Frank's Note on 12/25/99: this is one of the older post too.  Now days the NA combo of choice would be B20B/Z short block with B16A head on the top.  Crank choices?  Either B16A or B17A would provide good geometry.

 

TOO/Nitro: rpm bad, but exactly why?

Posted by eg2 frank (fmlin@kens.com) on July 02, 1998 at 23:12:35:

We all know you preach rpm = ruin people's motors. I've been thinking about it, is it more correctly state as high piston speeds = ruin people's motors?

Exactly what gets ruined by high piston speeds? Do the loads go up exponentially as rpm rises? Is there a point where engine wear goes exponentially too or is it always proportional to rpm/piston speed?

btw I bet you're more accustomed to working with feets/second. I seem to recall the figure American manufatures like to use for street motors is less than 4000 f/s (only about 20.32 m/s) for street motors.

I was checking over the F1 FAQ and it has these interesting facts:

5.6 Interesting engine facts. (Based on a 1996 Ford Zetec-R).

 *In an F1 engine revving at 14,500 rpm, one revolution
takes 4 thousandths of a second.
*Maximum piston acceleration is approximately 8,000g which
puts a load of over 3 tons on each connecting rod.
*Maximum piston speed is 47.2 meters per second - the
piston in a Ford Zetec-R accelerates from rest to that
speed in 1 thousandth of a second.
*If a connecting rod let go of its piston at maximum engine
speed, the released piston would have enough energy to
travel vertically over 100 meters.
*If a water hose were to blow off, the complete cooling
system would empty in just over a second.

Here are the Honda B block crank's piston speeds:

B16A
77.4 mm 8000 RPM 20.6 meters/sec
8500 RPM 21.9 m/s
9000 RPM 23.2 m/s
9500 RPM 24.5 m/s
10000 RPM 25.8 m/s
B17A
81.4 mm 8000 RPM 21.7 m/s
8500 RPM 23.1 m/s
9000 RPM 24.4 m/s
9500 RPM 25.8 m/s
B18C
87.2 mm 8000 RPM 23.3 m/s
8500 RPM 24.7 m/s
9000 RPM 26.2 m/s
9500 RPM 27.6 m/s
B18A/B18B/B20B
89.0 mm 7500 RPM 22.3 m/s
8000 RPM 23.7 m/s
8500 RPM 25.2 m/s
9000 RPM 26.7 m/s
9500 RPM 28.2 m/s
B20A
95.0 mm 7000 RPM 22.2 m/s
7500 RPM 23.8 m/s
8000 RPM 25.3 m/s
8500 RPM 26.9 m/s
9000 RPM 28.5 m/s

Look at it. No wonder B16A is so comfortable above 8000 RPM. My
dream motor would still have to be on B18C block but with B16A
crank. Superior rod/stroke ratio and angle.
I like mucho high RPM power.

Re: TOO/Nitro: rpm bad, but exactly why?

Posted by NITRO on July 03, 1998 at 09:24:41:

In reading your question, you have answered it with your research.
Regarding friction and wear, once again, you answered the question. If pistons travel at higher speed/ crank revolution, the amount of wear is greater. The anti friction composites we're now using help some, but T.O.O. also has another saying: Everything mechanical will eventually wear out and break.
The most common rod failures we've experienced over the years have always taken place on the "overlap" cycle, where the piston is traveling up at high velocities, with no compression up-top, and when the rod tries to slow the piston as it nears TDC, the rod goes, the piston pin can go, and the pin will sometimes pull the bosses out of the piston, or all of the above.
You're (simply) dealing with Mass x Velocity (squared). Now, examine the figures. Both mass and velocity are the players, but wich one is squared? = Velocity.
Regardless of rod ratio or any other player, the greater the RPM the higher the velocities, which = "ruined peoples motors".
What you like (regarding high rpm power), and what your engine likes are two different things. If you ask any engine in the world if it enjoys running at high rpm = max. Q or stress, everyone of them will tell you they don't like it, unless one has a death wish or something.
T.O.O.'ll probably be around to better answer your question, but I gaurantee that he'll touch on the same items, and he talks to engines as well, that's how he makes them do what he wants, although he does write their genetic codes in the pre-build engineering.

RPM's are nice...they are our friend

Posted by 82'Rolla on July 03, 1998 at 06:21:24:

I love the sound of a high revver as well. Unfortunately to make your engine do this, it must be very well guarded against the added stress.
"*Maximum piston acceleration is approximately 8,000g which
puts a load of over 3 tons on each connecting rod."
This is where a lot of the damage comes from, and it increases non-linearly, not sure if it's exponential, plus the fact that the piston actually travels further. The stresses that your engine endures by raising the rpm's by 1000rpms is much worse than increasing boost by 10psi.

I suppose if you start out with the intentions of building a high revver, and compensate accordingly, it can be reliably done, but it sure will get expensive...Carillo rods ain't cheap.

I think it was Louis (deVirgilio sp?)from honda-perf who was also looking at this at some time, and noted the differences in the internal construction of the engines in relation to it's revability.Posted some nice articles, I think I still have them.

Ted