is it safe to o past the redline

[Turd Ferguson]

Well the speed of the piston is always changing as the crank rotates.  Are you asking for its peak speed?  If the crank was rotating at a constant speed, the maximum speed would be when the journal on the crank shaft was 90 degrees from the centerline of the crank in the direction of rotation.  Anyways, I sold my dynamics book...so no calculations for you!

-Turd.

[GeeP]

3716 ft/min is the speed the piston will travel in a straight line (including reversal) at 10,000 RPM.  This unit is the standard measurement of piston speed.  It can be found by:

Stroke in feet x 2 x RPM = s

Maximum piston speed will be equal to the rotational speed of the center of the crankshaft journal at a given RPM.  This measurement is used mainly for determining balance, and the inertia of the piston-rod combination.  It can be calculated by;

(2.23 / 2 x Pi x RPM) / 12 =  Maximum piston speed, FPM

s = 3717 FPM

Peak speed = 2918 FPM

[Lukewarm Wilson]

I put the smaller sprocket on mine and lost some top end and gained better acceleration if your looking for a top speed run go the other way with a bigger sprocket, with the smaller I am now doing 500rpm more at any given speed so have actually lost the top end I got to 185kmh on standard gearing, I guess I would probably only get about 180kmh now mines been into redline a couple of times about 12000rpm and no problems so far but i wouldnt want to do it to often the only reason i really noticed was it was screaming but doing nothing more I looked down at the tacho shocked myself at where I was and backed off but while your in red line no more power is being made it really does start to stop past 10500rpm so I wouldn't bother to take it to redline through choice.

[rangerbrown]

cant be right, 33 mph it is moving faster than that

3716 ft/min is the speed the piston will travel in a straight line (including reversal) at 10,000 RPM.  This unit is the standard measurement of piston speed.  It can be found by:

Stroke in feet x 2 x RPM = s

Maximum piston speed will be equal to the rotational speed of the center of the crankshaft journal at a given RPM.  This measurement is used mainly for determining balance, and the inertia of the piston-rod combination.  It can be calculated by;

(2.23 / 2 x Pi x RPM) / 12 =  Maximum piston speed, FPM

s = 3717 FPM

Peak speed = 2918 FPM

[Alphamazing]

would i be able to say put a 15 tooth on the front and in 5th or 6th go past 180

According to AlphaFire's post in his own Hahahahahahahahahahahaha - aka Impressions of a 14T sprocket thread, a 14T front sprocket will do 110 MPH (176 KPM).  Don't know if he was limited mechanically or by his nerve.  (I'm surprised Alpha hasn't noticed & responded to this thread yet.)

Heh. I've been in San Antonio and working until now. 

The main limiter to how high you can rev is the valve float. As soon as they start to float the power drops off and it's a useless effort to rev higher (it's usually around 10.5k rpm anyways). It can damage your engine if you rev it extremely high (12k, 13k) numerous times. Once or twice and you'll probably be okay, but if you make a continuous thing of it be prepared for a busted up engine.

With the 14T sprocket I had 110 on the speedo at 10kRPM. I was limited mainly by the fact that I was following traffic (I-35 is crazy). I might be gearing limited to top speed now. That's not necessarily a bad thing though.

Also, my bike made peak power at 9500RPM. Revving it higher than that is not a bad thing, as mine makes more power at 10k than it does at 8.5 and 9k (I think). Shifiting above peak power can drop the RPMs from an upshift right into prime power territory. You just have to look at your dyno curve and see what it is telling you.

Summary: Over-revving is bad.

[GeeP]

cant be right, 33 mph it is moving faster than that

3,700 FPM is actually on the high side.  As an example, most aircraft engines operate at about 2,800 to 3,200 FPM at takeoff power.

[rangerbrown]

yea i was jsut taling with my buddy form school i was wrong it more like 21.11 mph top speed total, but one must consider

it goes up (pistion) and hits this speed, then stops and then goes the other way at the same speed


10000 times a min or 166 times a sec

now add that up for a total speed per sec that comes to 3505mph in on sec

[Egaeus]

yea i was jsut taling with my buddy form school i was wrong it more like 21.11 mph top speed total, but one must consider

it goes up (pistion) and hits this speed, then stops and then goes the other way at the same speed


10000 times a min or 166 times a sec

now add that up for a total speed per sec that comes to 3505mph in on sec

I think my brain just blew a fuse on your dimensional analysis. 

[rangerbrown]

its ok the pistion speed between top and bottom is only 21mph.
every revolution at 10,000 rpm


but the thing to remeber is, that this is only in 2.23in's thats fast as hell


in 2.23 inch's its at 21mph

[Egaeus]

Yeah, I got what you meant, it was just the way you said it.

[pantablo]

The purpose of the redline is as Sledge stated: It is the maximum safe operating speed. Past this speed it has been determined that some part of the engine will become over stressed.

most manufacturers put the redline at a safe distance from where it could actually cause major damage so the occasional misshift, or false neutral wont kill you. You will hear the valves floating after about 12k though. I've done it a few times accidentally.

[deathlucky]

what do u mean by valve floating

[MarkusN]

Valves are closed by springs, opened by the cams. When you overrev the springs are to weak to ceep the valve buckets in contact with the cams, they start to float. Which means that they don't close at the correct times and my collide with the pistons.

BTW, Google is your friend, so is Wiki

[deathlucky]

for real dam that sounds kinda fun can u get stronger springs like u must be able to the cbr250rr redlines at 18000rpm i have herd if u go past 20000 on it u will see ur pistons

[MarkusN]

if u rite like dat ima not going 2 bother reading what u rite.

It's to damn much work.

[LimaXray]

for real dam that sounds kinda fun can u get stronger springs like u must be able to the cbr250rr redlines at 18000rpm i have herd if u go past 20000 on it u will see ur pistons

lol, yeah you could get stiffer springs to minimize the valve float, but the pistons still need to move very very fast to rev that high, faster than the pistons in a CBR250RR would because the GS has a longer stroke.  So even if you fixed the valve issue, I bet bearing or rod/main bolt failure would follow right behind.  If you want to rev higher, either 1) buy a CBR or 2) rebuild the engine with a stronger bottom end and valve train.

[Reddog787]

Maximum piston velocity occurs at the midpoint of the cylinder wall.  You want to know the speed of the piston at this point when the engnine is at 10,000 rpm ??

Also bottom end on motorcycle engines rarely break as long as the correct amount of oil is in place.

[LimaXray]

ok lets see here... it's been a while since I've done circular motion in physics, but I'll give this my best shot, but tell me if I'm wrong:

w = 10,000 RPM = 166.67 RPS = 333.34 radians/sec
r = 56.6 mm / 2 = 28.3 mm = 0.0283 m
v = w * r = 333.34 radians/sec * 0.0283 m = 9.43 m/s or 21.09 MPH (peak velocity)

more importantly, the piston is constantly accelerating from 9.43 m/s to -9.43 m/s to 9.43 m/s and so on:
a = w^2*r = 333.34^2 * 0.0283 m = 3144.57 m/s^2 or 320.55 G's!!!

Anyone know how much the piston and rod weighs? 

Also bottom end on motorcycle engines rarely break as long as the correct amount of oil is in place.

things will break... maybe not instantly like with a piston hitting a valve... but with the amount of force being exerted on the bearings, the clearances between the moving parts and the bearings becomes very small, and eventually it doesn't matter how much oil you have because there will be metal to metal contact and therefore no where for the oil to go.  This will at the very least cause scoring on the bearings, crank, rods, and mains, all of which are bad.  You can tell if an engine has been over revved on a regular basis by looking at the bearings as they will have some nasty scratches on them.

[Egaeus]

You forgot pi.

[LimaXray]

crap... technically, I didn't forget pi... I just didn't convert to radians properly because I... umm... forgot pi...

T = 1/10,000 RPM * 60 = 0.006 sec/rev
w = (2*pi)/T = (2*3.14)/0.006 sec/rev= 1046.67 radians/sec

SO ANYWAY:

w = 10,000 RPM = 166.67 RPS = 1046.67 radians/sec
r = 56.6 mm / 2 = 28.3 mm = 0.0283 m
v = w * r = 1046.67 radians/sec * 0.0283 m = 29.62 m/s or 66.26 MPH (peak velocity)

more importantly, the piston is constantly accelerating from 29.62 m/s to -29.62 m/s to 29.62 m/s and so on:
a = w^2*r = 1046.67^2 * 0.0283 m = 31003.16 m/s^2 or 3160.36 G's!!!

wow thats really high... is that right?!  circular motion has never been one of my strong points