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Greg in Sydney
03-17-1998, 06:27 AM
Greetings fellow Z3ers. <p>Tonight's questions are about the "redline" on the tachometer of my Z3. For 10 points apiece, who can tell me:<p>1. Is the "redline" the first point on the tacho where the dial starts to be shaded red (ie around 6000rpm) or is it the last point of the red shaded section (ie around 7000rpm)?<p>2. Is it bad for my Z3 if I rev it all the way to the redline? (Note: I have about 2,000 miles on the clock.)<p>3. How exactly does the engine management system prevent me from revving past the "redline"?<p>4. When accerating, at how many revs should I generally change to a higher gear? <p>5. When decelerating, at how many revs should I generally change to a lower gear?<p>Cheers,<br>Greg in Sydney<br>Hang11@ibm.net<p>

Mike
03-17-1998, 06:48 AM
Let's see if I can field some of these...<p><i><br>: 1. Is the "redline" the first point on the tacho where the dial starts to be shaded red (ie around 6000rpm) or is it the last point of the red shaded section (ie around 7000rpm)?</i><br><b>The red line is actually when the engine cuts out. Closer to 7000 RPM, the first shaded area is to remind you to quit running the engine so hard.</b><p><i>: 2. Is it bad for my Z3 if I rev it all the way to the redline? (Note: I have about 2,000 miles on the clock.)</i><br><b>Bad is a relative term. If you run the engine to the redline off of every stop sigmn, it will wear out faster. The management system is designed to prevent the driver from overrevving, however.</b><p>: 3. How exactly does the engine management system prevent me from revving past the "redline"?<br><b>Very slick programming in the CPU allows the system to back off timing and cut fuel after a certain RPM. This results in a nice little power loss feeling, and keeps the engine from blowing up!</b><p>: 4. When accerating, at how many revs should I generally change to a higher gear? <br><b>Totally personal preference here. On a 1.9L Z3 like mine, I'd suggest 3800 in first, 3500 in second, at least 3000 in third and in fourth. I almost never shift my Z3 under 3000. I suspect that if everyone drove them this way, the press would realize how fast a 1.9l is. People tell me the car is slow, but when I ask where they shift, it is around 1800, 'like my old Mustang!' Ahh!!! A Z3 is NOT a Mustang, rev the engine!</b><p>: 5. When decelerating, at how many revs should I generally change to a lower gear?<br><b>3000 RPM</b><br>

Greg in Sydney
03-17-1998, 07:14 AM
<i>: Let's see if I can field some of these...<p>: <br>: : 1. Is the "redline" the first point on the tacho where the dial starts to be shaded red (ie around 6000rpm) or is it the last point of the red shaded section (ie around 7000rpm)?<br>: <b>The red line is actually when the engine cuts out. Closer to 7000 RPM, the first shaded area is to remind you to quit running the engine so hard.</b><p>: : 2. Is it bad for my Z3 if I rev it all the way to the redline? (Note: I have about 2,000 miles on the clock.)<br>: <b>Bad is a relative term. If you run the engine to the redline off of every stop sigmn, it will wear out faster. The management system is designed to prevent the driver from overrevving, however.</b><p>: : 3. How exactly does the engine management system prevent me from revving past the "redline"?<br>: <b>Very slick programming in the CPU allows the system to back off timing and cut fuel after a certain RPM. This results in a nice little power loss feeling, and keeps the engine from blowing up!</b><p>: : 4. When accerating, at how many revs should I generally change to a higher gear? <br>: <b>Totally personal preference here. On a 1.9L Z3 like mine, I'd suggest 3800 in first, 3500 in second, at least 3000 in third and in fourth. I almost never shift my Z3 under 3000. I suspect that if everyone drove them this way, the press would realize how fast a 1.9l is. People tell me the car is slow, but when I ask where they shift, it is around 1800, 'like my old Mustang!' Ahh!!! A Z3 is NOT a Mustang, rev the engine!</b><p>: : 5. When decelerating, at how many revs should I generally change to a lower gear?<br>: <b>3000 RPM</b><p></i>

Bruce
03-17-1998, 08:16 AM
<i>: <b>Totally personal preference here. On a 1.9L Z3 like mine, I'd suggest 3800 in first, 3500 in second, at least 3000 in third and in fourth. </b></i><p>i know you said it was your preference, but the engine doesn't get going til 3500 rpms, i don't shift until at least 4K and that is only when the engine is cold, when it gets to normal operating temp i shift around 5K (sometimes more :)<p><i>: : 5. When decelerating, at how many revs should I generally change to a lower gear?<br>: <b>3000 RPM</b></i><p>downshifting is unnecessary...modern brakes can handle the stress

Terry
03-17-1998, 10:15 AM
<i>: Let's see if I can field some of these...<p>: <br>: : 1. Is the "redline" the first point on the tacho where the dial starts to be shaded red (ie around 6000rpm) or is it the last point of the red shaded section (ie around 7000rpm)?<br>: <b>The red line is actually when the engine cuts out. Closer to 7000 RPM, the first shaded area is to remind you to quit running the engine so hard.</b><p>: : 2. Is it bad for my Z3 if I rev it all the way to the redline? (Note: I have about 2,000 miles on the clock.)<br>: <b>Bad is a relative term. If you run the engine to the redline off of every stop sigmn, it will wear out faster. The management system is designed to prevent the driver from overrevving, however.</b><p>: : 3. How exactly does the engine management system prevent me from revving past the "redline"?<br>: <b>Very slick programming in the CPU allows the system to back off timing and cut fuel after a certain RPM. This results in a nice little power loss feeling, and keeps the engine from blowing up!</b><p>: : 4. When accerating, at how many revs should I generally change to a higher gear? <br>: <b>Totally personal preference here. On a 1.9L Z3 like mine, I'd suggest 3800 in first, 3500 in second, at least 3000 in third and in fourth. I almost never shift my Z3 under 3000. I suspect that if everyone drove them this way, the press would realize how fast a 1.9l is. People tell me the car is slow, but when I ask where they shift, it is around 1800, 'like my old Mustang!' Ahh!!! A Z3 is NOT a Mustang, rev the engine!</b><p>: : 5. When decelerating, at how many revs should I generally change to a lower gear?<br>: <b>3000 RPM</b><p></i><p>I'm not debating or flame baiting but with many years of high performance stock four bangers underfoot (1+ hp/cu in) I'd like to add the following:<p>Four cylinder engines have a terrible time generating torque due to the 90 degree rotation of the crankshaft between cylinder ignition. So you have to rev them a bit higher than sixes and certainly eights.<p>The plot of the torque curve is important here, the idea is to upshift at a point that will place you at the steepest incline on the curve as you enter the next higher gear.<p>On the Z3 1.9 litre this point is just over 4000 rpm. This places less strain on the motor (rod & main bearings) and avoids "lugging" the engine. Old rule of thumb with small four bangers: Keep it <b>above</b> 3000 rpm.<p>BMW lists <i>redline</i> at 6200 rpm (I believe) but this is not the point at which the engine hand-grenades, you're just not to cruise at this speed. Reciprocating engines can rev quite high <b>under load<b> (accelerating), it's when you unload the engine that it's hazardous (cruising).<p>The rev limiter protects BMW from people who don't understand the mechanics involved more than it protects the engine. Engines such as the 1.9 easily rev to 8 grand and have for nearly 30 years, nothing exotic. The valve springs have usually been the limiting factor along with the quality of components (forged vs. cast) and the quality of assembly (bearing clearances). We used to rev completely stock but hand built '72 Ford Cortina 1600's to 8500 rpm at every shift and never lost a motor (Formula Ford).<p>I shift between 4 and 5 grand, at 6 when tryin' hard.<p>Note, never rev a fresh engine above 4000, you'll start shaving pure metal off the cylinder walls. This is why you let the rings "seat" first. In a consumer/production car this takes about 1200 to 1500 miles. At least 2000 miles before you tach 6000.<p>Terry :-)<p><br>

Karl Seeger
03-17-1998, 10:15 AM
I drive a 1.9 and it NEVER go's below 2000. I shift in the 5000 range and when "pushing it" I shift at 6400~6500.<p>Use your brakes to slow down, blip the throtle on down shift (heal toe) and keep the rev'es up. Using the "rear end" to slow down will upset your balance.<p>I cruse around at about 4000.<p>-Karl

Matt F.
03-17-1998, 10:24 AM
<B>OK, I just can't resist opening by big mouth</B><p><i>: : <b>Totally personal preference here. On a 1.9L Z3 like mine, I'd suggest 3800 in first, 3500 in second, at least 3000 in third and in fourth. </b><p>: i know you said it was your preference, but the engine doesn't get going til 3500 rpms, i don't shift until at least 4K and that is only when the engine is cold, when it gets to normal operating temp i shift around 5K (sometimes more :)</I><br><B>4K when cold?...Man I wouldn't want to be your beemer... your dealers going to <I>love</I> you at around 100,000 miles. <p> Do yourself a favor keep it under 3K until she's warmed up a bit. I believe thats also better for the Catalitic(sp) converter. <p>Even though no one likes to think about the environment, when you rev the engine too high before the Cat. can warm up you're not helping our Austalian Z3 drivers. Those poor guys can't enjoy a long top down drives in summer without risking skin cancer because of the veeerrry thin Ozone down there</B><p>: : : 5. When decelerating, at how many revs should I generally change to a lower gear?<br>: : <b>3000 RPM</b><p>: downshifting is unnecessary...modern brakes can handle the stress</i><p><B>The purpose of downshifting is to have the car in the right gear, at the right time, and with the clutch disengaged ready to apply power(like when exiting a corner). Not primarily to spare the brakes. More importantly, its just plain fun! <p>Boy, I'd like to autocross against you :-)</B><p>Matt F. <br>

Andrew - Sydney, Australia
03-17-1998, 04:45 PM
<i>: Tonight's questions are about the "redline" on the tachometer of my Z3<br></i><p><snip><p>You've already had serious & sensible answers to all of these, so I'm only throwing in my opinions on a couple...<p><i>: 4. When accerating, at how many revs should I generally change to a higher gear? <br></i><br>I have two modes, economy and sport (note: that's me, not my car - I don't want to be bombarded with questions about a weird Aussie Z3 configuration).<br>When in economy mode, I normally shift just shy of 3000 - in sport mode, it's over 5500 (depends on what's in the lane next to me :-)<p>Noone mentioned skipping gears, so here's one of my favourite Z3 occupations... toll gates (evil cackle).<br>Flat out in 1st, 2nd & 3rd gets you up to 90 kmh real quick, then into 5th and off the accelerator to stay there.<p>Cheers,<br>Andrew<br>Red/black 1.9

Bruce
03-17-1998, 06:45 PM
<i>:4K when cold?...Man I wouldn't want to be your beemer... your dealers going to <I>love</I> you at around 100,000 miles. <p>: Do yourself a favor keep it under 3K until she's warmed up a bit. I believe thats also better for the Catalitic(sp) converter. </i><p>just going by what the consensus is the the digest...4000 is the recommended limit for the break in, so makes sense for it to be for warmup too (IMHO)<p><i>The purpose of downshifting is to have the car in the right gear, at the right time, and with the clutch disengaged ready to apply power(like when exiting a corner). Not primarily to spare the brakes. More importantly, its just plain fun!</i> <p>i should have clarified myself...i don't downshift when i know i am coming to a complete stop...i do place the gearshift in the right gear if i am not coming to a complete stop but i don't use the engine to break (that was the point i was trying to make)

Matt F.
03-18-1998, 04:04 AM
: just going by what the consensus is the the digest...4000 is the recommended limit for the break in, so makes sense for it to be for warmup too (IMHO)</I><p>The breakin recomendation have nothing to do with driving with a cold motor. <p>A german BMW mechanic explained to me that motors are very sensitive when they are cold. The moving parts in a motor are designed to operate withing certain size/fit tolerances. These tolerances are calculated for a motor at operating tempurature. When the motor is cold the moving parts have not had a chance to expanded and reach the tolerances they were designed for, therefor causing more friction or scars due to "chattering".<p>Case in point:<p>I used to own a 316 and would rev the motor consistantly to 4000-4500 when it was cold. I used to live about 1/4 from the Autobahn on ramp I used to go to work. After only about 1 Minute I would enter the autobahn, accelerate to 75mph(120kmh), shifting at 4000 to 4500 RPM's. <p>In my case it was the crankshaft spacing shims (they keep the crankschaft from moving for or aft) wore prematuraly. Apperantly higher RPM's with the motor still cold caused too much friction on this part. The crankcase had not expanded whereas the crankshaft had, and the tolerance was to high. After 75,000 miles the motor developed some very strange sounds and shortly thereafter I experianced its horrable death.<p>All I wanted to say was "be carfull". If you plan on keeping your car for a long time, wait for the temp needle to reach a normal tempurature before fully accelerating or taking the motor above 3K-3.5K. That mistake ended up being an expensive one for me and I would hate to se someone else do the same.<p>Ok, Ok, I'll get of my soap box.<p><i>: i should have clarified myself...i don't downshift when i know i am coming to a complete stop...i do place the gearshift in the right gear if i am not coming to a complete stop but i don't use the engine to break (that was the point i was trying to make)</i><p>Point well taken (come to thing about it, I dont do that eather). I just thought you eather didn't downshift for turns or you drive an automatic :-). <p>Matt (Z-Less till Friday)

Kessler
03-18-1998, 10:08 AM
<i>: Four cylinder engines have a terrible time generating torque due to the 90 degree rotation of the crankshaft between cylinder ignition. So you have to rev them a bit higher than sixes and certainly eights.<p></i><br>Your premise is valid but there are actually 180 degrees of crankshart rotation between each ignition on a 4 cyl, 4 cycle engine (as opposed to 120 degrees on a 6 cyl).<p><i>: The plot of the torque curve is important here, the idea is to upshift at a point that will place you at the steepest incline on the curve as you enter the next higher gear.<p></i><br>Not entirely true. The way to maximize acceleration is to maximize the integral of torque with respect to time. A crude way to approximate this is to plot torque vs. RPM. Now figure out the RPM difference between gears (for the sake of example, lets say this is 1500 RPM). Now put two vertical lines on the graph that are 1500 RPM apart (or whatever the actual number is) and measure the area under the torque curve bounded by these two lines. Now move both lines and remeasure. When you find the spot that gives you the maximum area under the curve, the lines give you your shift point (the high line is the RPM you want to upshift at).<p><i>: On the Z3 1.9 litre this point is just over 4000 rpm. This places less strain on the motor (rod & main bearings) and avoids "lugging" the engine. Old rule of thumb with small four bangers: Keep it <b>above</b> 3000 rpm.<p></i><br>I don't have a copy of the torque curve for a 1.9 (anyone want to email me one?) so I can't verify your 4000 number. Keep it above 3000 (after warm up of course) does seem entirely reasonable.<p><i>: BMW lists redline at 6200 rpm (I believe) but this is not the point at which the engine hand-grenades, you're just not to cruise at this speed. Reciprocating engines can rev quite high <b>under load<b> (accelerating), it's when you unload the engine that it's hazardous (cruising).<p></i><br>I know of no scientific basis for this load vs. cruising premise. If X RPM under load for an extended period of time is safe, then it will be even more safe under no load. From a wear standpoint, load and number of revolutions determines the amount of engine wear. From a rev limit standpoint, the main concern is valve float, and strain on the bottom end. Valve float is independent of load and bottom end strain is goes down as the load decreases.<p><i>: The rev limiter protects BMW from people who don't understand the mechanics involved more than it protects the engine. Engines such as the 1.9 easily rev to 8 grand and have for nearly 30 years, nothing exotic. The valve springs have usually been the limiting factor along with the quality of components (forged vs. cast) and the quality of assembly (bearing clearances). We used to rev completely stock but hand built '72 Ford Cortina 1600's to 8500 rpm at every shift and never lost a motor (Formula Ford).<p></i><br>Correct. The limit is artificially imposed and is a trade off between performance and long term (100K+ mile) reliablity. Needless to say, people shouldn't fear getting close to the limit. If shifting near the rev limit imposed any kind of a risk to the engine, BMW engineers would have set the limit lower.<p>- Dave Kessler<br>- '88 Porsche 911, '97 BMW Z3 2.8l

BillJ
03-18-1998, 10:49 AM
While valve float is one limiting factor in max. RPM, it has a rather self limiting effect. Don't close, lost efficiency, poor compression, poor power. The single biggest factor in RPM limitations (assuming bearings are sized appropriately) is piston speed. You can only move that chunk of metal so fast before you lose the capillary oil film that keeps it from galling the cylinder wall and vice versa. High volume oil pumps help, but there is a limit. So - shorter stroke, higher RPM. Better metals, higher RPM. Lower contact area (friction) as in cutaway skirt racing pistons, higher rpm.<br> <br>: : Four cylinder engines have a terrible time generating torque due to the 90 degree rotation of the crankshaft between cylinder ignition. So you have to rev them a bit higher than sixes and certainly eights.<p>: <br>: Your premise is valid but there are actually 180 degrees of crankshart rotation between each ignition on a 4 cyl, 4 cycle engine (as opposed to 120 degrees on a 6 cyl).<p>: : The plot of the torque curve is important here, the idea is to upshift at a point that will place you at the steepest incline on the curve as you enter the next higher gear.<p>: <br>: Not entirely true. The way to maximize acceleration is to maximize the integral of torque with respect to time. A crude way to approximate this is to plot torque vs. RPM. Now figure out the RPM difference between gears (for the sake of example, lets say this is 1500 RPM). Now put two vertical lines on the graph that are 1500 RPM apart (or whatever the actual number is) and measure the area under the torque curve bounded by these two lines. Now move both lines and remeasure. When you find the spot that gives you the maximum area under the curve, the lines give you your shift point (the high line is the RPM you want to upshift at).<p>: : On the Z3 1.9 litre this point is just over 4000 rpm. This places less strain on the motor (rod & main bearings) and avoids "lugging" the engine. Old rule of thumb with small four bangers: Keep it <b>above</b> 3000 rpm.<p>: <br>: I don't have a copy of the torque curve for a 1.9 (anyone want to email me one?) so I can't verify your 4000 number. Keep it above 3000 (after warm up of course) does seem entirely reasonable.<p>: : BMW lists redline at 6200 rpm (I believe) but this is not the point at which the engine hand-grenades, you're just not to cruise at this speed. Reciprocating engines can rev quite high <b>under load<b> (accelerating), it's when you unload the engine that it's hazardous (cruising).<p>: <br>: I know of no scientific basis for this load vs. cruising premise. If X RPM under load for an extended period of time is safe, then it will be even more safe under no load. From a wear standpoint, load and number of revolutions determines the amount of engine wear. From a rev limit standpoint, the main concern is valve float, and strain on the bottom end. Valve float is independent of load and bottom end strain is goes down as the load decreases.<p>: : The rev limiter protects BMW from people who don't understand the mechanics involved more than it protects the engine. Engines such as the 1.9 easily rev to 8 grand and have for nearly 30 years, nothing exotic. The valve springs have usually been the limiting factor along with the quality of components (forged vs. cast) and the quality of assembly (bearing clearances). We used to rev completely stock but hand built '72 Ford Cortina 1600's to 8500 rpm at every shift and never lost a motor (Formula Ford).<p>: <br>: Correct. The limit is artificially imposed and is a trade off between performance and long term (100K+ mile) reliablity. Needless to say, people shouldn't fear getting close to the limit. If shifting near the rev limit imposed any kind of a risk to the engine, BMW engineers would have set the limit lower.<p>: - Dave Kessler<br>: - '88 Porsche 911, '97 BMW Z3 2.8l<p>

Kessler
03-18-1998, 04:28 PM
<i>: While valve float is one limiting factor in max. RPM, it has a rather self limiting effect. Don't close, lost efficiency, poor compression, poor power.<p></i><br>Depends on the engine. On engines with enough piston to valve interference, valves that stay opened too long will get closed the hard way :-)<p><i>: The single biggest factor in RPM limitations (assuming bearings are sized appropriately) is piston speed. You can only move that chunk of metal so fast before you lose the capillary oil film that keeps it from galling the cylinder wall and vice versa. High volume oil pumps help, but there is a limit. So - shorter stroke, higher RPM. Better metals, higher RPM. Lower contact area (friction) as in cutaway skirt racing pistons, higher rpm.<p></i><br>Excellent point and totally valid. Thanks for pointing that out :-)<p>- Dave Kessler<br>- '88 Porsche 911, '97 BMW Z3 2.8l<br>


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