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maximum piston speed?
10

maximum piston speed?

maximum piston speed?

(OP)
in my quest for more useful knowledge i am wondering what kind of piston speeds are the limit? i know some of you guys out there deal in F1 and such. i had jotted a number on a small piece of paper an F1 guy told me a few months ago but i have misplaced it and it is important now. i think it was 28m/s or was it f/s? thanks for the help i am really looking for a max this engine will only run for 200 miles then be rebuilt. i am trying to maximize breathing with the best trade off of stroke and rpm.

RE: maximum piston speed?

Normally people talk in terms of mean piston speed - ie, the stroke X 2 X revs per sec.  About 25 m/s is around the maximum for mean piston speed, if you know what I mean. This is true for a lot of high revving production motorcycle and car engines, to even things like F1 engines are about this mark.

The actual true maximum, as opposed to mean speed, also depends on the rod length as well as revs and stroke length, but people just normally talk in mean values.

RE: maximum piston speed?

(OP)
but does anyone know about some more concrete values. "about 25m/s" is nice but not exact enough. there is a big difference between 25m/s and 27m/s. i know that these are likely to be mean values and the engine is running about 1.96-2.1 l/d. depending on the stroke selected. i recall a honda b16 engine being at 22m/s oem but that could be way wrong. i guess i will have to go dig up some of the old IRL parts and measure the bore and knowing the displacement limit com up with a stroke and knowing the rpm they used will get me close. i was really trying to be as lazy as possible and also get info from others because people always say it cant be done and theres someone who does.

RE: maximum piston speed?

OK, what do you actually want?  No universal constant of piston speed has been found by physicists - although I suspect it's slower than the speed of light:)  Some mid 90s F1 engines reputedly approached 28m/s mean piston speed.  So use 28, but it may not be what you're after if you're not building a mid 90s F1 engine.

RE: maximum piston speed?

(OP)
hmmm i thought "Ps" was the constant for piston speed as found by the lithuanian scientist joren pistonovich. ha. i am just looking for some experience of what has been safe for people to use. i will try to stick it around 28m/s but if anyione thinks i can go faster let me know. i am in a ver competitive racing class and need every thing i can get.

basically the measure of power in a basic view is the amount of air(oxidizer) and fuel combusted per unit time. some people will run short stroke smaller displacement with higher rpm to yeild a certain amount of combusted fuel. a larger stroke with less rpm can yeild the same amount, but the idea is to do the most. and in either case it is limited physically by piston speed.

RE: maximum piston speed?

In my quest for more useful knowledge i am wondering what kind of piston speeds are the limit?

The best advice I can give you to date is that piston speeds are moot.

Chumley

RE: maximum piston speed?

Along time ago the maximum attainable piston velocity was limited by the materials and manufacturing quality of the engine internals. For many decades OEM engine designers considered 3500 ft/min (17.8 m/s) to be the threshold. Think low-grade cast iron construction.

With improved materials, design and manufacturing techniques, those days are long behind us. In the realm of purpose-built high performance engines, mach index (intake charge velocity) will bite you in the backside long before the tensile limits of a connecting rod will.

Regards,
Bryan Carter

RE: maximum piston speed?

4
In the mid and late 90's I worked for one of the 2 Japanese engine suppliers in CART. During the off season we were able to solve our valve train reliability issues to where we could run the engines @ 15,000rpm for 200 miles.
The maximum piston velocity was around 38m/s.
This was 200 miles of WOT track testing on a super speedway. As we approached the 250 mile distance (we had a 300 mile race coming up at Motegi in Japan in less than 6wks) when we discovered that the pistons were now the weak link. The center of the piston was cracking (due to inertial forces of the mass of the material in between the 4 valve reliefs in the center of the piston) and causing catastrophic failures. We spent ~$250k as a band aid fix to this problem since we didn’t have enough time to have new forging dies designed, built and new pistons tested.
I still have one of the band-aid pistons as a paperweight. It showed signs of cracking @ 250 miles, but it lived 350 miles before a pencil sized hole burnt through the crown.

RE: maximum piston speed?

(OP)
cnova

thanks for the good info. what kind of rings did you use at that speed. i was going to use something lightweight with gas porting. but there are a lot of options out there. any advice you have is apreciated. i have pretty much settled at a speed of 31 to 32m/s. my head wont flow much past that. not that you people really care.

RE: maximum piston speed?

Just bare in mind cnova is talking maximum piston velocity, not mean piston speed.  

RE: maximum piston speed?

(OP)
i see i will keep that in mind. that is actually much more helpful to know max. velocity anyway instead of mean speed.

RE: maximum piston speed?

We were using 2 beryllium copper compression rings, we were not using gas porting and a 3 piece oil control ring with a series of oil return ports. The oil control ring are steel but I don't recall what alloy. Bore and stroke were 93mm x 48.7mm.

RE: maximum piston speed?

(OP)
yes i did the math and the numbers you gave me pan out but i guess it still doesnt help too much because i know some guys are running  actual max piston velocity of 45 m/s. that is 86mm stroke at 10000. and there was talk that someone was running 94mm stroke at 9800 which is about 48 m/s. but all of the oem guys seem to stick in the range you had of 38 m/s. its the privateer guys  that are going nuts.

just thought i would kick that info back to you guys. ssems to make sense though. if you have a mean speed of 28m/s or so it makes a little sense that you would have peak speeds a little higher. cnova the mean sped on you data is 24.4 m/s. most of the applications seem to stick right around 28m/s mean speed. but i had a very reputable engine builder say he has done mean speed of 32m/s before with a peak velocity of 50 m/s. but he says it might only last for 100 miles.

RE: maximum piston speed?

I agree with what Chumley said. And like Bigtomwcp said in his post. They say it can't be done, then someone does it.
Those are the sayings of scientist and inventers of years past. Maybe they didn't want anyone passing them up???? LOL
That saying inhibits invention and science.

RE: maximum piston speed?

(OP)
cnova

why did you use the beryllium copper rings? was it because of the weight or the springiness of the material?

RE: maximum piston speed?

The book, "Classic Racing Engines," by Karl Ludvigsen has a chart on page 214-215 that shows piston speeds for fifty classic racing engines.  The highest piston speed listed is 5,964 feet per minute for the 1992 Honda V12.  It had an 88mm bore, a 47.9mm stroke, and ran at 14,000 RPM per the chart (14,400 RPM in the text part of the book).  Newer exotic materials would almost certainly enable still higher piston speeds.  This is adjusted piston speed.

RE: maximum piston speed?

Be-Cu was ultimately used due to it's wear charasteristics and strength.

We were experimenting with several different materials and coatings for our liners. Base materials ranged from cast iron to Be-Cu with hard chrome or Nikasil coatings, to an experimental Aluminum-ceramic fiber matrix.

The aluminum-ceramic matrix liners showed the greatest promise once we figured out how to 1) manufacture them (centrifugally vacuum cast), 2)then how to machine the castings and then 3) how to hone the cylinder bore to the proper finish. These 1st 3 steps were a "hemitsu" sp? (Japanese for big secret) project. Once we (the track development engineers) learned more about the materialused in these liners, we pointed out that the CART engine rules prohibited the use of composite materials in the internals of the engine. External use of composites (mounting brackets, sensor boxes, etc.) were OK.
Needless to say more than one person lost his job as a result of this oversight.

RE: maximum piston speed?

(OP)
cool i was looking into copper-tin rings is that wiorth a try? well i am looking for the least friction possible. but lord knows im not on a cart budget. i have only about 38k plus cam development to spend. so i will be into it for about 50k. any advice on options for the budget? this info is great but seems to be growing out of the budget quickly. if you want you can email me bigtom@sr20racing.com. where are you working now?

RE: maximum piston speed?

(OP)
thanks for the email. i will take all the info into consideration.

RE: maximum piston speed?

"i have only about 38k plus cam development to spend"

From the safety of my armchair I wonder if the best results might be obtained with the thinnest standard rings available, a low vacuum dry sump system with lots of scrapers, buying a few cams from a few can houses, fabbing an adjustable exhaust, then spending most of the rest on headwork and dyno time with a carburetion/fuel injection specialist.

Or simply crank up the boost on the turbo.  

RE: maximum piston speed?

Formula 1 engines are actually around 26 m/s mean piston speed and 41 m/s maximum piston velocity at redline.

RE: maximum piston speed?

Someone please correct me if I am wrong, but from what I have read, it it conrod strength that is really what limits piston speed, not the piston.

As I understand it, the greatest tensile stress in the rod is a TDC during the exhaust stroke, where there is no gas pressure to counterbalance the inertial loads. As a result the alternate tension and compression loads on the rod can quickly lead to fatigue of the rod, usually in the thinnest section just below the pin boss.

There is no real fixed limit. A lot depends on what the rod is made from, piston weight, and how long you expect it all to last.

RE: maximum piston speed?

2
I work for a company that races and sells high performance motorcycle engine parts...here's a post I put up on one of the enthusiast boards when people started talking about wanting to raise the redline of their bikes from 5K to 6K or more. FYI the bike is Yamaha's Warrior an air cooled V-twin that displaces 102ci stock and the connecting rods are scary long and skinny...lol


From the postings:

At 5000 rpm your piston goes from a complete stop to 66mph in 2 1/4 inches in just .003 seconds.

Interesting Warrior Engine facts/figures:

Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass.
1000 / 13.25 / 40.49
2000 / 26.50 / 161.98
3000 / 39.76 / 364.47
4000 / 53.01 / 647.95
5000 / 66.26 / 1012.43
6000 / 79.52 / 1457.90
7000 / 92.77 / 1984.36

For Comparison at "redline":

Chevy 350
Engine RPM/ Piston Velocity mph / G's exerted on rotating mass.
6000/ 62.20/ 1140.15

Formula 1 engine
Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass.
17,000/ 83.56/ 361.27

2004 R1 Engine
Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass.
12,500/ 78.58/ 250.12

2004 R6
Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass.
15,500/ 79.98/ 315.69

2004 V-Rod
Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass.
9000/ 76.14/ 174.50

OK guys for those who are not bored by this...here's the math.

I did my math in feet, just to keep from having to change the numbers up at the end, but trust me it's the same.

Warrior Stroke=113mm or .370735 feet.
Distance traveled by crank per revolution 1.16632 feet (remember that the circumfrence is "pie"* diameter)
Revolutions per minute=5000.
Distance crank travels per minute=5831.608202 feet
Distance crank travels per hour=349896.4921 feet or 66.2682 miles per hour.

So if the crank shaft is traveling at this rate the pistons reach this max velocity twice per revolution at 9 o'clock and 3 o'clock since they are traveling at the exact speed that the crankshaft is, remember at 12 and 6 o'clock the pistons are "stopped".

To calculate the G-Force you have to take your revolutions per second (rps) which is 83.3333 (at 5K)and figure how long it takes for one revolution or .0120 seconds (1/83.3333). The piston goes from a dead stop at 12 o'clock to full speed (or 97.1934 ft/second) in 1/4 a revolution or in .0030 seconds. So the average acceleration in a second needs to be calculated or how many times per second does this event occur 1/.0030 = 333.333 times per second, now multiply this by the speed at full acceleration (97.1934*333.333) gives the figure of 32397.82 ft/second/second as the average acceleration. G-Force is 32ft/second/second. Divide 32397.82 by 32 to get the average G's exerted on the parts...or 1012.432 G's. Whew....if you hung with my math you deserve a gold star...lol

A piston weighs in at around 400grams, so at full G's right when it is stopping it "weighs" an astonishing 892.79 lbs!!!

The g's are exponentially related to the RPM and crankshaft length relationship. The Warrior crankshaft goes from 33mph at 2500rpms with 253G's to 66mph at 5000rpms and 1012G's. At 10,000 it would be 132mph with 4050G's.

The F1 crankshafts are, I forget exactly, but like 1.65 inches. Do the math Gotta, no scare tactics here, pure physics. I was just joking about the connecting rods, but it is something to think about when you start wanting to get a few more revs out of your bike.

This calculation has nothing to do with bore or weights in the calculations demonstrated.

Rob Hughes
Orient Express Powersports

RE: maximum piston speed?

Wow, 133mm stroke eh !

That certainly is a man sized stroke on that Warrior. Makes the stroke on anything else look like just a bit of vibration.

RE: maximum piston speed?

Well close 113mm...still pretty big.

RE: maximum piston speed?

Why would the g's on the Chevy 350 be so much higher than everything else?  Piston speeds are slower, rpms are slower, so there is more time for the piston to reach its speed of 66mph.  Oh, and when you calculate the force exherted on the rod by the acceleration of the piston, don't forget that the rod exherts a significant force on itself too.

RE: maximum piston speed?

For piston speed to be maximum at 3 and 9 "O" clock, you need an infinitely long rod, but the math to do this for a defined rod length is beyond me I must admit.

Your example will be within a few % of actual I expect.

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: maximum piston speed?

Woops...i just re-checked my math....

Chevy 350
Engine RPM/ Piston Velocity mph / G's exerted on rotating mass.
6000/ 62.20/ 1140.15

Formula 1 engine
Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass.
17,000/ 83.56/ 4324.97

2004 R1 Engine
Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass.
12,500/ 78.58/ 3001.46

2004 R6
Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass.
15,500/ 80.89/ 3831.51

2004 V-Rod
Engine RPM/ Piston Velocity mph/ G's exerted on rotating mass.
9000/ 76.14/ 2094.07

Yikes...the math gremlins got in my excel program and jacked up my F1, R6, R1 and V-rod figures....sorry all.

4300+ g's....holy sheet batman.

RE: maximum piston speed?

2
Hi everybody and sorry for my bad english.
I try to put my little experience here for my 1st post.

Main limit for the mean piston speed comes from an aerodynamic limit.
Since mps=IM x Cso x Cem x Ar/S

IM= MACH Index, which has a top limit of 0.6 (see graph on TAYLOR-the internal combustion engine in Thery and practice)-MIT-London
Cso= Air speed in normal conditions is 340m/s at sea level
Cem= mean efflux coeff.is 0.436 (F1 engines middle '90s)
Ar/S= geometric area of valves/area of piston is 0.3 (F1 engines middle '90s)

So, the resul for the limit of the MPS is 26,7 m/s.
More or less MPS of 27m/s is the actual limit in F1 engines.

Bye.
Alex

RE: maximum piston speed?

So to raise the mena piston speed it would be a good idea to increase Cem or Ar/S or both. I know where the choking limit comes from, is there an absolute limit to the others?



Cheers

Greg Locock

RE: maximum piston speed?

2
Pat - try these:

InstantaneousPistonVelocity = -2*PI*(RPM/60)*(Throw/12)*(TAN(RodAngle*PI/180)*COS(CrankpinAngle*PI/180)+SIN(CrankpinAngle*PI/180))

InstantaneousPistonAcceleration = -(RodLength/12)*(COS(RodAngle*PI/180)*InstantaneousRodAngularVelocity^2-SIN(RodAngle*PI/180)*InstantaneousRodAngularAcceleration)-(Throw/12)*(COS(CrankpinAngle*PI/180)*CrankAngularVelocity^2-SIN(CrankpinAngle*PI/180)*BigEndAngularAccel)

All dimensions are in inches, angles are in degrees, angular velocities in rad/sec, angular accelerations in rad/sec^2.  Outputs are in ft/sec for piston velocity and ft/sec^2 for piston acceleration.
BigEndAngularAcceleration allows input of crank rotational acceleration.

As a side note, the rather largish spreadsheet that I took the above from gives -2320g (at ~0.070* ATDC) and +1259g (at ~214* ATDC) for the maximum negative and positive maximum piston accelerations for a Chevy 350 at 6000 rpm with 5.7" rods and 0.020" piston pin offset.  Maximum positive and negative piston speeds are 95.4 ft/sec (~286.01* ATDC)and -95.2 ft/sec (~74.47* ATDC) at that rpm.  It also gives a 10000-ish number for peak g's for the BMW P83 engine.  

I need to work on the ATDC angle lookups for the max values a little more, though.

Norm

RE: maximum piston speed?

Thanks Norm,

I'm surprised it took this long to reach the point about maximum acceleration. I always thought that the real issue is the maximum (not average) acceleration and the stress and fatigue this causes. One reason for longer rod ratios in high rpm engines is to reduce the max acceleration at TDC (there are also benefits from being near TDC for longer and better rod angularity during the combustion stroke.)
I found some interesting piston kinematic spreadsheets on this page (and page 2.)

http://e30m3performance.com/tech_articles/engine-t...

Saw an F1 piston at the Mahle stand at Automechanika last month and it was extremely short. The height reduction seemed limited by the pin diameter. The pin length was about half the piston diameter to reduce weight.

cheers, derek

RE: maximum piston speed?

Without looking up any references, and ignoring offsets, isn't the maximum piston and conrod acceleration the same as the centripetal acceleration of the crank pin?

ie
omega squared . r

At TDC and BDC all the elements are in a straight line and accelerating in the same direction

Jeff

RE: maximum piston speed?

Piston motion is not simple motion.  What you're saying is probably true in Pat's infinitely long rod engine (see his March 24 post above).  I hadn't added a centripetal acceleration check to the spreadsheet, as it didn't seem to have much significance.  But if I make the 350 SBC rod length something silly like 1E6 inches the magnitudes of the maximum positive and negative accelerations become equal (at +/- 1777.8g for 6000 rpm).  Basically what that does is to make the rod angular velocities and accelerations negligible so you'd be looking at only the crankpin effect.

Without attempting a rigorous derivation, decreasing the angularity of any given rod has the effect of raising the piston in the bore while increasing its angularity has the opposite effect.  So as you approach TDC both effects are raising the piston.  After TDC, both are lowering the piston.  Approaching BDC, the crankpin motion is lowering the piston while the reduction in rod angularity is raising it.  After BDC the crankpin raises while rod angle lowers.  Hence, taking these motions as velocities and differentiating for acceleration would be expected to show asymmetric TDC vs BDC results as well.

It's perhaps interesting as a side note that for most common rod:stroke ratios there are two relative maximum positive accelerations and (assuming zero pin offset) that the acceleration at BDC is a relative minimum (although still positive).  You have to get up to about a 6.6" conrod on that 350 for a single maximum positive acceleration to occur at BDC.

Norm

RE: maximum piston speed?

Just for clarity,

Quote:

as you approach TDC both effects are raising the piston
the two effects are
(1) crankpin movement, and
(2) change in rod angularity

Norm

RE: maximum piston speed?

Maximum piston velocity should be at the points where the connecting rod axis is perpendicular to the crankpin to main journal axis.  In the limit of infinite rod length, this is 3:00 and 9:00.

I must confess I did not plug into the formula but logically this must be true.

RE: maximum piston speed?

InstantaneousPistonAcceleration = -(RodLength/12)*(COS(RodAngle*PI/180)...

Interesting approximation.  That's based on the "piston motion is a combination of a sin and a cosine" approximation, right?  How does that compare to a  precise calculation?  As I recall, it's off by a couple of percent in a few places.

Piston axial acceleration (kinematic, closed-form solution for constant crankshaft angular velocity):
 -a*cos(o)*w^2 + (a^2*w^2) * (1-2*cos(o)^2)/(sqrt(r^2-a^2*sin(o)^2) - (a^2*sin(o)*cos(o))^2*w^2)/(r^2-a^2*sin(o)^2)^1.5

where
a = crank throw
r = rod centers length
o = crank angle in radians
w = crank angular velocity in rad/sec

The above is based on taking two derivatives with respect to time of the formula for piston position:
position = a*cos(o)+sqrt(r^2 - a^2*sin(o)^2)

I can provide a (more complicated) version if you want to include pin and crank offsets from the cylinder axis, or crankshaft angular acceleration.

RE: maximum piston speed?

Here's some equations for piston kinematics I had worked out some time ago. They might even be correct!

let r = rod ratio = (length conn rod)/(stroke)
let ? = crank angle from TDC
let ? = d?/dt = engine speed (radians/time, not rev/time)
let u = piston position from mid-stroke)
let ú = du/dt = piston velocity
let ? = d²u/dt² = piston acceleration
let ? = 2r
let ? = (?² - 1 + cos²?)^½

And first note that for infinitely long conn rod (r=?), piston motion approaches sinusoidal, where
max u = a
max ú = a?
max ? = a?² for constant engine speed (d?/dt = 0)

Actual motion for pistion (finite conn rod length) can then be expressed as ratio to max sinusoidal motion:

u/a   = -? + ? + cos?
ú/a?  = -sin?[1 + (cos?)/?]
?/a?² = -(cos? + [(sin²?)/?]•[(cos?)/? - 1])•[(cos?)/? - 1]

These normalized motion equations approach sinusoidal for larger rod ratios, with max/min values of ±1. The amount that the normalized velocity and acceleration max/min values exceed ±1 represent the amplification due to non-infinite conn rod length. Again, engine acceleration was neglected in deriving normalized acceleration equation.

Note that maximum piston acceleration is amplified over sinusoidal max (a?²) by factor of (1 + 1/?) = (1 + ½/r). Trends pointed out by Norm above can be seen (what's with the Structurals hanging out here?....)

FWIW, I've heard max piston accelerations for near-current F1 engines as being around 10,000g, as mentioned above. Same source reported engine accelerations of 25,000rpm/sec.

RE: maximum piston speed?

Whoops,
Looks like some fancy characters that showed fine in "Preview" of my post above didn't survive actual posting! They all turned into question marks!

I hope to repost with corrections later...

RE: maximum piston speed?

Trying again...

Here's some equations for piston kinematics I had worked out some time ago. They might even be correct!

let c = conn rod length
let s = stroke
let r = ½s
let p = "rod ratio" = c/s
let Q = crank angle from TDC
let w = dq/dt = engine speed (radians/time, not rev/time)
let x = piston position from mid-stroke)
let y = du/dt = piston velocity
let z = d²u/dt² = piston acceleration
let a = 2p (twice rod ratio)
let b = (a² - 1 + cos²Q)^½

And first note that for infinitely long conn rod, piston motion approaches sinusoidal, where
max x = r
max y = rw
max z = rw² for constant engine speed (dw/dt = 0)

Actual motion for pistion (finite conn rod length) can then be expressed as ratio to max sinusoidal motion:

x/r   = -a + b + cosQ
y/rw  = -sinQ[1 + (cosQ)/b]
z/rw² = -(cosQ + [(sin²Q)/b]•[(cosQ)/b - 1])•[(cosQ)/b - 1]

These normalized motion equations approach sinusoidal for larger rod ratios, with max/min values of ±1. The amount that the normalized velocity and acceleration max/min values exceed ±1 represent the amplification due to non-infinite conn rod length. Again, engine acceleration was neglected in deriving normalized acceleration equation.

Note that maximum piston acceleration is amplified over sinusoidal max (aw²) by factor of (1 + 1/a) = (1 + ½/p). Trends pointed out by Norm above can be seen (what's with the Structurals hanging out here?....)

FWIW, I've heard max piston accelerations for near-current F1 engines as being around 10,000g, as mentioned above. Same source reported engine accelerations of 25,000rpm/sec.

RE: maximum piston speed?

Quote:

Originally posted by ivymike

position = a*cos(o)+sqrt(r^2 - a^2*sin(o)^2)

That's the basic position formula that I used (piston pin offset being taken as an algebraic correction against 'a*sin(o)').  I've been looking for some old derivation notes that may still be around somewhere.  But I recall having used the rod angle as well as the crank angle in working the various velocity and acceleration components.  Seemed simpler at the time . . .

Have to admit, I hadn't considered the possibility of crankshaft offset.

Norm

RE: maximum piston speed?

To cnova: That's very interesting. Is there any more info on those ceramic-aluminum liners?

RE: maximum piston speed?

Nothegger:

Metal/matrix/composite (MMC) cylinder applications can be found if you do a search in Google. Porsche and I believe, Toyota use this material currently.

I worked in the engineering/testing dept. for a piston manufacturer a few years back that was experimenting with the material as a piston alloy. Machining is a real challenge.

Will

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