well in a perfect world ( no efficiency loss ), more psi = more power so you're essentially talking about the same thing here.

PSI itself, has no relation to your bottom end BUT the power that results from the PSI does.

Every time a piston hits TDC, it changes directions and starts going back down really really fast, putting the most stress on the rod cap. The higher your RPM, the more often this occurs, the more likely your the rod end is going to separate from the con rod itself, thus throwing it through the side of your block.

The other time that your bottom end is stressed is during combustion, the power generated from burning the fuel/air mixture literally tries to crush the connecting rod.

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TLDR:
High RPM = Risk of rod cap separating
High Power = Risk of bending the con rod itself
Both = Both

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As for how much power you can run on stock bottom end? no clue

I wouldn't push past 450 though.

This post was edited by SlyGoSu on Apr 23 2013 03:31pm

Yep... rpm has alot to do with longevity

I know of a pretty popular stock bottom end 5.0 with a 67mm turbo that put down 500+whp & 600+ ftlbs that lived for days tuned professionally and only reving to 5500rpm

Maximum Boost by Corky Bell


buy it.

Yes, but just because you increase horsepower doesn't mean the stress on the crank or rods increases the same. Double the HP isn't double the stress on internal engine parts. The excess heat generated by pressurized air exploding in the chamber is really the killer of blocks. That's why alot of serious 4 cyl guys like to get ceramic coatings on the pistons.

Here's a question for you guys....lol

Does the piston move down the bore faster than it goes up?

I would imagine so.. what about it?

Nowhere in my statement did I say that the changes were linear, I even went out of my way to point out that those situations are only in a perfect world where no efficiency loss occurs (aka not real life)

But yeah, you're right, pistons fail because of the heat generated,
but I was more referring to the rods and crankshaft.

did not answer my question

I would say no, it doesn't. Because all the pistons are connected to the crank, they're only moving up or down as fast as the crank is spinning. Thats where the issue of stress comes in.

this, though in a one cylinder, it would go: combustion > exhaust > intake > compression

What are you really getting at with that question though?

ps, people use ceramic coated pistons because they dissipate heat back through the combustion chamber instead of letting it form a hot spot on the piston. Thus preventing detonation.

So your statement actually should've been; "the pressurized air exploding generated by excess heat in the chamber is really the killer of blocks."

This post was edited by SlyGoSu on Apr 24 2013 09:22am

bump, still waiting to hear why that question was asked Krom