What's limiting power on stock internals?
 

Hey. I was thinking, what blows an engine running stock internals? Why do I hear I can run 30psi but not 35? I'm wondering, if I can run 35lbs with no detonation, what will break? Do the pressures blow holes through the stock pistons, or do the rods bend? What is keeping me from making 650hp on a stock bottom end, assuming I've got mods to support it?

Basically, I just got new cams, head ported, valves, dual valvesprings, gonna be turning 8.5k, and I'm worried it's gonna be too much power for stock internals.

I heard pistons are the first to go

rod bolts?

Rod bolts stretch at high revs. Your bearings would then endure unwanted stress. Then they eventually spin. If you dont have headstuds, the head would also lift. Just remember. Racecars brake. My Evo isnt a racecar so I dont expect it to brake anytime in the near future. Hell, I dont expect it to brake ever!!!

So you say pistons are first to go, what's your reasoning?

And rod bolts are something I hadn't really thought about. But that's still just fastening hardware, what I wanna know is why people spend so much on pistons and rods if it's the rod bolts that are the issue.

And notec, you say high revs are the cause, does this mean that torque doesn't necessarily have anything to do with it? As long as I keep the motor turning below 8k but lets assume I've got a GT42 running 40lbs. If I've got the fuel system to keep up with the turbo, and it's not detonating, could you still blow your motor from power alone?

we've lifted the head because of the factory bolts stretching...this was at 32 lbs

Fastening hardware keeps the big round end of the rod round. round is good as it lets the oil do it's job and protects your motor while under a ton of stress.

As for pistons and rods, folks spend a lot of money on pulling motors, labor, machine work and all the details you must attend to when you work a motor. Heaven forbid you toast the block or munch the head. Thats real money and a huge pain while having a large amount of time in which your car sits and you can't drive it, let alone track it. For that reason many folks feel it is worth the money to invest in better hard parts as depending on the power you want to make it's cheap insurance.

Revs are part of the cause but not all of it. There are so many forces at work in a race motor that all must be balanced and accounted for and motors blow up for all sorts of reasons. Some will have weak points but as strong as they are, there are a lot of ways to kill a 4g63.

As for your GT42 at 40lbs... Where do you expect to spool that turbo at? If your not going to 8k how wide of a power band do you expect to have? Are you going to stroke the motor? What are you going to use it for? How soon do you want to rip it apart and rebuild it? Can you afford to blow it up?

In the end it's about more than numbers, it's about balance and meeting your goals in the most sane way possible. At least I think it is anyway. take it for what it's worth.

There are not that many engine failures out there because most people do upgrades before a failure because it costs a lot less, and you have less down time. I am making 550 wheel HP (Dynapack dyno, 500 wheel HP on Buschurs Mustang dyno) on the stock botom end with ARP head studs and keeping RPM's under 8,000 along with a very good tune, and I feel like I am at my comfort limit on the stock bottom end and will be upgrading rods and pistons befor I push more power in my car.

Good points. I think I might be stretching the limits pretty soon. Anyone know what the fastest stock bottom end car is running?

looks like i'm not the only one who crossed the dark side... whats up bro, we kicked it during rim of the world a few years back... lol