What is the origin of maximum piston speed of 4,000 ft./min rpm limit?

[bbs]

Googling didn't help me.

GPT (you-com, huggingface-co/chat,chat-openai-com) indicates the origin of maximum piston speed of 4,000 ft./min rpm limit is from late 19th century when materials and engine design limited max piston speed. There are references to engines in 1907 reaching 4,000 ft./min.

I have a 383 with a 4.25" 440 source lightweight crank in the machine shop. If I stick with the Internet rule of thumb of 4,000 ft./min, my redline is 5,633rpm. Which sucks, and seems to be based on pre-1907 (obsolete) engineering rules of thumb.

Anyway, so many posts on so many forums reference the rule of thumb of 4,000 ft./min rpm limit, which seems to be a design rule from the days of the Model T. It 'feels like' my redline should be somewhere between 6400-6700rpm. Are there updated guidelines for determining piston speed, and subsequently redline?

Other parts I'm throwing in are:
- 1.6 stainless steel bushed rockers
- 440 source rods
- 440 source CNC ported (Modern Cylinder Head) heads
- Beehive springs 150/375lb w/ tool steel retainers (Talking to PAC racing springs)
- Bullet Cam CRB 301/306-08HR - 108lsa 246/[email protected] .574 cam
- Custom dished pistons 10.75:1
- [Undecided] Roller lifters - Short travel hydraulic or solid roller?
- Harmonic balancer (not ATI as they're 4x cost of others)

This will be carbureted, 727 auto trans, 4.10 rear Dana 60, '70 Barracuda.

[cornfedbill]

Actually, Formula 1 engines hit around 7800 feet per minute.

I used to work with large engines - like stationary engines, locomotives and ships. Some had pistons in exceess of 4 feet in diameter and a stroke significantly longer than that. The maximum piston speeds at rpm less than 1000 was about the same as a the F1 engine.

I am not sure where you got the 4000 feet per minute number. I don't doubt that it is old.

The speed of your engine is likely limited more by the valvetrain than the piston speed.

Sp

[bbs]

Thanks Bill. Around various forums the 4000 ft/min is treated as 'bible'.

I can't imagine 4' diameter pistons...

The heaviest parts of my valvetrain are the stainless rockers and hydraulic rollers if I don't go solid rollers with the hydraulic roller cam.

[J Poissant]

I was recently wondering the same.
Asked a well known engine builder and he said that at 7500rpm on 3.75” stroke, or block and good rotating assembly is acceptable/ comfortable.

That gives a bit over 4600 ft/min

I believe you could do FEA on the pistons, rods, etc and see what the forces are and if the materials are sufficiently strong. But, who has the time or resources for that.. I’d ask the guys building the rotating assembly what they are comfortable with assuming there’s a safety factor to the numbers they give.