Guys, I don't think this question has been asked before so I'm giving it a shot. It is concerning the cause of crank breakage.

I am currently on a budget and it looks like my budget is going to require me to go with a Scat 9000 series cast crank for my buildup w/ H-beams and SRP pistons on a solid roller 383 N/A setup w/ 150 shot on top.

My question is this, I have factored the price of the cast crank setup and can afford a Fluidampr harmonic balancer for it as well @ ~$400 BUT the 4340 Forged SCAT upgrade is an additional $400. So, that means I can run the cast crank and the Fluidampr or the forged crank and the stock harmonic balancer on my new 383 setup.

The question is Which one would be stronger and have less chance of breaking the crank / rotating assembly? Are the harmonics the ultimate cause in most cases (go with cast/fluidamper), or will the stresses from high RPM/high HP/nitrous more likely the cause (go with 4340/stock H.B.)?

My cam is set to peak at around 6,800-6,900 rpm so I will be shifting at or near 7,000rpm on the motor and probably ~6,600rpm on the gas. Give me your opinions and insight. The rods and pistons would stay the same in each setup and I am running a Vette 4-bolt non splayed main block w/ ARP main studs. Thanks.

 

Personally, I'd go with the stock elastomer damper because it's more effective at lower RPMs (7000 RPMs and below) than multi-elastomers (ATI) or fluid dampers.

If you'd rather run a fluid damper, check out eBay. There's a guy there that sells the F-body LT1 version for around $205 shipped (although it's not a Fluidamper, but looks similar). His feedback looked good too. Try searching for RP$. I almost went this route myself, but since I already have a brand new stock damper and have a keyed hub on order, I figured I didn't really need it.

 

A 383 @ 6600-7000 with a 150 shot? Go with the 4340 crank!
You are talking 650+ hp, right? You must have some awesome heads. Loads, not harmonics are your problem, especially @ 7k.

I don't believe you really want to twist a stock cast iron balancer that high either.

If this is externally balanced, I don't think the Signature series damper ($400) comes externally balanced) That saves you $75.

 

Thanks for the advice to far. Maybe I'm mistaken, does the stock elastomer rubber damper do a better job of silencing harmonics than a Fluidampr? I was under the impression that the Fluidampr does a better job...I know for sure it does a better job than the ATI, at least in the RPM range I am planning on.

Any other opinions?

Also, I run an U/D pulley that has the stock damper bolted to it on my stock motor and if I use the stock damper I will probably reuse this setup as I don't want to spin the alternator and PS pump to well over 7,000 rpm w/o a U/D pulley. Does this U/D setup that many people run reduce the damping abilities of the damper in quelching harmonics?

 

Something else to consider is that replacing the damper later is a much smaller issue than replacing the crank.

Go for the forged crank and replace the damper later. If you still want to that is.

 

Guys, that makes a lot of sense, since like you said, it would be easy to buy a new damper and put it in, but not a new crank. On top of that, this car only gets driven about 4k miles a year anyway, so there wouldn't be too many miles on it before the damper could conceivably be replaced.

Any engineering types care to address the idea of having the stock damper bolted to an U/D pulley? Any affect on damping?