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Uvreženo je mišljenje da motori koji se "radije" vrte kraće traju. Da se ipak radi o vise parametara vidi se iz jednog nepotpisanog usenet posta koji se referirao na Gordon Jenning's-ovu "Two stroke tuner's handbook". Naravno, u prvom planu je BMW.
John Allen commented on the higher redline and longer stroke
of the '91-'93 M5 engine:
>It's interesting that the longer-stroke motor (S38B36) also
>has the higher redline. Any thoughts?
John,
Yes, I can give you some "rules of thumb" about engine
reliability versus rpm. I happened to research this some
during the past week, so your question is timely.
The Metric Mechanic (MM) Catalog got me started with its
section on engine rpm versus life. Basically, high rpm
operation wears out engines faster, but there's more to it
than that. MM also mentions the critical top piston ring
area.
This sounded very familiar -- so familiar that I searched my
attic for Gordon Jenning's "Two Stroke Tuner's Handbook".
Now, M5s have four stroke engines, but the basics of pistons
and rings are the same for either.
Mean Piston Speed
- -----------------
The best known "rule of thumb" is mean piston speed (average
speed the piston travels at a fixed rpm). It goes like
this:
Mean Piston Speed Result
------------------ ------
Under 3,500 ft/min Good reliability
3,500-4,000 ft/min Stressful, needs good design
Over 4,000 ft/min Very short life
Mean piston speed is easy to determine. It's based on the
piston stroke and rpm.
Cm = 0.167 x L x N
Cm = mean piston speed in feet per min
L = stroke in inches
N = crankshaft speed in rpm
Using the 1988 E28 M5 as an example:
E28 M5, Bore and stroke 3.68 x 3.31 in (93.4 x 84 mm)
At 6,900 rpm (factory redline)
Cm = 0.167 x 3.31 x 6900 = 3,814 ft/min
At 7,200 rpm (Dinan chip redline) = 3,980 ft/min
At 6,500 rpm (max constant speed) = 3,593 ft/min
Here are some other piston speeds I figured for comparison.
Redline Stroke Piston Speed
Engine (rpm) in,mm (ft/min)
-------- ------- -------- ------------
BMW 2002 6,400 3.15, 80 3,367
BMW 318i 6,500 3.19, 81 3,463
BMW 325i 6,500 2.95, 75 3,202
BMW 3.0 6,400 3.15, 80 3,367
BMW 535i 6,200 3.39, 86 3,510
MM 4000 6,000 3.70, 94 3,707
MM 3500 6,400 3.39, 86 3,623
BMW E36 M3 6,800 3.38, 85.8 3,838
BMW E28 M5 6,900 3.31, 84 3,814
BMW E34 M5 7,200 3.39, 86 4,076
CBR600 13,250 1.78, 45.2 3,939 (motorcycle)
Notice that most production cars stay below 3,500 ft/min,
while the E36 M3 has the same 3,800 ft/min piston speed as
the E28 M5. With its longer stroke, the E34 M5 piston speed
is even higher than the screaming Honda CBR600 motorcycle!
The two Metric Mechanic (MM) engines also go above 3,500
ft/min.
>From the MM Catalog Engine Specification table, MM uses
thinner (lighter) 1.5 mm (0.059 in) top rings than the standard
BMW 1.75 mm (0.069 in) top rings. Lighter weight reduces
vertical ring acceleration force at high rpm. MM talks
about less "hammering" of the ring groove from the lighter
ring, but it also reduces piston and ring overheating.
Recommendations
- ---------------
Engines last a lot longer if they're never run at redline,
but what's the point. Enjoy your M-car. Considering piston
speed and acceleration calculations and ring thickness, M5
engine design allows reasonable reliability under high
engine revs, but the word "understressed" doesn't come to
mind.
My suggestion is be most careful about sustained high
(redline) rpms. It's probably okay to shift at redline, but
don't hold it there very long, because the pistons and rings
may suffer.
If you have a Dinan chip, maybe shift at the factory
recommended redline (6,900 versus Dinan 7,200 rpm). Even
shifting at 7,200 rpm won't cause any immediate
consequences, but over time it causes extra wear.
Postoji još i dodatak o principu rada karika, kako dolazi do njihovog pregrevanja, te zavisnosti debljine karike o brzini vrtnje klipa, ali to ce ici nekom drugom prilikom.
Primer:
Evo kako to izgleda za BMW 320i E36;
Cm = 0.167 x L x N;
Cm = 0,167 x 2,6 x 6700 = 2,910 ft/min ili ti good reliabillity
Podatke za L (hod (stroke) u inchima) i N (max obrtaje vrtnje) za svoje ljubimce mozete potraziti na
www.carfolio.com
John Allen commented on the higher redline and longer stroke
of the '91-'93 M5 engine:
>It's interesting that the longer-stroke motor (S38B36) also
>has the higher redline. Any thoughts?
John,
Yes, I can give you some "rules of thumb" about engine
reliability versus rpm. I happened to research this some
during the past week, so your question is timely.
The Metric Mechanic (MM) Catalog got me started with its
section on engine rpm versus life. Basically, high rpm
operation wears out engines faster, but there's more to it
than that. MM also mentions the critical top piston ring
area.
This sounded very familiar -- so familiar that I searched my
attic for Gordon Jenning's "Two Stroke Tuner's Handbook".
Now, M5s have four stroke engines, but the basics of pistons
and rings are the same for either.
Mean Piston Speed
- -----------------
The best known "rule of thumb" is mean piston speed (average
speed the piston travels at a fixed rpm). It goes like
this:
Mean Piston Speed Result
------------------ ------
Under 3,500 ft/min Good reliability
3,500-4,000 ft/min Stressful, needs good design
Over 4,000 ft/min Very short life
Mean piston speed is easy to determine. It's based on the
piston stroke and rpm.
Cm = 0.167 x L x N
Cm = mean piston speed in feet per min
L = stroke in inches
N = crankshaft speed in rpm
Using the 1988 E28 M5 as an example:
E28 M5, Bore and stroke 3.68 x 3.31 in (93.4 x 84 mm)
At 6,900 rpm (factory redline)
Cm = 0.167 x 3.31 x 6900 = 3,814 ft/min
At 7,200 rpm (Dinan chip redline) = 3,980 ft/min
At 6,500 rpm (max constant speed) = 3,593 ft/min
Here are some other piston speeds I figured for comparison.
Redline Stroke Piston Speed
Engine (rpm) in,mm (ft/min)
-------- ------- -------- ------------
BMW 2002 6,400 3.15, 80 3,367
BMW 318i 6,500 3.19, 81 3,463
BMW 325i 6,500 2.95, 75 3,202
BMW 3.0 6,400 3.15, 80 3,367
BMW 535i 6,200 3.39, 86 3,510
MM 4000 6,000 3.70, 94 3,707
MM 3500 6,400 3.39, 86 3,623
BMW E36 M3 6,800 3.38, 85.8 3,838
BMW E28 M5 6,900 3.31, 84 3,814
BMW E34 M5 7,200 3.39, 86 4,076
CBR600 13,250 1.78, 45.2 3,939 (motorcycle)
Notice that most production cars stay below 3,500 ft/min,
while the E36 M3 has the same 3,800 ft/min piston speed as
the E28 M5. With its longer stroke, the E34 M5 piston speed
is even higher than the screaming Honda CBR600 motorcycle!
The two Metric Mechanic (MM) engines also go above 3,500
ft/min.
>From the MM Catalog Engine Specification table, MM uses
thinner (lighter) 1.5 mm (0.059 in) top rings than the standard
BMW 1.75 mm (0.069 in) top rings. Lighter weight reduces
vertical ring acceleration force at high rpm. MM talks
about less "hammering" of the ring groove from the lighter
ring, but it also reduces piston and ring overheating.
Recommendations
- ---------------
Engines last a lot longer if they're never run at redline,
but what's the point. Enjoy your M-car. Considering piston
speed and acceleration calculations and ring thickness, M5
engine design allows reasonable reliability under high
engine revs, but the word "understressed" doesn't come to
mind.
My suggestion is be most careful about sustained high
(redline) rpms. It's probably okay to shift at redline, but
don't hold it there very long, because the pistons and rings
may suffer.
If you have a Dinan chip, maybe shift at the factory
recommended redline (6,900 versus Dinan 7,200 rpm). Even
shifting at 7,200 rpm won't cause any immediate
consequences, but over time it causes extra wear.
Postoji još i dodatak o principu rada karika, kako dolazi do njihovog pregrevanja, te zavisnosti debljine karike o brzini vrtnje klipa, ali to ce ici nekom drugom prilikom.
Primer:
Evo kako to izgleda za BMW 320i E36;
Cm = 0.167 x L x N;
Cm = 0,167 x 2,6 x 6700 = 2,910 ft/min ili ti good reliabillity
Podatke za L (hod (stroke) u inchima) i N (max obrtaje vrtnje) za svoje ljubimce mozete potraziti na
www.carfolio.com
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