maximum piston speed? 11

[bigtomwcp]

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.

 

[antti]

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.

 

[bigtomwcp]

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.

 

[antti]

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.

 

[bigtomwcp]

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.

 

[Chumley]

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

 

[Retracnic]

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

 

[cnova]

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.

 

[bigtomwcp]

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.

 

[antti]

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

 

[bigtomwcp]

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

 

[cnova]

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.

 

[bigtomwcp]

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.

 

[enginesrus]

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.

 

[bigtomwcp]

cnova

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

 

[dieselsmoke]

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.

 

[cnova]

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.

 

[bigtomwcp]

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?

 

[bigtomwcp]

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

 

[Tmoose]

"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.