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Re: Piston wrist pin length

Posted: Thu Feb 13, 2020 7:27 am
by LSP
ptuomov wrote: Fri Jun 29, 2018 7:17 am I’m looking at Mahle 100mm Subaru pistons with 23mm diameter piston wrist pins. The bare piston weighs 406g. The wrist pin is about 57mm long. The gap between pin bosses (for the rod small end) is about 29.5mm. This leaves about 13.75mm (0.54”) of pin inside the piston per side when the pin is perfectly centered. Seems low, no? Must be thoroughly optimized. Welcome to the modern era.
What is the motor's intended use?

Re: Piston wrist pin length

Posted: Thu Feb 13, 2020 8:14 am
by ptuomov
LSP wrote: Thu Feb 13, 2020 7:27 am
ptuomov wrote: Fri Jun 29, 2018 7:17 am I’m looking at Mahle 100mm Subaru pistons with 23mm diameter piston wrist pins. The bare piston weighs 406g. The wrist pin is about 57mm long. The gap between pin bosses (for the rod small end) is about 29.5mm. This leaves about 13.75mm (0.54”) of pin inside the piston per side when the pin is perfectly centered. Seems low, no? Must be thoroughly optimized. Welcome to the modern era.
What is the motor's intended use?
Street car, 5.0L, 93 octane pump gas, twin turbo, 8000 rpm fuel cutoff, 78.9mm stroke, probably about 800 lbf-ft torque over a fairly broad power band.

Re: Piston wrist pin length

Posted: Thu Feb 13, 2020 5:16 pm
by LSP
ptuomov wrote: Thu Feb 13, 2020 8:14 am
LSP wrote: Thu Feb 13, 2020 7:27 am
ptuomov wrote: Fri Jun 29, 2018 7:17 am I’m looking at Mahle 100mm Subaru pistons with 23mm diameter piston wrist pins. The bare piston weighs 406g. The wrist pin is about 57mm long. The gap between pin bosses (for the rod small end) is about 29.5mm. This leaves about 13.75mm (0.54”) of pin inside the piston per side when the pin is perfectly centered. Seems low, no? Must be thoroughly optimized. Welcome to the modern era.
What is the motor's intended use?
Street car, 5.0L, 93 octane pump gas, twin turbo, 8000 rpm fuel cutoff, 78.9mm stroke, probably about 800 lbf-ft torque over a fairly broad power band.
Putting Subaru pistons in a V-8?

Re: Piston wrist pin length

Posted: Thu Feb 13, 2020 5:32 pm
by ptuomov
LSP wrote: Thu Feb 13, 2020 5:16 pm
ptuomov wrote: Thu Feb 13, 2020 8:14 am
LSP wrote: Thu Feb 13, 2020 7:27 am

What is the motor's intended use?
Street car, 5.0L, 93 octane pump gas, twin turbo, 8000 rpm fuel cutoff, 78.9mm stroke, probably about 800 lbf-ft torque over a fairly broad power band.
Putting Subaru pistons in a V-8?
They didn’t end up being Subaru pistons but custom pistons from another 100mm forging. The overlap between the pin and the boss is similarly short, and the pin walls are stupid thick.

Re: Piston wrist pin length

Posted: Sat Feb 15, 2020 9:41 am
by LSP
ptuomov wrote: Thu Feb 13, 2020 5:32 pm
LSP wrote: Thu Feb 13, 2020 5:16 pm
ptuomov wrote: Thu Feb 13, 2020 8:14 am

Street car, 5.0L, 93 octane pump gas, twin turbo, 8000 rpm fuel cutoff, 78.9mm stroke, probably about 800 lbf-ft torque over a fairly broad power band.
Putting Subaru pistons in a V-8?
They didn’t end up being Subaru pistons but custom pistons from another 100mm forging. The overlap between the pin and the boss is similarly short, and the pin walls are stupid thick.
Can you show a pic of your piston from the bottom? And how thick is it in the center?

Re: Piston wrist pin length

Posted: Sat Feb 15, 2020 11:05 am
by ptuomov
Here:
5420845F-E4B0-4A3B-9E8D-9D8176012892.jpeg
10AC195F-4461-4955-A583-DC37F4320227.jpeg
AEC27DA5-ECC6-4C85-A85C-7FB93594F911.jpeg
05027747-8276-4F92-ABF8-249A9EB2BDFD.jpeg
369F4972-8D07-43C4-BEF7-7CAFFF685F11.jpeg

Re: Piston wrist pin length

Posted: Sat Feb 15, 2020 12:02 pm
by LSP
How thick is it in the center?

Re: Piston wrist pin length

Posted: Sat Feb 15, 2020 3:21 pm
by ptuomov
LSP wrote: Sat Feb 15, 2020 12:02 pm How thick is it in the center?
I don’t have the numbers here on the ski slopes, but it’s really thick. We wanted both ring lands to be really tall, and that allowed the crown to be really thick even in the center. From memory, something like 10mm, but I may be misremembering that.

The pin is short but 5.5mm wall thickness and 24mm diameter.

Re: Piston wrist pin length

Posted: Sun Feb 16, 2020 7:30 am
by ptuomov
It’s not quite 10mm, the thinnest part of the crown is 6.7mm/0.264” which is still very thick.