Pressure on the bearing is what's not to like about smaller journals. More hammering per power stroke, higher likelihood of running dry, and more wear, faster.
Talladega race is Sunday. 3 hours of not letting off the gas with 1.75" rod bearings. They rarely have a failure. 800+ hp at over 9500rpm's, that is enough durability testing for me. The down side as I see it is $$$$.
Three hours at 9500 equate to (IMO) 30 hours at 1000rpm, full throttle, or say 100 hours of less than 1/3 throttle, at 1000rpm.
Now in a street car, that isn't even continuous load. Street cars are started cold many times, started hot, placed under varying loads, run up well past 1000rpm, and over the lifetime of an engine should rack up much, MUCH more than the equivalent of 100 hours at 1000rpm at less that 1/3 throttle.
Sometimes race technologies don't transfer over into production vehicles well because the goals are different. A workhorse life is expected of a street engine, slogging away day after day, living in a paddock, grazing on the local greenery, whereas a race car is treated more like a thoroughbred race horse, all the best nutritious food, kept in a warm stable, trained and honed to be as fit as possible, then raced for a short period before going back to rest and training.
I don't know whether there's any real issues with very long term use of smaller journals like that, but the fact is, the contact area is smaller, and so under the same power conditions would endure greater pressures. Whether that's enough to increase the wear rate significantly I'm unsure of.
EDIT: The 800hp part of those cars certainly backs up the durability of the engine though, but I still believe the equivalent in personal car use terms would only be a year or so of use.
I think you're forgetting the centrifugal forces involved there route666. At 9500 rpms, that's way more stress than an engine running at 1000 rpms is generating.
Yeh but all the semi-dry cold starting / warming up, all the constantly changing throttle, on off, stop start, etc. Ok sure it's not 800hp at 9500rpm, but ok, say a car motor does 3000rpm on average, at 1/3 throttle ~ 50hp.
800 x 3 x 9500^2 (square of the velocity for the force, I think)
gives us 216,600,000,000 "wear units"
50 x 3000^2 = 450,000,000 "wear units per hour"
Now this isn't counting cold start wear, which is apparently 80% of all wear that occurs.
So anyway, the equivalent is 482 hours.
Say the average car engine does 4 hours worth per week, 50 weeks a year, that gives us about 2.5 years of service.
Double that, just in case my hypothesis wasn't close enough, and you've got 5 years, still not technically including cold wear, and to me one three hour race flat chat with a beast motor doesn't give a good indication of real world use.
Ok, so maybe you'd only use this technology in a toy car, so you don't drive it that often, and it has a lot more power, and when it is driven it gets a bit more of a flogging - less hours of use, but more strain from bigger rpms and throttle use.
Do those motors get rebuilt after every race or are they used more than once?
Hang on, wasn't it NASCAR where you'd duct tape all the cooling vents off to maximise aero, chuck a brand new motor in for qualifying and put a new one in for the race because after qualifying with no air to cool it it's stuffed?
Anyways, that's how I sees it, dunno if it's right, but I like to discuss and learn, and teach.
Talladega race is Sunday. 3 hours of not letting off the gas with 1.75" rod bearings. They rarely have a failure. 800+ hp at over 9500rpm's, that is enough durability testing for me. The down side as I see it is $$$$.
Hang on, wasn't it NASCAR where you'd duct tape all the cooling vents off to maximise aero, chuck a brand new motor in for qualifying and put a new one in for the race because after qualifying with no air to cool it it's stuffed?
Typically they are allowed one motor for the weekend. That includes practice, qualifying, happy hour and the race (see my previious post regarding total miles and hours). There is a provision for changing out the motor but doing so will require you to start the race from the back of the field. Coming from the back to the front during an afternoon is not a big problem for many of the teams/drivers. But if you are in the back or even the middle your chances for getting wrecked go up exponentially, and on a restrictor plate race it will take a lot longer to move through the field.
I don't watch it. I'll watch a little at the short tracks or road courses, but it seems they are going to a 1.5 mile standard with 2 restrictor plate tracks.
One of the Porsche engineers stated that 1 mile of racing equals 1000 miles of street driving. Nascar throws away most of an engine after a weekend of racing saving not much more than the block, heads, carb and intake. The abuse at the level they push motors is incredible.
Actually, many/most smaller displacement four strokes also have them, my Honda XR600 is an example. You're right about indexing the journals. Thats why most any engine with more than two cylinders has regular bolt-together rods and friction bearings(and still spin them into the 13,500 range). I've also seen two-piece needle bearing shells for a two-piece rod, but it wasnt a high performance application.