Also at that 1.8 max/mean ratio which is also around .93 R/S ratio you would have peak piston speed at around 65 degrees ATDC. Of course the pistons and crank would never clear with this setup but just saying if it did! At 9.800 deck height you could run over 4 inches of compression height on your piston though so you could run one hell of a dish for your turbo!!!

 

I know people that build F1 engines and I think they are more like 2.5 R/S ratio due to packaging of the heads and the V-angle? The 90 degree stuff allowed the rods to be shortened substantially over the old 72 degree stuff.

This rod ratio (2.5 to 1) would allow peak piston speeds around a 1.60 max/mean ratio or 40 M/S which is more likely if the average was 25 M/S?

 

Just read the Renault thread and it was a misprint I guess! I was really wondering there for a second Old Stroker!

 

Good catch Eric. The typo was mine. Peak piston speed was quoted by BMW at 40 m/s, not 45 as I said above. Sorry. 1.6:1 peak/avg is more believable, huh?

The also said "air intake volume" was 1995 cubic meters/hour or about 1174 cfm.

See Racecar Engineering V13 No.12 (Dec 03).

FWIW, using the 19200 peak rpm, 40 m/s peak piston speed and 25 m/s avg. piston speed on a 10 cylinder engine of just shy of 3000 cc, I got the following:

Stroke:
39.065 mm (1.538 in.)

Bore: 98.75 mm (3.888 in.)

Displacement: 2992 cc

Rod length: 98.0 mm (3.858 in. )

R/S ratio: 2.51:1

I get peak piston speed at about 80* ATDC

Rod length calculation is very sensitive to peak piston speed, so it's only a close approximation. I assume that BMW may have rounded off the p/s numbers a little just to keep us guessing.

 

Yes but they're all around there. 5000 FPM or so. They make real power higher but the friction curve drops the actual power down to that FPM.

 

Another take isn't necessarily friction hp, but the ability to live for a race.
I think you'll find that most endurance race engines like F1 and Nextel Cup which run maybe a million+ revs between teardown/replacement are right around the 5000 fpm mark you mentioned. Cup a little higher, F1 a little lower. That PS limit hasn't moved up a lot in the last years. Mainly strokes have been coming down. 10,000 rpm 3.5 in stroke drag engines are over 5500 avg. P/S, but they don't run long between rebuilds.

 

The F1 engine though sees almost double the stress and double the cycles per unit time because of the rpm. The G loading is not related to piston speed as much as rpm. Double the rpm at the same piston speed is double the forces at twice the frequency so it is more like 4 times as much wear!

 

Yep, doubling the rpm (Cup > F1) doubles the piston gs, but interestingly enough the practice, qualifying and race lengths are about the same number of total engine revs in both series! With F1 having half the piston mass (or less) of a Cup engine, twice the gs, about the same piston speed, and approximately the same number of revolutions in anger, wear, or load cycles or whatever should be fairly close. Remember load is proportional to gs and mass, and stress is load per area (lb/sq. inch).

I think lots of endurance engine builders think in terms of number of cycles (revs). I'm pretty sure the metal does.

 

I don't think that F1 pistons are that light. They weigh around 275 g as far as what I have seen but the pins are still up there, but the rods are certainly lighter as short as they are which is good. Maybe we can get someone on here thatknows more of what a current one weighs? They have to be aluminum now as far as I know now too. The Cup stuff has to weigh a certain amount now but I don't know what it is? You are right that the races are only half as long though. You can't make something that's only ten percent less bore weigh 50 per cent less with the same materials and have it see twice the loading usually and live. I'd say the F1 piston with two rings weighs 75 percent the weight of the NASCAR piston maybe. I will try to find out since I really don't know right now.

One thing way different though is the shock and jerk loads the F1 rotating assembly sees when shifting and accelerating over bumps etc. The NASCAR engine stays in the same gear almost constantly whereas the F1 engine sees thousands of shifts. Some tracks are all out hell on the engine and gearbox.

 

Actually they don't have a rule that states that the piston has to be aluminum. They just changed the rules to get rid of Beryllium in the parts because the dust produced by machining it is very toxic. The combination of Beryllium with Aluminum produces a very light yet extremely strong piston. The rules change just basically took Beryllium out of the equation but the parts are still very strong and very light. It makes no sense to see pistons with that much mass to them, at the RPM that F1 motors turn and the piston G's that reach 10,000 or more ever 5g's of mass is about 110 lbs of force on the rod/crank. That means that a 275g piston by itself would place 4/5ths of the total force that a Cup car sees on the rotating portion of the motor. (A Cup motor places about 8000 lbs of F on the crank and big end of the rod)That doesn't count the pin, the rings and the small end of the rod which adds another 30% to the mix or another 1800 lbs of F. With the metalurgy and technology that F1 engineers have I doubt that the modern F1 motors produced by Honda, BMW, Ferrari and Renault have pistons much over 200g's. The physics just don't warrant a piston with a mass that big.

A Cup motor has a 470g piston and pin mass and a 525g rod mass rule. They are restricted to a set mass and use aluminum pistons, Ti pins and steel rods. F1 doesn't have those limitations so they probably have much better mass to strength ratios for their base materials that allow them to place that many more G's on the parts. Considering that the piston G's double going to the F1 motor I would say they more than likely take advantage of better materials.

Bret

 

Bret,

I have some different F1 pistons and they are up to 300g with two rings. I think they are now aluminum only. Nextel primarily uses steel pins not Ti but F1 uses Ti rods. The F1 pins I have seen were also steel too although they have used all sorts of things.

The fact is that piston speed is not a good indicator of overall longevity compared to rpm. Otherwise an F1 engine costing much much more would be able to easily go 500 miles as well which it cannot even though it's average pistons speed is about the same. The valvetrain more than the shortblock is what's close to going on the Nextel engine too.

 

It's very surprising to me that you have access to modern F1 pistons. Almost no one outside of the users has that opportunity. How many valve reliefs? I'm dying to know the valve layouts.

When Be-Al alloys were outlawed, with a strength to mass ratio about 3-3.8 times that of plain aluminum (non-Be) alloy, the materials guys cooked up other alloys and MMC (metal matrix composites) which were legal and the same strength/mass. Everything I've ever read, and folks I've talked to at PRI have indicated F1 pistons are not just Aluminum alloys, but are very exotic.

Of course we differ on what determines modern race engine longevity, but that's ok. Agreeing to disagree makes a good discussion.

As I mentioned before, a Cup engine turns about the same number of revs in anger in a 500 mile race weekend (except for Plate races) as an F1 engine does in a typical race weekend. I believe F1 is going to a two-race engine rule for 2005. When they went from qualifying engines and race engines to the one-engine rule, power really didn't drop...just lap times.

No quarrel that valvetrain in Cup engines is iffy, but recent engine failures seemed to be internal/shortblock, but that could very well be from a dropped valve. Obviously the engine guys aren't telling us or each other. AFAIK, with current technology and extensive Spintron testing, Cup valvetrains are able to live at revs approaching 10,000. That puts the piston speed up over 5400 fpm, which I still think they can't yet survive. Isn't Cup going to a gear rule to limit rpm and "cut costs"? I haven't heard what that rpm limit will be. 9500 would be my first guess.

Didn't NASCAR recently outlaw some metals in the valvetrain?

My $.02

 

I am always amused by the rule changes in racing to "cut costs". They always seem to have the opposite effect. The only "cheap" racing, even at the amatuer level is a "spec" class. Like Sports 2000 in SCCA racing or even the IRL. But that eliminates the technical interest of most other race classes. I used to race Formula Ford. It was concieved as an inexpensive open wheel racing class by the SCCA. The rules were very restrictive but it was far from cheap. If you didn't have the latest chassis or the hottest new engine, you could forget winning at the National level. If I were to go road racing again, it would be in a "spec" class. Drag racing gets around this with brackets and such. Not a bad idea, but not going as fast as you possibly can somehow seems unilke "racing" to me.

Rich

 

I only am saying that piston speed is not a good indictor of overall longevity or stress as long stroke engines can operate at high pistons speeds in total endurance applications much better or by far than short stroke combinations can. These short stroke engines have good specific power but are extremely short lived as compared to their longer stroke counterparts.

I think now that MMC is also illegal in F1 as is the berylium stuff of any kind. The pistons are all two years old or older but they are all 4 valve reliefs since almost all are 4 valve engines and have been for some time. I know people that work in three F1 manufacturers. They are very trick but mostly just good engineering since they have outlawed so much of the special materials.

At one time they had some crazy pistons in F1 though! I will be at PRI like usual so maybe I can meet you guys there too.

 

Now I'm confused. Are you saying that longer stroke as opposed to shorter stroke is better for power and longevity for endurance (over a million revs) race engines? Why would you choose high piston speed (long stroke) instead of low piston speed (short stroke) for a given rpm? Haven't the high end engines like Cup, Pro Stock and F1 been increasing bore size and shortening strokes for the last 10 years or so, and thereby increasing rpm so that each lb-ft of extra torque produced near the max rpm is more hp? Please explain.

As for F1 materials, I think you are mistaken. Maybe IRL and CART (or whatever it's called now), but not F1. The 2004 F1 Technical specs specify steel or cast iron for the crank and camshafts, and prohibit composite materials using carbon or aramid fiber for pistons, cylinder heads or blocks. MMC doesn't seem to be prohibited.

Engines can have 5 valves. Strange that they don't.