 'think' ... unless you have a damn good resaon based on modifications to bottom end and valve train...
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Location:
Melbourne
Registered:
March 2003
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Re: How do you figure out redline?
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Sun, 09 November 2003 10:58
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if u consider the powerband, it would probably peak then drop off right?
What happens if it peaks at say 7000 rpm but u can rev it out to 8000, when u shift wouldn't the next gear be closer to the rev limit or is this a waste of time?
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I supported Toymods
Location:
I renounced punctuation
Registered:
May 2002
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Re: How do you figure out redline?
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Sun, 09 November 2003 11:01
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Very much in concordance with Ed.
The industry standard maximum average piston speed is 4000 ft/sec. Beyond this maximum average piston speed, the bottom end is likely to be suspect unless there have been significant modifications.
The engineers that designed the engine will have done this relatively simple calculation and then factor in a range of limitations in the engine so that fools who think 5Ms are safe at 9500 rpm don't ever actually get to take them there. Thank goodness for the rev limiter.
One then has to ask what is the "real life" redline. There may be little point in taking a motor to its theoretical redline as the power developed at that maximum engine speed may be significantly less than peak power. It only results in "wear and tear" and decreased engine lifespan.
Most people who claim their engine still feels like it is making power a some ungodly engine speed would be shocked if it were placed on a dyno and objectively tested.
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Location:
Adelaide
Registered:
May 2003
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Re: How do you figure out redline?
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Sun, 09 November 2003 11:04
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in my tacholess datsun many moons ago, redline was when the interior components rattled, sounds bad but prolly only like 5,000rpm
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Location:
Adelaide
Registered:
June 2003
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Re: How do you figure out redline?
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Sun, 09 November 2003 12:20
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| ed_ma61 wrote on Sun, 09 November 2003 21:39 |
rev until the engine stops making power??
ahhh, so if i push nos through my 5me, and its still making power at 9000rpm, this is ok????
redline is based on the mechanical and harmonic tolerances of the engine, not on its power characteristics. if i wanted to, i could fiddle the cam timing on my 7m to make 15hp extra at 200rpm past present redline, but i chose not to... why? cause the engine cant take it! piston velocities go through the roof, rod and crank forces the same, valves start to float etc etc
redline is what the manufcturer says, not what you 'think' ... unless you have a damn good resaon based on modifications to bottom end and valve train...
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i know its a bit different but im trying to make a point...
13b's are safe till around 9500 where destructive harmonics start to set in.
so how do you explain the 7000rpm redline, thats 2500 lower than where its still meant to be safe.
the difficult bit is getting it to spin that fast, ie porting, supplying enough fuel ect.
but im pretty sure that a safe redline would be once peak power starts to drop off is its set up properly
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Location:
Brisbane
Registered:
May 2002
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Re: How do you figure out redline?
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Sun, 09 November 2003 12:34
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A 13B safe at 9500 rpm? Sure you can take it there, but the factory apex seals will have a lifespan of about 5 seconds! Reliability is another factor the manufacturer has to consider when setting the redline; that's why 13B's are redlined at 7000.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: How do you figure out redline?
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Sun, 09 November 2003 14:49
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| gianttomato wrote on Sun, 09 November 2003 22:01 |
The industry standard maximum average piston speed is 4000 ft/sec. Beyond this maximum average piston speed, the bottom end is likely to be suspect unless there have been significant modifications.
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as an aside, that 4000ft is based on the material properties of the rods usually... in combination with the pistons weight and stroke etc...
fwiw, the S2000 motor has around 5000ft/sec, due to the lightweight piston design and excellent attention to detail with the design.. it's also designed within an inch of it's life 
funnily enough, F1 engines are also limited by these numbers and (at least used to) have around 5000, when everything else had 4000....
as for real life redline.. the higher you rev it, the shorter it's life, and the decrease in lifetime is larger than the increase in revs.... drive it hard, it's gonna die sooner...
as for sounding bad, no engine shuld be forced to keep going then, but components can fail before those revs....
just drive and see whre it breaks the first time heh heh
Cya, Stewart
[Updated on: Mon, 10 November 2003 02:16]
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Location:
Edmonton, Alberta, Canada
Registered:
October 2002
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Re: How do you figure out redline?
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Sun, 09 November 2003 16:57
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Okay, so if I blueprint the engine to theoretical factory tolerances and balance the bottom end using factory forged (polished) rods, AGZE 8:1 pistons, a steel sandwich head gasket, pocket ported heads with a 3 angle valve job and a custom port matched large plenum intake, I'll need to figure out what revs bring the piston speed up to 4000 ft/second and set my redline just under that? Is that right? What is the factory redline?
Obviously, I won't be bumping the redline everytime I drive but I have heard that taking an engine past the max piston speed even once can exceed the elastic limits of the steel and cause permanent deformation of the parts. I'm guessing thats what mrshin was talking about with his stretched rod bolts.
I certainly want to build a performer thats going to last a while. Thanks for all your help.
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Location:
Montrose, VIC
Registered:
May 2002
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Re: How do you figure out redline?
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Sun, 09 November 2003 22:49
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The one scary thing about my old 4ag turbo setup was that the power curve was still rising at 8200rpm, even with those horrible stock s/c cams. I could never quite work out why either. And yes, while I say it's somewhat safe to rev your engine as hard as I do mine, it's certainly not going to extend its life a great deal... Another factor that seems to influence engines breaking is how it's driven - if you take it up to 9000rpm and then let go of the throttle in a low gear, you're definately going to put absolutely unthinkable forces on the innards - this is where many breakages occur.
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Banned user
Location:
ADELAIDE - The Drift City
Registered:
July 2002
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Re: How do you figure out redline?
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Sun, 09 November 2003 23:14
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13B's are safe tile 8500 not 9500... and if you want to get technical.. 8400 is generally when harmonics start to distroy seals... i all depends on the tolerances of your motor.. if its quite loose then everything will self distruct before this
all manufacturs limit something BEFORE the actual limits of the motor... imgine if the redline was set at the ACTUAL limits of the motor... people taking it to redlin day in day out would soon find them selves one expired motor and who would be to blame? the manufactors...
| lang wrote on Sun, 09 November 2003 22:20 |
| ed_ma61 wrote on Sun, 09 November 2003 21:39 |
rev until the engine stops making power??
ahhh, so if i push nos through my 5me, and its still making power at 9000rpm, this is ok????
redline is based on the mechanical and harmonic tolerances of the engine, not on its power characteristics. if i wanted to, i could fiddle the cam timing on my 7m to make 15hp extra at 200rpm past present redline, but i chose not to... why? cause the engine cant take it! piston velocities go through the roof, rod and crank forces the same, valves start to float etc etc
redline is what the manufcturer says, not what you 'think' ... unless you have a damn good resaon based on modifications to bottom end and valve train...
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i know its a bit different but im trying to make a point...
13b's are safe till around 9500 where destructive harmonics start to set in.
so how do you explain the 7000rpm redline, thats 2500 lower than where its still meant to be safe.
the difficult bit is getting it to spin that fast, ie porting, supplying enough fuel ect.
but im pretty sure that a safe redline would be once peak power starts to drop off is its set up properly
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Location:
Adelaide
Registered:
June 2003
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Re: How do you figure out redline?
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Mon, 10 November 2003 00:12
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hey im just quoting what it said in a guru motorsport article.
im not getting into/trying to get into this argument especially on a toyota forum cos theres really no right answer.
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I supported Toymods
Location:
I renounced punctuation
Registered:
May 2002
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Location:
Perth
Registered:
May 2003
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Re: How do you figure out redline?
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Mon, 10 November 2003 00:48
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the 4m loves the 6000rpm  
I found out why my engine dropped 2 cylinders and made the most horrid noise ever (metal bashing the shit out of metal) the rod that holds the air cleaner on the holley came loose and went into the combustion chamber through the manifold left a mark on a piston and had to get the head machined and get new gaskets just to be safe. me & my brother put the head back on and clenaed up the manifold should be ready by next week
damn steel nob thing! 
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I supported Toymods
Location:
I renounced punctuation
Registered:
May 2002
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Re: How do you figure out redline?
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Mon, 10 November 2003 02:45
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| coronamark2 wrote on Mon, 10 November 2003 11:48 |
the 4m loves the 6000rpm
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Do a dyno, you'll be very suprised to see that it is all over by 5000-5500.
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Location:
Adelaide
Registered:
June 2003
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Re: How do you figure out redline?
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Mon, 10 November 2003 03:20
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| gianttomato wrote on Mon, 10 November 2003 11:31 |
| oldcorollas wrote on Mon, 10 November 2003 01:49 |
as an aside, that 4000ft is based on the material properties of the rods usually... in combination with the pistons weight and stroke etc...
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Exactly what I meant by "significant modifications". Given that there was some difficulty regarding the concept of a 'redline' and why one might be imposed, I thought I'd keep it simple. 
Guru Motorsport may decide that 9500 is a "safe redline" for a weekend of motorsport, but I'm tipping most people who want a daily driver would be rather displeased at having to replace apex seals or eccentric cranks every 4 days. I'd be very skeptical of what you read in the glossies or advertisements.
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well not a safe redline as such, but more they were saying that is the point where the engine starts to fall apart unless you start upgrading internal components
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Location:
Perth
Registered:
May 2003
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Re: How do you figure out redline?
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Mon, 10 November 2003 04:02
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| gianttomato wrote on Mon, 10 November 2003 10:45 |
| coronamark2 wrote on Mon, 10 November 2003 11:48 |
the 4m loves the 6000rpm
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Do a dyno, you'll be very suprised to see that it is all over by 5000-5500.
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yeah i've had it on the dyno it makes peak powr out 4500rpm but it CAN rev to 6000 it doesnt go anywhere but it sounds good 
whats the 2j like in the rpm's?
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