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MadRiver
01-20-2010, 04:35 PM
Howdy gents! Here's a random topic to get the juices flowing. My fiancee and I have been having an on-going debate about revving a modern car to the red line.

All of this stems from the recommended break-in procedures on her Mini Cooper S. The manual recommends not exceeding 4000 rpms for the initial 1400 miles. Given that we work very close to our house, it's taken us months and we're not there yet (316 miles, but who's counting). I realize that numerous manufacturers have different requirements. Some say vary the rpms for the first several thousand miles. Some say drive it any way you want out of the lot.

Setting aside that debate (because I've agreed to keep it under 4,000), we started to talk about revving a car to the red line. It all started when I began waxing eloquent about taking the Mini out once it's broken in, putting it in sport mode, and really getting the revs up.

To make a long story short, I have espoused the view that an engine is designed to function safely, without undue ware and tear, up to the red line, especially in a modern engine (heck, I also push my TR250 to the yellow line frequently). Moreover, modern engines have cut-off features that prevent over-reving (as does the Mini). In short, the rev zone below the red line is, from the standpoint of risking damage to the car, fair game with no danger.

Her view is somewhat the opposite. My beloved is of the view that one should not approach the red line at all, and while she is a heck of a driver (and better and more relaxed at high speeds), she doesn't approach the red line.

To be clear, I don't do this all the time, and I never go over. But sometimes it's just fun!

Ok, budding Klicks and Klacks, your thoughts are most welcome.

B.

swift6
01-20-2010, 04:47 PM
Should be well within the design limits. Rev it to red and have fun!

GregW
01-20-2010, 04:58 PM
Almost always (especially with a stock car) the peak torque and horsepower curve are far below redline. Anything above the peak is just making noise.

MadRiver
01-20-2010, 05:06 PM
Almost always (especially with a stock car) the peak torque and horsepower curve are far below redline. Anything above the peak is just making noise.

Quite right, but I freely admit that I do enjoy noise. :devilgrin:

martx-5
01-20-2010, 05:44 PM
It's not just noise. Car manufacturers put the red line just a little past where peak horsepower on the engine occurs. There may be exceptions, but that's what I've seen.

For example, my Miata's HP peaks at about 6600 rpm...red line is 7000 rpm. A honda S2000's HP peak is at 8400 rpm...red line 9000 rpm. TR3's peak HP occurs at about 4800 rpm...red line 5000 rpm.

If you plot the torque and horsepower curves of an engine, you will generally see that the fastest acceleration will occur if you shift at the red line, give or take a few rpm...and I do mean a few.

This article explains why this is so. (https://www.allpar.com/eek/hp-vs-torque.html)

Of course, if you modify the engine and shift the torque and HP curves, then you will have to come up with a new red line number...usually higher then stock. Like my TR3...I'm shifting it at 5500 rpm now, but I have a feeling it would do better shifting at 6000. I don't know if I want to go there on a regular basis. Although I've hit it a few times in first and second. :driving:

texas_bugeye
01-20-2010, 05:56 PM
My experence with red line on most of todays cars has come from rentals. They all seem to have rev limiters on them so .. Hey did ya know that the Ford Fusion can do like 126 MPH across Kansas ? FACT :laugh:

GregW
01-20-2010, 05:57 PM
Of course, if you modify the engine and shift the torque and HP curves, then you will have to come up with a new red line number...usually higher then stock.
No, unless you use higher strength parts in the motor. The redline is the maximum safe speed the engine parts can accelerate and decelerate I.E. connecting rods, crank, valve springs, etc.

Guest
01-20-2010, 06:00 PM
Paint the redline pink.

martx-5
01-20-2010, 06:04 PM
Yeah, all cars today have rev limiters in them. It's easy to program into the ECU, so why not. My Miata bounces off the rev limiter at 7200 rpm...200 more then the marked red line. I have a Saturn with an automatic that will shift at the red line if I keep it floored. I haven't checked to see where the engine would cut off in neutral, but I'm sure it isn't far past the red line. I'm sure the limiters have saved a few of engines from destruction. :laugh:

martx-5
01-20-2010, 06:43 PM
Of course, if you modify the engine and shift the torque and HP curves, then you will have to come up with a new red line number...usually higher then stock.
No, unless you use higher strength parts in the motor. The redline is the maximum safe speed the engine parts can accelerate and decelerate I.E. connecting rods, crank, valve springs, etc.

My point was that if you modify the engine, <span style="font-weight: bold">to get max acceleration, you will have to move up the red line.</span> BTW, this refers to naturally aspirated engines. Whether or not the engine will stay together is another matter. What you do to the engine internals will have to be addressed when you decide how far you want to go up the horsepower ladder.

Guest
01-20-2010, 06:45 PM
. I haven't checked to see where the engine would cut off in neutral, but I'm sure it isn't far past the red line :laugh:

4K on the Saturn.

GregW
01-20-2010, 07:18 PM
My point was that if you modify the engine, <span style="font-weight: bold">to get max acceleration, you will have to move up the red line.</span> BTW, this refers to naturally aspirated engines. Whether or not the engine will stay together is another matter. What you do to the engine internals will have to be addressed when you decide how far you want to go up the horsepower ladder.
What I'm getting at is the redline on an engine is independent of the torque or horsepower curve. I've done a fair amount to my engine to increase output. However, I didn't replace the crank or the connecting rods, so my redline remains the same.

14dna
01-20-2010, 09:12 PM
:iagree:

I used to crew for an IHRA pro stock race team.
Redline has to do with reciprocating mass limits not Hp
And Honda has a couple of motorcycle engines that rev to 17,000 RPM

By the way, not all cars have rev limiters. I had a 2000 Honda Civic with the 1.6 liter 160 Hp. It had a better top end than any Honda made that year and no limit in the 'puter.

Dave :driving:

Silverghost
01-20-2010, 09:51 PM
My experence with red line on most of todays cars has come from rentals. They all seem to have rev limiters on them so .. Hey did ya know that the Ford Fusion can do like 126 MPH across Kansas ? FACT :laugh:

I bet you could go even faster if you drove through a state that was all down hill!! :crazyeyes:

3798j
01-20-2010, 10:19 PM
What had alot to do with setting an engine's redline at one time was the ability of valve springs to get the valves to close - too high a rpm, a slow returning valve spring would allow the valve to "float" causing a bent valve or worse. Today's Formula 1 engines use compressed air to close valves. When the formula was changed to V8's of 2.4 liter capacity, shifting at 20,000 rpm's was the norm. As 21,000 was approached, supposedly incoming air reached the speed of sound causing turbulence and that effectively limited engine speed. Today they've regulated rev limits considerably lower.
My Ford Ranger's tach doesn't even have a red line. They say its got a "soft" rev limiter.

vagt6
01-21-2010, 09:00 AM
Bill, I drive an '05 MINI S, stock exept for an cold air box induction mod. I respected the 4,000 RPM redline dictate while breaking the engine in. About 30K miles later, car is perfect, runs like a scalded cat and burns zero oil.

My take on the 4K RPM limit during break in: why do anything else? Why go against factory recommendations from BMW experts who've forgotten more about engines than we'll ever know??? What's the point? :nonod:

Patience, grasshopper, patience! :lol: The break in period will come very, very soon, and then, rev to your heart's content! And as said above, there's no need to rev to the redline because the engine's top torque is well below the redline. Anything greater is just makin' noise. I just love the sound of that supercharger windin' up, sounds a bit like an old 4 barrel Holley!

My tuppence worth: do what the manual sez, ya can't go wrong that way! :thumbsup:

MadRiver
01-22-2010, 01:16 PM
Alas, I've resigned myself to follow the manual on not exceeding 4k. But I can't *wait* for the break-in period to be over.

Only...two...hundred...more...miles......

GregW
01-22-2010, 01:25 PM
I had a '91 GSXR1100 motorcycle that I bought new. The max break-in RPM was also 4k. On the freeway coming back from the dealer I was at 3k in top gear. The speedo indicated 85 MPH. The bikes redline was 11,500.

bgbassplyr
01-22-2010, 02:31 PM
I had a '91 GSXR1100 motorcycle that I bought new. The max break-in RPM was also 4k. On the freeway coming back from the dealer I was at 3k in top gear. The speedo indicated 85 MPH. The bikes redline was 11,500.

If the bike will run the red line in top gear.............DON'T FALL OFF!