Got an option between the two, which should I run. Will there be that much gain in the 7lbs in a motor making about 550hp? When I do run the nitrous I'm only planning on a 100 shot at the most. Looking at low 10s on motor and high 9s on the bottle. Also, would there be any concern turning a SCAT 9000 cast crank 7000rpms?

408 10.75:1 cr
Ported Canfields
Kook 1 7/8 lt headers
Turing no more then 7000 rpms

thanks

 

IMO go with the forged.The engine won't accelerate any faster than the weight of the car will let it.
Light stuff is great if ya have a 2500lb car.

 

'Dude: A local Texas cat had an LT1 vette with a stock clutch that made around ~420rwhp. After swapping to a Street Twin, he re-dyno'd ~10+rwhp less. Granted, the Street Twin clutch is probably like ~20+lbs heavier than a stock setup.

The details of that case are sketchy, but I know there was a significant decrease in output. My question: would a HEAVY crank show a loss like this clutch case, or does it "count" or is it "seen" differently than a flywheel/clutch? From this vette owner's case, it seems that 10+rwhp would make a difference.

Ryan

 

I always thought the benefit of having a quicker revving engine was to be able to get back to peak torque quicker after shifts, which meant you'd be lengthening the time span of being at peak torque through any given distance travelled?

 

If your engine can't pull the car then it CAN'T accelerate if it can outpull the weight of the car and accelerates faster than the weight it's called wheel spin.
It can only accelerate as fast as the load it is pulling will let it.

 

A 30# flywheel should not loose any power. It will accelerate slower and be harder to brake at the other end but it will not loose power.
Heavy flywheels are to keep the engine from boggng when ya drop the hammer on it out of the hole ran a bunch of them on medium HP heavy cars.

 

Someone needs to go back to physics class. Reducing rotating weight especially if it rotates at engine RPMs does pay off that is a part of why the 9.5" torque converters are so great. How far from center of rotation the weight is matter as well.
Any mass the engine has to accelerate has a parasitic effect even before the power can begin to turn a tire. I am not saying go with the cast I am just saying 1racerdude's argument is WRONG. By his logic skinny front tires and light drag rims should be worth very little because they really don't cut much weight out of the car. REALITY is they help a lot because that is ROTATING weight, want a demonstration go spin a bike tire then spin one on your car which one can you get to spin more easily?

 

To the original question.... I think you're at the level where you really need a forged crank.

As for the lightweight, "what's it worth" question...

You won't see much on a dyno... but the engine WILL accelerate quicker down the track. I can tell you a story of a very good Moldex crank that was costing me a very consistent tenth. Was a good crank but the Bryant that replaced it was almost 5lbs lighter.

I agree with Dwayne... the 'dude is wrong on this one but boy..... watch out......

-Mindgame

 

If ya were under light load,yes I agree or on a dyno.
If ya hook it to 4,000lbs ya can't accelerate any faster than the weight will move or ya just spin the tires just like a tractor pull.
Ya can spend thousands on light weight stuff and run the same number.
I never said light wasn't good, if ya had a 2500lb car like I posted. I think it is useless on anything but a trailer queen.

 

HP and torque are two different things....for race cars we want acceleration(HP) out of the turn, so light rotating parts allow less power to be use to turn the motor, and more to be transmitted to the drivetrain. For pull trucks, the added weight of parts helps because as the truck is already at max rpm when it gets loaded, the extra mass hense inertia keeps the motor and truck at speed longer(torque).

I may not be entirely clear in my explination, but to know HP there has to be a change in RPM, you have to accelerate something...if there is less weight to be accelerated(rotating)...hp increases. You also have to remember that any weight inside the motor has a larger effect on it than changes to the weight of the vehicle...combining transmission and rear gear ratio multipliers means that those weights are not "seen" equally by the motor.

BTW what crank weighs 60lbs

 

'Dude, you are neglecting the fact that rotational components store energy. The faster they accelerate, the greater the rotational kinetic energy they store. Energy stored is energy lost in terms of accelerating a car in a linear direction. The goal here being to reduce our reciprocating assembly's moment of inertia and use that energy to accelerate the car.

-Mindgame

 

Man,it's a good thing them BB boys that are winning races don't know their crank is to heavy to be running in the 8's.

I will say again if ya got a RACE car that is built for that, there is everything right in light. For the average Camaro ya won't see that much difference in a 48 to a 54lb crank at the strip.
I am aware of motoring HP and what it is and does.

 

A forged 4340 SCAT 4" 351w crank with 3" mains.

I was under the assumption that less rotating weight would almost always equal motor hp. After doing some reading and some thinking, wouldn't it be better to have a crank that is a little heavy in a heavier car to keep the rpms up on launch at the track?

 

lighter is better. get the forged piece, because its stronger.
what mind game said.

lighter parts will show gains on a intertia type dyno, that is accelerating. a water brake type setup that only allows the engine to accerlerate slowly, will not show the same gains.

Same reason the crank will help more in 1st, than 2nd, 2nd more than 3rd, etc. the rate that the crank is changing velocity(acceleration) is lower.

 

I'm betting that the heavier, more expensive, forged crank won't need as much heavy metal added to it to balance.