Steel VS Cast Crank

[Demon_Jeff_71]

Save yourself the money and just use a cast crank and have it internally balanced for that horsepower range in your street car. If you're going to race it every weekend and become a serious racer then go for the forged unit. I've been running a 415sb in my street car with a cast crank that's internally balanced for 4 years with over 100 passes on it running mid 11's. No problems. jysnflem

Ok so I have another question now regarding the whole internal balancing. You can get a crank internally balanced so that you don't have to worry about an external harmonic balencer? How exactly does that work? I want a motor that is going to last so I want to build everything the right way the first time so I am trying to find out as much information now so I dont have to hassle with it later.


Jeff

 

[70aarcuda]

you will need to take your

crank
pistons with pins and locks if used..
rods..
one rod bearing..
one set of piston rings..
nuetral balanced flexplate
nuetral balanced damper/ balancer

when i say neutral balanced flexplate and balancer...that means no weights on them...no offset weights...

then tell the machine to internally balanced the engine...any additional weight that is necessary...that would have gone on the flexplate and balancer will be put into the crank with mallory metal...

the machine shop will drill a hole in the journal of the crank and put slugs of mallory metal into that hole...the mallory metal is much denser..thefore heaviers...

and expect to pay extral money for each slug of mallory metal

that is why it is important to use lighter pistons with pins and rods .....it is easier and cheaper to balance the engine

 

[moper]

Ok so I have another question now regarding the whole internal balancing. You can get a crank internally balanced so that you don't have to worry about an external harmonic balencer? How exactly does that work? I want a motor that is going to last so I want to build everything the right way the first time so I am trying to find out as much information now so I dont have to hassle with it later. Jeff

Ok, to clarify... the harmonic "balancer" is really a dampner. It dampens harmonics that are twisting forces, not lateral or longitudinal forces. The factories also use it to counter the reciprocating weight on engines where the crank's counterweights cannot be made heavy enough. reciprocating weight is the up and down of the pistons, small ends of rods, and crank journals as the crank spins in the block. Mopar also used the torque convertor as a place to add weight on really bad stuff.

Internal balancing means the reciprocating weight of the parts mentioned is counterwieghted and balanced by the crank's counterweights inside the main webbing of the block. It is the preferred method of balancing as it adds the least stress to the crank and mains because of the forces basically being opposite each other. It may require adding "heavy metal" or Mallory metal to the counterweights to get them heavy enough to do the job. Cast crank 4" strokers and 360s are good examples of almost always needing metal. Most forged cranks are heavy enough on thier own, regardless of displacement.

External balancing means the counterweights were not heavy enough by themselves, and no weight was added to them. Instead, the weight is added by the convertor, certain aftermarket flex plates, and the harmonic dampner. As these are outside the main webbing on the ends of the crank, it tends to add stress to the crank and mains as the crank flexes and deflects.

Both types require a dampner because regardless of the balancing, the torsional harmonics are always there. Internal costs more, but means nuetral balancers and any convertor can be used and swapped. I do not externally balance any of my builds for those reasons.

 

[sublimeswinger]

Hi Jeff, I built a low-buck 318 for my 68 cuda drag car that runs 11.50's at 115 on unleaded gas. 400 hp is a snap. Use a pre-71 core engine with a steel crank, so all the internals should be forged. I bored mine +.030, stock 9.2:1 flat top pistons, cast iron rings, clevite bearings, stoick oil pump with the high pressure relief spring kit installed. The cam and heads are the key to the combination ( and getting the power to the ground) I used the DC 4120653 cam/lifter pkg (284/.528") and a set of home ported 587 non-smog 360 heads with 2.02/1.60 valves and the DC dual springs. The 360 heads were milled .040 on the compression face and .020 on the intake face. This gave me .100" clearance on the valves. The intake is a port matched Victor 340 with a 750 Holley annular discharge carb. 4200 stall Hughes converter, JW wheel flex plate and a roller bearing 904 trans with reverse pattern manual valve body. Rear gears are 4.86 with 12x29 slicks. I have over 2000 passes on this combo with no problems.

Good luck!

WOW! How much juice was on that? Got any video? That is impressive!