Is it a misconception that you need forged parts for MOST high performance applications? I've read here and there that there is a need to step up the internals to forged to protect from breaking parts.

My project for the time being has a goal of 400-500hp with 9psi of boost. I'll have no trouble keeping the air/fuel ratio as close to perfect but rich if anything. Detonation is not a worry for me. I'm wondering if I can get away with aftermarket cast parts. Like 4340 rods, nodular crank, and just use either performance case pistons or forged. Making the only forged piece possibly the pistons.

Thoughts?

Ryan

 

RPM's kills parts more than hp except when detonation is present. Nodular cranks are rated to 500 hp so those should be OK, hyp pistons are used in stock low ends and people boost them all the time, stock rods with good ARP bolts should be good to 500 hp, forged pistons might be the only series upgrade parts you want to look at UNLESS you see your self pushing the limits higher in the future then you may want to build a bullet proof low end to start.

 

Something else to think about is that the bottom end can theoretically handle more power with boost than the same bottom end on a naturally aspirated engine, due to the effects of boost 'cushioning' the change in direction of every stroke. This is mostly true for the rods, but I don't see why it wouldn't be true for the crank as well, being that's what the rods are stressing against.
Of course superchargers create more stress on the crank snout, but that's not what I'm talking about (but there's a good reason for turbos instead right there ).

As Fevre said, detonation is more of a problem than power related failures it seems with 500hp and less. If that's truly not a worry for you (why do you say that, out of curiousity?), then you're doing pretty good.

From everything I've researched for the turbo-friendlier bottom end that I just put together and got running in my car, most people don't even break stock cranks, some are running around racetracks or down dragstrips with 500hp on stock 2-bolt bottom ends with them, but it seems less people have problems when they have the rotating assembly balanced. There's where RPM's come in, which also obviously makes a difference. IMO, balancing is a must. It's just good juju to be balanced and smooth. I've read about many many more success stories with these setups than I have failure stories.

I have, however, heard of more stock rods breaking in higher hp applications, but not by much. Like I said previously, boost helps them to a degree anyway.
It seems that no one has problems with the pistons unless they encounter severe detonation, pre-ignition, heat, or unless something just plain gets in their way, but not from the power. The good reason to get better pistons is because they will handle more abuse before failing (and to play with compression ratios). Combine that with some mildly decent rods (like GM PM rods), and use ARP hardware as extra protection, and you shouldn't have a problem with ~500 boosted hp. I'll be sure to let you know how it works out when I install my TT kit and tune.

Now I'd say if you want to go all out and have much more than 500hp, I would start being weary of stock or even mild aftermarket parts for longevity, but who knows. It's quite possible that someone could reliably handle much more on a proper setup.

My thoughts.

 

I'm pretty confident in my no detonation because i'll be using megasquirt and tuning the **** out of it under light load before abusing it on the street or track. With the right tune and safety procautions in buildup I feel detonation will be the least of my breakage issues.

 

Turbo motors are a lot easier on parts. I personaly have used many cast cranks and stock rods. My last motor had a scat L9000 crank and an ok rod manliy sportmaster the motor made 450 hp at the tire and went 11.0s on motor and a 275hp nos kit it went 9.60s. Put it together and have fun. I dont think you will have any problems.

 

Im a believer in forged pistons, but you could meet that goal with cast crand and stock prepped rods...